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I have a car radiator fan which when measured with a multimeter on a 12 V car battery draws 4.7 A. I've been trying to run it off an old PC SMPS which is rated at 450 W with a max. current of 18 A at 12 V.

The SMPS doesn't start when I connect the fan to the power supply while the SMPS fan starts running when there is no load. What would be the problem? Can adding a capacitor make the radiator fan start working? If yes, what values should the capacitors be? What is the right solution to get it working?

ocrdu
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Annu
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2 Answers2

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DC motors take high currents to start. you'll need some sort of soft-start to get that fan going on that power supply.

Jasen Слава Україні
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You need to limit the start current drawn by the fan motor, which could be 20A or more at first.

Simplest would be to connect a rheostat (large variable resistor) of about 10 ohms in series with the fan (though you might have difficulty finding one with enough power handling). Start at the highest resistance and reduce it as your fan comes up to speed.

Another option is to connect a light bulb in series with the fan, e.g. a 100W 12V bulb should work. Once the fan starts to spin, close a switch to "bypass" the bulb.

A third option is to build a buck converter (PWM driver), and gradually increase the voltage supplied to the motor.

Liam
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