Help! Battery BMS wiring, do I have this correct?

[spleenharvester]

Hi all!

I have an Ansmann-style 36V 10S3P battery here which failed in an odd way (BMS stuck in a permanently on state). No-name brand but seems to have genuine INR18650-29E cells so worth saving. I'm planning to replace the BMS with a Bestway model, the '10S 20A with switch' at this link and a new case/charge indicator too. The problem is the existing BMS is some weird ass non-standard proprietary thing with a 9-pin balancing connector instead of 11-pin and other oddities. Best I can tell, the 9-pin connector omits the common connection to B- and the positive discharge from either end and seems to pull them indirectly from the PCB, so I'll need to wire these in.

Can someone please check the below makes sense? Thank you!

 

[Nealh]

Yes that all looks good for the new BMS.

 

[saneagle]

There's no standard for the number of connector pins. You can get 9, 10 or 11 because they can get B0 from the B- ground wire and/or B10 from the B+. It makes no difference when you get a new BMS. You just wire it accordingly. Even if you find one with the right connector, it still might not work because either the whole sequence is reversed or they use B+ instead of B- in the 10 pins, so be careful.

When you say stuck in the on state, do you mean that the switch doesn't work or it doesn’t cut off at low voltage, because there's a workaround for the former?

 

[spleenharvester]

There's no standard for the number of connector pins. You can get 9, 10 or 11 because they can get B0 from the B- ground wire and/or B10 from the B+. It makes no difference when you get a new BMS. You just wire it accordingly. Even if you find one with the right connector, it still might not work because either the whole sequence is reversed or they use B+ instead of B- in the 10 pins, so be careful.

When you say stuck in the on state, do you mean that the switch doesn't work or it doesn’t cut off at low voltage, because there's a workaround for the former?

It didn't actually have an on/off switch, you'd press and hold the charge indicator button to switch it on/off. Only this time pressing the indicator button wouldn't switch it off. It also wouldn't power the bike. Blade fuses were all fine etc. This happened after accidentally trying to move the bike with the charger plugged in (which broke it off), I'm guessing that must have shorted VIN.

 

[spleenharvester]

Hi all

I've rewired the battery successfully, followed the wiring diagram presented in the OP but had to use this BMS instead: https://www.aliexpress.com/item/1005004050876755.html

It runs and charges perfectly fine, but by coincidence I found one peculiarity, which is that the battery voltage is always present at the DC jack terminals (i.e. between C- and Vout), regardless of whether it's switched on or whether there's a charger plugged in. My other Ansmann style battery does not do this (C- is only high when a DC jack is plugged in) but obviously it's a different BMS in there so I don't know if this is just an odd behaviour of this BMS. Is this safe, I presume not as it would short if it gets wet?

 

[saneagle]

Hi all

I've rewired the battery successfully, followed the wiring diagram presented in the OP but had to use this BMS instead: https://www.aliexpress.com/item/1005004050876755.html

It runs and charges perfectly fine, but by coincidence I found one peculiarity, which is that the battery voltage is always present at the DC jack terminals (i.e. between C- and Vout), regardless of whether it's switched on or whether there's a charger plugged in. My other Ansmann style battery does not do this (C- is only high when a DC jack is plugged in) but obviously it's a different BMS in there so I don't know if this is just an odd behaviour of this BMS. Is this safe, I presume not as it would short if it gets wet?

That's normal behaviour. The switching is done on the negative. C- should only switch off when a cell goes below 2.5v or above 3.5v. The main battery switch that switches off the battery's power (if you have one) sometimes switches off only the output power and sometime both output and charging. From what I've seen, it's about 70% of Chinese batteries (BMSs) that switch off just the output.

 

[spleenharvester]

That's normal behaviour. The switching is done on the negative. C- should only switch off when a cell goes below 2.5v or above 3.5v. The main battery switch that switches off the battery's power (if you have one) sometimes switches off only the output power and sometime both output and charging. From what I've seen, it's about 70% of Chinese batteries (BMSs) that switch off just the output.

Thank you, good to know it's not just a faulty BMS. I'm not terribly comfortable with voltage always being present at VIN though given it's only weakly splashproof - what circuitry would I need to add to stop the voltage appearing at the DC jack? Would something like a zener diode work?

 

[saneagle]

Thank you, good to know it's not just a faulty BMS. I'm not terribly comfortable with voltage always being present at VIN though given it's only weakly splashproof - what circuitry would I need to add to stop the voltage appearing at the DC jack? Would something like a zener diode work?

Assuming that your charger is 2A, a 2A switch.

You're worrying about nothing. 70% of Chinese batteries are like that. Nobody has ever complained. I never even put the cover on the socket. it's open all the time, though that might not be such a good idea for long journeys on salty winter roads.

 

[spleenharvester]

Assuming that your charger is 2A, a 2A switch.

You're worrying about nothing. 70% of Chinese batteries are like that. Nobody has ever complained. I never even put the cover on the socket. it's open all the time, though that might not be such a good idea for long journeys on salty winter roads.

More than likely I am yeah, it's just for my own piece of mind really - I've been caught in some real downpours and have found water inside the battery cases before, so always cautious! Someone reckons just putting a schottky diode on C- should stop the backflow so for the sake of 50p I might just do that. It would make sense too because the package size of the required diode would be slightly too large to fit under those metal heatspreaders

 

[spleenharvester]

Update, a simple SR560 Schottky diode on VIN has fixed the reverse current issue. It's not a perfect solution as there's a voltage drop across the diode (it only charges to 41.4V rather than 42.0V now) but otherwise works perfectly.

 

[saneagle]

Update, a simple SR560 Schottky diode on VIN has fixed the reverse current issue. It's not a perfect solution as there's a voltage drop across the diode (it only charges to 41.4V rather than 42.0V now) but otherwise works perfectly.

You need to check what voltage the bleed resistors start bleeding. If it's above 4.14v, your battery will never balance! Or you just check that they get hot when the battery is fully charged by touching them or use a thermal camera.

 

[spleenharvester]

You need to check what voltage the bleed resistors start bleeding. If it's above 4.14v, your battery will never balance! Or you just check that they get hot when the battery is fully charged by touching them or use a thermal camera.

Right you are, this BMS balances at 4.18v. Bum. I'll have to think of another way

 

[spleenharvester]

Anyone in the future - I fixed this by using a DG7512 ideal diode board on the jack. Only drops voltage by about 0.1V so works fine!