10s BMS for 9 cell LiPo battery setup - wiring diagram

Nice diagram btw.

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Yep, leave off the last lead. I’m thinking it will work but you never know.

Diagram looks good. If your adding a fuse though you might as well have the charge port fused as well. That way if anything is connected wrong or something gets in the plug the fuse will blow and not your battery. It’s not essential just my opinion

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Makes sense. Based on my diagram I’ll put the charging positive wire into the xt-90. Not literally, but you know what I mean.

I’ll report back with my findings tomorrow :grin:

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Hi everyone,

Sorry about the delay in posting but I’ve only just been able to finish doing some of the wiring.

Okay so far I’ve wired everything up apart from the charging socket. Using my diagram above, the skateboard starts up when I turn on the switch. The FOCBOX works and everything happens as normal. I’ve only done a bench test so I’ll be unable to tell what the cell voltages are like until I use it. The cells are currently full with power. I’ll ride it for a little and then see what the cells are again.

However I feel the real testing will happen when I connect the charging port and attempt to charge it. I can’t seem to find a charger suitable for 9 cells (37v?) that charges higher than the standard 2 amps. I want to get a quick charger of sorts that had an automatic cutting of when it reaches max voltage. If anyone has any suggestions on this then I’ll be happy to hear them!

Question: How do I wire the charging plug? There’s 3 pins, I presume they’re positive, negative and earth. How do I know which wire goes where? If I need to test it with a voltage meter, how would I do that? Please excuse the nooby question but I’m not great with a voltage meter!

Thanks, Daniel

@Namasaki @pat.speed @fottaz @b264 @mmaner

when you get a charger, plug it into the charge port and use a multimeter to define the pins. You only need POS & NEG.

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Perfect idea! I didn’t think of that. Another noob question - what setting would I have it on and what method should I use to test it?

Also, any recommendations on a 37v charger which does fast charging? :thinking:

Set the multimeter to DC 60a. Be careful using a high amp charger, I would suggest getting a 2a to test with and then after the battery is proven (2 complete discharges and charges) get a 4a. I never charge over 4a and mostly at 2a or 3a.

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Typically the 3 pins are

Ground (negative) Charging (connected to negative when NOT charging, disconnected while charging) Positive (positive)

Use a multimeter NO MATTER WHAT to verify though.

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@mmaner I’ll do as you suggest. A 3a charger should be okay for testing though, right? If I monitor it closely? Or should I not run the risk and get a 2a charger aswell? Thank you for a mini lesson on voltage meters :smile:

@b264 negative and positive are easy enough to wire up but how would I wire up the charging pin? Mmaner says the 3rd pin isn’t required?

I mean, your the one buying it so get what you want. If it’s not an affordability thing I would get a 2a and a 4a. Use the 2a when your just sitting around and not in a hurry, use the 4a when you wanna charge fast. By charging to 4.1v per cell and discharging to 3.5v per cell you more than double the possible charge cycles.

To be completely honest, I never do that. I use a lab power supply to charge most of the time, at 3a and a brick charger when I’m not home and I only carry the 4a bricks with me. That being said, I try to give my packs a decent burn in by charging with 2a the first few charge cycles.

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I don’t…

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@mmaner cost isn’t a huge concern of mine at the moment. I’ll get a 2a and 4a charger. I work from home so I can have it plugged in while I’m working.

Thanks for the picture. Which one is positive and which is negative? My guessing is the 90° point is positive because the other two match, which would make sense for a negative and earth connection (or charging as @b264 said). Also, what awg cable is that? I’ve only got 12awg at the moment which seems a little overkill?

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Oh, I just realised. 4a charging so atleast 4 amps!

yep, the big lug/pin is the positive, but check with a multimeter just to be sure.

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You absolutely have to use a multimeter to check this, EVEN IF YOU KNOW. It’s not exactly negotiable or optional. Lithium cells are essentially fire-in-a-bottle.

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I tried to order that 3a charger but they can’t send it to my address. I’m in the UK so I’m guessing that’s why :frowning_face:

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That was just an example, check gear best or something.

It will turn on and works, because the circuit of cell 10 is not closed BUT the bms will cut the whole pack if it is lower then 3v*10=30v (Over discharge detection voltage)

A 9cell pack is empty when it is at 27v -> you can’t use the whole capacity of the pack

So buy a 9s bms :wink:

The only test that I did with this bms was that I connected the battery mains and not the balance wires and tried to turn the bms on. It would not turn on with the balance wires disconnected. It was my understanding that this bms monitors individual cell voltages by the balance leads and shuts down if even one cell falls to 3v or what ever the detection voltage is set at.

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Yeah, I was thinking just the same but a friend from me use a 10s bestechpower bms with 8s battery and it works until it reach the over discharge detection voltage and then the bms cut the load.