different voltage on one string

[Raul]

After inetdog pointed out on a different tread(thank you) that a shunt to monitor a battery bank is not absolute reliable as you will need to measure individual batteries as well, I did and to my surprise I found 12.65;12.60;12.72;12.65. This is string of 4 batteries of 12v into a 48v system. That's a difference of 0.12v between the 2 of them under a constant 250w load as the bank is feeding the inverter where I got a fridge/freezer ,tv and lighting . This translates to about 0.02 per cell , is it acceptable ?
I came across on the net a while ago about a device that you fit in the string between the batteries to direct current accordingly so it balances out but can't find it anymore.

The battery links are 25mm copper cable with crimped and soldered copper end lugs.
Any input is much appreciated . Thank you

[Sunking]

It means you need to run an EQ charge.

[Raul]

They are AGM sealed so I cancelled the equalising charge on the controller . I can change the bulk , absorb but cant change the float , is set at 55.20 unless I download the soft and purchase a pc link cable.

[SunEagle]

After inetdog pointed out on a different tread(thank you) that a shunt to monitor a battery bank is not absolute reliable as you will need to measure individual batteries as well, I did and to my surprise I found 12.65;12.60;12.72;12.65. This is string of 4 batteries of 12v into a 48v system. That's a difference of 0.12v between the 2 of them under a constant 250w load as the bank is feeding the inverter where I got a fridge/freezer ,tv and lighting . This translates to about 0.02 per cell , is it acceptable ?
I came across on the net a while ago about a device that you fit in the string between the batteries to direct current accordingly so it balances out but can't find it anymore.

The battery links are 25mm copper cable with crimped and soldered copper end lugs.
Any input is much appreciated . Thank you

Did you measure each battery more than once and was the 0.12v difference the same each time?

I found that using even an expensive "middle end" fluke digital voltmeter there would be slight differences in voltage measurements of the same source. Mostly has to do with how the probes make contact with the battery terminals and the built in error of the meter.

[Raul]

I had different readings maybe 5 times? But this was the highest difference. I will take the bank off line tonight and let it rest . Will see what I get in the morning . Today got a full absorb as it was a brighter day and the Pv output covered my consumption and more .
This is the system I done to fit it to my Holliday home in the mountains so it gets a good test here before I take it over . I'm trying to replicate almost the same loads I would run over there and so far I'm impressed.

Pv - 300+250w one string
-285 +260w 2nd string
6mm Pv cable into Dc disconnect
Then 16mm into CC
Highest output with load on 927w partially sunny.

Mppt 150v/35a-98% efficiency
Connected with 16mm copper to the bank.
8x12v 100a agm = 2 paralel strings of 48v
And a 1200w pure sine wave 96% efficiency with a Eco function for stand by (2w) connected via a 10mm copper cable 30a fuse.
Total cost £1380

[inetdog]

You cannot run a high voltage EQ charge on AGM batteries, but you can run an extended absorb/float at a slightly higher voltage with limited current to get the same effect. Check the instructions for your particular batteries. (If your AGM are not really VRLA sealed, all bets are off.)

Or you can separate the batteries and charge them individually.

[Naptown]

Actually some you can
But I doubt the OP has Concorde bstteries

[Raul]

They are VRLA and actually I did turn the bulk/absorb down a bit maybe that's why. The settings I run now are for gel to avoid gasing but it may be to low? .
I will reset it to agm and see how it goes.
This bank are used batts that I bought for a tad above scrap value so I don't ruin a expensive bank.
They are quite healthy still as with a 250w load over 10 hrs I get 50.6~ 50.8v in the morning left in the bank. That's a good 75% capacity unused . The actual load that I'm going to use will be far less than that so its good to know that will do the job.
Thanks guys.

[almac]

whats the story with my battery bank? iv got 4 x 12v marine batteries 2 sets of 2 batteries in series to make a 24v bank. so i have 2 x 12v batteries in parallel and another 2 x 12v batteries in parallel. then these 2 sets in series. after charging all day on the solar panels i put them all in parallel and put them on a 12v charger. they register as full , drawing 6amps over all 4 batteries. when i do the SG on each battery, one is 1.250 the other 3 are about 1.240

[inetdog]

whats the story with my battery bank? iv got 4 x 12v marine batteries 2 sets of 2 batteries in series to make a 24v bank. so i have 2 x 12v batteries in parallel and another 2 x 12v batteries in parallel. then these 2 sets in series. after charging all day on the solar panels i put them all in parallel and put them on a 12v charger. they register as full , drawing 6amps over all 4 batteries. when i do the SG on each battery, one is 1.250 the other 3 are about 1.240

Not sure what is going on with your batteries, but you should be aware that the recommended configuration for Lead Acid chemistry, but not for Lithium, is to put two batteries in each series string and then put the two strings in parallel.
See if that makes a difference.

[almac]

Not sure what is going on with your batteries, but you should be aware that the recommended configuration for Lead Acid chemistry, but not for Lithium, is to put two batteries in each series string and then put the two strings in parallel.
See if that makes a difference.

thanks, after doing some research i have concluded that the solar charger charged with a gentle lower current with limited gassing so the electrolyte did not rise to the top where my hydrometer took the reading. i often charge off the gen at 40amps for 300ah bank at 14.8v. it is winter here the temp is around 13 deg c so the higher voltage. although this might be a bit high. the CC is set at 29.6v to compensate for the cool short days but this might also be a bit high. looks like the panels charged the bank well, it was a sunny day .

[almac]

Not sure what is going on with your batteries, but you should be aware that the recommended configuration for Lead Acid chemistry, but not for Lithium, is to put two batteries in each series string and then put the two strings in parallel.
See if that makes a difference.

after another day charging the SG is about 1.225 on all but one of the batteries.
have reconfigured the batteries to 2 separate series strings arranges in parallel. will find out if the SG improves

[Raul]

Update
I swiched back the absorb from 2.3 to 2.4 pc and at rest open voltage 13.24 , 13.25, 13.25 ,13.26 that's more like it . Under load the same difference 0.01 .
The cc has a clever function . When it switches on at sun rise it measures the voltage left in the bank then it works out the absorb duration for the day according to the voltage found .
If is very low 4 hrs then 3, 2 , and 1 or less up , if voltage found is high . That's to protect for overcharge if bank is idle.