fan cooler or thermal paste?

[leonheard]

Hi

I have a dc motor and my transistor get very hot after a while, so i have probably to use some heat sink, my question is, if i put a heat sink then i will need to put also a thermal paste, so do i need to add a fan? Or is just enought without a fan?

 

[clayt]

All depends on how big the heatsink is and the amount of power you need to get rid of (i.e. the amount of heat).
Try just a heatsink. If it still gets too hot, add a fan.

 

[alexan_e]

A heatsink has a specific cooling efficiency based on the size and share (and material etc), a fan can increase that.
The paste is used to reduce the thermal resistance (better heat transfer) between the transistor case and the heatsink, the better the thermal contact between these two the better.

The question thermal paste or fan doesn't make sense.