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ZEVA BMS reading wrong Voltages.

1885 Views 6 Replies 3 Participants Last post by  Hollie Maea, 
M
Hello All,

So i have a setup of a ZEVA Bms system with two slave units (BMS 12's), but unfortunately they are sending some incorrect voltage information to the Master (EVMS).

I am reading 9 cells from each one (18 total), but 6/7 are coming up wrong. The difference is over 0.5v in some cases which is enough to make the BMS read them as high cells and obviously makes balancing abit problematic.

I had to replace some of the shunt resistors on the BMS 12s. They were previously 47 Ohms and i replaced them with some 43 Ohms as they were what i had at hand.
I was told by ZEVA that this shouldn't cause an issue and some of the lines to which the shunt resistors have been replaced are still reading correct.

I have also tried reading the cell voltages from some completely different batteries and i am getting the same fault.

Does anyone have some insight into what might be wrong or what i could check next?

Thank you
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frodus
Why'd you replace the shunt resistors?
Did you clean the flux off of the board when you replaced them?
How long are the sense wires?
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M
The shunt resistors had to be replaced due to a short.
I have now given the boards an extra clean but no luck.
Longest Sense wire is about 2 ft long, but there are the same issues even if they are changed.

119942


So i have measured the voltage of each cell across the screw terminals, i have then compared it to what was displayed on the Monitor at the time. I then swapped each BMS12 so it was in the other location and repeated the readings. The results are above.

So there are faulty readings in the exact same location even if they are reading different cells.
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frodus
Swapping the BMS board doesn't help?
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M
So i tried each BMS12 board in the two locations, and both boards showed the same errors no matter where they are.

Due to the short that was had i can only presume something has gone wrong on the board, but nothing is obviously damaged.

You can see the replaced shunt resistors in the attached image. I can only think of replacing them with the exact same values and hope that solves the problem. Unless anyone has an idea of what to check next?

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M
So it seems some of the mosfets were damaged during the short, as they were stuck partially open.
I have ordered some replacements and will see how swapping them out works.
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H
Not too surprising. There really should be fuses on the voltage inputs...of course then you have to replace THOSE when you short, but at least it helps with troubleshooting.
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