In the last chapter in this Online Book we looked at splitters and relays to combine battery banks for charging and concluded that while usable, both had a fundamental problem: engine battery overcharge.
Now let's move on to a solution that fixes that, albeit at a price in both money and complexity.
There are two variants to think about:
- DC/DC chargers, like the one from Victron I just installed on our new-to-us J/109.
- Alternator-to-battery chargers from Sterling Power.
Have you looked the Battery Bank Manager Plus for Emily and Clarks Adventure? This seems like an interesting device for mixing lead and lithium batteries. Would be interested to here thoughts on this device.
Hi Foster,
Yes, I’m aware of that gadget, but not a fan. I have watched his videos. Bottom line, mixing lead acid and lithium in the same bank is both dangerous, and in my view, pointless. The whole point of lithium is higher energy density for a given weight and volume, so my thinking is either do it right, or stick with lead acid.
In my view this guy is a better YouTube presenter than he is battery engineer. In fact this show cases the danger of YouTube: a good presenter, which he is, can make a bad idea look like a good one. One of the danger signals of this kind of thing is the presenter who claims to have it all figured out and know better than the companies that build batteries. Also note that he has changed his tune since the first videos—at least he is learning.
We also only need to look at his boat to see he is much more interested in making YouTube videos than actually going anywhere, particularly offshore, where his ideas would be really tested.
If we want a fully integrated system from real engineers we need to turn to Victron, Mastervolt, or Lithionics or some others, all sell full systems that do what his will, and far more. And probably the best, or at least one of the best, places to buy it is from Ocean Planet Energy.
And if we want a lead acid backup, and I think we should, serial, not parallel, is, in my view, the right and safer way to do it: https://www.morganscloud.com/2022/07/03/building-a-seamanlike-lithium-battery-system/
Sorry to be so harsh, but that kind of thing gives me gas.
Not harsh at all to me (I have dog in the fight either way) Thanks for taking the time to answer and generally I agree with what you are saying. Say their device a while back and never heard it mentioned anywhere. Wanted to hear some experts advice/opinion. thx
Hi Foster,
Glad it was useful. One thing I will give them is that I do think their idea of a battery current measuring solar regulator is a good one. That said, I think Victron’s kit can do that when all connected together with their monitoring back bone, but I have not actualy dug into that.
Hi John,
Victron’s solar charge controllers can and do use current data from BMV monitors when networked over bluetooth (no monitoring device necessary). The tail current needs to be adjusted in battery settings in expert mode. Otherwise they default to 1A.
I wish Victron made an alternator regulator. They have all the pieces to make a competitor product for Wakespeed WS500 and probably with even better user experience.
Hi Alex,
That was my guess, but thanks for the confirmation, saves me a bunch of research. The good news on the Wakespeed is that Al tells me they have worked very closely with Victron on integration so I’m not sure if a Victron product would be any better. I’m also on the the Wakespeed Beta test list and I see a lot of updates coming through adding functionality to work ever more closely with Victron. That said, I do wish that Victron had bought Wakespeed, rather than Battle Born…or maybe not, since that might have resulted in Victron making the WS 500 more proprietary…hum, don’t know.
For an all lead acid system, with a modern sealed starter battery how big an issue is the overcharging of the start battery that you’ll get with a charging relay system? Is this actually likely to shorten the start battery life enough to justify the additional cost and complexity of a battery to battery charger? I guess that’s probably one of the many unanswerable “it depends” type questions.
Hi. John answered this pretty good in the relevant chapter, but as you say, it depends. On my boat, I set everything for the house bank, and just let the starter battery suffer. The voltages are not very different for the two batteries, and I don’t motor much, so I can’t imagine that it will have a huge impact, at least not until I am upgrading the whole system and implement a DC-DC charger.
Hi Bruce,
I covered that in the last chapter, but the short answer is if you have a charging relay and all is working fine, it’s probably not broken, that said, there are other factors, again covered in the last chapter.
As has been said – probably not a problem. I have run our boat this way (with a simple Cytrix charge relay to tie in the engine start batt when voltage is over 13V) for 10 years with zero issues, on the same batteries (all FLA), same alternator and no changes to the system over that period. Is there some reduction in reserve capacity of the starter battery? probably – it’s 10 years old! but it has not seemed to matter to me – and I (regrettably) have done a fair amount of motoring on our last 3 summers excursions to Newfoundland, Bermuda and Sable Island – probably in the region of 550-600 hours (I could find out exactly – but i’m not on the boat right now…).
Hi John,
I have a separate alternators for house bank and engine start batteries 24V. And for that matter generator alternator. For gen start battery 12v. The big main alternator with WS500 and all the bells and whistles. Do to recommend regulators for the start batteries and gen. I thought the internal regulator would take care of overcharge but not sure. Start batteries 2 Northstar AGM31’s and 1 12V for gen. By the By; 10 FireFly carbon Foam and so far no quality issues as of yet.
Hi James,
You should be fine with he standard alternators and internal regulators on the engine and generator start, as long as you are not using the same alternators for house charging.
They dedicated to the start batteries only.
Hi James,
I understand that, just making things clear to others.
When I purchased the boat it appeared to be a factory setup (Swan) which at the time I thought was brilliant. Also I used the existing Victron Skylla 24V 80amp charger for the engine start batteries only; Big Quattro inverter/charger for mains, probably complicated overkill. I would love to have you out for an audit on all the refit work done, mostly inspired by what you have written about.
Hi James,
Be careful what you wish for, I could cost you a fortune! 🙂
John have you looked into Planar Transformers? they get over the limited DC/DC Convertor output limitations as you say Victron currently max out at 360W but these Planar Transformers are 3000W! I know of only two companies selling them ‘American Power Systems’ & ‘Safiery’. They are not Chargers (as far as i’m aware) only Converters but thought i’d mention them. I wouldn’t be surprised to see one with a ‘Victron Blue’ Cover on it one day;)
Hi Mal,
No, I have not looked into them and probably won’t given that I believe the right way to set up a system is with all charging sources feeding the house bank, and therefore a DC/DC charger at 30 Amps is plenty to keep an engine start bank happy.
Also, I was always under the impression that transformers only work on AC current, not DC?
A planar transformer is just a transformer whose windings are made of thin copper sheets, or etched on a PCB, instead of being wire-wound. They’re a common component of DC-DC converters. (All DC-DC converters work by inverting DC to AC at high frequency, usually tens of kilohertz, changing its voltage with a transformer, and then rectifying that output back to DC.)
There’s no fundamental limit to how big you can make a DC-DC converter. The ones sold for boats are only a couple hundred watts because that’s all we ever need in our applications. But I can go buy a 4 kW one off the shelf today from Bel Power or Vicor, and semi-custom DC-DC converters rated at over 1 megawatt have existed since the early 1990s.
I don’t know which specific products you are referring to, but APS & Safiery both sell a variety of power electronics parts that are all based on standard switching-mode and DC-DC conversion topologies.
Hi Matt,
Thanks for the fill on that.
Hi John
I’m using the Victron DC/DC charger. Stock Yanmar alternator (80amp) Since the Victron charger max’s out at 30amp I should be well within your recommended 75% max of alternator’s output. I’ve been keeping the maximum charge time at 3 hours. Not sure if this is correct. I would like to be able to charge longer but I don’t want to toast my stock alternator. Overall, love the system and the adjustment available. Just need to do some finally tweaking.
Hi Mark,
I’m guessing that your usage is comparatively low in which case that will be fine, although my guess would be. that the alternator will still only go less than 500 hours at best, before needing replacement. The bottom line is that stock engine alternators are not designed for continues duty and so have short lives when asked to do that. More here: https://www.morganscloud.com/2013/11/06/10-tips-to-buy-and-install-a-liveaboards-alternator/
Hi John
Thanks for the great articles on battery systems.
I suggest to finish it off it requires one or two proper electrical drawings detailing all you have recommended? Cheers Ray
Hi Raymond,
I agree that at least block diagrams are required, although maybe not detailed schematics. I have already started that process on recent chapters and will do more once I have taken a break from electrical stuff.
Hi John
The Victron Orion can have higher output than 30 amps. It is rated at 360 watts (30 amps) at 40 C but 430 watts at 25 C. I know of at least one person who has installed a fan below it for cooling and achieves 35 amps continuous.
Hi Brian,
Sure, that’s true, but I would not stress the Orion in that way. Most all gear lasts way longer if used a bit under it’s rated capacity. And anyway, if we do as I believe best practice and connect all charging sources to the house bank, there is no need to push DC/DC chargers like that: https://www.morganscloud.com/2022/09/04/battery-bank-separation-and-cross-charging-best-practices/
I have tried looking at the Victron demo app and the webpage, but these DC-DC chargers don’t seem to have a “storage” setting, only bulk, absorption and float. Is it correct that they will leave the starter battery on float voltage “permanently” then until you pull the fuse to give it a rest? That seems to me will fry the AGM starter battery eventually, unless you put the float voltage a fair bit lower?
Arne.
Hi Arne,
That’s true, but not a problem. The answer is simply to set the charger so it goes to sleep when the input voltage is lower than say 14.2 volts. That way it only wakes up when the engine is running or there is another charging source active and the house battery is still in acceptance. The rest of the time it won’t be charging the engine start bank at all.
I have been using an Enerdrive DC2DC+ for a few years now, Input is alternator and separate mppt solar, automatically switches between the 2. Output is up to 50 Amps. Charge parameters are adjustable.
Hi Paul,
Looks like an interesting alternative. However, as a general rule for an offshore boat I prefer separate devices for separate functions, also for a live aboard boat just 50 amps from the alternator would be rather limiting.
All that said, it looks like a nice easy to install option for less demanding usage profiles.
I am looking into using a 24v alternator to charge a large 24v house bank from the engine. I had looked into using a B2B 12 to 24v charger but the currents are quite low for a large bank. I see the new (available 1Q 2023) Sterling B2B chargers have been completely redesigned and one model can support 12 to 24v at 120 amp input amps:
https://sterling-power.com/collections/battery-to-battery-chargers
https://www.youtube.com/watch?v=gBiaiJRSqKc
This is much higher than a Victron 30 amp Orion (Orion more of a choke point unless you parallel a few of them). Do you see any downside to using such a higher capacity B2B device instead of my replacing the 12v stock alternator with a 24v one, or adding a second alternator that is 24v?
I don’t think your criticism of the Sterling unit is fair – because you are applying different standards when commenting on this compared to other bits of kit. And I think one your main criticisms is wrong as a point of fact.
The criticisms about the alternator requirements make no sense to me because *whatever* approach you take to achieve high charge rates will involve replacing the alternator. Anything over maybe 120ah and you will need to replace the pulley as well.
So this is not a disadvantage of the sterling kit – it is just an underlying fact that achieving a high charge rate will need a high output alternator. It is a ‘whole category’ issue that applies to every alternative approach.
Indeed your own recomended approach is “good big continuous-duty alternator, external regulator, and DC/DC charger.”
And I think using terms like ‘magic’ to refer to one bit of kit – but not your favoured approach – runs counter to your generally high standards of objectivity!
The sterling unit is no more ‘magic’ than all those blue boxes you recomend and *certainly* no more so than the highly sophisticated Wakespeed.
Finally, you say “ If the thing dies there is no way to use the engine to charge any of the batteries on the boat without replacing it.”
This is simply NOT TRUE – because it requires no modification of the alternator, if the sterling unit fails you can simply failsafe back to the (be it inneficient) factory default.
I am not arguing that your own recomendation is wrong, but that the dismissal of an alternative is using arguments that do not really stand up.
Sorry that seems harsh – maybe you have answers on these points!
Hi Richard,
You are certainly entitled to your opinion on this, and have argued it well, but on the other hand I’m comfortable with my position on the Sterling solution, so I’m not going to get into debate on this except to say that I don’t think falling back on the internal regulator is a viable backup solution, at least for an offshore live aboard cruising boat.
I guess the obvious question is what happens if your wakespeed fails?
My approach is two Sterling B2B chargers. If one fails I can switch to the other. If both fail at least the alternator is providing charge and I am not entirely stuck.
My most likely point of failure is if the alternator itself crashes out – and I very much have in mind a wise man who recomended carrying a spare alternator!
Hi Richard,
I think we are at the point on this where agreeing to disagree is the best way forward.
In addition to my comment about the Sterling Alternator to Battery Charger – I think there is another solution to the problems you describe that is – for *some* people at least – that better than either of the options you describe here!
That is, the Sterling Battery to Battery Charger. This offers a simpler than your recomended approach – and I think is more fail safe. It is not the same as their alternator to battery charger but has some similarities.
You have a normal configuration of vanilla high output alternator with factory controller – wired to charge the engine starter battery. So *no* changes to alternator wiring at all. If anything later in this system fails, engine starter charges as normal and the alternator is not left in suicidal open circuit.
Then, you simply wire a B2B between the starter battery and LifePo4 or LA cabin battery and select the chemistry on the B2B settings.
Thats it. You are done. You now have an optimised multi stage charge of your cabin – with your starter batter also getting charged.
So you have gone from two bits of magic (expensive alternator controler and DC – DC charger) to one, that does both of these tasks.
As I say, if the B2B fails, the normal alternator controller takes over so you have starter charge and thus options.
The only problem I have identified is that it is possible for the B2B to drive the alternator too hard and overheat it, but that is easy to configure out of the system.
I have a 120ah alternator and have a 60ah B2B so it drives the alternator at 50% reliably and without overheating.
And since I got this so cheap (far less than half of the cost of a wakespeed plus victron dc->dc) – I got two of them. Rather than having one in the locker as fallback, I have wired in both of them but one has an isolation swich which takes it out of service.
If my B2B fails, I can flip a switch and the fallback comes into play. I also have the option (tested, but not used in anger) to turn on both B2B at the same time, pushing the alternator to work at full capacity – though shortening its life.
I like this system on KISS principles – and I like it that it provides a robust seperation between the alternator and the LifePo4 bank, reducing chances of voltage spikes wrecking the BMS or battery.
Oh and in the event the BMS shuts down, the B2B shuts down as well – but (presumably by magic!) manages to settle the alternator voltage without frying anything. The alternator settles at the normal float voltage for the starter battery.
But there might be something I have missed and really am open to feedback!
>> it’s the only option for systems with, for example, 24-volt house and 12-volt start, as is becoming more common.<<
There is a sterling B2B that has that one covered as well
https://sterling-power.com/collections/battery-to-battery-chargers/products/12v-to-24v-120a-input-60a-output-battery-to-battery-charger-w-reverse-charging-feature
Hi Richard,
One can do that, and, as you say, it might be the best bet for some usage profiles. Still, as a general rule I think that connecting all charge sources to the house battery is a better and more elegant solution. I have made my reasons clear over some five chapters, so I’m not going to argue it again here.
As to damage to the alternator, that can be managed in better ways, in my view, as I have already covered.
Bottom line on all of this for me is that I believe it is best for live aboard cruising boats if the alternator charging solution can supply at least 150 amps at ~14 volts to the house battery and for many situations 200 amps at 14 volts is better, and that’s a driver of all of my recommendations—based on living aboard and ocean voyaging for 30 years.
https://www.morganscloud.com/2013/11/06/10-tips-to-buy-and-install-a-liveaboards-alternator/
Clearly you are happy with less than half that, so you will have a different view on all of this and that’s fine.
>>if the alternator charging solution can supply at least 150 amps at ~14 volts to the house battery and for many situations 200 amps at 14 volts<<
The approach I use would scale to this, but obviously I can’t get 150 amps out of my 120 amp alternator!
My approach can get 120amps out of a 120 amp alternator at the flick of a switch – but I choose to run it cool most of the time.
But the same approach could get ~ 200amps out of a 200 amp alternator.
That is just a question of scale – not the underlying technology choice.
I am using lithium house and flooded cell for start. Charging: 120 amp alternator with brush box and Balmar regulator charging the start battery and Victron Dc to DC 30 amp charging the house bank. Works great. I know I am not taking advantage of the alternator but my intentions are to add more DC to DC charging to make 90 amps output. Your thoughts?
Hi Dan,
My thoughts remain he same that it’s generally better to have all charging sources connected to the house batteries, so as to take full advantage of the alternator. To me even 90 amps is not enough for most offshore live-aboard boats.
I have a 200Ah lithium house battery and 80Ah lead acid starter battery. The starter battery hangs directly on my stock Yanmar alternator while the house battery gets charged via a Redarc BCDC1225D charger from the alternator or solar. House and starter circuits are isolated by the Redarc. Since my boat lives on a mooring and solar / alternator are my only charging sources, I needed to figure out a way to maintain my starter battery. I installed a Victron DC/DC charger that uses the house bank to charge the starter battery. I use a relay that switches off the charger whenever the starter battery isolator is closed, i.e. when the engine may be running and Redarc would be charging the lithium battery as this would “short-circuit” the Redarc and the Victron and drain the house bank rather than charge it. On the Victron I have set a minimum input voltage level to prevent excessive discharging of the lithium battery (its internal BMS serves as ultimate protection). I also have a Victron battery monitor which could control the DC/DC charger based on state of charger rather than voltage of the house battery but feel like this is not adding much value. This is system is simple, quite cheap and once installed pretty much fool proof.
HI JP,
If it’s working for you great. That said, from your comment I’m assuming you are not a full time offshore live aboard voyager. For that usage profile the system is pretty much always more efficient, simpler, and more elegant, if all charging sources are connected to the house battery and the engine battery kept charged with a single small DC/DC charger.
I explain why in this Online Book starting here: https://www.morganscloud.com/2022/09/04/battery-bank-separation-and-cross-charging-best-practices/
Hi John, that’s correct. I use my boat for day sails and the odd holiday cruises. The reason why I decided to leave my starter battery connected to the alternator is to protect the alternator where the lithium battery charger switches off because the lithium house bank is fully charged. The dc/dc charger from the house bank to the starter battery is merely used to maintain the starter battery when the boat is not used for a few weeks.
Hi JP,
That makes sense. That said, I’m not sure you need to “maintain the starter battery”. Even liquid filled lead-acid batteries self discharge a lot less that I used to think they did. The other simple option when the starter batteries dies is to just replace it with a lifeline AGM which hardly self discharges at all and will easily start an engine after being uncharged for a whole winter—first hand experience over years.
How about an Echo Charger, which is connected to the House Bank along with all charging sources, and takes from the house bank to charge the starting battery?
Hi Stephen,
Sure, that’s fine, although I have had better luck with Victron products than Xantrex.
Any opinions on the Renology DC-DC 50A charger? Dual inputs for alt and solar. Flooded start to two 200A Li house batteries.
Hi Gregg,
Like the Sterling, the Renology is primarily designed for a situation where the alternator is connected to the starter battery. Since that’s not my preferred solution I don’t recommend either: https://www.morganscloud.com/2022/09/04/battery-bank-separation-and-cross-charging-best-practices/
I’m also not generally a fan of boxes that combine functions, just too many eggs in one basket.
In summary, my thoughts on the Renology are much the same as my thoughts on the Sterling above.
Thanks Cap!
John you touched on the fact you installed an ‘Isolated’ DC/DC as thats what Ocean Planet Energy had in stock but a ‘Non Isolated’ is all we need, i assume both your Negs tie in together anyway? but is there a place for the ‘Isolated’ DC/DC type aboard?
I was thinking of Nav Gear like VHF & HF to give cleaner ripple free power supply (as we all have Inverters these days), or will fitting any DC/DC Isolated Ground or Not give cleaner power regardless as its interupting the House Supply?
Or my new boat has a separate Bow Thruster Battery Bank not in the original wiring drawings presently charged via a Battery Isolator/Splitter, i plan to change that and charge via a DC/DC but could i/ should i charge that as if it was a separate Power Source via an ‘Isolated’ DC/DC and keep it away from the House Negative? Or should we be tying everything onboard to a common Negative! which then begs the original Question, where to use an ‘Isolated’ DC/DC? Something iv’e always wondered about;0
Hi Mal,
As far as I know, the only reason to use an isolated ground DC/DC charger is on an aluminium boat where we want to ground the electronics to the hull but keep the rest of the system floating. That said, I recommend grounding electronics on an aluminium boat with capacitors.
Other than that, I can’t think of any good reason, but there may be one I have not thought of.
The article states a DC-DC charger must be directly wired to batteries:
Is that a vender recommendation? Is there a reason a regular battery switch could not be used to interrupt the input or output wire instead? That would be way easier than pulling a fuse, if a little overkill for a low-amp charger
Or wiring it to a breaker on the DC panel which avoids the use of a separate fuse (on one end at least)? I’m planning an install between two battery banks and I want to have a way to turn off the charger, say, for storage to avoid one bank draining the other while self-discharging
Hi Justin,
Not withstanding my comment above, I do disconnect the DC/DC charger, and all other battery direct loads, when the boat is in storage. But that’s five minutes work twice a year to pull the fuses and put them back, so I have not bothered with a breaker, and would not.
Hi Justin,
Sorry, I missed this. Yes, that’s the recommendation, at least from Victron.
I have wondered about putting the DC-DC the other side of the battery switches but don’t know what the unintended consequences would be.
Anyway, with the Victron, at least, you can set a “lockout voltage” so the charger only comes on when the house batteries are being charged. The result is that the rest of the time the charger is in standby and using a tiny amount of current.
Thanks, John. Yeah, I’ve poured over the Victron docs, and they definitely seem to want you to use the little remote connections for a switch and wire them direct to each battery. I assume they have their reasons.
Setting a lockout voltage could also make me feel less anxious.
Hi Justin,
I have not bothered with a switch on those connections, but rather just jumpered them out. My experiments showed that the lock out performs the same function.