Help: Why is my BMS balance wire melting on custom Evolve GT battery build?

Hello Everybody!

Thanks to all the information on this forum I have succesfully built my own custom battery for Bamboo GT. I used VTC6 cells in a 10s5p config making a 15ah battery. I lengthened the case and stacked the BMS on the VESC to make room.

MY PROBLEM: It rides great with no voltage sag and double the range…BUT I CANT PUSH THE MOTORS PAST ABOUT 45 AMPS (ie no hills!), when i do the BMS B0 balance wire melts and the board shuts down. The B0 sense/balance wire is the one the goes to the negative end of my first battery pack in parellel. I have replaced the B0 wire a few times now but every time i push the motor hard (up steep hills etc) the same thing happens, the wire melts and the board shuts down.

Any thoughts from the forum on how to fix this melting B0 wire issue?

I dont think this makes sense, but is my battery “too powerful” ? Another strange observation I have made is that on a second Evolve GT I have that I took apart I noticed that the B0 sense wire is actually cut (by the factory) and only the 10 remaining B1-B10 wires are used…I have tried just not connecting the B0 wire on my build but the board will not turn on unless I also use this wire. Very strange that from the factory Evolve has some GT boards that require 11 balance wires to be used and then some that only 10 are used.

Thanks so much for everyones input, I am also including a few pics of my build for viewing pleasure.

If the wire is melting, then that means that it has quite a lot current going through it. I suspect that the discharge current is going through both of the negative terminal wire and B0 balance wire.

Can you draw a diagram of the BMS wiring?


I believe these motors have a 35A - 40A max current limit, why would you want to push 45A through a 50mm, 150KV motor in the first place? Don’t they get boiling hot when you push them? I don’t think that the Evolve system is designed for such a powerful battery. We are talking about 100a continuous current with these cells in a 10s5p configuration.

There is not such thing as a very powerful battery. If I made a 10s20p pack out of 30q wicu can push 300A discharge that in no way means that it is going to push 300A to my motors at all. That depends entirely on how you configure your esc. You will however have a hell of range. If this wouldnt be the case absolutely every board would have a range of approximately 1 hour, or straight up melt…

To week batteries however actually are a thing.

So assuming you have your wires properly dimensione, it looks like your bms is taking too much of its negative out of the b0 on the balance instead of the b- thick wire. Check this last cable


@SimosMCmuffin Please see attached drawing.

@BoostedBuilder I should have clarified when I say it starts melting around 45a that is for the combined two motors, i.e. it starts melting with about 25a going to each motor. And my understanding is the same as krloz— the amps out to motor is limited by the esc so I cannot “overamp” the motor

@krloz I think it makes total sense the the b0 cable is taking too much load instead of the thick b- wire…so how do I take the load off the b0 cable? FYI i am using the same gauge wire that the evolve originally was built with: 16gauge for the b- wire and 22gauge for the balance wires.

As a side note: I dont understand the purpose of the b0 wire— it seems a liability, but as I said this is how this board was originally configured and it does not turn on if I dont connect the b0. It is very interesting that the second GT board I have the b0 wire is cut off the BMS harness (maybe to address this very issue??) but it obviously does turn on without the wire used.

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My BMS layout:

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I am also attaching a more closeup view of the negative end of pack #1 where you can see the b0 and b- wires

What if you cut the B0 wire and add a 100 Ohm resistor in-line to it?

Dont do that. The b0 is used for monitoring cell voltage. You would screw with the protections.

If you are absolutely certain the b- is correctly soldered and has continuity I would recommend to decrease the b0 wire gauge. But this would only move your problem to a path inside the bms. All power should be traveling through the b- and b0 should only be used to measure cell voltage and balance cell, usually around 50mA. If you are positive about b- wire I would consider swapping the bms

Can you take a close-up from the marked area? image

EDIT: If possible try to get the markings from the top of the chips

Yea, it’s used for monitoring cell voltage, not passing load discharge current.

I’m quite familiar with BMS’ and in fact I’m developing an open source one for the community. Having a 100R inline in the cell inputs is not anything dangerous. In fact my current working prototype has them and they are also in the battery stack monitor ICs reference design.

Resistor of around 100Ω is used to terminate direct signal and as a small fuse or etc for MCU designs :wink:

No. Evolve BMS has a 65AMP max ouput. That’s less than 33amps per motor, which is fine.

Something has to be hooked up incorrectly here. I used really thin wires for my charging port, and for my bms leads. I haven’t had any trouble with melting of wires so far at all.

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Doesn’t work that way. If it did, replacing the 7.5Ah shit-pack with a 12ah 10S4P 30Q pack would also be a problem as it is capable of 60 amps or more. This is not a problem, i can assure you of that. I’ve done about 30 of these mods now.

That is correct.

That wiring diagram is correct. Its possible that you didn’t follow it precisely. I know you have probably already done this, but check your wiring one more time.

Grab your volt meter. Put the negative probe on pin 0 of the balance lead. Then put the positive probe on 1. It should read 3.6 or something, then pin 2 should read 7.2 or close, then each one shouolld be progresivley more by around 3.6 volts at half a charge. if you progressivley move up and the numbers don’t get progressively bigger, you have a miswire.


Is it possibly that the connection between the main negative lead is faulty and thus the esc is drawing the power through the b0 lead instead

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Hello, that problem seems to be to difficult to fix for me.

I have an Evolve Bamboo that had died on me last week, I went to check all electronics and it seems the BMS is dead already.

However, this is a good thing for me, I’m sick of the throttle sensitivity, one motor no engaging randomly, low torque at medium speed, I don’t like to reengage speed at half throttle when I want to continue accelerating after I left the throttle off.

Dead board, no parts can be purchased through Evolve:

This is the perfect time to replace it with a couple of Focboxes and 6374s, a BMS and a Mini remote.

Problem fixed forever

You should do the same.


My assumption is that the broken BMS / Cut off wire of the main powerline. This enforces high current flowing through the balance port instead of the low gauge wire.

From the photo, your BMS is definitely wired up correctly.

In that photo though, there’s no discharge wires? Do you have the main discharge wire connected to P- or B-? Are you bypassing the BMS for discharge and if so, in that case do you have the neg main discharge wire connected to the B- wire and also connected to the B- on the BMS?