Hi,

I opened the cover of my 600 VA computer UPS to check the battery voltage and left it with the cover open (ups switched off)

After about 15 min ( i was not near the UPS) i smelt something burning and saw one mosfet of the ups had become completly black and burnt( i disconnected the battery terminal immediately)

There were two mosfets (IRFL1104S) one was ok the other completly burnt

My question is how and why did the mosfet burn with the ups switched off and second i cannot get the IRFL1104S, can i substitue that with IRF 3205S

Thanks

 

You must have shorted it out on the batt leads, they don't blow on their own!, as for replacement do the specs equal each other.

 

I really dont know what happened, i left the multimeter on reading the battery voltage.

i dont know much abt mosfets, the original is Vdss=40V, Rds(on)=0.009 ohm, Id=100A

plan to replace with irf3205 Vdss=55V, Rds(on)=8.0 mohm, Id=110A. do i need to match any other parameter with the original

thanks
viki

 

As long as the Volts//Current are greater its ok, looks like the specs should take it, but you really need to know how it got shorted out.

Mosfets dont usually need a gate drive resistor, and are ideal for Zero resistance at high currents.