22A fan motor turn on question 2

[knowlittle]

I have a 2-fan radiator cooler. At idle it draws 22A, or 11A each fan. Each fan is on its own relay. But the relays are turned on-off simultaneously. Should I turn the fans staggered to reduce transient? I have no idea how much is excessive motor current. Thank you.

 

[LionelHutz]

For protection, put a reversed biased diode across the motor to handle any inductive spikes and a a MOV across the FET to help protect it from over voltages.

I've seen similar modules with TO220 devices so you could attach a heatsink to the tab. Find a similar device with a higher current rating if the device the board comes with isn't rated for enough current.

You can parallel FET's, but you have to be careful to keep the lead lengths and lead inductance the same going to each FET. I suppose if you parallel those boards then split the large gauge power and ground wires to a smaller gauge and use same length of wire from the split to each board. Try to keep the wires routed similarly too.

The most likely failure of that FET board is a shorted FET so I don't see you gaining much for reliability by paralleling them.

 

[knowlittle]

Thank you for the explanation. I think I am ready to experiment with PWM and FET for the first time.

 

[waross]

The reason for staggered start is to not use more cooling than is needed. As long as one fan is enough, you don't need the second fan so why bother to run it?
Use a two step thermostat to start one fan and, when needed, the second fan.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MacGyverS2000]

If you do go the PWM route, you still need to stagger the start times to avoid a huge inrush current.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[knowlittle]

Thank you for the notes. Will follow your suggestions.

I have a related question. I have not seen a flyback diode on any radiator fan motor. Is there a good reason?