BMS Readings....YIKES!!

[DaveTM]

So, I've had my cart in my shed for about 3-4 weeks. The digital read out was 55.5V or so.

Today I went to use it and when I took the ZEVA out of "sleep" mode I got buzzed and a big overcharge message. Well, it has done this a few other times but when I reset it all was good.

But this time not so much. I could see what my digital VM on the dash was reading....which seemed to be correct at 55.4V. (See pics)



So I then switched the screen to see what each individual cell was reading....and YIKES.... 6 of the cells were 6.150V. I knew that could not be correct unless there was some magic charging going on in my shed.


So, I put my MM on each BMS wire that is connected to the battery and the ZEVA. I started at the first cell and it read the correct 3.98\3.99V. Then as I "walked up" the probe it shows the correct increase of each cell to be roughly the 4V. So I figured the cells were good and not over or undercharged.....but I think the ZEVA has bit the dust.

Then after some power disconnect and reconnect, I got a "more better" per cell reading.



So....what would be a good BMS replacement these days?

[jasonojordan]

You just discovered truly wireless charging for your cart! lol.

I like the JK offerings.

[Volt_Ampere]

Looks like your BMS is taking a dump - at least the voltage sense portion. I'm running Leaf cells too. I like them better than any of the LiFePO4 cells for traction applications. I was able to get discharge curves for the Leaf cells and I built my own SOC meter that computes SOC from the battery voltage. It's good to a percent or two which is better than most of the SOC meters out there. Cell voltage does change a bit with temperature which I don't correct for. I don't have any experience with modern BMS's.

[davros]

I don't know zeva at all but I might try jiggling the connector?

[DaveTM]

There's lots of things I've jiggled in my life to get them to give into my ....umm....whims. Wires usually aren't one.

[DaveTM]

Ok....some questions about these JK-BMS's. This one https://www.aliexpress.us/item/32568...2usa4itemAdapt shows it will work on 8S-17S (and since I have 14 cells this should work) but it states the Charge\Discharge rate is 80amp.

Does the draw current "run through" this BMS? And does this 80amp rate mean the max discharge rate is 80amp? If so it will never work with my cart.

[jasonojordan]

80a is far to low for a cart.

This is the one I would run.

JK BT 7S-20S 200A 2A
https://srikobatteries.com/product/j...th-uart-rs485/

[Volt_Ampere]

Most BMS's have the charge / discharge current going through them to monitor currents. You need at least a 200 Amp BMS.

[DaveTM]

My Zeva doesn’t run the current through the BMS.

Jason, thanks for the link but that 200amp won’t cut it. I need 300amp minimum and prefer 400amp. Where I hunt there are hills. Big hills that draw a lot of current for a short time period.

[TheCartBoy]

JK has a contactor based one that goes up to 500 amps