Help! Daly Smart BMS refusing to charge

DIY Builds Battery Builds
#1

What changed? Nothing. One day after a ride, my friend plugs his YZPower 4A 10s charger into his board, and the charger light flickers between red and green.

Oh well, this is what Smart BMSes are for. He checks his phone, and the BMS appears to be cutting the charge on and off, not saying why, and all the cell voltages + settings look fine.

cell-voltages
cell-voltages591×1280 51.2 KB

We try restarting the BMS through the app, no success. Voltmeters says the charger is at 42.7V, but that’s probably fine. (We tried changing the overvoltage cutoff, no difference)

Without another charger to test, and unwilling to open his board because it’s water-sealed with butyl tape, he goes on another ride since he still had some charge left. Now when he tries to charge again, it works! And the battery even charges up to full again. Problem magically went away!

Yet now, after another ride, the problem is back again. This battery has been working perfectly for months, it was built properly by @Anubis (he shared lots of pictures to me) and has padding all around it and stuff. I’ll have to update that build thread eventually…

image
image960×1280 163 KB

Anyway:

  1. How likely is this to be the charger’s fault?
  2. Has anyone ever experienced something like this on a Daly Smart BMS?
  3. Is this covid related? If it is, what do we do about it? Ouh
1 Like
The Penetrator | A waterproof Evo for commuting in the UK
#2

easy, load the charger to see if it works.
Power resistor should do fine.

my bet is on intermittent connection, theres something loose somewhere…

#3

We tried that, but problem is that the charger stays in constant voltage mode for such a test, but maybe it’s the constant current mode that is faulty.

2 Likes
#4

Do you have a load that would exceed the chargers’ current rating/setting (if not CC limited) so it forces it into CC mode?

#5

Friend opened the board up, looks like the positive charge lead was soldered onto the main positive battery wire, which resulted in a cold joint that came loose. I’ll have him resolder it and report back.

1 Like
#6

What’s a good example of a load that we could try? I have no idea :sweat_smile:

#7

Lol, apparently the negative wire was loose too, amazing

2 Likes
#8
  • Light bulbs with a voltage rating higher than the charger.
  • “Dumb” heaters.
  • Power resistors.
  • Paralleled long lengths of wire (with the right total resistance to draw the desired amount of current) cooled by a fan. I’ve used 12AWG-4AWG for this very successfully. It might take 100ft of cable but it has the resistance I need to limit the current to what I want.
2 Likes
#9

Seems like I didnt rough up the nickel deep enough there, if you’re going to resolder it make sure you use something to make deep scratches in it (I dont think its a cold joint, looks like the solder just didnt adhere to the nickel enough). I do the main leads seperatly so they should have much deeper scratches but you could check them with a good tug