24V parralel imbalances

My friend has 2x12V batteries connected in parallel. When i checked the voltage on each batterry, one is showing 12.0V, the other 14.8V and the system 26.9.

I think I know what his issue may be... he has a DC 12/24V fridge connected to one battery (yes... the one that reads 12V).

My system consists of 4x12V in parallel/series and all batterries are showing the same Voltage and i haveno DC loads.

Is the solution as simple as to connect his fridge at the 24V terminals? Did he possibly damage his batterries? They are AGM's and as i understand, not to be equalized... right?

Thanks!

CoachMcG said:

My friend has 2x12V batteries connected in parallel. When i checked the voltage on each batterry, one is showing 12.0V, the other 14.8V and the system 26.9.

I think I know what his issue may be... he has a DC 12/24V fridge connected to one battery (yes... the one that reads 12V).

My system consists of 4x12V in parallel/series and all batterries are showing the same Voltage and i haveno DC loads.

Is the solution as simple as to connect his fridge at the 24V terminals? Did he possibly damage his batterries? They are AGM's and as i understand, not to be equalized... right?

Thanks!

Click to expand...

Don’t you mean ‘connected in series’?

12V + 14.8V = 26.8V

If so, either the 2 batteries have very different capacities or they were not properly top-balanced.

Or, if he is tapping off 12V for a fridge, then of course he is depleting that one cell far more than the second and creating imbalance.

If he can run the fridge at 24V and properly balance both cells by charging to 12V in parallel before connecting in parallel, there is a chance he has not damaged the 14+V cell from overcharging with a 24V charger...

Your friend has two 12V batteries in SERIES, not parallel.

He's demonstrated exactly why you can't pull 12V from one battery in a 24V system. There's a good chance he severely damaged both batteries. 12V from a 24V battery should use a 24 to 12VDC converter. Lots of cheap ones on Amazon.

If his fridge truly is 24V, then yes, just connect it to the battery.

What needs to happen first is the batteries need to be placed in PARALLEL where there voltage measures in the 12V arena. They need to be fully charged in parallel with the + charge lead placed on one 12V battery and the - charge lead placed on the other 12V. Once charged, place in series for 24V. They should then be monitored for voltage deviations. Good chance they both need to be replaced.

Charge both batteries before connecting the fridge?

He is running a 24V inverter charger so can he still connect in 12V parallel and charge that way?

Or, should he disconnect the Inverter charger altogether then connect the leads that are coming frome the charge controller to the batteries?

CoachMcG said:

Or, should he disconnect the Inverter charger altogether then connect the leads that are coming frome the charge controller to the batteries?

Click to expand...

This or use a different 12V charger. Sometimes SCCs don't like to switch back and forth. it would likely need to be reprogrammed for the optimal voltages.

Thanks! Fingers crossed!

Yes my bad...he's connected in Series!

fafrd said:

Don’t you mean ‘connected in series’?

12V + 14.8V = 26.8V

If so, either the 2 batteries have very different capacities or they were not properly top-balanced.

Or, if he is tapping off 12V for a fridge, then of course he is depleting that one cell far more than the second and creating imbalance.

If he can run the fridge at 24V and properly balance both cells by charging to 12V in parallel before connecting in parallel, there is a chance he has not damaged the 14+V cell from overcharging with a 24V charger...

Click to expand...

Ju

snoobler said:

Your friend has two 12V batteries in SERIES, not parallel.

He's demonstrated exactly why you can't pull 12V from one battery in a 24V system. There's a good chance he severely damaged both batteries. 12V from a 24V battery should use a 24 to 12VDC converter. Lots of cheap ones on Amazon.

If his fridge truly is 24V, then yes, just connect it to the battery.

What needs to happen first is the batteries need to be placed in PARALLEL where there voltage measures in the 12V arena. They need to be fully charged in parallel with the + charge lead placed on one 12V battery and the - charge lead placed on the other 12V. Once charged, place in series for 24V. They should then be monitored for voltage deviations. Good chance they both need to be replaced.

Click to expand...

Just to be certain...

Battery A's + terminal to Batt B's + terminal;
Batt A's - terminal to Batt B's - terminal

Positive Lead from 12V charger to Batt A + terminal; Negative lead of 12VCharger to - terminal of Battery A OR Batt B?

I use a Ha01 24v balancer, works well,

CoachMcG said:

Ju

Just to be certain...

Battery A's + terminal to Batt B's + terminal;
Batt A's - terminal to Batt B's - terminal

Positive Lead from 12V charger to Batt A + terminal; Negative lead of 12VCharger to - terminal of Battery A OR Batt B?

Click to expand...

+ to + and - to -

charger + to Batt A +
charger - to Batt B -

You want the charger to go "across" the batteries, not just attached to one.

pollenface said:

I use a Ha01 24v balancer, works well,

https://www.amazon.com/PowMr-Battery-Equalizer-Voltage-Balancer/dp/B07L8XKZ71/ref=sr_1_5?dchild=1&keywords=ha01+balancer&qid=1615590546&sr=8-5

Click to expand...

Probably a good go-forward option, but best to parallel charge before re-deploying 24V.

This is different than equalization right? Pretty sure i read that these types of batteries shouldn't be charged in a four stage but just Bulk, absorption, float... makes sense?

Correct. Equalization is a deliberate over charge to higher voltage to break up light sulfidation on FLA batteries.

You are "equalizing" these batteries to the same 100% SoC via a bulk/absorp charge.

snoobler said:

+ to + and - to -

charger + to Batt A +
charger - to Batt B -

You want the charger to go "across" the batteries, not just attached to one.



Probably a good go-forward option, but best to parallel charge before re-deploying 24V.

Click to expand...

Update...

Parallel charged for approximately 3 hours. Each Battery showed same Voltage. Voltage was measured during charge (13.8) and with charger disconnected (13.4). Took batteries off the charger and removed the parallel connection. Batteries showed some improvements but were again showing different voltage 12.9 and 13.5 (can't remember exactly but very close to those numbers). Makes sense since they were no longer connected together in parallel.

Will charging for a longer period in parallel improve this? High amperage (40) for shorter period (Amps gradually decrease on his charger) or lower (2A) for a longer period (12 hrs? 24? 3 days?). We'll be monitoring for a bit to see if it'll come closer now that his fridge is properly connected.

The balancer suggested above would improve over time or it keeps adjusting to keep them balanced?

He wants to get one, i'm just curious on how it works. I'll have do do some more research this week?

Lead-acid batteries aren't fully charged until they've achieved 14.X and are held there typically for 2+ hours.

Lead-acid batteries shouldn't be charged at more than their rated charge current. In the absence of data, one assumes 10%, maybe 15%, e.g., a 100Ah battery should be charged at no more than 10A. Two in parallel, 20A.

Unless you're 100% certain the batteries attained 100% SoC, I would charge them individually to ensure they are each fully charged and then return them to series and assess.

As I indicated, there is a good chance that both batteries have been damaged. An AGM at 14.8V is over-volt and severe damage can occur. I expect that during charging voltage was even higher. An AGM at 12.0V is at < 50% SoC, and will eat itself. If the battery was ever used in that state, the low 12V was excessively discharged, and the high 12V was obviously over charged.

The balancers simply connect to each 12V and compare voltages. If one is lower, it actually transfers charge from the higher voltage battery to the lower voltage.

Depending on the application, balancers are only effective for batteries that are about 0.1-0.2V out of sync. More than that, and they can't keep up. They are vastly more effective at maintaining than they are at fixing.

I expect the outcome of this exercise will be replacement of both batteries.

Thanks for clarifying! Will try your suggestion!

If i'm reading this spec sheet correctly... 280Ah at 10% so max charge 28A or 56A if connected in parallel?

0.10-0.25C20. C20 is 280, so 28-70A/battery or about 56-140A for a parallel pair.

Absorption should be 14.7V. Curious that these have something like an equalization charge - the "Balance phase" permits up to 15.6V at 2.8A.

Again, I would charge them individually at this point. Charge as follows:

28-70A to 14.7V. Hold 14.7V until current drops to 2.8A or 5 hours.

Awesome!! Thanks

UPDATE
After charging as suggested above, the batteries showed 13.2V and 13.6V 4hours after they were removed from the charger.

Hoping this is an indicator of minimal damage and a long life ahead!

0.4V is huge 4 hours after being charged.

Once in series, I suspect you will see substantial voltage deviation.

Again, likely need to replace both.