Hey everyone (sorry about the long read, but I like to provide context)
I’ve been working on a DIY build, but ran into a small (actually… it’s gigantic) issue with the pre-built battery pack I purchased online from a vendor here in the US (it rhymes with Mboards). After having plugged it in to charge, it popped scaring the shit out of me. It appears some debris shorted the charge port, and I thought I had blown the BMS. I emailed the vendor asking whether I should send it back to him to have a look or whether I can do it myself - he never responded. I’ve seen others complain about how much of a flake this guy is and quite frankly that has been my experience as well. He has only responded back 1 time out of 3 queries I’ve had.
I opened it being careful and found that the BMS (it’s actually a 50A and not a 60A as he states) had not fried, but in fact the charging port wiring had burned up. There was a 3 stage wire reduction starting with 18AWG wire from the C- on the BMS, down to 20, and then once again down to 22 to the charge port itself in short segments very poorly soldered together, but at the very least heat shrinked (small victories, right?). Measured voltage at the BMS and all packs looks great. Easy fix - so I thought.
From a high level, looking at the pack without even having to perform any deeper inspection, it’s scary. I decided to inspect the rest of the pack. On the outside the package looks very well built, but once you open it up, it’s a cancerous nightmare that is a fire hazard waiting to happen.
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Balance wires are brittle and sit atop of the cells with only 4 pieces of 1cm tape holding the BMS, and all balance wires in place. Over time vibration + heat generated could easily cause a short potential
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Balance wires connected to the positive terminal using a right angle piece of nickel. The balance terminals do have heat shrink, but are sharp creating another short potential
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The BMS sits on top of a piece of adhesive backed fish paper with one small piece of tape (~1cm in width) holding it to the battery pack
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Now the scary part. Some of the stock wrap around each of the 30Q cells (pink wrap) is compromised BADLY. They’re torn exposing the cell body. Others look like they have been cut during the build process and never repaired. This is the worst part. I cannot believe this shit. I could have been injured badly
Safe to say I have no plans on using this battery in this state.
I’m now in the process of building a new flexible pack (purchased PCBs from Kaly, all new 100 x 30Q from Nkon, 2 x 80A HCX-D223v1 with eswitch BMS, looking at the SUNKKO 737G+ spot welder) and hoping to further salvage the individual cells on this pack.
Is it possible for me to remove the wrap off of very cell and replace it? My google-fu hasn’t yielded any results looking for heat shrink for each cell. Any leads? Would it be ok to simply wrap each compromised cell with kapton tape instead?
Lesson learned. Never purchasing mass produced pre-built battery packs for any DIY build ever again and building my own from here on out. This has actually inspired me to seriously consider starting a battery build service because I actually have empathy and standards that I like to exceed. I don’t want to see anyone get hurt and my goal is to provide packs that take all necessary precautions to reduce the likelihood of injury due to a short.
Thoughts welcome (sorry new users can only put up one pic in a post…)