Nissan Leaf Over Voltage

S4TA

I may have made a big mistake today but hoping it isn’t. I converted my cart to lithium with Nissan Leaf modules 14 cells. I have had everything running perfect for a month now. Today, I decided to finish the build by properly mounting the sleep switch to a nice panel I made. I accidentally dropped it and something shorted on the contractor. About half of my cells jumped to 6V, when they should be closer to 4V. Prior to me doing this they were all right at about 4V. I am hoping I didn’t damage the batteries.

Does this mean I fried the cells?
If not, what’s the best way to balance the ones that are out of whack? Is there a trick with the BMS I can try?

Also, now when I turn the BMS to sleep it goes to sleep as it should but when I turn it back on, it shuts down. I have to hit the power button on top of the BMS to turn it back on. Wondering if I fried something in the BMS as well.





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BGW

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MCJEFE

I would message Ian at Zeva first. I'm pretty sure that if you take a multi-meter and measure the voltage on the cells they are fine. The worlds energy problems would be solved if we were able to double the voltage in batteries by momentarily shorting a BMS control wire. My guess is that you messed up the BMS and its miss reading half of the cells...

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S4TA

I actually tested the cells with a multimeter at the top of the BMS and they show the same as the BMS. I know you can’t charge a battery that quick so unless something fried internal to the module.

I sent a message to Ian first but thought I would see if anyone else has any thought in the meantime.


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NCPW

You need to check them at the cell taps with the multimeter to get actual voltages

Sounds like you wired your sleep switch incorrectly. It should only be connected to the sleep terminal and a ground. Nothing that should've short circuited.

BBBHC

Interesting... So your saying that the actual readings from the cells match what the monitor is telling you?

If that is the case it would seem only one of the two voltage sampling chips was effected, or somehow just the cells that are terminated to the first sample chip (00 - 08 ) were effected.

The "contractor" you dropped something on, is that the contactor you are using for HV/LV cutoff or the drive system solenoid/contactor? Or are you utilizing relays for your HV/LV cutoff?

Seems weird to me that not all of your cells were affected by the situation. I'm wondering if it would be a good idea to disconnect the pack, and possibly disconnect all the cells from each other to try and make sure there is no further damage to the cells not effected?

Either way, that is not a good scenario for those cells, if they truly read the 6v+. In theory, I believe, those cells have irreversible damage... I'm not an expert when it comes to this, so wait for one to chime in on this point.

S4TA

Update... to clarify, the ground side of the sleep switch touched the positive of the contactor, the HV LV contactor. The Zeva was saying 73V total pack voltage and my multimeter said the same thing. A few hours later, I tried unplugging the harness from the BMS and used the multimeter again and this time it was showing 103V, which made no sense unless I created a fusion reactor. I asked PingEye3 and he suggested the multimeter was bad. I grabbed an old dash mount voltmeter I had sitting in a box and my batteries measured 55V.

So... batteries fine (thank God)... multimeter and BMS not. The bad multimeter was an unfortunate coincidence that created extra undo worry. Now just waiting for Ian to respond about fixing my BMS.


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BBBHC

Well that's a relief! Time for a new multimeter...

Interesting that the BMS failed like that. The reading of 6.150v per cell must be a default maximum it will display.

I'm hoping you will share what ever information you get from Ian on this and how it s rectified.

Glad the scenario went this way for you!

BBBHC

S4TA, did you get any information from Ian on this yet?

S4TA

Yes. He said he “couldn’t make out any visible damage in the pictures, but from the information provided it narrows the fault down to pretty much either one of the voltage sampling chips (the righthand LTC6802, one of the two chips with lots of very small pins) or the polyfuse on its power supply (the little green component in the middle of the board). The LTCs are fairly tricky to replace, unless you have the right gear (e.g SMD rework station). It can certainly be fixed if you can send it back here though.”

So... I’m sending the BMS to him.


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BBBHC

Good information! Out of curiosity, did he say how much it will cost for them to repair it?