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diy solar

How to handle having too much battery/solar for my loads

rmaddy

Full-time Solar-powered Trailer Life
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I seem to have a good problem to have but I'm worried about the effects on my batteries.

I have two 12V 206Ah LiFePO4 batteries in series (24V) and 990W of solar (3 330W in series) setup for my cargo trailer camper. On a sunny day I can run the A/C from noon until an hour or two after dark, run the fridge, charge my phone and laptop, and use a few lights. By morning my battery is only down to 85% SOC and the solar has them fully recharged well before noon. If I don't run the A/C after dark the battery is never below 95% in the morning. I've only been doing this for about 2 weeks so not a lot of data yet.

Basically my LiFePO4 batteries have only been below 95% SOC twice in 2 weeks. I'm sure a few cloudy hot days will give me a chance to get the SOC lower. But with the Fall coming there won't be many more days of A/C use.

It's my understanding that LiFePO4 doesn't like being kept at such a high SOC all of the time. Would it make sense for me to throw my PV disconnect breaker for a few days and let the SOC get down below 40% or 50% once in a while for the sake of the batteries?

I have a Victron 150/45 SCC but I don't any setting to say "hey, let the batteries get down to X before trying to charge them".
 
I think you will be fine. The key is that you are not keeping them at 100%. Even though they still pretty full, they are not at the max, and that is where most of the issue is.

On the victron, you can set the float voltage really low and increase the rebulk offset, and charging will not start again until that voltage is reached, or until the next day if it is not reached. But running A/C, I expect you would reach it.
 
I seem to have a good problem to have but I'm worried about the effects on my batteries.

I have two 12V 206Ah LiFePO4 batteries in series (24V) and 990W of solar (3 330W in series) setup for my cargo trailer camper. On a sunny day I can run the A/C from noon until an hour or two after dark, run the fridge, charge my phone and laptop, and use a few lights. By morning my battery is only down to 85% SOC and the solar has them fully recharged well before noon. If I don't run the A/C after dark the battery is never below 95% in the morning. I've only been doing this for about 2 weeks so not a lot of data yet.

Basically my LiFePO4 batteries have only been below 95% SOC twice in 2 weeks. I'm sure a few cloudy hot days will give me a chance to get the SOC lower. But with the Fall coming there won't be many more days of A/C use.

It's my understanding that LiFePO4 doesn't like being kept at such a high SOC all of the time. Would it make sense for me to throw my PV disconnect breaker for a few days and let the SOC get down below 40% or 50% once in a while for the sake of the batteries?

I have a Victron 150/45 SCC but I don't any setting to say "hey, let the batteries get down to X before trying to charge them".
? great problem to have. I suggest you celebrate. Wholy's advice sounded good, as well.
 
? great problem to have. I suggest you celebrate. Wholy's advice sounded good, as well.
I'm having a nice IPA at the moment while I watch the rain stop from a passing thunderstorm. I'm still getting 100W of solar at 6pm with only the slightest break in the clouds.
 
What are your charge settings?
What voltage are your batteries at 95% and how are you calculating 95%? (mostly curiosity)
Same curiosity for 85%.
I have a BMV-712 showing me actual SOC of the battery. Right now I'm back to 99.1% SOC and 26.64V.

Here are the battery settings from VictronConnect for the SCC. I haven't tried playing with the "Re-bulk voltage offset" yet.

IMG_3331.PNG
 
I think you will be fine. The key is that you are not keeping them at 100%. Even though they still pretty full, they are not at the max, and that is where most of the issue is.

On the victron, you can set the float voltage really low and increase the rebulk offset, and charging will not start again until that voltage is reached, or until the next day if it is not reached. But running A/C, I expect you would reach it.
Thanks. I hadn't noticed that setting under the Expert mode. I'll have to give it a try.
 
Right now I'm back to 99.1% SOC and 26.64V.
Thats 3.33V per cell. I think you have absolutely nothing to worry about holding your batteries/cells there. Thats a nice conservative charge. You are very fortunate that you don't need to stress your batteries to satisfy your power needs. Nice system.

Its interesting that your absorption takes you to 28.4V (3.55V per cell) for only .9% more capacity.
 
Its interesting that your absorption takes you to 28.4V (3.55V per cell) for only .9% more capacity.
It's possible my BMV settings and SCC settings are just a tiny bit off from each other. I'm now at 99.3% and 26.73V and a 48W load (but 80W coming in). I doubt I'll hit 100% tonight given the really low sun now.

Here's the battery settings from the BMV:

IMG_3332.PNG
 
I seem to have a good problem to have but I'm worried about the effects on my batteries.
All the solutions suggested so far only solve the problem by increasing the demand beyond your supply. A solution you are already aware of - " If I don't run the A/C after dark the battery is never below 95% in the morning."

I have dump loads that come on at certain over voltages. But these were all on early this morning so disconnected half my panels as the fix for now. I'll come back later to see other suggestions for your problem that I can use.
 
What inverter are you running that has such nice low idle consumption?
 
What inverter are you running that has such nice low idle consumption?
I have a Victron Multiplus Compact 24V/2000W/50A but it's so low because it's off :)

When it is on but idle it uses 13W. I have it setup in "search mode" which really lowers the idle power.

My only regular AC load is the A/C and I haven't actually needed it the last three days. I'll only need AC to recharge my electric razor once every two weeks, and rare uses with my power screwdriver batteries.
 
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What air conditioner are you running?

my system is not far from your specs with my charge settings almost identical to yours. I also only use 5-15% of the battery overnight on a regular basis. Very seldom deep discharges. I return to 100% almost every day
The system has been up and running close to three years and the resting voltage of my batteries (everything off) has not changed even .01v

I have talked to Battle Born several times and their usual response is “keep on using them, they’re going to last you a long time!”
 
What air conditioner are you running?
I have a window A/C. It's a Frigidaire 5000BTU model FFRE053WAE. It uses about 430W when running full on in Eco mode. I had an afternoon where it was 95+ºF and the A/C pretty much stayed on for two hours and the solar kept up with it the whole time. That was nice. In theory my batteries alone could run the A/C on full for over 11 hours but with my other regular loads it would be more like 9 hours. And that's at 100% duty cycle.

my system is not far from your specs with my charge settings almost identical to yours. I also only use 5-15% of the battery overnight on a regular basis. Very seldom deep discharges. I return to 100% almost every day
The system has been up and running close to three years and the resting voltage of my batteries (everything off) has not changed even .01v

I have talked to Battle Born several times and their usual response is “keep on using them, they’re going to last you a long time!”
That's nice to hear. Based on this and other feedback I guess I won't worry about it for now.
 
Its interesting that your absorption takes you to 28.4V (3.55V per cell) for only .9% more capacity.
Here's some info about today. I hit a low SOC of 93% at 26.53V about 6:40am. Then the solar started to trickle in and by about 9am the bulk charge was complete and I saw 100% SOC at 28.4V. Over the next 30 minutes the battery voltage settled to 27.0V where the solar kept it the rest of the day. During this time the SOC was being shown as 99.8%. I was gone most of the day so there was only a 15W load with spikes of 77W when the fridge cycled on. About 4pm I turned on the A/C. The solar is mostly shaded now so the A/C is on battery. I'm down to 92% SOC and falling. 92% SOC at 26.51V. Last night I was seeing 99.1% SOC at 26.64V. 7.1% SOC with only a 0.13V difference.
 
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