4 ms·

I bought a low speed vehicle last summer that the previous owner had outfitted with a home made 24-cell LiFePO4 pack, complete with a cheap Chinese BMS and bala

by ttul 3y ago

I bought a low speed vehicle last summer that the previous owner had outfitted with a home made 24-cell LiFePO4 pack, complete with a cheap Chinese BMS and balancer unit. Within a week of purchase, his haphazardly installed balancer wires had melted in various places where they pressed against the high current conductors. Long story short, balancing didn’t work properly on account of the sensor wires being shorted together and, resultingly, many cells went to zero and I suppose I’m glad it didn’t also catch fire. These things are fun, but they pack a whole lot of energy!

jacquesm 3y ago
This is a pretty common error and the reason why in my long distance e-bike pack I spent a lot of time getting the balance wire routing done without any wires crossing. Even Bosch got this wrong on their pannier mounted battery packs, I've opened up a whole pile of failed Bosch packs to see how they fail as a guide to my own pack design and the most common failure was water ingestion due to bad seals followed by burned out balancing wires that some how got worn out or pinched. This stuff is very critical and I would (1) never buy a pack that some other hobbyist made and (2) never sell the pack that I made to someone else.
louwrentius 3y ago
Building batteries like these based on LiFePO4 is very easy to do, but you have to think about safety, especially if you put a battery in a moving vehicle. If something goes wrong with these kind of batteries, it's never the batteries themselves (specifically LiFePO4) but it's always a bad connection or an undersized wire causing high resistance and thus heat --> fire. In my case, my wires are quite oversized and I bought a proper lug nut crimping tool (and not use a vice or soldering (Don't do it)) to make the connections. I've also really made all connections tight, double-checking them.
- ttul 3y ago
  Yeah for sure. I am redoing all the wiring and replacing about half the cells because they went to zero… Will be over-specifying everything and making the routing super tidy. If you have the patience for that, DIY batteries are fun!

by ttul 3y ago

jacquesm 3y ago

This is a pretty common error and the reason why in my long distance e-bike pack I spent a lot of time getting the balance wire routing done without any wires crossing. Even Bosch got this wrong on their pannier mounted battery packs, I've opened up a whole pile of failed Bosch packs to see how they fail as a guide to my own pack design and the most common failure was water ingestion due to bad seals followed by burned out balancing wires that some how got worn out or pinched. This stuff is very critical and I would (1) never buy a pack that some other hobbyist made and (2) never sell the pack that I made to someone else.

louwrentius 3y ago

Building batteries like these based on LiFePO4 is very easy to do, but you have to think about safety, especially if you put a battery in a moving vehicle. If something goes wrong with these kind of batteries, it's never the batteries themselves (specifically LiFePO4) but it's always a bad connection or an undersized wire causing high resistance and thus heat --> fire. In my case, my wires are quite oversized and I bought a proper lug nut crimping tool (and not use a vice or soldering (Don't do it)) to make the connections. I've also really made all connections tight, double-checking them.

ttul 3y ago
Yeah for sure. I am redoing all the wiring and replacing about half the cells because they went to zero… Will be over-specifying everything and making the routing super tidy. If you have the patience for that, DIY batteries are fun!