2 40mm fans at once with one printrboard?

[JamesTuthill]

Hi, I have a question that I was wondering if someone may be able to answer. Is it possible to run two 40 mm fans with only one printrboard? Could I splice the wires and connect two fans?

[Compro01]

According to this question on printrbot, the fan is powered by a IRLML2060TRPBF MOSFET (Q3 on the schematic). Specs on digikey say the maximum power from that is 1.25W.


Looking at various 40mm fans, most draw about 100mA @ 12V, so the output of the FET is just barely enough to run them, so running two is out of the question.

[printbus]

According to this question on printrbot, the fan is powered by a IRLML2060TRPBF MOSFET (Q3 on the schematic). Specs on digikey say the maximum power from that is 1.25W.


Looking at various 40mm fans, most draw about 100mA @ 12V, so the output of the FET is just barely enough to run them, so running two is out of the question.

It might not be a good idea for me to argue with a moderator , but let me apply some of my electronics background here. One important spec is the max drain current - this is how much current the part can handle. The part is spec'd for 1.2A, so in that regard the part can handle two 100mA fans just fine. The 1.25W max power dissipation spec is with regards to how much power (ie, heat) is being dissipated within the part itself, not how much power is being applied to the load ( which is 12v x 100mA = 1.2W into each fan). The internal power dissipation comes from the load current going through the internal on resistance. The part has a maximum on-resistance spec (Rds) of 480 milliohms, so at a 200mA load current for two fans, the part will be dissipating just 0.02W using P=V*I and substituting I*R for V. Or, P=0.2*0.2*0.480W.

My vote is that two fans should be fine.