Disconnecting the neutral wire between batteries will burn the balance leads. Any switch must be in B+ or B-.
If the heavy series cable is loose or disconnected, the small 20awg wires will carry the load. More than a couple amps will overload them.
@Inwo
Could you please eplain this a little further? We have our disconnt between our two banks of Volt batteris. Is this not correct with the BMS in place?
Negitive In -24v-24v (disconnect runing between B- to B+) 24v-24v - Positive out
The problem is as you observed. A balance lead is connected from cell #12+ to bms. Another lead is connected from cell #13- to the same pin of bms. Essentially a 20awg wire across the switch. It may even be smaller internal to battery.
The reason that both wires go to bms, is for bms to have a better chance to read cell 12 & 13 accurately. Any voltage drop across the neutral connection, between modules, affects voltage sensing.
It is also not safe to disconnect shunt from B- unless disconnected from bms. A switch can be in B+ or B- after the shunt.
I’ve adjusted the Over Charge/Discharge numbers in the BMS to be a little more conservative. Thoughts? Did I adjust the right things, and do these numbers look reasonable? The discharge seemed very low from factory, and I may still lower the charge number, but figured starting here would be good.
I also set the “Balance” option to “ON”. Balance in Charge was already selected. From the manual it looks like if Balance in Charge and Discharge are off, then it will Balance in storage. I’m not clear on the advantages of choosing to balance in Charge/Discharge/Storage. Thoughts?
You are probably not using the discharge protection.
The first cell to reach 4.15v will stop charger, if connected. “P” protect
Charger will restart at 4.1v, depending on charger. “R” reset
For storage, if charger can restart, set it lower. No need to keep battery full.
Balance is user preference. Energy is burned off balancing. I set conservatively.
Set to balance in idle mode only when over a high number. Something it will reach after charging.
Then it won’t be trying to continually balance cells when under load.
20mv is near enough for me.
If cells stay balanced easily, then set to balance in charge only. Then it will only balance at the end of each charge cycle. Say over 3.8 or 3.9 volts. See what works for you!
Voltages often spread with discharge if top balanced. Make no difference. Don’t fight it. Only needs to be balanced on top, as you never reach bottom.
Not following what that means. Do you mean I have it set so low, that its never kicking in? What do you suggest setting it to for long battery life? Also, what actually happens when I hit the P and R discharge numbers? Does it just sound an alarm, and flash something on the screen? It can’t shut the car off can it?
So if I leave it plugged in, with these settings, it would charge up to 4.15v, and then shut the charger off until it dropped back down to 4.1v, and kick the charger back on until it went back up to 4.15 right?
I’m not really following most of this.
Right now as far as I can tell, it’s not balancing at all. Is there any indication when its doing a balance? After one full charge, and driving it around some, I have a 200mv spread between highest and lowest cell. What does the “Balance Start Voltage” do? Does it not start balancing until the voltage drops to 3.6v?
Does balancing ever add voltage to a cell, or just drop voltage in the highest cells to bring them closer to the lowest cells?
Thanks for being so helpful with all my dumb questions 
Bms can shut down the system, but must be connected with relay or sutch. I depend on the Gem LVC. Low voltage cutout.
Led and audible alarms are available. I don’t connect them.
So if I leave it plugged in,
If interrupted, dq will not restart. If the white enable wire is used the bms can start and stop charger.
Other than that, yes. Control through P&R.
BMS-24 has no indication of balance, except heat. BMS gets warm. Shunt balance only. Ie. draws down high cells.
If its that far off, set to on, on, on, and balance start to below the lowest cell. 3.6 or so.
Bms only balances when on. Set lcd timer as low as it goes = always on.
Bms should get warm and bring down even 200mv over a day or two.
Yes, balance only starts when all cells are over set point.
There may be other things interfering with balance. Something I haven’t run into.
Such as balance alarm setting. Amp calibration not going to near zero. Cell overvoltage.
When everything is normal, it just works. If things are abnormal???
Awesome. That helps a lot. Thanks (as usual!).
Also, my T1 controller is indeed cutting out when I’m at 96v+ When I charged up to 96v, it would cut out with error code 76, once I let off the throttle after semi aggressive throttle. If I granny-footed it, it would often not cut out. Turning the key off and on again, reset the code, and I was able to drive it again. Anything below 96v has been just fine. For now I’m just setting my charge limits so I don’t go over 96v.
More balance information.
Adding to low cells is called active balancing. Much more complex and expensive method.
Using active balancers, only, is not a bad idea. It would only be in an extreme case that a cell could be over charged.
Simpler system to use. No set up or programming required. It works 24/7 charging the low cells from the high cells. Stopping only when cells are within 30mv.
I have them available with lcd display that charge/discharge very aggressively. 4 amps.
Work separately or with a bms.
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In theory set “P” to 4 volts then.
As battery is unbalanced it will not fully charge. Stopping at “P” but most cells lagging behind.
Turn on everything you can think of to get balanced. BMS should get very warm. Keeping it cool will let it work harder.
Were ther any mishaps during connection that could have damaged bms?
Balancing is quite aggressive at 1.2 amp drain.
Not that I know of. I tested every plug in the harness for the right low to high voltages several times. I clipped off and taped up the “mistake” extra wires I referenced earlier in the thread. One time when I had the harness already plugged into the BMS (switch turned off), I got a small spark when I plugged the harness into the battery module. But it was a very small spark, didn’t leave any marks or anything, and I likely wouldn’t have noticed had it not been dimly lit.
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I doubt it’s possible to damage all the balance circuits, and leave bms still working.
Just thinking ahead.
Is bms warm yet?
If not, set the balance settings all on. Voltage as low as you can 3.3v?
Set dif. Volts over actual dif. 300mv?
Is one cell low or 1 cell high?
It may be that the spark shorted 1 balance transistor. Then it is stuck “on”. Always draining that cell. Happened to Grant I believe.
If it seem on cell is always draining, send me bms to test.
BMS is warm. 93*
BMS is working at least somewhat because the rest of the cells are all balanced.
One cell is low.
Here are current settings, and cell readings. I’m going to leave it unplugged over night, and see what it looks like in the morning.
That doesn’t look good. See if #13 is really that low. If it continues to go down something is wrong.
If everything is correct it will take a week to drain all the high cells.
#12 and #13 are the cells between modules. Wiring is critical and easily damaged with resistance between modules. Such as the connection between modules being loose.
Yeah, it was lower this morning after about 9 hours of sitting (not charging, with bms set to “ON ON ON”).
I pulled the cover off, and checked the cell individually, and got 3.67v, which seems close enough to the 3.645 displaying on BMS this morning.
Also noticed for the first time two marks on the battery module that I didn’t make. I can’t identify what the one is next to my cell “13”. FWIW, I made the silver sharpie “-” mark up by the post. The other two marks I didn’t make.
To troubleshoot this, would it make sense to charge that cell individually, then do a drive/charge cycle with BMS unhooked and see if I get a drop again? If so then its likely a battery problem. If not, then seems likely its a BMS problem? If that’s a good idea, whats the best way to charge that cell individually? I have traditional battery chargers, and float chargers. I don’t mind babysitting it to make sure I don’t overcharge.
Other notes: I used lock washers, and di-electric grease on all the connections. The cable ends are a little oversized (5/16), vs the battery posts (3/16), but they’re all tight. None of the posts get hot while charging or driving.
Also it may have sparked again when I unplugged the harness from the battery module. The BMS was shut off at the time.
Any power supply or single cell charger will work to charge the low cell.
I’m set up for that and do it all the time to get batteries back in balance.
A little 5 or 6v wall wart might work. 1amp or more if you can find something.
To disconnect bms after turning it off. Unplug the three plugs starting from the top. 96v B+ one.
Opposite to reconnect. Check each pin for proper voltage. The extra time it takes may prevent inserting incorrectly.
Check bms for shorts if you want. Pin to adjacent pin.
Over 100k ohm.
I’ve got a 5v/2a wall wart I can throw some aligator clips on. I should NOT use a 12v charger right?
Just connect negative to the negative post on the battery, and positive to the low cell, right?
I’m not sure how much time I’ll have this weekend, but I will try to check the bms for shorts as well.
Thanks.
Any voltage is worth a shot. It depends on internal design.
It may overheat connected to a 3.7v cell. You could always put some resistance in series, such as a 1157 lamp or such. Then I’m sure a 12v will work. Even a 12v charger. The larger the lamp the more current to the cell.