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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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JohnC avatar image JohnC ♦ danjwilko commented ·
@Danjwilko

Take care what you read on the webs. V is a coarse guide only. And a 50% SOC in my real world is useless for anything more than a trickle load under alarm conditions. 75% for me is as low as I budget for, and 70% is an absolute emergency.

I've a well tuned Smartshunt, and recommend you put your worries towards setting that up correctly. You need to be able to trust something, but V isn't up there for me.

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danjwilko avatar image danjwilko JohnC ♦ commented ·

img-6045.png

So added the additional 2 batteries in, set the ah to 345 (6 115 batteries wired into 24v).

Looks like it holds up fairly well, so voltage will read a little lower than being stood, they do have a 0.5amp constant draw due to the inverter and ancillaries.

I think I’ve got the shunt set up properly from info I’ve read.

I thought the voltage would drop off more the lower the state of charge went but seems to be holding up well around the 24.4-24.2 region given that the fridge/freezer draws 100-200w so 5-10 amp periodically.

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christern avatar image christern danjwilko commented ·

Some notes.

Looking at the voltage to identify the state of your batteries is not that precise and assumes the batteries are left without charging/discharging for at least 24 hours. This is often forgotten.
I agree with @JohnC that you should focus on the shunt and its settings.

(I have stopped using Ctek-chargers since they kick in full charging once connected and with my usage, where I connect my boat once a week during winter, they start a new charging schedule every time. They also use a function of increasing the voltage a short time every now and then to learn how the batteries behave. This could damage the batteries. Instead I have started using a Victron Smart charger which I set in Power Supply mode at Storage voltage (13,2V) during winter. A safer way to keep my batteries healthy.)

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danjwilko avatar image danjwilko christern commented ·

yes very true, regarding resting voltage I did wonder when your technically supposed to take the reading.

I do try keep tabs on it but with the constant use with the appliances it makes it difficult.

Now the supply feature sounds a great feature, I’ve literally just bought a noco genius 5 to assist charging all the batteries every one in a while for balancing purposes, which I know the 10 has the supply feature but it doesn’t play well with long term supply and usually shows faulty battery after a few days, anywho I will return the genius 5 and look into the victron smart chargers would you stick with a 12v or go 24v considering that’s the what the bank as a whole is (didn’t even realise victron did them).

Will also have a look at a victron battery balancer while I’m at it.

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