Some lessons are hard to learn. When working on the second battery I’ve got stacked on the step 4 – Make sure that the circuit is No Short.
Measuring the resistance between the BMS cables I should be getting values between 0.0-5 Ω (Ohm), but it was constantly returning something between 8-10Ω.
I even searched for the User Guide for our Multi-meter to check if I am measuring things properly!
Knowing a little about what I am measuring I’ve connected our BMS and it started warming up a bit, but not too much to get me worried. Quick answer to all this was – it is just balancing those cells in series! Well, balancing was a good idea, but when I measured everything again after 24hrs and it was still balancing it started not feeling right. Also the resistance wasn’t dropping, but rather growing. This really ruined my night thinking where I messed up and mainly if I could somehow burn our precious DALY BMS.
I’ve unplugged BMS and started with a cross-check:
- Battery voltage between its ends – 20.4V (tiny drop from yesterday) – OK
- Balancing cables properly connected in a right order – OK
- Voltage between each balancing cable ~3.6V – OK
- Connection with BMS – Looks stable
- No shorts – couldn’t find any
So help me to find two differences! Except the obvious – they are same … unless
… checking a voltage on the first one shows 25.2V and the second one -25.2!!!! Well it took us 15 minutes to rewire everything and solder it together again, but all good now – working resistance is down to 0.2Ω.
So after some wrapping we ended up with two (almost identical) super-cool power packs. 🙂
As always, let us know what you think, all comments and ideas are welcome! There has been already a note from Vlada to come up with some case for those to protect them from a mechanical damage – I think it is worth considering! But that’s for another day again.