Batteries - Balancing.

[solarnoobie]

Hello -

Do batteries in series connected to a load auto-balance?

Say you had a series of "12V" batteries at:

11V / 12.0V / 10.0 V

Since the 12.0V has a higher volt, the current would flow out of that battery, and into both the 11.0V and 10.0V (to a greater extent), no?

[russ]

Like water in connected buckets?

[billvon]

Say you had a series of "12V" batteries at: 11V / 12.0V / 10.0 V

Since the 12.0V has a higher volt, the current would flow out of that battery, and into both the 11.0V and 10.0V (to a greater extent), no?

No. Current cannot flow within series connected batteries. The only way to balance such a system is to overcharge the battery string. The 12V battery will overcharge and outgas (lose water) while the rest of the batteries charge to full. This is hard on the batteries.

If you want to balance two 12V batteries, use a battery balancer like the EQ 12/24-20A.

[russ]

No. Current cannot flow within series connected batteries. The only way to balance such a system is to overcharge the battery string. The 12V battery will overcharge and outgas (lose water) while the rest of the batteries charge to full. This is hard on the batteries.

If you want to balance two 12V batteries, use a battery balancer like the EQ 12/24-20A.

Did you see the battery voltages he gave? 11V / 12.0V / 10.0 V

That means the batteries are not usable - Forget any equalization for such a case.

Water levels in interconnected buckets and battery voltages have zero in common.

[Wy_White_Wolf]

Did you see the battery voltages he gave? 11V / 12.0V / 10.0 V

That means the batteries are not usable - Forget any equalization for such a case.

Water levels in interconnected buckets and battery voltages have zero in common.

I would agree if the batteries are wired parallel, but not when wired in series. There is no way for the batterys or cells to self equalize (balance) when wired in series.

WWW

[Sunking]

In a series circuit, the current is equal in all components. Yes over time the cells will become unbalanced because each cell is not exactly identical. That is why Flooded Lead Acid batteries need an Equalization Charge periodically when indicated by specific gravity test. An EQ Charge is a controlled over charge.

[inetdog]

In a series circuit, the current is equal in all components. Yes over time the cells will become unbalanced because each cell is not exactly identical. That is why Flooded Lead Acid batteries need an Equalization Charge periodically when indicated by specific gravity test. An EQ Charge is a controlled over charge.

The only other option to overcharging the full batteries to get a full charge on the low ones is to take them out of the series string and put them on individual chargers. Or (serious technical difficulty and not to be attempted casually) putting a floating charger onto each weak cell while it is still series connected.

The reason that the equalize method is not a universal solution is that for some battery types the forced overcharge will damage the full cells. FLA and NiFe (don't go there in this thread!) can tolerate controlled overcharge just by topping off the electrolyte. A Gel or AGM battery cannot.
High tech series strings (think EV, Hybrid, etc.) can include a mechanism for bypassing charging current around the full cells to get equalization without overcharge.

[billvon]

There is no way for the batterys or cells to self equalize (balance) when wired in series.

They do, actually. (Although as Russ pointed out even equalization won't recover completely dead batteries.) This is due to the characteristic of lead acid batteries that allows overcharge - so the high battery overcharges and the low battery is charged until it's full. Same current to all batteries, but the highest charge batteries "waste" that current by outgassing. In flooded batteries the water can be replenished; in VRLA batteries it's lost permanently so it's not a good solution.

Many technologies (like Li-ion) absolutely cannot handle overcharge - and thus need external equalizers/balancers to ensure that overcharge never happens.