Battery balancing

[zvizdic]

I wonder if any one would review  this circuit for balancing of 48v battery bank.
I have no skills to do that .

[joestue]

its a switched capacitor converter, cascascaded.

there's a couple problems. this will only work for 3 volt lithium cells for 4 in series due to the gate voltage limitation of ~20 volts.

also, its not really efficient for more than 4 or 5 batteries in series because to get power from the bottom cell to the top it has to go through 6 switches and 3 capacitors.

instead its better to build it up in sections, one board for every 2/3 batteries and a separate board for equalizing the higher voltage banks.
of course you can also throw a transformer in there and use one board for all of them.
one option would be to use complimentary p and n fets, using a single optical isolator to turn them on/off. (by default the battery would turn one of them on)

[zvizdic]

I found that circuit on EV forum with not much info, and they like resistive balancing better.
Next question is what would be good balancing for RE? Circuit that would balance batteries at discharge and charge if possible.
Since resistive balancing does not make sense.
 At list not to charge controllers that we are using,unless is set for 14.5v and a dump controller to 56v.
Or forget everything and build Ghurd controller for each battery.

I am using old batteries now and before I invest in a new set would like to have balancing in place.
Something that I can build and maintain TS45 is on a shelf I like to play.

Resistive balancing circuit

[zvizdic]

Hi Joestue,

First thank you for review of the circuit that I forget to do.

I have other one I was told it should be better so PLEASE  check this one to.

[joestue]

I'd get rid of the ir2117s.

use a half bridge driver, there's 150 on newark.com, most are under 3$ each.
I haven't combed through them lately but you could probably find one of the 2$ drivers for this application (low voltage, easy drive, etc)
That will save you ~3$ per battery.

an optical isolator and two resistors per half bridge woudl probably be the easiest route.
run all the leds in series of course.

[ghurd]

Looks like an awful lot of effort for what it really needs to do.

If you plan to build your own boards anyway, could use 4 x the 1st 2/3rds of a ghurd controller to a logic level power fet (where the 2N7000 is) for a single power resistor.
Pretty low parts count.  Mostly cheap parts too.

A guy with an unusual voltage (84V? 132V?) EV just used one ghurd kit and 2 of my power resistors for each battery.
He is happy.
I had my doubts about.
G-

[joestue]

for lead acid  that's probably true.
for lithium not so much.

with active resistive equalization (capacitive isn't much better, peak efficiency is 50%) it still don't help you out untill you're at the last 20% of charge and the weakest cell is falling fast.

using an active charge pump (two fets and an inductor) supposing it can push enough current to equalize the difference you can then push through the 10% limitation and a single ten percent weak cell out of three would be reduced to a battery pack of about 4% reduced capacity.
this becomes more important for hybrid cars and such when there's 80 in series per string.

[zvizdic]

So not the best design but it is the one that would work.
I can get one for 50$.

Thanks for opinions