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danjwilko avatar image
danjwilko asked

Are my lead acid batteries about done?

Hi all,

I have a 24v battery bank consisting of 4 12v 115ah batteries.

i fully charged all the batteries with a ctek charger before hand and the. reconnected everything up.

I’ve set the battery bank capacity to 200ah for age of the batteries and not wanting to discharge past 50% too much.

Anyway the shunt was reset to 100%, and I’ve had it hooked up to the fridge freezer for the last day or so.

Image below shows from 94% didn’t quite fit the 100% frame in without making it all tiny.

The shunt is indicating 84% yet the batteries are already down to 24.3v.

I’ve tested the batteries for balance, 2 are 12.15 the other two are 12.20.

I’ve double and triple checked the setting for the shunt and the mppt.

Any help would be appreciated.

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1 Answer
JohnC avatar image
JohnC answered ·

Hi @Danjwilko

Those figures indicate no issues whatsoever to me. In fact they're holding up V better than my own do. But you've doctored the Ah, so can't compare really. You don't mention batt Temperature either, cold batts suffer V sag under load more than warm ones do.

I'd put your Ah setting back to where it should be, and treat them normally.

That Mid Point Deviation is a good thing to keep an eye on. A weak cell will soon jump that level way higher. You may not have the midpoint of your 2 batt strings connected, so you could move (or switch) that occasionally to check.

Charging them all as a 24V group might show issues that discharge won't.

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danjwilko avatar image danjwilko commented ·

Appreciate the info, I think it’s more that the depth of discharge figures for 50% are frequently talked about on the solar forum as being around 12.2v, so with the 24v setup I assumed 24.4v would be around that figure. Which made me think with the voltage dropping down to that level something might have been amiss.

Or am I missing something on the voltage front?

The midpoint is connected and so far hovers around the same % during discharge, stays around 0.2% when sat resting, but on charging I have seen it spike to around 1.9% but settles down soon after.

Il try switching occasionally to see if we do get any issues.

The batteries are kept indoors, which the room temp hovers around 16-18C



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