Not Applying Thermal Paste When Installing Mosphets in APC UPS

[Anonymous user]

Please are there any negative effect when installing mosphets without applying thermal paste?

Cos I have this APC UPS that's making noise and vibrating (only when running on battery) after installing new mosphet though without thermal paste.

I don't know if its cos I didn't apply thermal paste or something else is going wrong.

Please can someone help out as this is making the frequency unstable though the unit is working but the noise is annoying

[BillP]

hello Samuel , the mosfets you changed are the same that originals?  you must apply thermal paste because if you don't do it the mosfets can take more temperature and give a little diferent values than can produce a louder noice in filters , verify if that is the problem ,

regards. 

[Anonymous user]

Yes they're same as the originals.

I don't have thermal paste at the moment hope solder paste won't be a bad idea as in using it in place of thermal paste?

Thanks.

[Anonymous user · Accepted solution]

Hello Chris,

I tried the soldering paste the noise still persist. This time, i bought the thermal paste, thoroughly cleaned the mosphets and the heat sink, applied the thermal paste but the noise still persist and this is making the mosphets overheating but surprisingly, it charges batteries very well without the noise.

Please what could be the cause, hope I've not screwed up?

Looking forward to your response.

Thanks.