EVE LF280K cells testing positive between negative pole and the blue body

[WindWizard]

Time to get a meter out and measure to see where it is shorting out. If you get sparks with just one bus bar then it has to be shorting somewhere.

 

[guidecca]

I'm glad to hear you are adding insulation between the cells. Are the sheets the same size as the cells? Not undersized?

Can you draw out or demonstrate where you are adding bus bars?


Are the cells sitting on something conductive?

I was drilling holes in copper bus bars and made a bit of a mess but I think I cleaned the shavings up. That was awhile back.

 

[WindWizard]

Current has to flow from the negative terminal to the positive.

 

[timselectric]

I put some plasti-dip on the bus bars to insulate them. Could that be it?

I wouldn't think so.

 

[WindWizard]

What you are describing does not work. There must be something that you are not aware of happening.

 

[400bird]

Can you show you bus bar lay out?

 

[WindWizard]

Make sure the bus bar clears the body of the Cell and the plastigoop does not rest on the body of the Cell.

 

[timselectric]

Somewhere, there is contact between two or more cell casings.

 

[guidecca]

Current has to flow from the negative terminal to the positive.

Where do you start and how to you find the short?

Can you show you bus bar lay out?

 

[guidecca]

Could be the insulation is not the same size as the cells and cells are touching. Not sure if the Plasti-Dip is touching the cell body or not. I'll check it. Thank you all for your insight.

 

[WindWizard]

One of the bus bars has goop on the contact and needs to be cleaned.

 

[guidecca]

One of the bus bars has goop on the contact and needs to be cleaned.

The Plasti-Dip did me in. I didn't see it. I'll clean up that mess before I try it again.

 

[WindWizard]

Take one of the bus bars and put it on one of the terminals. Put gloves on. Push the one side of the bus bar to the other terminal momentarily. You should not get a spark.

 

[guidecca]

I will try it tomorrow. I need a break. Just clean the bus bar and slide it on momentarily. I can try it but I'm going blind tonight

 

[WindWizard]

If you want to be totally safe then get a voltmeter. Connect one end to the + terminal and the other end to the - terminal. You should measure zero volts. The set your meter to current and do the same. You should measure no current. If your fuse blows then you need to figure out why you have current flowing through it.

 

[Sun in Lithium]

Or you could just check for continuity between the cell casings, with your multimeter. By placing the leads on the QR code of the cells beside each other.

 

[WindWizard]

This is what I suspect that seems to make sense to me. The casings of the cells are shorted and when you move them it just makes it worse. I suspect that some of the copper shavings got between the cells and is breaking through the thin plastic insulation. When the cells are compressed then the thin copper shavings are just shorting out your casings and then when you connect the bus bar then sparks start to fly. This can easily be verified with a voltmeter. To remedy the issue then as others have suggested, remove the copper debris and place an insulation material between the cells. Also remove all of the copper shavings from the bottom of the cells as well.

 

[400bird]

Looks like you are installing the bus bars in series correctly.

With all the bus bars off measure voltage from one cell to the next. Try lots of combinations of terminals and cell casings from one battery to about. In no situation should you see any voltage. If you do there's a connection between the cases that your FR4 insulation missed.

 

[rodrick]

Sounds like he has some copper chips shorting cells and it’s like trying to parallel and series the same cell

 

[justgary]

And definitely inspect under the cells to make sure you aren't shorting on the threaded rods below. If you have more PC board, consider using a layer under the cells also.

I would not use Plastidip for this job, by the way. A more durable and reliable way to cover the threaded rods is with plastic pipe such as PEX or PVC.

 

[guidecca]

All's well that ends well. I didn't find traces of copper. I covered the QR Code next to the blue "window" area with Kapton tape to insulate the cell casing from any stray electricity and patched a few dings with rubber cement and Kapton tape. Covered the bottom of a couple of cells with Kapton tape. I checked the threaded bars/ screws for any touching and made sure the four cells in the compression assembly were flat/ even. That seemed to fix the sparking.

Now, I'm assembling the OverKill 100 amp, 8s, 24 volt BMS and I'm not sure what gage of wire to use for plus and minus (B- and C-). I'm using one BMS per 8 EVE LF280K cells and both bank will be connected to the same bus bars. The company gave me these directions:
"If you are having a cable come from both M6 terminal blocks I would recommend 4awg wire. If you are putting a
bus bar across the two terminals I would go with a 2/0 AWG wire." I'm not sure what that means exactly. I have plenty of 1/0 AWG wire from the last project.

 

[guidecca]

What I think is going to happen is this: Below is a picture of the terminals to connect the bus bar to. Then yes tap a screw hole and secure a 2/0 wire from there. Not real sure how many bus bars attach to the BMS in the circled terminals or how many 2/0 wires are attached to the bus bars. Is it one wire per bus bar? Can the screw hole be skipped and the 2/0 AWG wire connect to one of the terminal screws?

 

[Ampster]

Can the screw hole be skipped and the 2/0 AWG wire connect to one of the terminal screws?

To be clear, the flat part of the cable lug should be fastened by the screw to the BMS port. Overkill has a fairly extensive instruction set. For more surface area two or three positions are available for attaching multiple smaller wires all going to the same battery terminal or bus bar, as seen in the picture you posted above.

 

[guidecca]

I think I will have to email them unless someone has a telephone number. I don't see the gauge or the positioning of the wires on this BMS. I should have ordered it with the wires. I didn't think it would be this complicated. They did not explain much and added more confusion than anything. The impression from their email is that a bus bar can be joined to the two terminals on both B- and C-.

 

[Sun in Lithium]

Does this help?