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Electrical questions

Discussion in '40- & 55-Series Tech' started by Degnol, Feb 5, 2003.

  1. Degnol

    Degnol

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    I just took apart a rear heater, and found out that the only thing that makes a motor a two-speed motor is a resistor(DUH!). So... the ceramic ballast resistor could be used to make my heater(front) motor blow on two speeds, right? Wire low speed through the resistor and high bypasses the resistor, eh? &nbsp:Do I need to use the bulky ceramic type ballast resistor, like used on the points or is ther another smaller more compact resistor like Toyo uses on the heater motor? I guess that's an obvious question with an obvious answer, but what do I ask for like at an electronics shop?
    Any Sparky's out there? Thanks, I'm a newbie to this board. Still use CCOT, that's where I learned a lot. Pin Head???
     
  2. barghini

    barghini

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    Resistors are rated in power. This rating specifies how much power can be dissipated by the resistor in the form of heat. Therefore what you need to do is ballpark how much power this resistor needs to dissipate.

    To do this I would first measure the current (I) that the motor sinks when its on. Hopefully you have a Multi-meter that will allow you to do this. This value will be higher than the resistor will ever see but its good to be conservative.

    Next you'll need to guess how much voltage you need to drop in order to get the heater fan to the speed you want. I really don't know this but I'd guess that you might want to drop it from 12V to 9V, thats a 3V drop across the resistor. Use V = IR or rewritten as R = V/I. If you measured 2Amps through the motor you'll need a 3/2 = 1.5ohm resistor.

    Power is: P = V * I and units are W(Watts). Then you would need a 3*2 = 6 W or higher power rated resitor. I would almost double this and just get a 12 W resistor in order to make sure that it doesn't get too hot. Go to an electronics shop and get a 1.5ohm 10 or 12W power resistor!

    You can get one through www.mouser.com for about 2 bucks.

    You might want to get a couple so you can put them in series if it is too fast with just one. Just make sure you get a high enough Power rated resistor. If you don't the resistor will get very hot and will burn up or burn things next to it up.

    Hope this helps. I know its wordy, but I'm a nerd sometimes.

    Barghini
     
  3. Degnol

    Degnol

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    Thanks for your very complete explanation! Now I'm glad I asked...that is BEFORE burning up the cruiser. I do have a multimeter, but I don't believe it measures amps, just a/c, dc, and continuity.
    I've printed your post and will refer to it in the future, Thanks
     
  4. toddslater

    toddslater SILVER Star

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    Excellent explanation, now for the low tech answer, in leiu of doing all this ...you can probably head to your local ford dealer and by one for an 86 bronco, 76 granada, etc..etc..etc.. or head to the nearest bone yard and pull it yourself for a couple pennies. The only thing is most of these resistors will be a multiple resistor unit (they had more than just low and high...sometimes even a medium...whoo hooo). Just think of the possibilities ;) At any rate wire it so high is high and make low be whatever you want. Sometime I'll tell you the story of the Merkur, the resisitor, the dealer and the judge :eek:
     
  5. Guest

    Guest Guest

    what I think would be cool is to make a H-Bridge for the motors that way you just turn a knob and you can fully adjust the motor speed. hmmm wait I might have one already. slow not right and still not right is what the settings should be called.