After replacing a MOSFET, how do you stop it blowing again

[JonathanAnon]

Just replaced a MOSFET on a treadmill motor controller and it seems to be back working.. But I just want to make sure it doesnt blow again.. Is there any good practices for preventing a recurrence of the MOSFET blowing..

There is a huge heatsink on it, an isolation pad between the heatsink and the MOSFET, and it is screwed to the heatsink with an M4 nut, washer and bolt. Aside from swopping the MOSFET for a more powerful chip, is there anything else I could do to help it from re-blowing.

[tom66]

Re: After replacing a MOSFET, how do you stop it blowing again

Re-apply any thermal paste that may have been used.

[joshnz]

Re: After replacing a MOSFET, how do you stop it blowing again

Most semiconductors do wear out it may be that the mosfet is been exposed to kickback from the motor or gross overload.

kickback can be removed with a snuber of some sort.

[JonathanAnon]

Re: After replacing a MOSFET, how do you stop it blowing again

Hi josh, I had been assuming that it was overheating that killed the old MOSFET, but I guess the kickback from the motor is also a significant possbility. But I was sort of assuming they would have put a snubber circuit in already, as with every inductive load.. Especially with such a large 8 amp motor.. ?

Hi again tom, I basically just put it back the way it was.. i.e. screwed to the heatsink with an isolation pad... I've looked through all my old boards, and most seem to have thermal paste OR an isolation pad, but not both.. I'm basically at the stage that it's fixed but I want to put in the best preventative measures..

[joshnz]

Re: After replacing a MOSFET, how do you stop it blowing again

If you have a ir thermometer you could check the temp but will need to load it.

[JonathanAnon]

Re: After replacing a MOSFET, how do you stop it blowing again

If you have a ir thermometer you could check the temp but will need to load it.

Hah, that's funny Josh... I was just looking at IR thermometers online, in relation to working I'm doing with a printing company (making sure that their heat press has uniform heating).. I never though about using it on ICs but it's certainly a good suggestion..

[euromatlox]

Re: After replacing a MOSFET, how do you stop it blowing again

Lot's of interesting reading, mica sheets vs silicone pads, in various forums. Silicone pads are popular, easier to use than mica with grease, but 'old school' prefer mica. Google for more.