Two questions on BMS wiring

that’s why i just went with the modded vedder switches and dropped the BMSs with built-ins. So annoying.

To each his own I guess. Turning the board on to charge hasn’t bothered me.

you totally should make a YouTube tutorial on battery build, BMS with LCD, charge port and power button. I would love to learn the process from professor Damon

well there’s this thing that the motors do when the board’s on the the remote is off… it doesn’t do it when reverse is disabled but the motors sit there and tick-n-twitch. it drove me nuts so bad that i swore off reverse and swore off bms’s with built ins.

i know i know… i’m just a picky little bastard

I’ve never used reverse. I have gotten twitching with remote off when down by the coast (maybe some interference) I don’t seem to have any twitching when at home.

My ordering was corrected for me… :slight_smile:

I have a question that’s relevant to this thread, as I’m about to start soldering my BMS connections. I was told that I should connect the B- and P- points before making the sensor connection. My plan was to do a bullet connection between the segment of wire already connected to the battery and one running to the BMS that I will solder.

Is it ok for me to solder all the sensor wires without the B- connected and then Connect the B- bullet joint first, and then connect the sensor wires to the BMS?

My assumption is this is fine as there wouldn’t be any completed circuits until the connections are made, but as I’m new confirmation feels appropriate. Thanks!

Why don’t you have a wire going the positive side of the cell where the main B- lead is? Or maybe it’s just the marking that is not at the right place as it gives the impression you have two on the B+

i would run all of the balance leads first, before connecting to the BMS. Then use a volt meter to make sure you have them in the proper order.

Then solder the pack into the BMS, then connect the balance leads. Then check the voltage again, and also to be triple sure, hold the bms for a few minutes and make sure its not getting warm.

I do all of those things. I measure, i measure again, then i feel it and smell it. You just never know how something will go wrong so try to involve all of your senses, not just your eyes and logic centers.

I was wondering that too… but all of the spots @kaly provided for me to do the soldering are on the negative in the chain… EXCEPT # 12… I don’t know enough about how the Sensor cables actually function to provide an answer… just enough to do the soldering and hook-up. :slight_smile: with the correct instruction.

Thanks @longhairedboy! any confirmation on the order on the pack and the question brought up by @jga?

if you’re using the BMSs from, the balance lead ordering will start at 1 at the first positive after the main negative.

then if its a 12S, number 12 balance lead will be on the same metal as the positive terminal.

I think it must be a different one that Ernesto uses… I was just double checking the diagram he sent after the question and all the connection points are (while between + and -) they are made on the negative side of the (is it “parallels”?) He’s built a number of function boards, so I can only imagine this is the correct way to do it for this BMS, I just don’t know the “why.”

I’ll certainly take the advice on the checking and double checking after I get it all hooked up… and will solder first and connect after. Thanks!

no, they’re not. They’re on the positive side. The diagram is ambiguous because its a 1P. But look at #12, and notice there is no balance on the negative side of #1

? so then are all these spots opened and waiting for me to solder in the incorrect location? @kaly can you chime in here? I think I’ve read some posts from @Eboosted who’s done a Kaly build? Also… I can simply solder this together as indicated in my photograph, where the current solder points were provided for me (not hook it to the BMS) and see if I’m getting the correct Voltage readings via the voltmeter… ya… I think I’ll do that.

Hi there the spots are marked correctly, you are going to start connecting the balance leads by the positive side of the negative main wire, that is the one marked #1 on the picture above and them follow the diagram. notice that the balance lead has to be connected on the bridge part of the cell connection it can be on the positive side or negative side but on that join connection.

As you can see on the picture i choose to put the tap on the negative side of the connection because in the event that the shrink wrap on the cell get scratch the metal tab will only touch the negative side of the cell on which is already connected minimizing any possible complication.

for more info check

Thanks for the clarification Kaly! I gathered you had it done right, but with the new question there was some hesitation on my part. Uncertainty, I can do without when dealing with this much battery. :slight_smile: Huge help here, thanks!

kaly, how do I get info and pricing on a build? Thanks.

Practical question: how do you check the balance wires with the voltmeter?

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attach your negative probe to the negative side of the pack using a clip or something, then place your positive probe on each one of the connector contacts starting at pin 1. They should get progressively higher in voltage on each pin and the differences between each pin should be very very close in measurement, in fact they should all be the same as the measurement of one cell because the cells should have arrived with all the same voltages, which should be somewhere close to nominal (about half charge). So pin 1 should be around 3.6v while pin 12 should be around 43.2 for example. if they’re at 3.2 or something like that its ok, i’ve seen cells arrive at 20% charge before and they turned out fine once the pack was built, charged, and balanced.


Perfect! Thank you, I will give it a try tonight.