Best practices for managing 4 -12v 100ah as 48v pack

[trad]

Ok, now I've had a year with a 6000xp hooked up to 4 - 100ah 12v lithium batteries and being treated as lead acid. Mostly it's been fine, but just recently I had a battery start losing capacity (now it is down to 50ah). This throws the other 3 batteries way out of balance as the problem battery goes into high voltage shutdown way before the other batteries do, and it goes into low voltage shutdown way early as well.

I've seen this universal battery balancer proposed as a solution at Watts247 but I am not totally convinced that we should be constantly balancing from high voltage to low voltage. In the above case, where one battery begins to die, simply re-balancing from high voltage to low voltage like crazy only hides the real problem.

I know that buying a 48v server rack battery with battery communications is the accepted solution, but is there any way to go with 100ah 12v batteries and get the same set-it-and-forget-it ease of use?

 

[robbob2112]

If you are stringing 4 - 12v together you need to use an active balancer that is capable of 10amp. If you don't they will drift like you describe because of difference in internal resistance.

The math shows the more regular your charge/discharge cycle/amount is the quicker they will drift apart. The more random the pattern the less they will drift. If you charged and discharged exactly 4000Wh each day they would drift in only a week or so.

Typical solar usage means a fairly consistent charge with enough variance in usage to take a while. There are a couple of threads linked under my signature that have the results of simulation.

So, yes add the balancer and you will most likely cure your issue.

 

[timselectric]

but I am not totally convinced that we should be constantly balancing from high voltage to low voltage. In the above case, where one battery begins to die, simply re-balancing from high voltage to low voltage like crazy only hides the real problem.

A battery balancer is the only bandaid for your booboo.
But you should pull the batteries apart and charge them in parallel, so that they begin in balance.
And chalk it up to a lesson learned. So that you don't make the same mistake again.
Putting lead acid batteries in series is fine, because equalization charging balances them. But BMS controlled batteries should always be purchased at the correct system voltage.
BMS controlled batteries individually balance their own cells. But because each battery (group of cells) have no control over the other batteries, drift is inevitable.

 

[trad]

Has anyone used the Watts247 one referenced?

 

[robbob2112]

I'm using the LiTime version to string 2 - 12v to get 24v. It doesn't seem as full function as that one.

 

[trad]

I'm using the LiTime version to string 2 - 12v to get 24v. It doesn't seem as full function as that one.

This one on Watts247 site seems to also exist on AlieExpress with a different brand sticker on it for about the same price. (at least the same image is used however Watts247 admits this has been updated to...

• NOTE , this model is now a 5 wire solution ( 1 black wire and 4 Red wires [ between each battery + to – link ]) With Bluetooth capability

 

[pollenface]

I have the PowMR version, looks identical to all the other 48v balancers.

Any time I check the voltage of all 4 x 12v batteries, the voltages are identical.