Close

Fuse test mode

A project log for REMB - Raz0r Electric Mountain Board

An electric mountain board, built from scooter parts.

Daren SchwenkeDaren Schwenke 09/02/2019 at 06:003 Comments

It was all going so well.  I tested forward and brake for both channels and it was working perfectly.

Then..

That is the magic smoke being released from the left braking mosfet. It was quite the event and I can tell you that mosfet never gave up.. it was positively glowing before I cut power.  Perhaps I should have actually included the fuses in the test.  :)

Somehow it seems to have taken the two drive mosfets with it during its demise.  So it seems I will need to rebuild half of my board here to fix it.  Ugh.

I have since discovered that the 2N3904 transistors I picked to drive my braking P channel mosfets have two different ratings online.  One group is rated for 40v, the other for 60v. My battery voltage maxes out at 42v, so can only assume I have the cheaper ones.  I am driving the P channel via a voltage divider to keep the gate voltage within the max Vgs of my mosfet here, so I'm basically left with that.

Currently rebuilding it with spade connectors, and seeing if I have some higher voltage rated NPN transistors here.  Cross your fingers.

Discussions

Xasin wrote 09/02/2019 at 17:13 point

Ouch, that really sucks ... 
I know and hate the feeling of vital or hard to desolder components giving up. Had to deal with a few (like a 40 pin SSOP), but luckily nothing as bad as a BGA or so.

In any case, I really hope fixing things will go well, and that you can figure out the problem with the FET!

Broken BJTs due to the voltage are definitely a possible culprit, especially if they drive the FET gate improperly.

  Are you sure? yes | no

Daren Schwenke wrote 09/02/2019 at 18:27 point

Pretty sure it was either the gate of the BJT floated up (somewhat unlikely) or it failed shorted due to overvoltage (pretty likely).  I didn't have a pulldown resistor on that BJT gate but I won't need it when actually hooked up to the MCU.

In either case it turned on my braking FET while I was testing forward... so.. pop.  I got spares of everything I used and a handful of BC337 NPN transistors rated at 50v, so.. just more work.

  Are you sure? yes | no

Xasin wrote 09/02/2019 at 18:58 point

As usual.

I'm working on a small series of Lasertag sets, 4 at once, so... That'll be fun to solder <.<

Good luck!

  Are you sure? yes | no