Anyone good with car electrics?

Thread in 'Technical Questions' started by Cheshire190e, Feb 14, 2012.

  1. Cheshire190e

    Cheshire190e Active Member

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    Hey,

    I'm running twin electric fans on my PS rather than the viscous. Currently the fans are wired with a fan controller to turn them both on full power when the car gets to 100[SUP]o[/SUP]c and off again at 85[SUP]o[/SUP]c.

    What I want to do is to have the fans spinning at a low speed constantly whilst the engine is running. I plan on using 2 parallel resistors to drop the voltage down to about 4V. Now I know how to work out the size of resistors needed to get the required voltage; but I am unsure of the current they will cope with.

    I know some oem electric fans come with a similar set up but all the ones I have found only make the fans spin at about 75% of full power. Whereas I would ideally like the fans running about 30%

    Would anyone know what resistors I need to handle the current drawn from the fans. about 30A.

    Ta

    Matt
     
  2. alperin-s14

    alperin-s14 Member

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    You could buy one of those switches that have speed 1, 2, 3 And it Wil be from slow to fast...
     
  3. 4_Stroke

    4_Stroke Member

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    You will need to sink about 120W of power to drop 30A @12V down to 4V. Thats a HUGE resistor. If they are DC motors wire them together in series and you would have 6V on each one. The have a 2 pole changeover relay operated by the theromostat switch to change from parallel to series operation. Even if you wanted to drop the power from 6V to 4 you would only need a 20-30W rated resistor so its much more achievable.
     
  4. Cheshire190e

    Cheshire190e Active Member

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    Cheers for your reply mate, I was thinking the resistors needed would have to be pretty huge, which is probably why the stock ones don't lower the speed that much.

    they do each have a dc motor so could wire them in series rather than parallel, they have a 3 pin plug but only 2 are used so maybe I can utilise this 3rd pin for the series wiring. If they are being powered in series so 6V each, when the fan controller kicks in and sends 12v to each would it override the series circuit or blow things up?

    Ta
     
  5. Struggle

    Struggle Active Member

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    best answer ever!!!! gutty how did you not know this????
     
  6. Cheshire190e

    Cheshire190e Active Member

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    I have thought of that but cant be arsed spending money on another fan controller when I can get what I need with different wiring or a couple of resistors which are cheap as.
     
  7. proseal

    proseal Member

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    I have some big ass resistors in work Guttman :)
     

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