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

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. http://www.electric-skateboard.builders/t/flexibms-first-prototype-kicad-project-files-released-flexible-configuration-and-charging-bms/46117

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.

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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.

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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?

THANK YOU everybody for your comments so far. Sorry for the delay in responding to your diagnositc questions, I live in Japan so my awake hours are different from yours :slight_smile:

@krloz Decreasing the b0 wire guage would have never crossed my mind to decrease current going through it, I would have thought that would only make the problem worse by making it even hotter and melt faster. If anything I would have thought to increase the gauge of the b0 to make it run “cooler”. Can you explain your reasoning?

@SimosMCmuffin Can you please explain why adding an in-line b0 100ohm resistor would help? Does it cut down on current going through it and redirect it to b- wire? Does doing this affect the b0 sense function when I add the resistor? I am including the closeup view of the BMS that you requested. The b0 attachment you can see is a little browned/melted from the many wire melts that have occured on this lead. Is adding a resister effectively the same thing as down gauging the wire as per krolz’s suggestion (they are both adding resistance to the lead right?) or the electrical effects different of these two options?

@longhairedboy Here are my BMS leads volt meter readings: b0-0v, b1-3.68v, b2-7.35v, b3-11.03v, b4-14.7v, b5-18.38v, b6-22v, b7-25.7v, b8-29.4v, b9-33.1v, b10-36.7v, battery pack voltage-36.7v. Since you have done so many of these evolve packs now, have you noticed like I have that some of the evolve BMS units do not have b0 wired and some do?

@darkkevind Sorry for the confusion, in the original photo I had not soldered all the other discharge wires in yet. No, I am not bypassing the BMS. I am attaching the final BMS layout below where you can see the b-/c-/p- discharge wires correctly attached.

SO, here are my new set of questions:

  1. What is the purpose of b0? Not all BMS units have a b0 and I thought the cell balancing of pack #1 is already accomplished with b1.

  2. I have redone a very careful comparison of my setup compared to the second stock evolve board I have and I realized they used a 14awg wire for b- and I used a 16awg for my setup…can this minor difference in awg be shunting more current through b0 as a result?

  3. I am using a 10awg for my b+ wire, and as just mentioned my b- is 16awg, Is there a problem caused by having an awg mismatach between b+ and b-? Do you need both wires to have matching awg?

THANK YOU !

My BMS closeup pics as requested:

In AWG big value number means small wire thickness. And low number means thick wire. So with decrease the awg I meant increase the wire thickness. Sorry for the confusion

Balancing of cell 1 is accomplished between b0 and b1. Balance of cell 2 is between b1 Ann’s b2. The thing is some bms dont carry a connecting for the first balance wire because it’s the same than battery negative, so they just measure there instead.

16awg sounds way too thin. If it was 14awg to start with, definitely dont go thinner than 12awg with your new battery. I’d probably just use 10awg like the positive wire.

16 AWG can handle 10amps or even more according to some sources… These wires should have 4 amps MAX flowing through them. Most of the time it’s less than 2 amps. I’m sure this is not a wire thickness issue.