Options for manually balancing 16s modules

993 Views 33 Replies 8 Participants Last post by remy_martian, 8 d ago

joekitch

Discussion Starter · 12 d ago

i got some LG chem pacifica modules i'd like to get into a very nice balance before trying to put in parallel

im currently trying to make this combo work

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without success, it seems to do -something- to the low cells, but not actually charge them

short of fully assembling my system of model 3 power conversion system, aem bms-18 units, and vcu200 to control it all, what are my options to balance cells in my batteries?

for context in one of my modules, two of the cells are 3.740v, and the rest are 3.904v

here's how i have it wired up

Circuit component Passive circuit component Electrical wiring Electricity Hardware programmer

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1 - 20 of 34 Posts

floydr

· #2 · 12 d ago

Get a 24s smart active balancer run it on the modules that have the low cells. You might have to charge the modules while active balancing is happening to raise the voltage on the low voltage cells. Once the cells are within an acceptable range remove the active balancer.

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Later floyd

remy_martian

· #3 · 12 d ago

Balance them with a resistor between two going in parallel. Once you have no voltage across the resistor, hook them in parallel.

Rinse & repeat to create each parallel block.

Then balance each block to the other blocks going in series.

MattsAwesomeStuff

· #4 · 12 d ago

Don't you have a (current limited) variable bench power supply?

Set it to 3.9v, clip it onto a low cell and walk away for a few hours. No need for any brains beyond that, it won't overfill, it'll max out at 3.9v.

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joekitch

Discussion Starter · #5 · 12 d ago (Edited)

Could work, I'd assume id be putting the two power supply leads across two adjacent cell leads?
Volt meter across cell 7's lead and cell 8's lead is 3.740

If I were to go from cell 8's lead to the common negative (in this case, the purple one) it'd be reading more like 29.6v

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reiderM

· #6 · 12 d ago

joekitch said:
Could work, I'd assume id be putting the two power supply leads across two adjacent cell leads?
Volt meter across cell 7's lead and cell 8's lead is 3.740

If I were to go from cell 8's lead to the common negative (in this case, the purple one) it'd be reading more like 29.6v

Yes - cell 7 positive is the same tap point as cell 8 negative. So you'd be charging just cell 8 in this case.

MattsAwesomeStuff

· #7 · 12 d ago

joekitch said:
Could work, I'd assume id be putting the two power supply leads across two adjacent cell leads?
Volt meter across cell 7's lead and cell 8's lead is 3.740

Presumably yes, but, to avoid confusion about what you're measuring and what I'm suggesting, I'll make it more foolproof:

Whatever you're measuring to be 3.740v, that is the same place where you will place the leads to give it 3.9v, with the same polarity. Then it doesn't really matter what you're thinking the start or end of one cell is, if you're measuring 3.740v, that's what you turn into 3.9v.

And, it's a good idea to measure it to verify it before you connect things up.

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oudevolvo

· #8 · 12 d ago

Make sure you set a low max. current and in case of balancer tools pay attention to the balancing current.
You don’t want to blow up your cell tap wires (or their fuses if they have them).

joekitch

Discussion Starter · #9 · 11 d ago (Edited)

Got my handy lil benchtop guy running, although what's concerning is the amp readout is always showing zero no matter the amp knob adjustment, unsure if it's just pulling so little it doesn't show up or something else is going on

Ok apparently that didn't do sh!t because a few hours later, the cell voltage is still 3.740, exactly where it started, meaning absolutely no power went in.

I have no idea what the hell is going on anyone, this battery just won't charge in any way

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MattsAwesomeStuff

· #10 · 11 d ago

joekitch said:
Got my handy lil benchtop guy running, although what's concerning is the amp readout is always showing zero no matter the amp knob adjustment, unsure if it's just pulling so little it doesn't show up or something else is going on

The fact that it doesn't say any current is flowing, and, that the battery voltage didn't rise, both indicate... no current was flowing. I.E. You have your power supply in current limited mode, and your current limit set to zero.

Even if the cell was damaged, you could dump current into it (it would just show up as heat).

Disconnect your power supply leads, and then short them together. Do you see any current flowing then? Do they get warm? If not, no current is flowing.

joekitch

Discussion Starter · #11 · 11 d ago

Double checked the instruction manual for the power supply and it indicated setting the current settings with the leads shorted then turning it off an on again, then putting it on the desired circuit.

That sort of worked, I saw amp activity and it switched to CC (constant current mode), I'm a paranoid sort though so only tuned the fine knob up to 0.5a. it made an interesting buzzing sound I haven't heard from it before but I assume that means it had some activity.
Imagine is using a huge resistor at first just to see what would happen.

I put it back on the battery cell and.... no current visible again, although this time it was making that ominous buzzing sound which I assume meant it was doing .... something
Tomorrow I'll try setting it to 0.75a with the leads shorted then put it back on the battery cell, hopefully get some activity after an hour or two that way

This is extra confusing considering that if it's providing a proper current the cooling fan should kick on, which it absolutely does when I have it set up to power my VCU In benchtop mode.....

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Duncan

· #12 · 11 d ago

joekitch said:
Double checked the instruction manual for the power supply and it indicated setting the current settings with the leads shorted then turning it off an on again, then putting it on the desired circuit.

That sort of worked, I saw amp activity and it switched to CC (constant current mode), I'm a paranoid sort though so only tuned the fine knob up to 0.5a. it made an interesting buzzing sound I haven't heard from it before but I assume that means it had some activity.
Imagine is using a huge resistor at first just to see what would happen.

View attachment 137523

I put it back on the battery cell and.... no current visible again, although this time it was making that ominous buzzing sound which I assume meant it was doing .... something
Tomorrow I'll try setting it to 0.75a with the leads shorted then put it back on the battery cell, hopefully get some activity after an hour or two that way

This is extra confusing considering that if it's providing a proper current the cooling fan should kick on, which it absolutely does when I have it set up to power my VCU In benchtop mode.....

You can do it the other way about - I use an old kettle element as a load resister to drop the high cells

The disadvantage with that method compared to the power supply is that you have to monitor the voltage yourself -

joekitch

Discussion Starter · #13 · 11 d ago

yeah, and bringing down 14 cells will take a hell of a lot longer than bringing up 2

MattsAwesomeStuff

· #14 · 11 d ago

Are you wiring it through the BMS or something, or directly onto the cell leads? I'd remove any sourced of ambiguity and go straight to the cell if you can.

I've never heard of a lithium battery that won't take voltage, (other than ones at zero volts, or quickly plummeting).

Is there a passive BMS that's running? Is is possible that the cell is entirely dead and the 3.7v you're reading is a ghost of the BMS trying to feed it power and the cell just sitting there doing nothing? If so, yeah, giving it 3.9v when it wasn't even taking the 3.7v the BMS was trying to feed it makes sense.

Best bet is to electrically isolate the cell itself, and measure it and figure out wtf is going on.

joekitch

Discussion Starter · #15 · 11 d ago

If that was the case I'd expect the entire module to read lower than it's current 62.7v

Last thing I tried last night was hooking directly to the cell leads, removed from that distribution block thing entirely. I'll try doing that for about an hour today, setting it to 0.75a beforehand with the leads shorted, see how that works out

MattsAwesomeStuff

· #16 · 11 d ago

joekitch said:
setting it to 0.75a beforehand

3.9v @ 0.75 = 2.9 watts.

Not even 3 watts. I wouldn't be scared. You can probably throw 100 watts at those cells each without them even getting warm.

joekitch

Discussion Starter · #17 · 11 d ago

25 amps? nice, although my little bench supply doesn't go above 10 amps unfortunately, also that'd likely blow the cell tap leads, but i'll do like 3 amps

joekitch

Discussion Starter · #18 · 11 d ago

2

Update;
So uh, I put 4 amps through the leads, or at least I set it up to

But back on the cells, nothing.

So, something is causing this power supply to not realize it can actually push any power through these leads and I'm not sure why it's deciding that

In this case the green lead on the left is for cell 8 and the white/pink lead on the right goes to cell 9

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remy_martian

· #19 · 10 d ago

Turn the voltage up to your target voltage (3.9V?) with that 4A current limit.

Right now you have it set to 0.3V, or maybe the short is doing that.

The short circuit you are doing is worthless. Set the voltage, sneak up on the current from 0A.

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joekitch

Discussion Starter · #20 · 9 d ago

Probable is, either I can change the volts but not the amps, or visa versa

With the leads held together, I can change the amos all I want but the volts can't change

With the leads on the battery cells I can change the volts all I want but the amps won't change

It's really weird

1 - 20 of 34 Posts