DIY Electric Car Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
66 Posts
Discussion Starter #1
I have an aluminium battery box with a row of lithium ion cells in it.

I dropped a small bolt which made contact between a busbar and the aluminium box - There was a spark and some soot -

So I did a test with the meter -

I hold the prongs, one on the box and one on a terminal (or busbar) a spike in voltage for a split second of sometimes 1 volt is shown - then it drops down to .089 volts

Is this normal? is it bad?

I tested for resistance and always get the OL
 

·
Registered
Joined
·
1,498 Posts
What cells are you using, do they have a metal container covered on the sides and bottom with plastic shrink wrap?

The case of metal jacket cells will measure a voltage between either electrode due to the electrolyte touching the inside wall.

Is your battery box tied to the pack (-), either on purpose or unintentionally?

Did you do any drilling or pop rivets, etc in the vicinity of your battery box, whereby swarf may have lodged between the box and a cell? Boeing had a couple of lithium battery fires on the screamliner, in one case there was a punch thru spot on a cell wall directly below a hole in the box which was drilled and pop rivets for the lid. Gotta say i'm not impressed with that slotted hole with all the burrs and debris hanging and ready to fall in your box--and it's right above the burn spot...?

The other possibility is that the plastic wrap between the case and cell wall acts as a capacitor, and the voltage you were reading was due to the charge difference across that gap. The voltage decayed due to the load of the meter measuring circuit.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #4 (Edited)
I tried to avoid any small shavings dropping in the small gaps - used a vacuum cleaner while drilling - the cells are covered in shrink wrap but if you take the shrink wrap off it seems to have a plastic coating over the metal body.

I have not tied the negative or any terminals to the battery box - Like I said the meter shows open loop when I do a resistance test so if it were tied in any fashion I suspect I would get a reading.

The slot was done before the bracket was riveted in place and it looks worse in the photo than it does in real life. I suppose I can get a tiny little file and make it look more professional ???

The real question is the build up explainable by some other reason than me doing something wrong? I suppose I should take out 4 or 6 batteries in that end of the battery box and do a close exam just in case there is some problem.

But at the end of the day if it is something that can not be made to go away if it is caused by the wrap around the cells will it be OK ?? will it be safe or dangerous?
 

·
Registered
Joined
·
1,498 Posts
Dropping a bolt that touched between the buss bar and the aluminum battery box--should not have caused a spark.

The pack should be isolated from chassis, but you have a sneak path somewhere. It is dangerous and you should investigate and search to get to the bottom of this.

How much of your car is wired up? do you have a charger, dc/dc converter, main contactors, etc. Wiring diagram or schematic available?
 

·
Registered
Joined
·
1,007 Posts
Depending on the design of the batteries, capacitance between the cells and the box can be significant, enough to create a spark. I can't see the image you posted for some reason, so I can't say how likely that is to be the cause.
 

·
Registered
Joined
·
506 Posts
Is this box connected to *anything* or is it simply a metal box of cells? How are the cells connected (xSyP)? What's holding the cells and busbars in place in the box -- you can't tell us it's not fixated somehow.

According to your meter reading, you seem to have a capacitor somewhere, though, but I personally think that the box to cells capacitance being the source of enough charge to create a spark, let alone soot, is highly unlikely. Your cells are connected to something you've missed telling us about (like a contactor for precharge). I'd bet one of your caps is bolted down to the sheet metal, or at least in contact with it.
 
1 - 7 of 7 Posts
Top