I want to run an old VW Fox's radiator fan on a 12V DC power supply. I have managed to burn out two of the PSUs so far. They work for a while but after a while they start overheating and die.

I am now trying a car battery charger. Haven't had it on for longer than 10 minutes as I don't want this one to burn out too.

There are no indication of voltage, amps or anything on the fan itself so it might have more or less volts than needed.

Please tell me what am I doing wrong.

  • 2
    \$\begingroup\$ What were the ratings of the late 12V power supplies and what's the rating of the battery charger? \$\endgroup\$ – Huisman Feb 8 '19 at 21:39
  • \$\begingroup\$ visit a VW repair shop .... they may know the current draw of the fan \$\endgroup\$ – jsotola Feb 8 '19 at 22:04
  • \$\begingroup\$ The fans are normally on their own fuses circuit so look at the car electrical diagram. \$\endgroup\$ – Passerby Feb 8 '19 at 22:33
  • \$\begingroup\$ AFAIK OLD VW's used 6 volt systems. Try it on 6V and see how well it works. \$\endgroup\$ – Russell McMahon Feb 8 '19 at 22:44
  • 2
    \$\begingroup\$ The VW Fox, iirc, has a 12V system, but the fan can draw about 20 or 25 A as it is designed for an intermittent high airflow use ie it only comes on when the engine coolant is too hot then once the temperature is under control it is turned off, so it is designed to move as much air as it can - not minimizing the current it takes as it is usually on when the alternator can provide the power and the alternator is 70A or more... I would hazard a guess that your power supply is rated less than 20A... \$\endgroup\$ – Solar Mike Feb 8 '19 at 23:17

There are several possibilities:

  1. The continuous current required by the fan is more than the continuous current rating of the power supply.

  2. The short-time current required to start the fan is more than the short-time overload rating of the power supply.

  3. The fan is started and stopped more frequently than the repetition rating for short-time overload of the fan.

  4. The fan's bearings are failing causing the motor current to increase when the fan gets warm.

If the fan was taken from a vehicle that has a 12-volt electrical system, a 12-volt power supply that has an adequate current rating is what should be fine. A battery charger probably has an output of 15-volts or so. The vehicle may output 15 volts when the battery is being charged, so that should not harm the fan, but it will not make a good comparison for the power supply that has failed.

For re-purposing a motor, it is always helpful to have the means to measure the continuous motor current. Measuring the starting current is more difficult, but that would also be helpful.

If you have another power supply to try, it essential to know at least the current rating of that supply and compare it with the supply that has failed.

| improve this answer | |
  • \$\begingroup\$ The fan fuse rating and the car's battery voltage would help op alot. \$\endgroup\$ – Passerby Feb 8 '19 at 22:42
  • \$\begingroup\$ If your lack of points prevents posting pictures, post them on a free site and revise your question to add a link. \$\endgroup\$ – Charles Cowie Feb 9 '19 at 16:14
  • \$\begingroup\$ It may be useful to add fan motor length and diameter. \$\endgroup\$ – Charles Cowie Feb 9 '19 at 16:18
  • \$\begingroup\$ The previous power supply that failed had an 500mA output and was a 9V. And the other one that failed was an 18V but can't remember how much mA's \$\endgroup\$ – Kabous Pieterse Feb 9 '19 at 16:39
  • \$\begingroup\$ I am surprised that you had any success at all with either of those. The 9V supply would have run the fan at about 3/4 of the normal speed. The fan would have required only a little more than 1/2 of rated torque at that speed, but it still seems like it would have needed quite a bit more that half an amp. The 18V supply would have tried to run the fan at 150% of rated speed and more that twice the rated torque. \$\endgroup\$ – Charles Cowie Feb 9 '19 at 18:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.