Wow, figuring out how to put a lithium battery-based system together that will be functional for an offshore boat (not a camper van) and not break the bank, is even more complicated than I thought when I started this.
The good news is that we are getting a handle on it. So far we have covered:
- Why the BMS must be able to communicate with charging sources.
- Why we need a good monitoring system down to the cell level so we can properly manage charging.
Wait, it gets better. I’m confident that I can end this series with a reasonably simple checklist of buying criteria, although we will have to wade through at least two more in-depth chapters first, so I can link each checklist item to an explanation.
We need real understanding, not:
- Cruiser looks at YouTube.
- Cruiser installs unseamanlike system.
- Cruiser maybe gets by, but knows it could have been better.
And the best news is that, at least as far as I can see at this point, doing it right won’t cost much more than doing it half-assed. Cost is about the DIY, or not, decision and/or bank size, more than the do it right or do it half-assed decision—analysis coming soon.
With all that out of the way, let’s dig into how much peak current (amps) we need our system to be able to supply. Oh, no one ever mentions that on YouTube?…Exactly…
The Amps We Need
First, let’s cover the minimum current capability that any BMS should have for us to consider it.
We all know that lithium batteries can supply huge amounts of current, and accept prodigious charging rates—think a Tesla with amazing acceleration that can be recharged in less than an hour—but that does not mean that the BMSs and batteries we will be considering can do that.
In fact, many (perhaps most) boat lithium battery-based systems can actually supply less peak current (amps) than a good1 lead-acid battery.
What gives?
It’s all about the Battery Management System we choose and how robust the internal wiring of the battery is. Let’s deal with the BMS first.
Hi John,
Maybe I missed something, but I don’t understand your position on 48v. Why would we end up with 3 voltages? If I was installing a 48v bank, I would only have a 48v bus and a 12v bus; I would not have 24v anywhere on the boat. Why would you complicate things with 24v in this situation?
In a 48 V system, you would run the main bus and all the high-power loads at 48 V. You would step down from 48 V to 12 V using a DC/DC power supply, or a DC/DC charger hooked up to a small AGM or gel cell, near the point where each 12 V load is connected.
This only works if you can buy all the equipment you need with 48 V motors and circuitry. If you want a 48 V main bus, but have your heart set on a particular fridge and watermaker that are 24 V, and electronics are of course all 12 V…. now you’re building a 3-bus system, and making a mess, and need to go home and rethink your life.
For the moment, a 48 V main bus on most boats under about 70 feet only makes sense if you have electric motors for main propulsion or if you are running air conditioning from battery power. That may change in a few years as more of the car/truck industry adopts a 48 V architecture and compatible parts (eg. refrigeration compressors & controllers) become more common.
Hi Emile,
Sure, you are right in theory, but as Matt wrote, the problem is that there are very few things that run on 48 volts right now. A few bow thrusters and I think that’s about it. And running everything else off 12 volts makes no sense on a boat with high power needs, hence the need for 24 volts and three systems.
I just completed an install of a 48v “storage bank” that charges the 12v house bank through a DC to DC. Since the boat came from the factory with 12v house bank, everything is already installed and wired to 12v (so no complicated 24v decisions). If the system completely shuts down (unlikely because it is Victron) then the owner is back to where they started with the same lead house bank and 12v alternators.
The DC to DC is made by sterling energy, 12 to 48 bi-directional, so while motoring, it charges the 48 from the 12 and then when engines shut off, it back feeds to keep lead acid house bank topped off.
What is amazing is that the 48v can charge from the generator at about 7kw, (110-140 amps at 56v).
In my view, it is the best system I have installed yet. It inherently takes care of having lead backup and I think the two Cerbo monitors is really easy and intuitive.
Spoiler Alert: I chose a 48V bank, and not because I was wowed at a bar! See above.
Conor, I think you have hit on the biggest advantage of going 48V, if you have one of the newer 48V alternators you can charge at ~100A ( 400A@12V equivalent), that along with the small wire size and bi-directional DC-DC makes this a great option.
Hi Conor,
Interesting but I still wonder if 24 Volt would not have been even better. The primary reason to go up in voltage on any boat is because it’s a more efficient way to supply loads and also because higher voltage alternators are more efficient. So at the very least, to justify this added complication I would like to see an alternator charging the 48 Volt bank. And, if you had gone 24 volt, you could have slowly transferred over loads to get the added efficiency, although I do see your point about the complications of doing that.
That said, I see that the the Sterling charger are a bit of a choke point in all of this with only 1500 Watts of charging to the 48 volt and 40 amp to 12 volt the other way, although I do agree that the Sterling unit is way cool in many way.
When you say you can charge off the generator at 7kW, are you doing that directly with a 48 volt AC charger? I’m guessing yes. If so, this all makes more sense to me.
Still, on an overall basis I think 24 volt might have done just as well and been more flexible going forward.
Here is the American Power Systems output chart for their HPI series at 12, 24, & 48v. Balmar also makes 48v alternators. You can see how engine run time would drop and generators could be obviated.
This increased power generation combined with lithium’s massive improvement in charge acceptance opens up feasible use of 110v appliances for cooking, washers, watermakers, Starlink, etc. For many coastal cruisers, you could keep the batteries charged just by motoring in and out of the harbors.
Yes, 48v appliances are rare and in most cases don’t exist yet. Yes, 24v gets you much of the way there but most still need 12v anyway (starters, NMEA2000, electronics) so you will need 2 voltages. New converters say they are 95% efficient, so that loss does not overcome the clear charge capacities and efficiencies of 48v.
Finally, I believe the RV and automotive worlds will shift to 48v. The marine world will follow. I don’t know when but I see it as inevitable.
MasterVolt has a new converter, the MacPlus 48/12-50. This way, all the DC loads can just stay at 12v while an AGM can absorb the induction loads and basically stay in float.
Hi Whitall,
Sure, I agree that 48 Volt may be the future. But having been in high tech most of my life I have seen an awful lot of systems disappointment as the result of trying to anticipate the future so I prefer to specify systems with what I can buy off the shelf today.
The key reason I like 24 over 48 is that we can, today, run everything on a boat on 24 volt and just have a small 24/12 DC/Dc power supply to supple NMEA 2000 backbone. Starter batteries should be separate anyway, and lead acid, so that’s not an issue, either way.
One of the big things I like about 24 Volts is that it’s much more fault tolerant when measured against 48 volt systems that have many more single points of potential failure that can bring the whole thing down. Sketch out a 48 volt system in a block diagram and you will see what I mean on fault tolerance. And anyway, building a system where the primary service bank is a different voltage than most all the loads is just inelegant design, in my view. Why on earth would we do that?
Also, don’t be too sure that we can have all that stuff, particularly cooking on electric, without a generator. I know everyone is saying that, but do the numbers. I did and it didn’t come out well: https://www.morganscloud.com/2020/10/25/induction-cooking-for-boats-part-1-is-it-practical/
And again, get rid of the generator and keep/add all that stuff and we have created another single point of failure and poor fault tolerance.
Bottom line, we have to actually draw stuff out and do real numbers before being sure of any architecture. Having done both, I’m confident that 24 Volts is optimal for most usage profiles today. Five years from now, who knows? But given how long it took 24 Volts to get really mature I’m not holding my breath.
We have gone through this quite a bit over the last 3 years and have come to the same conclusion except that we end up doing quite a bit with 230 V as well (see other comment). 24V is there now. I think 48V will be there in the future, but I won’t wait/anticipate
Hi Mal,
Looks like a nice way to make the transition to 24 Volt and lithium in a controlled and phased way. Good call.
On the question, definitely leave the watermaker on the lead acid battery and up size the DC/DC charger. Watermakes have high start currents that would probably damage a DC/DC power supply over time, and worse still, I’m guessing the it might not even be able to start the watermaker without shutting down, even a 70A one. Bummer that the motor change was so expensive.
Hi Mal,
2900 us dollars / 2600 euros seems like an insane price for an electric motor for a high pressure pump. I’ve come across similar pricing style on other items sometimes, and it has always been a local distributor with some kind of issue. Dessalator is a French brand. Perhaps they can give a better answer or give the local representative a solid kick in the rear? You could also check price levels in other markets. Or perhaps not just the motor. A complete generic high pressure pump including the motor should be in the region of 400 euros retail. I haven’t checked recently, but it seems very likely that you can find some better deals.
Hi Mal,
400 Euros was my guess, yes, but as mentioned that’s not based on recent research. My point is that what Dessalator sells is mostly generic parts they have from external sources, like you found out about the filters.
I have no experience with the company, but they were the first or among the first on the watermaker market, so perhaps they feel they can capitalise on that?
An experience from about 5 years ago: I was insulating the boat and wanted a specific type of foam, Armacell EA B1. It’s made in Germany, which is the neighbour of the Netherlands, where I’m located. Both are members of the EU, so we have common market, no tax difference.
Still the prices in the NL were about 5 times higher, from all NL sources I found. 5 times! I bought it from Germany, of course. This type of differences are quite normal, albeit rarely such a huge difference. It’s worth looking around.
In the case of Dessalator, I’d not look for lower prices on branded parts, but try to find alternative brands that fit the system. How much that can be done depends on the physical design of the watermaker, of course. Some watermakers are totally modular and all parts can be replaced by anything else that does a similar job.
Hello,
Nice article, more balanced than some LifePo fan boys videos.
About inverters and capacitors, is it better to turn off completely the inverter when the 230V loads are not needed or leave it in standby ? Our natural inclination was to turn them off most of the time and on when they are needed. Is the on off multiple cycles during a day doing harm to the inverters?
Thanks.
Denis
Hi Denis,
Thanks for the kind words.
You are right that turning electrical and electronic stuff off and on repeatedly tends to stress it more than having it on. However, practicality depends on how much the inverter draws when on standby. Most modern ones are pretty good in this regard drawing around 10 watts so probably better to leave them on say through the day and then shut down at night. Some of the older ones take far more, so worth actually measuring.
All this does depend on how much power we have to spare. For example I did not even install an inverter on our J/109 because she has a small bank so I need to be a real power miser to make things come out right. On The McCurdy and Rhodes with a 800 Ah bank (12 volts) we tended to leave the inverter on all day. The point here is that a lot of small loads can add up to a problem, so we do need to think about this stuff in relation to our bank size and charge capabilities.
Inverters don’t like being switched off while under heavy load. Turn off the AC loads first, and then turn off the DC to the inverter, and you’re unlikely to ever have an issue.
I just completed switching my house bank from 6 x 110A/h Firefly (660Ah) batteries to 2 x 460A/h (920 Ah) Epoch LiFePO4 batteries. (These batteries are Victron Canbus compatible & actually show total capacity of 960 Ah. )
I won’t get into too many specifics but I had to work hard to ensure that the LFP & LA systems could not be inadvertently placed in parallel and it was quite clear that despite the high current capabilities of the Epoch batteries, all high current motor supplies needed to be serviced by lead acid batteries.
3 Fireflies were redeployed to form an accessory stern thruster bank and 3 went to be the new main engine start bank. These are all now charged together via a battery isolator along with the forward AGM bow thruster / windlass AGM.
The alternator & a single 40 Amp AC charger charges the lead acid group directly and the house bank gets charged by 2 x 30 Amp Orion DC-DC converters. (This is in addition to 3 dedicated AC house bank chargers totaling 180A +/- ~40A solar.)
So far it is working very well but keeping the 2 battery systems separate took a lot more work and thought than I anticipated.
Yes. It is a real pain working with all that 2/0 & 4/0 cable but most of it was already in place & on board. The advantages of going to 24VDC were not really very compelling for our application.
HI Evan,
Thanks for the information on your system. I was hoping we would hear from someone trying the Epoch batteries out. Very good to hear that the Epoch batteries are working with the Victron Monitoring. Does that include monitory down to the cell level?
Question for you: Have you managed to make the it so the Epoch batteries can work with the Victron system to actually control charging sources? I’m thinking not given you have connected the alternator to the lead acid.
The other thing that strikes me is that this is a huge bank but with very little relative charge capacity. So I’m guessing this works for you because you are on shore power quite often? In that usage profile I can see how this would work, since the bank could be fully charged with the high capacity of AC chargers you have. Or perhaps you have a generator?
As a general rule I have found for a cruising boat that does not get to shore power much alternator charge capacity is optimal at a minimum of 20% of bank size.
For others: more on matching charge capacity and bank size: https://www.morganscloud.com/2023/01/24/balancing-battery-bank-and-solar-array-size/
Hi John,
The vessel is a powerboat (Nordic Tug 37) with a 120A Alternator controlled by a Balmar external regulator.
I do have a 9+KW generator on board so charging capacity could be as high as 240A +/- any solar contribution (550W) while underway and with the generator running. (The batteries are rated for 230A of continuous charging each for maximum 460A with 2 batteries in parallel.)
I chose to keep the alternator feeding the LA bank directly under the relatively clumsy Balmar settings and to charge the LFP via Victron DC-DC chargers; as, I could have better control, via bluetooth, over the charging settings with the DC-DC chargers. In addition, the alternator would be protected from any rare but potentially damaging BMS disconnect. I appreciate that the this does not exploit my alternator’s capacity to the maximum but like many things represents a conservative compromise. A Zeus or Wakespeed controller might be a worthy upgrade but for now, I think this can work safely.
https://eheffa.zenfolio.com/img/s/v-10/p3755930088.jpg
So far, I am finding that the new LFP bank readily accepts the full charge capacity with a Bulk / Absorption voltage of 13.9 VDC and “Float” values in the 13.35-13.40 VDC range. (This float value while on shore power is really set to allow house loads to be serviced whilst keeping the LFP bank in a ~ 95% SOC range. The cell balancing appears to be more than adequate at these settings and there is virtually no risk of overcharging the LFP.)
I have not yet installed a Cerbo GX but can do so in the future if I feel that the LFP bank would be better served by the BMS controlling the charging. I am not convinced that this is needed though as I am finding that with the BT Victron smart shunt and BT access to the BMS status, I have enough information to manually oversee the charging. Compared to Lead Acid charging, I am finding the charge settings for the LFP are rather simple and straightforward with all the Victron chargers using the same 13.9V/13.35V settings.
On shore power, I can let the two Victron IP22 chargers do their thing with the Magnum 120A inverter/charger in a standby mode. When off the grid, I always start the generator manually, maxing out the chargers and monitoring the SOC manually electing to discontinue charging when a reasonable SOC is achieved.
The excellent charge acceptance is really very satisfying to see.
-Evan
Hi Evan,
Ah, a motor boat, with a generator, all is explained. Now I better understand the reasoning behind your system. Everything changes when we are always charging when underway and have a generator, particularly the importance of an optimized alternator.
And sure, a diligent owner can take the place of a fully automated charge management system, particularly on a motor boat where there are less distractions and all gauges are easy to hand at all times.
That said, beware any charging sources that have a daily acceptance cycle regardless of battery state. Any with acceptance cycles over about 13.4 volts can damage lithium batteries over time. But I think you know that judging from your comment.
I also recently installed a system with Epoch batteries but am less than satisfied.
The tech support is pretty good, someone almost always picks up the phone right away!
But the brochure and manuals are lacking. I do this for a living and the manual did not easily explain how to connect the Victron Cerbo to the batteries.
But once you call tech support, they walked me through it, and all was good. Appears the BMS works through CAN Bus and with DVCC on, appears to control charging sources correctly. Maybe called me paranoid, but I dont know if I would trust the batteries controlling a Wakespeed through the DVCC. In this instance, spec’d a DC to DC for now.
Most annoyingly, when charging the batteries, there is a high voltage alarm that goes off (even though the system is within voltage range). The company said they are working on a firmware fix for this issue. In the meantime, my customer can not fully charge their batteries (which will affect balancing in long-term if we can not resolve this) in the meantime.
The companies response:
“Hello Conor,
We are aware of the high voltage alarm issues and are working now on the fix. We can provide you with a battery firmware update soon that should resolve the issue. As soon as it’s available we will let you know.
Thanks!”
I think Panbo has produced videos on youtube about the same issue I experienced.
That’s interesting. I have not yet had any high voltage alarms with my system but I am charging with rather conservative parameters (13.9 V bulk / absorption 13.35 float) with mostly Victron chargers and a Magnum 120A charger in CC/CV mode.
I have not gone the Cerbo DVCC route (yet) as I wasn’t convinced it was worth the expense & now… maybe trouble?
Why are the values set so low? Did you set them low because of the alarms or because you are trying to maximize cell life by holding the voltage low?
After experimenting a bit, it’s quite clear that higher charging voltages do not increase the rate of charge acceptance so there is no advantage to higher Bulk/absorption voltages. And yes, in the interest of protecting the cells, I do not want or need to get to an absolute 100% SOC. 900 Ah of storage is more than enough for our needs.
Hi Conor,
Sorry to hear of the aggravation. I totally get it, poor documentation is incredibly irritating and a huge time sink. Also one of my pet peeves!
That said, thanks for a comment that will be useful for others. And I think you are right not to trust the batteries to control the charging sources, even though that appears to work, given the other bugs you are experiencing.
Hi John,
Many thanks for the ongoing education! Great information as always! I’d make the point that voltage drop under load may have unforeseen consequences! Component specifications don’t always tell the whole story.
Last year I replaced my defunct AGM bank with 4 Kilovault 120Ah Li batteries with internal BMS. Connections are 4/0. They are each rated for 100A maximum draw, so 400 A in total max draw. I was surprised to find that my Victron Multiplus inverter (set to <12.0V cutoff per Kilovault spec) trips out when I turn on the microwave! With the existing firmware, my Multiplus doesn’t have a “temporary low voltage” setting to deal with short duration voltage drop.
I’m still experimenting with settings, but will likely need to set the inverter low voltage cutoff at a point lower than recommended for the batteries in order to avoid inverter nuisance shutdowns. But then I will potentially be bumping up against the battery internal BMS, which cuts off (per the battery spec) at 10-11.5V.
Were I to start afresh, I’d be taking your advice to use an external BMS – and perhaps going with “Victron everything” to ensure compatibility.
I may find a setting that works. Or not. Getting components to play well together is sometimes an iterative process, despite published specifications that “should” work on paper!
Hi Peter,
Thanks for the kind words.
About this voltage restriction. If I understand you correctly this is the Kilovault requiring this? If so something is fishy. A small boat microwave should take no more than 1 kW and even a large one 2kW. So if we assume the worst case 2kW, that’s only 180 Amps at 12 volt, assuming a 10% inverter loss or 90 Amps if one of the smaller microwaves common on boats. And yet Kilovault claim 400 amps for the bank. So our worst case is less than half that. So there is no way that that load should pull the battery down to its low voltage cut off.
This simply does not add up, given the very low internal resistance of lithium batteries which means that the bank should easily be able to supply that many amps without the voltage dropping too much.
Two possibilities I can think of:
If I’m right about #2 I think your safest bet maybe a lead acid buffer battery to handle the inverter, charged by a DC/DC charger from the lithium bank.
I’m interested in this, so I will try and find the time to dig into the KiloVault manuals and see if I can figure this out, although it won’t be for a couple at weeks, at best.
In the mean time, could you advise the spec on the microwave and which multiplus inverter you are using?
Hi John,
Thanks for your thoughts on this.
I’m in Canada getting a new hip and my boat’s on the dry in Florida this winter, so I don’t have access to test alternative approaches at present.
More details: The inverter is a Multiplus 3kW with 120A charger. It has a peak/surge capacity of 6kW. The microwave is a big honker installed by the a previous owner, complete with convection oven (I’ve never tried the latter feature but it’s a high power microwave, so say it draws ~1200W on “microwave only”).
The inverter is doing its low voltage shutdown @ 12V as noted above. KiloVault tech support says not to go below that, so I haven’t tried lower inverter LVD settings yet.
The inverter is located inches from the battery bank and all connections are new and tight so I don’t think there’s any appreciable voltage drop in the cabling.
Now for the punchline: According to this morning’s always-infallible internet search, microwave ovens have a substantial inrush current of 2-3x rated capacity! Who knew? So to start the beast up, it’d want about 550A (@ 3x inrush) – well in excess of the battery banks max 400A draw. I can see why the battery voltage plummets below the inverter’s LVD!
Possible solutions:
1. Your suggestion of an AGM buffer battery might work, but I’m not clear on how one would isolate the battery chemistries on the load side. I have an existing DC/DC converter that I’m using for my AGM starter battery, so could use that to charge the buffer battery in parallel.
2. Just go ahead and invest in more KiloVault batteries to provide the needed surge capacity and maintain consistent battery chemistry on the main house bank. (But, based purely on personal speculation, I think the KiloVault batteries are perhaps being phased out. Several of the dealers are out of stock on most sizes, with a “get them while you can” riff for the in-stock size.)
3. The most bullet-proof option for the long term would likely be to fit a Victron BMS & batteries and relegate the existing KiloVaults to “deep backup”.
Then again, I could always get a smaller microwave and forego my dream of baking bread with the convection oven… Choices, choices…
Thanks as always! Your thoughts have stimulated a better analysis. Hope you get out for a Spring sail soon!
We have a 1200W microwave that, when running off the inverter, draws ~ 100A from the house bank. I recently stress tested our new Epoch LFP bank by running the HW heater and the microwave off the Magnum inverter at the same time (total draw 230 Amps). It showed some voltage drop from 13.2 VDC to 12.65 VDC but that’s as low as it goes. Your LFP bank should tolerate the draw of a microwave without a problematic voltage drop. I suspect there may be an issue with your cabling or some other fault creating this problem?
Thanks for your thoughts Evan. Your battery bank has over two times my capacity. I don’t know which Epoch batteries you have. Their 300Ah battery has 400A surge capacity for 3 seconds, so if you have 3 of those your surge capacity would be 1200A! So you wouldn’t have any issues with inrush current when starting your microwave. I think my problem is that I didn’t compare surge capacities between the old AGM bank and the new LFP bank. I think John’s article above made reference to “stupid” decisions, and I’m feeling kinda “who, me?” in that regard!
Sorry… To clarify: Our house bank is comprised of 2 x Epoch 460 Ah 12VDC in parallel.
No worries! I should have read your comments above more closely. In that case, your 1 second battery surge capacity is a whopping 2600 A!!! You could start up pretty much anything with that! Hope you have good fuses!
Hi Peter,
I should have thought of that, particularly since I had been writing about inrush currents. That said, this is a little different in that a good quality inverter like yours, and a big one too, has big capacitors in it which should smooth a lot of the inrush and in so doing relieve the battery, so I’m still a bit surprised that you are getting shut downs, and a bit suspicious about the true current carrying capacity of the batteries.
Anyway, the nice thing about lead acid is none of this matters at least as long as they are fully charged, which they will be.
As to the convection oven, I don’t think that’s ever happening on a bank of that size: https://www.morganscloud.com/2021/01/04/cooking-options-for-live-aboard-voyagers-part-1-electric/
But that does depend on how much of a foodie you are.
If the surge occurs when the alternating current voltage is crossing zero, can a capacitor add any current to the inrush?
Hi William,
Well that got me thinking! The answer is yes, because some of the capacitors are on the DC side of the inverter where they act as dampers. I guess a way to think of this is that on the DC side a capacitor is like a little battery capable of supplying a lot of current (if big enough) for a very short time.
Inverters also have capacitors on the AC side but this is more complex to think about since they, in effect, pass current to the neutral (which is clamped to ground) at an amount that is governed by their capacitance in relation to the frequency. In this case they damp spikes too and smooth the AC wave form.
I think I have this right, but conformation, fill, or correction, from any engineers out there is always welcome.
Hi John,
Here’s an alternative thought for you: Instead of using a lead acid buffer, I could repurpose my Kilovault LFP batteries as a secondary bank, and install a Victron Lynx BMS with LFP for my main bank. If the load disconnects from the main bank for whatever reason, then the BMS triggers a latching relay to bring the backup bank online within a few milliseconds.
Normal operation would have a 1/OFF/2 manual switch to select banks and a DC/DC charger to isolate. That would allow exercising of the backup from time to time, and I could save some weight and make use of my sunk cost for the drop-ins.
Ignoring my specific case, what do you think of using comparatively ‘cheap’ drop-in LFPs instead of LA buffer batteries to provide redundancy and protect against load dumps. They’d be independent of the external BMS, and the inverter would be tripped off by the BMS and offline when using the backup (so sidestepping the inrush current issue).
Also, my 250A alternator & Wakespeed would be protected by the BMS. I currently have an add-on spike protector for the alternator but that’s likely a one-time-only protection.
…with apologies for the terrible schematic…https://www.icloud.com/iclouddrive/078EHqudXCQ7que25yYFuE9IQ#Diddikai_power_system/alternator_upgrade_
Hi Peter,
Given this whole thread started because of a low voltage shutdown I would get that sorted out first. We think it’s a high resistance issue but it could possible be that the Kilovaults are not up to the job, so that needs a definitive answer.
Also, yes, lithium can be used for backup bank under ABYC but I generally don’t recommend it since lead acid is intrinsically more reliable and less complicated and therefore better for backups.
And, as I explore in the above article, lithium batteries with an internal BMS are the very worst option for a battery that will buffer loads with high starting currents since that will stress the MOSFETs in them.
Update: I checked the KiloVault specs for peak discharge current, and the 100Ah batteries have a 3-sec peak discharge current of 350 A each (100 A is the continuous rating), so 1400 A peak for my battery bank. The inverter shouldn’t be tripping off due to low voltage/microwave inrush current, period.
I’m inclined to agree with John’s and Evan’s first guess, that there’s unknown resistance somewhere. I will pull out the multimeter when I next get to the boat. Thanks Gents.
A good way to check for resistance is to feel all the connections under load >100amps. If there is any resistance it will heat up real quick. As a boat electrician I almost always find a bad connection somewhere in a system. These can be very dangerous with the high loads most boats are pulling with big inverters and other electrical goodies. I’ve seen molten heathshrink on cables and heatcoloured stainless bolts due to the heat generated from a high resistance connection.
Hi Hugo,
Very good tip, but I would advise using a temperature gun because of the danger of a bad burn by using a hand and added accuracy. The other thought is that sometimes, if the resistance is not that high, there won’t be enough of a temperature change to identify a problem that is only showing up with high start up currents. In this case measuring the voltage drop across the contact/cables with a meter that records peak high and low voltage will identify problems that temperature will not.
helpful series of articles,thanks.
second your recommendations concerning voltages, at least on a new installation. Almost everything is available now in 24V – lights, appliances, winches, windlasses, etc. with the exception of
We keep the engine circuits completely separate and supply the electronics with a small 24/12 transformer. Due to the cost of wiring, it is actually cheaper to go to 24V for the rest. Ended up with lead-acid for starter, bow thruster and windlass for the reasons you wrote.
We also run quite a bit of 230V AC kit; which is also what the generators supply.
Hi George,
I agree, for new builds 24 Volts has pretty much entered no-brainer status.
However, I disagree on the alternator. Most OEM alternators are inadequate and need replacing anyway, and there are big time efficiency gains, and ease of wiring, to be gained from changing to a 24 Volt alternator.
Well, it would have been 4K extra, which I didn’t feel like spending. We only use them to charge the starter batteries. They are inefficient PoS, but I don’t think it matters for that purpose.
The generation of the house electricity is on separate units off the PTO, and these are highly efficient permanent magnet units that are derated (as are the engines). So I think we aren’t that far apart.
John, I may have misunderstood the paragraph attached below but in the context I would have thought you would be looking for a higher margin of error, thus in this case increasing available capacity, rather than “down rating” to less….
Quote: All that said, when designing a system, I always want a margin of error, so I would downrate at least 25%, in this case to 300 and 150 amps respectively; still adequate for most boats, but with caveats we will discuss in a minute. Unquote
Please delete if I have missed the point….
What John wrote is just another way of stating the safety factor (or “factor of ignorance” as I sometimes prefer to call it).
The battery manufacturer states on their spec sheet that this product is rated for 400 A discharge and 200 A charge. I would therefore specify everything I’m hooking up to it to stay below 300 A discharge and 150 A charge.
As with most things in the electrical world, the failure probability and the expected lifespan for power electronics and batteries are highly nonlinear functions of actual working load relative to the nameplate ratings. Once you get through the infant mortality / factory defect period, a device that is run continuously at 50% of its rated capacity might have a mean time to failure (MTTF) of 30 years. At 90% of capacity, MTTF might be 20 years. At 100% of capacity, 10 years. At 110% of capacity, it might be 1 year.
Stressing electronic systems right to the limit is only worthwhile if you are severely weight constrained and have a high budget for testing, eg. in an orbital launch rocket. Where longevity is desired, it’s always best to err on the side of caution.
Hi again Richard,
Just changed the paragraph. My wording was definitely fuzzy, thanks for the heads up.
Thanks John!
That is now clear!!!!
You can delete the tread.
Great article. And thanks for raising contactors vs. FETs. I had missed the FET failure mode issue…. The best is latching contactors…
Hi Richard,
Maybe I was not as clear as I should have been, I will take a look. If someone does not get it, it’s usually that I was not clear enough. Usually Phyllis catches these things, but not always.
What I’m doing is taking the total for the bank of 400 amps (peak current, not capacity) so setting my limit at 300 is indeed downrating by 25%.
Hi John
Again a great article, unfortunately for me it looks like the move to “lithium” wouldn’t make much sense for us, as much as I’d like to switch over.
We have a 24v sailboat with 24/12 converters for the electronics.
At present, she has 6X165ah Victron AGM’s and one 100AH AGM start battery. The AGM’s are getting up in age >10 years on a boat that has been lightly used connected to shore power while at dock/winterstorage.
The potential problem is the heavy electrical startup currents you’ve mentioned.
The 24v housebank supplies everything, which includes the Bowthruster, Lewmar Commander Hydraulic power pack that powers the winches, jib and genoa hyd. furlers.
The idea of Lithium is attractive for many reasons but weight is certainly a major plus, adding separate AGM’s for startup currents would pretty much negate the weight savings and create an overly complicated setup.
Have mis read the articles or is my interpretation of what you written correct.
Thanks for the help/advise.
Cheers
Hans
Hi Hans,
You may be right that it’s not worth it, but to be sure you need to measure the startup loads (see grey box in the articlke) and then check the specs of the batteries you are thinking about. At 24 Volts you may find that a good lithium bank, probably controlled by an external BMS will be able to handle the loads. And even if you still need to use lead acid there maybe compelling benefits to lithium, given that the combined weight and volume may be less than you have now. Remember the lead acid bank may not need to be that big, since it will be constantly recharged from the lithium. Again, there is no way to know without measurement and doing the math, but my wild guess is that, assuming you wish to spend the money and take on the complications, lithium could work for you. I base this guess on the fact you are already 24 Volt, which gives you a huge advantage since all current (amps) will be halved against a 12 volt boat.
Hi John,
I have written to you guys years ago on this topic and I’m heartened to see the effort and time you are all spending on this remarkable battery technology topic. We commissioned a DIY system onboard in March 2016. We have 722 pack cycles on the system (as measured by our Orion Jr BMS). We have lived onboard now for 35 years!! Time flies….
Our system is 12volt.
We imported the cells from China directly (EVLithium.com)
The information to put our system together came from RC at Compass Marine, Eric Bretscher at Nordkyn Design, Cam Murray at Trans Marine Pro and Andrew Ewert (The Orion BMS).
It has been a ‘game-changer’ experience for us energy wise. The Lifeline AGMs were ‘bleeding us dry’. Not to mention the environmental waste involved with being forced to buy new every 3-4 years. This was hugely expensive.
The investment in LFP has more than paid for itself.
We run everything through the LFP/Orion Jr BMS system: windlass, refrigeration, starter motor (for Perkins 4-108), hot water heaterT…. We have adopted the Nordkyn ‘Parallel’ concept: a smaller 100ah AGM battery is cabled in parallel with our LFP system. In the event that the BMS opens the Gigavac contractors in our system, the boat systems will continue to function a short time while we sort out the reason for the interruption.
I read what you have stated re inverter loads (we use a Victron 3000watt), windlass loads, charging sources etc… We have not experienced any issues what-so-ever with these larger loads interrupting/tripping the BMS.
Eric Bretscher goes into a lot of detail on his website about ‘theory’ and ‘application’….. he is to be commended for this effort. Like I stated years ago, it is an easy decision to convert to LFP. One must understand the technology and then invest in quality components to support the cells.
We run the system throughout the day on the flat part of the charge/discharge curve: 13.1 volts. As loads and charge sources (solar, hydro, wind) play out during the day it is easy to see the effect and our remote system display (we have programmed PIDs into the Torque App that display the parameters we want to observe. The App is loaded onto a small Tablet computer that is velcroed to a spot at our chart table). The MAIN point is to avoid the ‘knees’ on the C/D curve: voltages below 12.8 and above 13.4. These cells will happily run thousands of cycles, ten’s of years if kept in the flat spot of the C/D curve….in our experience! This matches what RC of Compass Marine wrote many years ago.
We run our pack at 20%-80% SOC day in, day out. Our 400 ah pack has the equivalent ‘usable’ amp hours of a 900 ah lead acid pack. It weighs a fraction of what our Lifeline AGMs did.
On a personal aside: I do NOT like the Lifeline people. I once called them on the phone to query what I could be doing differently to get better performance. The person I spoke with was VERY disparaging. He said that as a yachtie, I fundamentally lacked the knowledge to use their batteries! I’m NOT kidding!
The biggest issue with LFP we have witnessed with other adopters is they have a ‘programmed’ Lead Acid mindset: they feel the need to keep the LFP ‘topped up’ …. this is really a disability when it comes to LFP. I have lots of our install photos if anyone is interested.
Hi Devon,
Great to hear from someone who has walked the walk, for years. Our system isn’t finished, (will any system ever be?), but I’ve paid attention to the same sources you mention for a decade and my work is with electric boats, where some are lithium, so your words make sense.
I don’t feel comfortable with putting lead acid in line with lithium, as they don’t match, so we have programmable DC to DC chargers to the LA start batteries, (catamaran). However, I might be wrong. A system with an external BMS and proper contactors, with no automatic fake “balancing”, should work fine that way. Then the LA battery will work as a consumable, similar to a fuse. It won’t be treated ideally, but will still last for years. It’s relatively cheap anyway. I see how that can be justified.
The lead acid mindset you mention, desperately trying to top up the bank, = destroying it many years too early, is so true! I’ve tried endlessly to explain to boaters why that’s very bad. Most get what I say, as “an interesting theory”, but seem to not be able to change their convictions. Good for battery vendors…
Our system is 24 Volt. Very happy with the transition. Made the change gradually, before we got lithium. Windlass and some more needed change anyway. Several items were already dual voltage. Almost all our loads are now 24V. My intention is to have only 24V. The navigation electronics are still on a Whisper Power converter. Not ideal. We need at least a new 24V autopilot. We do have an inverter, a modern Victron, but it’s almost never in use, as any inverter dependent system is ridiculously wasteful, if all losses are counted. The reason for going 24V is also efficiency, not copper/weight savings.
We use predominantly the same cables as we had with 12V. That means voltage drop and power loss has seemingly disappeared. I can’t quantify how much power that saves, but it’s significant. Our solar is also far more capable on 24V. The regulators can provide 50 Amp, no matter what Voltage, so 24V means potentially twice the power. We have also increased the area. Cats are easy that way.
Thank you Stein for the response. Yes… I have heard similar reservations from others about mixing battery chemistries. The arrangement has worked really well for us for 8 years. Eric Bretscher of Nordkyn design is the person I learned about this from and he does a good job explaining the concept on his website (at the time I read it many years ago). The Parallel battery we have is seperately switched and fused in order to fend off any unexpected surprises. So far we have not had any. You will be really pleasantly surprised at how well LFP manages. It does not ‘blink’ (NO significant voltage drop) at heavy loads. With your 24 volt system I imagine the reduced amps will augment that observation. I’m not sure I understand what you mean when you write ‘efficiency’? If I was designing a system from scratch I would perhaps entertain the idea, but our system (like yours by sound of it) was a conversion from LA to LFP and everything was already 12VDC.
Hi Devon,
I’ve also read plenty of explanations, including Eric Bretchers, supporting your layout with an LA battery in parallel. It still doesn’t quite make me comfortable, but as mentioned I might be wrong, or too nitpicky.
What I mean with improved efficiency from going to 24v is that when Amps get halved, the same wire has half the resistance, or if it was close to its limit, much more. Our 12 v anchor windlass was 1 kW. The 24v one is the exact same and uses the same cables, from the house bank. They’re 3 m (10 feet) apart. The old one definitely suffered from some voltage drop in the cables and some sag in the LA batteries. Now there’s close to nothing of that and the windlass seems way more powerful.
I haven’t changed our alternators to 24v yet, but certainly will. I expect at least similar benefits from that transition. I’m really happy with the decision to change from 12v to 24v, but I wanted to completely rebuild the system and replace several core units anyway, so the cost and work difference was minimal. To me it was a no brainer. On a well functioning 12v boat, that won’t be the same.
On that note, total rebuild of the electric system, I did look into going all CanBus. It has several benefits, apart from the bling effect. Especially a greatly simplified wiring system. However, I didn’t like several other issues, especially parasitic power draw of the electronics, so I went traditional. Happy with that too.
Hi Stein,
Good point on a hidden benefit of a 24 volt conversion: with the old cabling that was for 12 Volt in place, voltage drops will be very low. Always a good thing.
I also like the idea of a gradual change to 24Volt over time. That used to be difficult, but with the weight and size advantage of lithium, as well as better DC/DC chargers, having two house banks and systems, one 12 and the other 24 volts is a lot more viable than it once was.
I need to update the voltage chapters to point that out, thanks.
Hi John,
Our conversion from a 12v LA system to 24v lithium was in several steps.
1. Gather knowledge and make a plan.
2. Collect parts.
3. Start implementing some of the new layout while leaving all 12v. A lot of the items like fridge, freezer, solar regulators, LED lights and more are dual voltage.
4. When step 3 has made enough change, change the house bank to 24V and feed the whole system from a 24 to 12V converter. Don’t run any big loads.
5. Move circuits one by one from the 12V panel to the 24V panel. This stage will probably never be complete, as some circuits just need 12v.
This method keeps the boat operational all but a few minutes while switching the house bank. Also the gradual progress gives plenty of time to ponder and make totally certain that everything is done right. I know a fair bit about electric systems, but I loved the pondering time I got from the slow transition.
Hi Deven,
Good to hear that this has worked out well. Also sorry to hear that LifeLine were rude, there is never an excuse for that. I guess you got someone having a bad day, or just a jerk, since I have always had very good interactions with them.
That said, to be fair, I do need to point out that if you were only getting 3-4 years out of the Lifelines there must have been a problem with your set up. That’s not a personal criticism since I had the same problems with AGMs until Justin at LifeLine helped me sort them out. After that I got many years and about 1500 cycles from a set of LifeLine AGMs or about double what you have on your lithiums since 2016, so that would be well over 10 years on your boat, but of course a bigger and heavier bank for the same usable capacity. Note I’m not saying you should have stayed with LifeLines, just that when evaluating a use case we need to start from a fair base line.
And yes, I can certainly see that since you are using individual cells, probably heavily wired (buss bars) and an external BMS without MOSFETs you would have no trouble with high start up currents, and nor should you. As I write in the article, lithium cells can supply very high currents, it’s the wiring and/or MOSFETs in internal BMSs that restrict them and I think I’m right in saying you have neither.
The other thing I need to point out for others is that paralleling a lead acid without isolation (assuming that’s the case) is not really recommended by Nordkyn. Rather he discusses that option, but, if memory serves, he also covers the dangers of so doing.
And I agree, managing lithium with a lead-acid mind set is a very bad idea.
Thanks John, The reason I called Lifeline was for exactly the support that you mention: ‘what was I not doing right to get such poor performance?’ To be rebuked as someone not capable of understanding how to use the batteries because I was a ‘yachtie’ is just not what anyone on a boat wants to hear.
It also just shows how one person having a bad day at work or just an idiot can ruin an otherwise good brand. Oh well…. I still won’t recommend Lifeline AGMs as I still don’t know what the problem was…..
This all said, life on boats is an evolutionary process.
All the stuff that I have been through onboard (as I am sure you can relate to) have brought me to where I am now with it. As I have mentioned in previous posts: ‘nothing better than living onboard!’ For me I enjoy the “process”……You guys are a part of that with the wonderful support you provide for so many. Bravo!
The parallel LA battery (an AGM) has not been an issue onboard for us. Any battery system installed can introduce safety risks if not executed properly. I have not read Eric’s section on the Parallel LA idea in awhile either. He may have edited it by now. At the time he even suggested a way that the Parallel system could be executed that could eliminate the need for a BMS!!
Hi Devon,
Not that it matters now, but the main reason you were getting short life from your LifeLines was almost certainly that you were not equalizing them, or not for long enough at a higher enough voltage often enough. For others: here’s a simple list of stuff to do that will give you at least 1000 cycles and probably 1500 from LifeLine AGMs: https://www.morganscloud.com/2011/02/10/eleven-steps-to-better-battery-life/
And yes, many people have paralleled AGM and Lead acid without isolation and not had problems, but It’s clearly not best practice and has dangers, so given that we have better ways today, I don’t recommend it. I explain why here: https://www.morganscloud.com/2022/09/04/battery-bank-separation-and-cross-charging-best-practices/
Thanks for that John.
AGM’s, I believe are a Lead Acid variant. The battery I write of that is in Parallel with our LFP pack is a an AGM. When I write LA and AGM and I am describing the same thing. Sorry for the confusion. I should have been more clear. ,
The LA (lead acid) ‘family’ I am writing of as ‘LA’ include ‘flooded’ LA (liquid electrolyte), ‘AGM’ (absorbed glass matt) and lastly, ‘Gel’.
Again…I’m not an expert, I read a lot. If I have mistaken any of this, I apologise.
And yes you are correct about equalisation of the AGM’s periodically. I did later discover from another cruiser that I mentioned this particular vendor to (after we had switched to LFP), that one is expected to equalise Lifelines’ AGMs. Just like you wrote….
This ‘dovetails’ with what I have written about any battery technology posing a potential safety hazard if not executed properly. What I mean is equalisation of a ‘sealed’ cell battery is a dubious, time intensive, potentially unsafe process. The fellow cruiser that I mention above, told me one had to do this monthly. Where am I supposed to be doing this: out at anchor in some lovely spot?? On a cruising boat the place/resources simply do not exist to routinely do this. Nor the discipline to monthly babysit the bank for hours at a time while the explosive, toxic hydrogen gases vent…..
I did try it once…. no thank you! Not a pleasant experience and certainly NOT something I am prepared to do monthly!!
Well done you that you managed so well with this. But, IMHO, not a good investment of limited funds for the average cruiser.
In 9 years of pain with these Lifeline AGM batteries we spent $10,500.00. The 3rd bank was deteriorating with poorer & poorer performance. We were on the verge of another $3500.00 spend for a 4th bank…… $14,000.00 in just 9 years! I look back at the entire experience and see myself as stupid, a glutton for punishment, or both!
It was time to find an alternative… enter Rod Collin’s excellent online tutorial. 8 years now using the information available from RC has saved us another $3500.00-$7,000.00+ on AGMs : the additional money we would have had to spend on the Lifeline AGMs had we continued with them these past 8 years. The entire LFP project cost us approx $6500.00 start to finish including shipping. The project was NOT simply changing batteries. It involved an entire electrical system refit: Fuses, Contactors, Cabling, Buss Bars, BMS, Alternator Voltage regulators…. and a long list of other stuff… $6500.00!!
These figures are in New Zealand dollars.
At the time we were taking a ‘chance’. We had never bought and imported anything direct from China. It was a totally different battery technology. One cannot project themselves into the future to know if it was going to all turn out well.
As it is now, the LFP pack will ‘see us out’: at our current usage/pack cycles, we should not need to replace them.
We owe the Lifeline AGM people a big thank you for pushing us to look for a better alternative!!
Kind of funny when one thinks about it!! Again: for you and all the others who have managed so well with their Lifeline AGM experience…BRAVO!!!
Hi Devon,
You are right, AGM is a subset of lead acid.
Equalization of LifeLine AGMs is routine, documented in the manual, and not at all dangerous. The same applies to most all liquid filled batteries. Gell cells and some AGMs should not be equalized. Also, these days with solar, equalization is not needed nearly so often. It can also be done with a good solar array and a programable controller.
I know you like lithium, and that’s great, and had a bad experience with AGMs, which sucks, but let’s not spread FUD about a tried and proven technology.
Hi Devon,
About equalising LA batteries, on our boat it’s was very easy:
1. Open the Victron Connect app on my phone or iPad.
2. Choose the solar controller or the shore power charger.
3. Under Settings, choose Equalization.
4. Nothing more needed. No need to watch. Battery compartment already has ventilation with a thermostat fan to the outside of the boat.
I agree that some lead acid batteries are far from as safe as many see them. Notably the flooded type. While charging, these give off extremely explosive gas. Some years ago I was about 50 meters away when a very large bank of such cells exploded. I fell on my ass, probably mostly from surprise, but it was LOUD. Luckily it was an open boat and nobody being too close. One guy was dunked in the water, to rinse off the acid, and then taken to the hospital. He was fine, apart from the shock and beeping ears for a few days.
However, with LA battery types and charging regimes normal on modern cruising boats, this type of event is rare, as well as far less violent. Getting sprayed in acid is not nice, but rinse off quickly and only your clothes will notice. They get holes. AGMs contain very little free fluid, and only let out gas in unusual cases, so they would be far safer.
I absolutely think flooded 2 Volt cells, golf cart type, are better than AGM, far cheaper and far longer life, but they’re absolutely not for the install and forget type of person, as they need attention regularly. Water should be checked/refilled weekly and equalisation must be done at the right time. AGM and lithium are far easier.
I think the conclusions are rather clear to most here. Things are moving towards lithium and perhaps other chemistries that have many great advantages. At the moment, they also have significant disadvantages. Some boaters are definitely better off with some type of LA battery than with lithium. Some the opposite.
The two groups will merge sometime in the future. The market operators pretend that has already happened, and try to push us towards solutions that make them more money, which is not LA solutions… Lithium is awesome, but the sellers are not our friends.
To anyone wondering about making the leap: Read loads before you pull the trigger. You MUST be knowledgeable enough to advise yourself reasonably well. If not, you’re gambling. That’s not an exaggeration.
Hi Stein
I suspect that the bank you saw explode was a huge one used in a ferry for propulsion. And it sounds to me like the installer had made some very bad mistakes since even a little venting of the compartment would have avoided the explosion. Hydrogen, the explosive gas that lead acid batteries give off if overcharged, is almost impossible to contain, particularly in the quantities given off by a yacht battery bank being equalized. I have never heard of a battery gas explosion on a yacht despite the fact that most yacht battery storage compartments are not properly vented.
Stories like these are not relevant to the batteries on a yacht and are just as misleading as the people who hate lithium and cite incidences where lithium nickel batteries have exploded to damn all lithium, like I called out here: https://www.morganscloud.com/jhhtips/no-lithium-batteries-dont-burn-boats/
Let’s keep it relevant please, and not get all clannish.
As to liquid being better than AGM, depends what your usage profile is, which was your point, but it would have been better without the “better”. There are good reasons for both types and no better.
Hi John,
What I meant with “better” was specified, and not a sweeping conclusion: Much cheaper and much more durable. I also mentioned that it will fit for few cruisers, and I recommended a lot of critical awareness before going for lithium.
The battery bank was indeed very big and for propulsion on a professionally run boat. Still a completely open boat, like a classic lifeboat. Just 10 meters (33 feet) and typically 25 passengers. No ferry but runs consecutive tourist rounds on the canals. 1, sometimes 2 hours continuous trips, with 15 mins from end until next departure, usually 7 to 14 hours per day. It had been run like this almost every day for a bit over a year.
10 identical brand new boats were delivered on the same day the year before, 2015. The 9 others preemptively got a new bank about 4 years later, meaning 5 years super heavy duty life. (The cells get 100% recycled and the company gets a significant amount of money for them). Many sometimes careless skippers means they get pushed quite low. Often to 30% SoC and sometimes 10%. No other LA battery type can get this durability. The closest, but still not quite there, would be gel cells, but at a way higher cost and some other issues. Everything in the install was top notch heavy duty and meticulously maintained. Way beyond the attention any private boat battery gets.
When the explosion happened, the battery box was lifted off, all the cells completely exposed to the outside air. It was a sunny day with no wind. The two big Mastervolt chargers (2x60Amp@48V, equivalent to 480Amp@12V) had been disconnected a bit over 10 minutes earlier, (means gassing was still ongoing, but at a low rate). A routine system inspection was being done by an electrical engineer. He had done an IR camera inspection to look for hot areas. All good. He was the guy closest, who was taken to hospital. He stood on the pier next to the boat, about 3 meters (10 feet) away, having a break (non smoker).
What triggered the explosion remains unsolved. Must have been a spark very close, but what made it? Electronics inspection hadn’t been done yet, but nothing was wrong with that after the explosion. It was all researched by the insurance company, even though the damage was fairly minimal cost wise. Just about 10 cells had blown. They really wanted to know… My guess is some tool left on top of the cells that rolled onto two poles when the boat moved. Stupid but realistic. Nothing such was found, no “weld” marks anywhere and the EE was certain he hadn’t done that, but I still think he had.
The only points of telling this story is to make people aware of a possible risk, and that it isn’t as relevant as some lithium prophets say. Not as dangerous either. If nobody was damaged by this, it means it’s not that dangerous. It’s still real, if a flooded lead acid battery is chosen. I’ve had this type of batteries on most of my boats, including the previous bank on our present cat. Before AGM, most boats did. Still many do. They’re smaller and weaker than in this story, but the points are valid. It’s general battery knowledge that it’s nice to have so one can know more about why the battery in our own boat was chosen as it was.
Almost forgot! Sorry! 48volts, 24 volts, 12 volts…. I am not an expert but the only advantages of higher voltages are less amps, smaller cables. The ‘step down’ conversion of 48 to 12 volts sounds great. IMHO all this manoeuvring adds complexity to a system that simply does not need it,…. after using the 12VDC LFP for 8 years. Just saying…..
First, thanks for this series. I built a DIY lithium bank in my last boat by closely following all advice from Rod Collins, Stan Honey, and Eric Bretscher, in links you provided years ago. The articles you have written since then are wonderfully clear and supplement what I used to think were the last words on the subject. I am now completely sold on the reasoning for LA backup and the solution you propose; however, there is one minor detail that I am wondering about. With the lithium system (BMS, CAN bus, alternator field current, etc.) all dark, how do you foresee getting a Wakespeed regulator and the CAN controlled alternator up and running in emergency mode for “get me home” charging of the backup bank? I am considering a dumb, single voltage, regulator set to acceptance voltage that can be switched into the field circuit and 100% manual control of charging, but that seems very suboptimal. Even if the Wakespeed were wired in somehow, I am not sure about reprogramming it for charging the backup bank at sea. I feel like i might be missing something simple.
I understand the sophisticated appeal of the CAN control / Wakespeed option but a simpler solution might be just to use a dumb external alternator regulator set to service the house bank / windlass thruster LA banks and charge the LFP house bank indirectly with DC-DC chargers.
For backup for the instruments, autopilot, house loads etc., one can have a DC-DC converter in place powered from the LA banks to the DC panel with the voltage set to something less than LFP working voltages (eg 12.5 VDC).
That way, in the event of a BMS failure, you still have the alternator protected and charging to the LA bank is maintained with instantaneous backup power for the essential DC loads.
Hi Evan,
Sure, you could do that, but then we are back to the same old problem of bottlenecking the best charging source on the boat, (the alternator) and we are also losing out on one of the greatest benefits of lithium: its ability to absorb high charge current all the way to fully charged, at least when being charged by an alternator managed by a WS500.
Worst still, we would not be able to use the smarts of the WS 500 to properly charge the lithium battery since the shunt and sense wire etc will be on the lead acid side.
And that also requires big DC/DC charger(s), which will cost more than the spare regulator Andrew suggests, which has the added benefit of giving us a spare regulator, which is pretty much required on any offshore boat.
OK John. Fair enough; but a Wakespeed regulator with harness is ~$1100- CAD whereas 2 x Orion XS 50A DC-DC chargers run about the same. So from a cost perspective it’s a wash.
A 30 Amp DC-DC converter / charger to provide the DC panel backup power runs around $300-. Pretty cheap insurance IMO.
(I am seeing that charging LFP is much simpler than it was with the LA house bank. I can throw a continuous 200A of charge at the 960 Ah LFP bank and do not see the voltage get to 13.9 VDC until we are close to 95% SOC. The Wakespeed advantages seem less compelling when achieving a voltage of 13.9 VDC with LFP is indicative of an adequate SOC. LA charging is much more dynamic with higher voltages and diminishing charge acceptance rates making the Wakespeed shunt-regulated charging more compelling… )
Are sailboats with their relatively small diesels routinely running alternators bigger than 100-120A? If so, the metrics might be quite different.
(A backup alternator onboard makes perfect sense in either scenario.)
-evan
Hi Evan,
To me at least, the benefits of a large alternator regulated by a truly smart regulator like the WS 500 are so compelling that it’s a no brainer. Whether or not other the majority of cruisers do that is a different question. The majority of cruisers do many things that are sub optimal. For example many cruisers end up ruining the sailing capabilities of their boats—drag and obstruction of sail handling—with huge solar arrays that would be unnecessary if they got the alternator right.
And, as before, I disagree with the idea that a dumb regulator can properly charge lithium batteries. Even at 13.9 volts damage will be done if regulator stays at acceptance after the battery is fully charged, and only a regulator with a shunt can actually detect when the battery is full, I explain all this here at length: https://www.morganscloud.com/2022/01/30/wakespeed-ws500-best-alternator-regulator-for-lead-acid¹-and-lithium-batteries/
I agree that one wants the chargers to utilize shunt derived SOC data. I don’t wish to be argumentative; but, the Victron Orion XS 50A DC-DC charger can Network with Bluetooth and use the BMV Voltage & SOC values to regulate charging. So there are a number of ways to skin this cat and still provide safety and redundancy in case of a BMV shutdown.
Hi Evan,
Sure, there are plenty of solutions, you and I differ on which is optimal.
Mea Culpa,
I feel sheepish but thought that I would confess to changing my mind as to thinking that using DC/DC chargers to charge the LFP house bank was a good idea..
You were right John.
We have been out on our boat for week now and I am feeling a little irritated to not be exploiting more of our alternator’s capacity while underway. 60Amps doesn’t cut it when there is a 360 Ah deficit in the morning and 3 hours of running time doesn’t replenish the house bank. (To add to the angst, I thought we had a 120 Amp alternator but just looked to confirm that and see that it’s actually a 160A alternator on a good robust serpentine belt system.)
So, I am indeed wasting a lot of capacity. Adding more DC/DC chargers does not make sense. (The currently installed DC/DC chargers can be repurposed to charge the Start and Thruster banks…)
Now to explore the best external regulator for our application… (The existing Balmar MC-612 is not able to do CC/CV charging or respond to input from the BMV shunt.)
I am leaning towards the Arco Zeus (vs the Wakespeed) as I would very much like to monitor the alternator performance and adjust parameters via Bluetooth or some other continuous real-time connectivity. Arco Zeus does now claim Victron compatibility but I’m not sure to what extent…
More homework to do but clearly, utilizing the alternator’s superior capacity makes a lot of sense.
Hi Evan,
What a drag. It’s so frustrating when we go to all the trouble of building a system and then it does not meet expectations. That said very often this kind of thing, as I have found many times, is just part of the road to success. Only in YouTube lithium battery videos does everyone get everything perfect the first time!
And while I agree that getting the alternator directly feeding the lithium bank is the right way to go, now you have all this invested another DC/DC charger would not be the end of the world. Victron has a new higher capacity line that have just come out.
On the Zeus, I get that BlueTooth is great but don’t lose sight of the fact that monitoring is only the sizzle. Claims are easy to make and frankly Zeus make me nervous because of all the claims they made on day one. Maybe it’s all true, but I have seen the other option way too often. The sausage is a proven regulator that will work well with the BMS you select: https://www.morganscloud.com/jhhtips/an-even-better-alternator-regulator/
And if you go Victron you want a regulator with full on DVCC compatibility :https://www.morganscloud.com/jhhtips/wakespeed-and-victron-get-even-more-cuddly/
Also, you can plug the WS 500 into NMEA 2000 for monitoring and if Victron what the WS 500 is doing can be displayed on the Victron monitoring system.
Thanks.
It’s not the end of the world; but the current setup is more like ‘good enough but could be better’…
I will do my homework before making any further changes.
Hi Andrew,
Great question, and thanks for the kind words. All the more valued considering the experienced source.
To be honest, I had not thought of that. The problem is that the WS 500 will not be set up with a shunt on the lead acid side.
I will think on in some more, but I like your idea the best of anything that has come to me so far. And it’s a great idea to have a spare and simple alternator regulator anyway. I always carried one on the McCurdy and Rhodes and even had it wired in so I could easily switch over.
So given that the spare won’t use a shunt its sense wire can be on charge buss side of the switch used for changing over charge busses, so all we need to do is switch over alternator controllers when we switch to backup.
Unless I think of a better idea, I will add that to the article: https://www.morganscloud.com/2022/07/03/building-a-seamanlike-lithium-battery-system/
Thanks for the heads up and good idea for a solution.
John: Sorry, but I posted the above comment in the wrong chapter … My comment plus your and Evan’s replies should be under Chapter 28 “Building A Seamanlike ….” where you recommend a LA backup bank.
Hi Andrew,
Yes, but we don’t have a good way to move comments any more. It’s the theoretically possible, and we used to do it, but it’s more of a PITA than you might expect due to threading, so I decided some years ago not to. Anyway, no matter since I will update the post in question.