Short Circuited my 48V 120Ah Build (I'm fine)

[AussieInSeattle]

Rather than post this into my build thread (linked below) I thought it would be better to post a new thread so others might learn something from my experience.

The build was using Sergios approach that is well documented in this forum - special thanks to him for all of his help before and after this happened.

Firstly, I'm fine - was wearing safety glasses and gloves at the time and the top of the pack was covered - I do need some new underwear though. In short (no pun intended) I spent the past 3+ weeks building my 120Ah 48V pack ever so carefully and managed to short it while hooking the finalized pack up to my golf cart by not having a correctly protected socket handle (left small piece of metal exposed near where you switch direction). I shorted between the end of the fuse that is external to the pack and the through bolt going through the OBC - I had already hooked up main pack negative which goes through this stud. I was in the process of hooking up main pack positive which is why the end of the fuse was exposed - the OBC stud was not insulated and my tool was not fully insulated. At the end of the day I was not fully concentrating and picked up a socket extension without thinking to complete the connection and ended up shorting the pack resulting in a "huge spark" between the end of the socket I was holding and the OBC stud.

Pics attached of the carnage - I've since dismantled the pack and it appears I have lost one cell with cosmetic damage to 7 others and 8 cells totally fine out of the 16. Cell #14 has a severely melted terminal which we think was not connected tightly to the busbar, resulting in high resistance during the short and blasting the busbar towards cell #9. All 16 cells have a voltage of 3.340V so all are "functional" but that one cell cant be used due to it's terminal being melted. None of the cells vented even though it looks like #14 did (only molten metal busbar went through the "vent window").

After some soul searching and processing all the "what if's" in my head, I purchased 2 more Higee 120Ah cells from alibaba over the weekend so I have one spare and I'll continue with the build with some better insulated tools and a fresh appreciation for how dangerous building your own pack can be.

And here's my build thread which shows the process until the above happened:
https://www.buggiesgonewild.com/show....php?p=1803438

I've also cross posted this to the diysolarforum about 10 days ago (when it happened) for advice on how to move forward - lots of smart folks over there that know a lot about LifePo4 and battery pack builds. If you are planning your own build that forum is a great resource:
https://diysolarforum.com/threads/sh...im-fine.17257/

Note that pic 1-3 are from prior to the carnage.

Insulate your tools!

[rib33024]

Glad everything is Ok

[Mooncarter]

Glad you are OK.

I don't know anything about lithium but I'm sure it could have been much worse.

[Volt_Ampere]

I worked on electric cars as a major project when I was in school back in the early 70's and I still have a wrench that one of the guys got across the 120V battery pack. It's cut in half. He was ok too but his shorts were soiled for sure. This was FLA batteries and one exploded during the short.

[ThreeCW]

Thanks for sharing your short circuit experience.

I'm sure that anyone who reads this thread (and the diysolarforum thread) will have a better understanding and a deeper appreciation of the risks associated with working on a battery pack whether it be lithium or lead acid.

[BBBHC]

Glad you are ok. There were times while building my lithium buggy that I thought I was being overly cautious. Maybe I was, but no unwanted incidents occurred, so I'm good with it.

Good on you for sharing the experience. Not many would. Much respect from me to you.

[simicrintz]

Sad to see but very happy that you are okay!

[Sergio]

I made a couple of observations to AussieInSeattle when we exchanged emails about this incident that may be helpful to other users.

First, make sure you go over every single cell tap (again) to ensure they were properly torqued.

If You look closely at the first picture (before accident), the cell tap that blew up is the third one from pack positive connection, you will notice there is not much thread showing above the nut (likely not tightened).

This could also have been an issue down the road if that connection was faulty.

Second observation based on the fact the bus-bar blew up but the fuse did not is the fuse rating for lithium applications.

I lot of folks, myself included, use the ANL-400 that came with the Alltrax controllers or were recommended by other vendors.

Those work fine for a Lead Acid pack that can sustain very high discharge rates and a surge of 700amps or more so the fuse will protect the wiring and not damage the battery in case of a direct short.

I think for Lithium packs the ANL-250 is a better option.

Those fuses sustain currents of 125% its rating and not blow until over 150% the rating.

Just a reminder, the controller current rating is more about the maximum Motor Current and not the battery current.