Why did our MOSFET fail?

[Altay]

Hi, we're preparing for a rocket contest and we have few days left and we got a crucial problem.

We were testing our Avoinics for the last time combined with our recovery system. While getting flight computers and MOSFET circuit ready we had a problem. While we were putting battery of MOSFET circuit in, nichrome igniter heated up and did release some smoke. There were no power in flight computers, it heated up moments after we did put battery of MOSFET (irfz44n) in. We must prevent this from happening on the launch day, we need your help.

So our question is this: Why did our MOSFET irfz44n fail in this situation? How can we prevent it from failing? Please help us if you can, this is really important for us, we're bunch of students trying to improve theirselves.

This is our circuit (Note: diodes are shown as resistor symbols, in header places we use terminal blocks):

Spoiler

 

[UhClem]

Has the irfz44 in fact failed?

A battery attached with reverse polarity would do this.

 

[davel]

1. Are you **sure** the firing battery was connected with the correct polarity. If backwards, the internal diode in the MOSFET will conduct and current will flow.
2. Are you **sure** the gate voltage settled below 2.0 volts before you connected the firing battery?

 

[Crayok]

I echo the above two comments 90% chance battery was in backwards.

some other thoughts:

• R1 is what value? if high enough a close EM source can trigger the FET.
• Was the input connector from the flight computers hooked up?
• Which way are the blocking diodes placed, Anode to the fet gate?

Make proper drawings guys, sloppy here means others have to guess your intent, team or not