Fan question

Discussion in 'General Electronics Chat' started by dustiin, Feb 24, 2010.

  1. dustiin

    Thread Starter Member

    Jan 13, 2010
    Hi all. I'm wanting to buy a Spal fan to cool a dirtbike. I assume this fan wants DC power so I'll be using a rectifier to add to the bike.

    The rectifier's forward voltage drop is 1.1. Bike puts out 12v. This means the rectifier will put out 10.9v. The fan wants 12volts.

    The question is will a DC fan work well with AC or spin at all and will the 1.1v drop stop it from spinning fast? It pulls 290cfm at 12v 4amps.
  2. VoodooMojo

    Active Member

    Nov 28, 2009
    the fan will not run on ac unless it is polarity protected with a diode then it may move because of a bit of half-wave rectification.
    the voltage drop from the rectifier if it is 10.9 will be low enough it may not provide much of a cooling effect.
    The stator of the bike engine is probably putting out 16 - 18 volts ac, which will leave 13 some volts dc when rectified


    "Dirt Bike Regulator/Rectifiers

    [​IMG]Dirt bikes use several different types of power systems depending on whether they have an ignition system only, lights, or a full electrical system with a battery.

    Motocross style bikes with no lights use a very simple stator consisting of a source coil that provides power to the ignition system. These bikes do not have anything to control the power coming from the stator.

    Dirt bikes with lights use a slightly more complex system. The stator still has a source coil to power the ignition system but it also has a lighting coil or winding to provide power to the lights. Often these lights run in AC power using no battery. The power provided by the stator varies with the engine speed. When the engine is running at idle, the lights tend to go slightly dim. Once the throttle is opened, the lights brighten. To prevent the lights from burning out from too much power, an AC regulator is used. Once the voltage reaches a certain point, between 12 and 14 volts, the regulator takes the extra AC power from the power wire and throws it away by sending it to ground which, in the case of a dirt bike, is the frame.

    [​IMG]Motorcycles with batteries must convert the AC power from the stator into DC. In order to do this, the power coming from the stator must be converted by a regulator/rectifier. The rectifier actually converts the power from AC to DC, while the regulator keeps the power level (voltage) from going above the 13.8 -14.5 volts needed to power a standard 12 volt battery. It is important that the stator provides more power than needed by the motorcycle so that the battery will stay charged. If the motorcycle uses more power than the stator can provide, the battery will start to drain. This will typically happen if the voltage drops below 13 volts.

    ElectroSport regulator/rectifiers are designed to be direct replacements to original equipment by using stock mounting locations and OEM style connectors. These parts are designed to handle higher power loads than their OEM counterparts.

    * It should be noted that when a motorcycle is converted from an AC system to a DC power system, a regulator rectifier is used to replace the AC regulator. The AC regulator should be removed. Often the mounting location must change because a regulator/rectifier is larger than an AC regulator. As with any electrical part, it is important to follow the included directions when installing them. When mounting a regulator/rectifier, especially to a bike with upgraded lighting and stators, these parts will get warm and should be allowed cooling airflow."

    4 amps is a considerable drain.
    you may want to add a small battery if it does not have one to keep the drain on the ignition system to a minimum.
    be sure that the bike's electrical system can handle the demand


    Last edited: Feb 26, 2010
  3. BMorse

    Senior Member

    Sep 26, 2009

    If you are reading 12V dc from the bike, then it already has a rectifier in VoodoMojo said, the bikes output should be around 16v to 18v ac......
  4. VoodooMojo

    Active Member

    Nov 28, 2009
    What is the make and model of the bike?
    we can give specific advice.