Tested on a 12s pack that was being fixed. Manually drained cells 5, 6, and 11 down to a voltage where bms balanding would NOT work (bms won’t go into balance charge if delta is ±0.075v or so).
Starting voltages, out of balance cells in RED
Drained pack down, variances have grown
Attached balancer, LEDs on the balancer lights up when balancing, let it go until all lights turned off - resulting voltages
Charge pack up again to about 50v, variance within 0.1v of max cell voltage
Discharge pack down again, 0.15v drift seen in cells 5 and 6
Charge it back up, seeing same figures as step 4
So what the hell’s going on.
Balancer compares cell’s voltage to its adjacent cells (not sure if higher or lower), and if voltage difference is 0.1v, it leeches charge from that adjacent cell until that variance comes under 0.1v. If that process drains the adjacent cells below 0.1v to its neighbor, it repeats the process. So there’s this cascading effect which is apparent when you see the LEDs light up.
You can see voltage variance between adjacent cells is never greater than 0.1v, but can be greater than that compared to the pack’s MAX cell voltage.
So far I’m kind of sold on these in place on bms.
But there some considerations before switching to these balancers.
Balance’s quickly (rated at 1a balancing current)
Stays cool at all times (bms gets above 250f during balancing), so can be attached directly to the battery
Balances through all voltage ranges
Easier installation (only needs B- and each cell’s balance leads)
Always “bms bypassed”
No bms max charging amperage limitations
Max and min cell voltage difference can be high
May lead to over charge
No over / under charge protection, no over current protection
Anything else you can think of?
I’m going to install this battery in one of my boards and put it into use, continue monitoring the pack and see if it’s a long term solution.
Nice write-up man. When I get home today I’m going to read into it a little more.
I know that my Bluetooth bms has an option to either ‘active balance’ or ‘charge only balance’ but I’ve never tried the active balance. I was always worried the balancing while discharging at Max currrent while riding might blow the thing up.
i’d like to have a couple of these just to rebalance packs that had broken welds, bad BMSs or broken balance leads leading to imbalancing of otherwise perfectly good pgroups.
I would be concerned about what this would do in a situation where one pgroup is well below 2 volts because of cell damage or shorting though. I’ve also seen pgroups end up at zero, so i’m curious how this would work with “black hole” pgroups that would literally siphon the power out of good cells and try to shove it into cells that can’t hold it.
Exactly. And on the upside, something like this could actually keep a battery with mixed ages of pgroups pretty close to perfectly balanced most of the time, making surgery of this type more of a viable option. Usually unless its got less than a couple months of maybe up to a dozen charge cycles of age difference i won’t be enthusiastic about simply swapping cells.
I‘m not ready with my tests but my first impression was unfortunately not that good.
First I had in mind that the balance board start at 0.03V to balance. Idk why I thought so, but fact is, that it will not switch on/work as long as the difference between the cells is lower than 0.1V.
My test was as following.
I used two 6s lipos
One at storage charge, 3.8V all cells
The second at 4.0V all cells.
I wired the lips up in series to get a 12s pack.
The balance board switched on only for 2 cells instead of 6.
After 5h the leds switched off.
I checked the voltage.
so… put this pack aside for a while, didn’t really think about it.
but, need to put it to use so took voltage readings today.
and…some interesting changes:
by some unknown mechanism the drift has nearly balanced out.
voltage across all cells have reduced, some more than others.
cells 5 and 6 have dropped by 0.02v, while cell 1 has dropped 0.12v.
this could also be caused by not letting the cells settle after charging on the previous reading…
not sure what’s happening here, but the balancer itself does draw a bit current so this can’t be plugged in and forgotten forever. i bet after a few months the current draw will be significant enough to drain the cells down to dangerous levels, especially if it’s not fully charged.
anyway, i was checking voltages by reading the pins here:
After installing the balancer leave it overnight and all the indicators lights are off meaning it’s done balancing. Check all the voltage to my surprise every cells 3.9v this thing really works!
I just want share it my finding and experience. Pardon my English second language
I have a question that is somewhat relevant to the topic. I have also received the same active balancer and plan to install it on the 10s4p I just built but I don’t want to add in a bms for charging. I have both evolve charges that I had planned to use. What charger have you guys been talking about that I can set cut off voltages to charge to? I’d love to just have this little guy and not the bms to.
I plan to use the balancer quarterly or Monthly just maintenance purpose only. You don’t need attached the balancer on battery all the time. What I did? leave the balancer connectors outside the heat shrink so, I can access easily next time want to use the balancer. I have custom charger 2amps stop at 40v from AliExpress.
A lab bench power supply? I read they are pretty easy to DIY with boost/buck converters… I’m trying to do this with solar…
I use a boost converter for adjustable voltage/amperage that I plan on connecting to a large battery bank charged by a 100W solar panel. Basically with enough energy from recycled batteries to charge my board + some, wired to a solar panel that will stay outside, maybe a display so I don’t have to probe when changing volts/amps, and some nice little dials instead of pots on the boost converter PCB in a 3D printed box.