Can you balance batteries by putting them in parallel?

[coalfield]

Can batteries (AGM) simply be connected in parallel and left to rest to balance themselves?

I am awaiting a balancer to be delivered, and curretly have 4xAGM with mismatched voltages between 13-14Volts. Would like to be able to balance them just to ensure the charger does not over volt single battery when charging while waiting for my balancer.

My understanding was if you but them in parallel (no charger) then will balance themselves out.

Note they are all the same 12v, age, brand and Ah.

 

[MurphyGuy]

Yes. But why would you use a balancer on lead acid? Any decent charger will have an equalize function.

 

[Topper]

Hooking them up in parallel will simply average out the voltages overall.
If you're going through the motions anyway, I would parallel charge them as per manufacturer spec to bring them back up to capacity.
It should assist in regaining some lost capacity of any partially sulfated cells.
Any aged lead acids of any kind (flooded, AGM, gel) will eventually stray high and low in a series connected application.

 

[mikefitz]

. But why would you use a balancer on lead acid?

if you are series connected.

Battery Balancer - Victron Energy

Equalize the state of charge of two series connected 12V batteries using the Battery Balancer. Find a Victron Energy dealer near you.

www.victronenergy.com

section 3.4

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

Mike

 

[MichaelK]

Since they are AGM batteries, I'd check first with the manufacturer whether or not they can even be equalized? Equalization usually requires higher than normal voltage, which might be a no-no for AGM. I think your best solution is to fully charge both strings first, then parallel them.

 

[time2roll]

Some balancing will occur. If you put them in series service watch the voltage of each closely to avoid going too far above the voltage specification. Maybe set the charger voltage on the low side until the balancer is connected.

 

[coalfield]

Thanks for the feedback and for clarity I have 4 to run in a 2S 2P configuration to 24v.

i cant charge them in parallel as it would give me 48V, unless I did it in 2 batches (which is an option).

The voltages are only up to 0.2V out, however when on the charger I was having one battery hit 15V on the charge hence I stopped it.

Maybe best to just wait for the balancer, but its from China and taking a while. was tempted to get this in the meantime

 

[coalfield]

if you are series connected.

Battery Balancer - Victron Energy

Equalize the state of charge of two series connected 12V batteries using the Battery Balancer. Find a Victron Energy dealer near you.

www.victronenergy.com

section 3.4

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

Mike

This is a really useful doc, it looks like it will be perfect for my needs..



What I am not 100% sure of is the 2nd part here, it says make sure each string is connected with a common busbar. I don't see many people use this on a lead acid. Will it really make much difference if the cables are a decent quality>.

Wiring and cabling alone will be a nightmare with a common busbar... so keen to know if this is essential!

 

[Topper]

I ran a fused common on my old agm set. 1 fuse per pair leading to the balancer. It worked well.
I never like any wiring without some level of protection .

 

[LB3]

AGM’s can take a bit of abuse. To top balance you basically just boil all the batteries until the lowest one catches up.

 

[Hedges]

I would fully charge individually.
I've been using a little 4A Harbor Freight charger for that. It supports both 6V and 12V batteries.

Busbar? for 4 batteries connected 2s2p, just wiring the together than connecting leads to diagonally opposite corners makes perfect balance.
If a busbar is convenient, the one lead coming off corner of four batteries can go to the busbar.
In my case I have 8s (6V) batteries so no corners, but the wire go to a negative busbar for four loads (inverters).

 

[coalfield]

Has anyone had experience connecting the midpoints, is this a standard thing to do? Victron require it for their balancer...



I presume this would not cause any issues especially as they require it however I have not seen this before in a 2P 2S (or 3P 2S as in the diagram) before? Is this common practice?

EDIT: Looks like people are saying midpoints need to be connected with a fuse (5A). I don't really understand as there is a conflict between the Victron manual which says that the midpoint cabling needs to carry the full current between the batteries, but with a 5A fuse this would imply it never needs to carry much current.

Any advise on this appreciated!

 

[mikefitz]

says that the midpoint cabling needs to carry the full current

to reduce volt drops, and ensure the mid point is the same for all the batteries, the balancer itself only takes around one amp. ( as shown in the diagram the final cable to the balancer from the mid point is a smaller gauge)

Mike

 

[coalfield]

to reduce volt drops, and ensure the mid point is the same for all the batteries, the balancer itself only takes around one amp. ( as shown in the diagram the final cable to the balancer from the mid point is a smaller gauge)

Mike

thanks so I can connect the midpoints with 35mm cable (same cable my batteries are connected with), and a smaller gauge for the balancer.

Should the link between the 2 midpoints be fused?

 

[mikefitz]

Should the link between the 2 midpoints be fused?

Dont think think that would be an good idea as may introduce volt drops. Only needs a fuse where the connection to the balancer is made.
With your 4 x 12v batteries the min point heavy duty cable is effectively connecting each 12v pair in parallel ensuring they appear as one 'big battery' to the balance unit. It also ensures the pairs self balance as '12v batteries in parallel'.

Mike

 

[coalfield]

Dont think think that would be an good idea as may introduce volt drops. Only needs a fuse where the connection to the balancer is made.
With your 4 x 12v batteries the min point heavy duty cable is effectively connecting each 12v pair in parallel ensuring they appear as one 'big battery' to the balance unit. It also ensures the pairs self balance as '12v batteries in parallel'.

Mike

OK thank you, that was my concern getting a 5A fuse on a 35mm cable would be difficult.

I haven't currently fused the midpoint connection to the balancer so will look into that!