Solar charging batteries

tpenfield

tpenfield

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Those voltage readings look a bit suspect. It will be interesting to see what you get with the batteries at their 'resting' voltage (charger disconnected) after a day or 2 of charging.

Those are 50 Ah batteries, IIRC, so they should charge in a day or so. I know my AGM batteries, which were almost flat dead, took a few days to charge up. But my LiFePO4 batteries were not as difficult, since the low-voltage protection kicked in.

I am wondering if the BMS is those batteries do not have all of the typical features? :unsure:

Once you get charged, you should have a resting voltage of about 13.3 volts.
 
Grub54891

Grub54891

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At the shop we have a yard trailer, one tech put a small solar charger on it and it did not work well. Another tech put a regulator on the charger of some kind and now it works perfectly. I’ll try to get a model of the regulator this coming week. Note: I did not read all the responses on this thread.
 
A

airshot

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Why so slow ? My LifePo4 battery charges over nite and that is 140 ah...do you have enough charger ?
 
redneck joe

redneck joe

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It is a 20 amp. If you have not read the whole thread these were left unattended for a couple years and when I started this a few days ago this one read less than 1v. Im assuming, since I don't know sh.t about them that it is waking g up from the dead and that may take longer.

Iirc 11.6 is the magic number to know if there is a chance at resurrection,
 
tpenfield

tpenfield

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If/When the voltage gets up into the 12.5+ range, I would disconnect from the charger to see if the voltage holds.

When charging a battery is often difficult to determine how much of the voltage is the battery vs. how much is the charger.

Anyway, the rate of charging is suspect. It is almost at the rate that you might expect from a trickle charger.
 
A

airshot

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It will be a miracle if they come back, usually once dead, they are dead forever.
 
tpenfield

tpenfield

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Following this battery charging saga . . . here is the progress summary.
Screenshot 2025-10-14 at 6.16.40 AM.png
I do better with pictures :LOL:
 
tpenfield

tpenfield

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I think on the other battery, where the charger would go on & off, it is probably dead.

The 0.49v and then the 14.48v readings are the charger cycling for '0 volt activation', but the battery is not activating.

Still a puzzle as to why/how the other battery is taking so long to come up. Might be more of a charger issue than a battery issue.
 
Grub54891

Grub54891

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Can you “trick” the charge into thinking there is life in it? I know with modern chargers you have to have a load of sorts to get the chargers to sense it. Solar may not work like that.
 
tpenfield

tpenfield

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If the voltage numbers are correct, and you assume that the battery has no more than 20% charge after 4 days based on the voltage, then it looks like the charger is running at about 100 milliamps (basically float charging).
 
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