DIY Mosfet Issues

[wildturkey]

Hi all

So I decided to DIY build a mosfet using this schematic

http://kuba-t1000.com/minigun/obrazk...sfet_mod_2.png

Mosfet build spec;

20K Resistor
100r resistor
IRF540 Mosfet

Prior to assembly I tested the resistors for correct resistance. Everything was soldered bar the drain channel as i've been told that too much heat can kill the mosfet.

Anyhow everything is properly heatshrinked and insulated, rifle is wired up correctly and all parts checked for no shorts etc.

connect the mosfet to the gearbox wiring and then connect up a battery (have tried a fully charged 9.6nimh and a 7.2v lipo) and pull the trigger and nothing.

i can hear the motor attempting to turn when the trigger is pulled but the rifle wont cycle. All i get is the little bit of an attempt from the motor an nothing. Its almost how the rifle is when the battery is near flat and it cant overcome the spring to turn the gears.

anyhow... advice would be seriously helpful.

thanks
Tom

[sj_asc]

Re: DIY Mosfet Issues

For your FET, the resistor value between gate and source is too high. Also, its worth noting that the FET you have chosen will be really on the edge of its capability with your average AEG setup. If you want the TO220 Package, you would be far better sticking to the IRLB3034 which is rated at 310 amps higher than the IRF540!
It's initial startup curent that will be the killer for the lower powered FETs.

[wildturkey]

Re: DIY Mosfet Issues

For your FET, the resistor value between gate and source is too high. Also, its worth noting that the FET you have chosen will be really on the edge of its capability with your average AEG setup. If you want the TO220 Package, you would be far better sticking to the IRLB3034 which is rated at 310 amps higher than the IRF540!
It's initial startup curent that will be the killer for the lower powered FETs.

Thanks for the reply!

what size resistor would you suggest for both the gate and source and then the gate to trigger?

and the mosfet package isnt especially important to me. is there one you would recommend?

[dave38x]

Re: DIY Mosfet Issues

IRLB3034 is the one I've used in 5 DIY mosfets, all of which I've used a 100R resistor on the trigger line and a 2k2 resister bridge. All five still work today (some are over two years old).

Can't go wrong using those components