Relay that can be triggered by pwm signal

Thread Starter

stryped

Joined Sep 17, 2023
41
Is there a relay that can be triggered by a 3 to 6 v dc pwm signal to control a 14 v dc fan? It a refrigerator project to add an extra fan to turn on when the original evaporator fan is on.
thanks!
 

Ya’akov

Joined Jan 27, 2019
8,954
There’s no reason why it can’t be done.

I would suggest that you use an optocoupler which can be used to operate a relay or a solid state switch like a MOSFET.
 

BobTPH

Joined Jun 5, 2013
8,642
Why are you using a pwm signal, rather than the evaporator fan supply switch, to control a relay?
Most likely, the supply to the fan is the PWM “signal”. I do not like calling pulsed power a “signal”.

To operate a relay, we would want a peak detector, which is just a diode and capacitor.

And what is a 3 to 6V PWM signal? PWM normally means switching between 0 and some voltage with variable duty cycle. Something that varies the voltage between 3 and 6V is an analog signal. So which is it, or do both voltage and duty cycle vary?
 

Thread Starter

stryped

Joined Sep 17, 2023
41
Most likely, the supply to the fan is the PWM “signal”. I do not like calling pulsed power a “signal”.

To operate a relay, we would want a peak detector, which is just a diode and capacitor.

And what is a 3 to 6V PWM signal? PWM normally means switching between 0 and some voltage with variable duty cycle. Something that varies the voltage between 3 and 6V is an analog signal. So which is it, or do both voltage and duty cycle vary?
Sorry, I was mistaken it is a 14 v dc signal to fan but there are three wires so I assume it is pwm
 

BobTPH

Joined Jun 5, 2013
8,642
The third pin could be a tachometer output, it is on 3-pin PC cooling fans.

A motor does not generally have a PWM logic input. 4-pin cooling fans have both. You just modulate the power.
 
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