The above is a graph of battery voltage on our J/109, currently still out of the water but uncovered.
As you can see, each day shortly after dawn our solar panel starts charging and since, other than the first day when I was aboard and using power, there are no significant loads and the batteries are fully charged, the voltage rises rapidly to ~14.4 (temperature dependant): acceptance for our AGM lead-acid batteries.
And, after a predetermined time, and because the batteries were full anyway, our solar regulator drops the charge voltage a bit, and then at dusk it shuts down.
Lead Loves It
This is absolutely wonderful for lead-acid batteries because that chemistry is:
- Tolerant of being held for long periods at acceptance voltage, even when already full.
- Lead-acid battery internal resistance rises a lot with state of charge, so even though the voltage is still at acceptance very little current flows (amps) so little or no damage is done.
- Quickly wrecked due to sulphating from being left in a partial state of charge.
We might even say that solar makes lead-acid batteries wonderful again.
Lithium Not So Much
But this same pattern would shorten the life of lithium batteries because:
During a refit this year, I removed three lead acid and replaced with two, 100amp lithium. Starting battery is still lead acid and the alternator charges the starting battery and the house bank is charged by one 30 amp Victron DC to DC charger and 150 watt solar array with Victron charge controller.
I am wondering if I sent the solar charge the the starting lead acid and used the DC to DC charger to charge the house bank and use the Cerbo GX to set the DC to DC charger to regulate the solar?
Just a thought…
Dan
Hi Dan,
Sure you could do that. But recognize that by moving your charging sources to the lead acid you are sacrificing one of the largest benefits of changing to lithium in the first place: it’s ability to absorb large charge currents right up to fully charged. Or to put it another way, bottle necking all your charging to 30 amps with the DC/Dc charger is as pity when that lithium bank could easily absorb 100 amps.
And moving the solar to the lead acid side will not solve the overcharge problem unless you can get the battery BMS (possible through Cerbo) to tell the DC/DC when to shut down. Otherwise the DC/DC will be using a timed charge acceptance cycle, which will be just as damaging as the solar panels and worse still if you motor for long periods you will have the same problem.
Bottom line: there is really no optimal substitute for having all charging sources properly controlled by the BMS. And once we have that, then all charging sources can be moved to the service bank.
What kind of batteries and BMS do you have?
I installed Li Time (low cost Amazon) I used these in the past with great results. I do not live aboard and my longest cruises are around three nights at sea. I have a backup navigation (Ipad) to my 9″ Flir chartplotter, Octopus ram, LED lights. I would be able to jump critical loads to the starting bat if needed. My issue is I have so little draw on the batteries I think 200 AH’s is too much.
I am thinking about installing Technautics CoolBlue fridge which would burn around 25 amps per day. Still not bad considering my solar panels should give that back each day (and on cloudy days this may help my lithium bank live longer as I am not sending a charge to fully charged batts.
Hi Dan,
Thanks for the fill on the batteries. Another option would be, as I think you were thinking above, to use the Victron Cerbo to turn off the DC/DC and/or the solar when it estimates that the batteries are full. I say estimate since without a BMS that communicates it can’t know for sure, but I’m pretty sure (would have to read the manual) the Cerbo can be programmed to measure charge current going into the battery at acceptance voltage and then raise a signal wire connected to a Victron DC/DC or solar controller when the current drops to the point indicating full charge which would be about 0.015C or 3 Amps in your case.
The only drawbacks with that is you probably won’t ever fully charge the batteries so they may drift out of balance over time, which you will need to watch for.
I have always assumed that this function (sensing charge current at a specific voltage and terminating charge) is available if you combine a Victron smart shunt with a Victron dc-dc charger.
In that case it might be a more frugal investment for a small lithium system in comparison to the Victron Cerbo.
Hi Henrick,
I don’t believe that’s the case. The smartshunt will display the charging situation on an app and has coms with Cerbo, but I don’t think it will work directly with a DC/DC charger. That said, I could be wrong so if you have found that in a manual somewhere please cite the page and manual so I can learn more.
I spent some quality time this morning with good coffe and some victron manuals.
Without any satire I can say that I love good manuals. This is maybe… 70% of the reason why I tend to buy victron products.
Below I am paraphrasing from the manual for Orion XS:
My conclusion is that a victron smartshunt/bmw can work together with the victron DC-DC chargers. Although I am not sure if this is applicable for older models.
ps. I also think that there is a method to set up a signal wire from the relay on the BMW 712. But I would like to try it out in real life before I am a 100% sure.
References:
BMW 712
relevant chapters:
4.4.3 Charger Mode – Battery settings
4.6 Remote Sensing with VE. Smart Networking
Hi Henrik,
That’s great news! I have to confess that even though I, like you, am a big fan of Victron manual reading I’m a bit burned out after all the research for the lithium series, so thanks for doing the research, very useful.
Hi Henrik and John,
The SmartShunt, and indeed the BMV 712 as well, can cooperate with Victron chargers that have VE net or similar. They can both use Bluetooth as well as a VE cable connection. The BMV 702 is the same unit as the 712, but has no Bluetooth so it can only use the cable.
The info from the battery monitors will by default become the preferred battery sensing method, ditching the DC-DC, AC charger or solar regulator sensors. The units with such functionality can also use the info to adapt the charging.
However, to remedy the issues mentioned in this article, you need to go into the expert settings, which isn’t always for the faint of heart. I’m also not entirely sure that the currently available settings options are sufficient. I haven’t researched enough to become certain, but I think there are still issues.
At the moment, I’ve set the saturation time (constant Voltage, 13,8V @ diminishing Amps) to 10 minutes, which is plenty for batteries that are properly balanced. Still this isn’t a full solution to the problem. I’m still looking for a better method. I don’t have a Victron BMS, so it’s not a walk in the park.
Hi, Stein,
Thanks for the further research. I fear you are right and that to get the kind of functionality we want here, in the absence of a smart BMS, Victron Cerbo may be required. Anyway, I need to dig deep into this. In fact I have got interested enough that I’m thinking of going back to Victron monitoring on the J/109, as I had on the M&R 56, since I hate the Balmar I tried as an experiment. I might even fit Cerbo as well. In the mean time, there is some deep manual reading in my future!
There really is no substitute for having the BMS – the only automation system aboard that really knows what’s happening inside the battery – control the shutdown of charging sources.
Most electric cars now have a user-intent-aware BMS. If you aren’t planning a long trip that day, the BMS has the option to terminate charging at about 80% full. And if the car is going to be mothballed for six weeks, holding the charge closer to 50% might be preferred. Only if you tell it that you need the full capacity for the next morning’s run will it bring the state of charge to 100% overnight. For maximum longevity of a boat’s LFP house bank when solar panels or shorepower chargers are in use, a similar capability may be desirable.
Hi Matt,
Yes, I think user-intent charging will be the next step forward on boats too. Or better yet a system that learns charge and discharge patterns and then cuts off charging accordingly, probably with a user override. The latest Macs have exactly this functionality built in to the operating system.
Hi John,
Totally agree on solar being great for lead acid and potentially very detrimental to lithium if not managed correctly.
I am curious what your charge profile looks like. It appears you may be going to bulk briefly then holding at absorption for a while, is that right? If so, why is it holding in absorption for so long? Or am I misinterpreting and you have your float set that high?
I have been kind of debating how to program ours. The last 2 years we have used a Victron SmartSolar controller. When just weekending, I use their adaptive absorption which seems to do a decent job. We transition from bulk to absorption at a pretty high state of charge when the alternator isn’t helping but when the alternator is on, that kind of confuses it and we end up floating early. Even if we don’t get fully charged that day, the next day we certainly will so I don’t worry about it. Interestingly, our charger seems to put 4-6Ah into the batteries everyday when the batteries have no load (there is a DC to DC charger that is always on but draws less than 1/4 that). However, when cruising we switch to a manual absorption setting based on time as the adaptive one floats early more than I like and I would rather over than undercharge our lead acids.
Eric
Hi Eric,
Well first off the boat monitoring system voltage reads about 0.2 volts high. The regulator is from Genasun and not very smart. It’s not programmable and tends to stay in absorption for longer than it should. I would have preferred one from Victron that I could mess with but since my solar panel is just 50 Watts I needed a boost controller and Victron don’t make one. Bruce at OPE recommended this one.
Anyway, I don’t worry much about staying in absorption for too long. In my experience on the M&R 56 good quality AGM batteries really don’t seem to mind. On that boat the start battery was held at acceptance most of the time the service bank was being charged by the alternator, probably some 4000 hours over 10 years and it was still fine.
Not ideal I know, and today I would have used a DC/DC to avoid that, as I do on the J/109.
Anyway, as you say, with lead acid, better a bit overcharged than under.
Hi John,
Thanks, that makes sense. It is good to hear that you are comfortable overcharging AGM’s that much, I would definitely be comfortable overcharging flooded batteries that much, we would just add a bit of extra water. Most of my experience with AGM was in applications where we were struggling to generate enough power so undercharging was the concern and not overcharging.
We used a Genasun charger for our panel for 9 years on Rod Collin’s recommendation and there didn’t seem to be any ill effect on the batteries, at the time we got it there were not as many options and it seemed to be the best for the batteries. We switched to the Victron when the Genasun stopped working and I opened it up to find that one of the through hole solder points had the solder melted out. Our panel was the max rated size for that controller so rather than soldering it back together, I decided to swap as there were other signs of things getting warm.
Eric
Perhaps you already have it, but I couldn’t find anything here detailing your solar panel setup. I’m a laggard – still running 2x 12V Lifeline AGMs GPL-8DL 255Ah. I am now wanting to add a solar panel to keep them topped up when I’m away from the boat for extended periods. As always, I come here to see “best practice” but my search didn’t flush out info on the panels. Can anyone point me in the right direction?
Hi Steven,
You are right, it is some time since we have done anything specifically on solar panels. That said, here is one by Colin that’s a bit out of date, but the fundamentals are still right: https://www.morganscloud.com/2012/11/10/staying-in-charge-part-iii-solar-power/
And here is one by Eric on sizing: https://www.morganscloud.com/2023/01/24/balancing-battery-bank-and-solar-array-size/
I would add that you really can’t go wrong with controllers from Victron.
Note that Victron don’t make a boost controller so if the panel voltage is less than the battery voltage (very small panel) they won’t work for you.
And OPE has a good page on solar panel options: https://oceanplanetenergy.com/solar-overview/
I’m using a small Solbian SP stuck to the deck and so far (one season) it’s working well.
I love these articles, and very much appreciate the detailed explanations and follow up comments….. As someone who can’t (or won’t) afford a Victron backbone or core components I have been researching a combination of Lead Acid AND Lithium via Emily&Clark’s Adventures Bank Manager … Without going into all the details it appears to solve for the issue you mention above (including user intent options) and wondered if this is something you have reviewed or researched?
Hi Brian,
Yes, I have reviewed and researched that option and am not a fan. Paralleling lead and lithium is fundamental dangerous and that’s just one of many problems with his system. That guy is a classic example of someone who is a such a great YouTube presenter that he can hide that, in my opinion, he has no idea what he is doing.
Also, one look at his boat confirms that he rarely—solar panels on the pulpit for crying out loud—,if ever, goes anywhere, another reason not to listen to him.
If you want a less expensive option that is not dangerous and will last well, and can be upgraded as required, I will be detailing it in the next part of the buyer’s guide. All written and due in two weeks.
Victron stuff fills the bill quite well. Many say they can’t pay for it but in the end they are paying up by doing without. Are there others that can do the same. Possibly but most of the crap from you know where should be avoided. Lithium setups can be used quite well if the right controls are in place. I went all victron with my lithium DC system
Upgrade because I wanted full control and something that worked Well.