PDA

View Full Version : smoke?


rickyb
2009.02.04, 02:20 PM
hi i just attempted to replace burnt out fets for the first time. got everything back togther and o.m.g. it works :eek: but. after a few laps on the track i went to do some tweekng. i turned the car over and the wheels started spinning???? the switch is off?? crazy thing is if i turn the car back over it stops! when i turn the car back on everything works fine??? could it be something in the switch??? :eek: please help

marc
2009.02.04, 03:09 PM
Sounds like you might have a loose wire that's possibly touching something when flipped over.

EMU
2009.02.04, 04:16 PM
I doubt it is in the switch, could be wires going to the switch... make sure that there are no wires that are frayed or slightly loose anywhere on the board.

rickyb
2009.02.04, 04:49 PM
by what i have said, it sounds as though i was succesful with the fets though right????

x_zminiracer
2009.02.05, 09:42 AM
Have pooped a few fet's...did you replace just the single layer or do a stack? either way check that all the solder connections are good (re-flow them). I had my MA010 do that, had my work checked and it was fine after that. If you continue on using it (yes i did because I myself could not find were i missed with the iron) the reverse might go out like it did on mine, it cooked one of the fets on the bottom of the stack. dvsstrike went over it for me and re-soldered everything , started from scratch, pulled all the fets off the board and put em back. Worked fine after that.

z3zinho
2009.02.06, 12:28 PM
It might be a bad a loose wire as already stated... but it's worth mentioning a problem i had, might help you if you find out the problem is only related to the switch, and not the position of the car :rolleyes:

This happened with a batch of boards/fet's never bothered to see were the problem was coming from... everything was soldered properly but sometimes when the switch was of the motors would just start spinning and it would short the fet's...

This only happened with 02 boards... the thing is that with 02 boards, when you turn the switch off you get +vbat voltage on both terminals in the motor. The board should force Vgs on the N channel mosfet be 0v, so that it's not conducting, but with some boards the voltage slowly started raising so the N channel started conducting imedeatly shorting that fet... The fet's that burned were usualy the ones closest to the power wires on the board...

There are two easy ways to solve this, one is jus replace the switch with a wire :D Problem solved (That's what I do to my cars anyway...) You can also get a resistor to between the N chanel gate and -vbat to force Vgs to be 0. Get a high value resistor so the current on the fet drivers is low enough so it doesn't burn ruining your board :D try a 10k 1/4w resistor for each gate...

English is not my native language, and i'm so tired that this probably doesnt make any sense, so if you have any questions just ask and I will try to help