Unequal voltages in AGM battery bank

[SamDeleted]

Hi all, I'm a bit confused here. I'm getting different voltages across my 6 AGM 12v battery bank. Have I done something wrong ?

Each battery was fully charged before I linked them together , battery #1 is reading 13.18v, battery #2 12.97v

I think I've wired it up right? 24v , 2 series, 3 parallel

Pos to Neg to make 24v , and then each set of two batteries wired to a central bus (big 200amp block)

All wires are the same length,

Forgive my not so technical drawing

 

[SamDeleted]

When I put them on charge just now

Even though the Victron charger is set to the correct float voltage stated in the batteries data sheet (28v in this weather) , the first battery shot up to 14.5v , the second went down to 13.5v ??

Very strange...
I am confused .

 

[Substrate]

A few possibilities:

The battery that shoots up to 14.5v may either be the healthiest out of the rest, OR, it may be the most sulfated, and shooting up to 14.5v long before the rest, due to reduced capacity from hard sulfation.

How much current did you use when you charged each one up individually? Those SBS batteries are TPPL, (thin plate pure lead), and generally pure-leads can be pampered to death. Look for your SBS technical manual, and you *may* find that they recommend a *minimum* of 0.3C or more when charging.

And of course afterwards, these agm's should not be pampered either by weak solar array current. If they are, suggest use of some sort of higher-current refresh from time to time.

Check with your Enersys / SBS technical manual to see if there is a minimum current recommendation.

 

[OzSolar]

Each battery was fully charged before I linked them together , battery #1 is reading 13.18v, battery #2 12.97v

It does appear that you've wired them correctly.

I've fiddled with that family of battery and had similar experiences.

I finally ended up using a 30V/10a power supply on them individually to hold them at the voltage the SBS manual (can't remember what that was now) recommended until the amps tapered down to less than 2. Then I could finally call them fully charged(ish). Put them back in series and had less of a delta that got better after a few cycles but never fully corrected. I finally solved it when I quit checking them. LOL

Another option would be a permanently installed battery balancer on each 24v set.

YMMV

 

[T-486 Ashepoo]

The flat washer with the wingnut may be preventing a flat secure connection. Try replacing both with a regular bolt and tighten to spec.

 

[SamDeleted]

Put them back in series and had less of a delta that got better after a few cycles but never fully corrected. I finally solved it when I quit checking them. LOL

Hahaha !

 

[SamDeleted]

I will try all suggestions and get back, thanks all

 

[SamDeleted]

Right first off I have checked all connections, I'm going to get some proper nuts but right now they look pretty flat and firm to me



I put a small load on the bank only about 100w , under load all 6 batteries have equalised to within 0.1v.

I'm going to keep drawing on them for a good while and then I'll let them sit, see what happens , I'm hopeful

 

[OzSolar]

Hahaha !

Sometimes you just have to move on, right?

 

[Substrate]

Were you able to actually measure what amount of current the 30v/10A power supply was putting out when charging?

It could be far less than 10A !

Perhaps you are annoying them more than charging them. TPPL doesn't like the baby-touch. Consider that the primary purpose of these is usually for UPS duties, where fast recharge and high-currents to do so are the norm.