Help with power supply for small DC motors

Discussion in 'The Projects Forum' started by alan7s, Jan 9, 2015.

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  1. alan7s

    Thread Starter New Member

    Jan 9, 2015
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    Over the years, I'm faced with simple Ohm's law problems in projects but not sure how to proceed practically. Here's one example:

    I upgraded my 6 volt Willys Jeep ('58) to 12 volt which means all electrical components now run fine on the 12 volt battery - except the one thing I didn't have: a heater motor. I wired an old light bulb in series, and it runs OK hanging from under the dash, but I'd like to understand how to wire it properly.

    I have a basic understanding of Ohm's law; Watts; have tools, VOM etc. Have lots of supplies (wire wound pots; variacs; large ceramics etc.) but there has to be a better answer than "buy a 12 volt motor" or "try substituting various resistances." This week raised another similar problem with a small appliance motor - a question for another day, but seems like it's a good time to understand some basics.

    If I'm not in the right place, just tell me and I'll ask in a different area, or on a different forum. Thanks to any for help.
     
  2. #12

    Expert

    Nov 30, 2010
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    Motors are a PIB about regulating voltage because they use so much more current when they start than when they are running. So, start with how much current the motor needs, than go to electrotechonline because we're not allowed to play with automotive modifications here.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Get a 12v version from a wrecker yard?.
    Max.
     
  4. alan7s

    Thread Starter New Member

    Jan 9, 2015
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    OK thanks; I'm dealing with motors small enough that don't have starter windings; you mentioned "how much current the motor needs" - understanding how that's measured
    (no labels or info available) is part of the question; if we can't talk about a heater motor;
    fine then let's talk about an appliance motor; same principles No?
     
  5. #12

    Expert

    Nov 30, 2010
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    No. Appliance motors use AC Car motors use DC.
    It's likely that a car blower will use more than the 10 amps available on cheap meters, so try smaller fuses until you blow one.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Heaters motors of that vintage used switched in resistors to control the speed of the fan, often 3 sp, you could wire a resister in permanently, experiment with low value high wattage.
    Max.
     
  7. alan7s

    Thread Starter New Member

    Jan 9, 2015
    6
    1
    Thanks for replies; 1) The West Bend Poppery corn popper has 4 diodes on the motor base to convert the AC 20 volts to DC. It runs a cooling fan.
    The 20 volts comes from being in series with one of the heating coils. If I can substitute a resistor for the nichrome heater, I can run the popper
    with fan, without heat - which is what I need for my application. But don't want to burn out the motor trying stuff. There must be some way to
    measure and figure a proper substitute.

    2) Yes, the idea of 3 speed fans using resistors is getting somewhere. But burning up wire wounds that are too small tells me the wattage must be
    wrong. That's what I'm hoping not learn; how to calculate roughly what size is needed. I love trial and error, as it's all I've ever done, so now it's
    time to learn how to measure and calculate.
     
  8. #12

    Expert

    Nov 30, 2010
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    I'm stepping out of this before Bill Marsden raps my knuckles with a ruler.
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I am closing this thread as it violates AAC policy and/or safety issues.

    Quote:
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    The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

    • Any kind of over-unity devices and systems
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    • LEDs to mains
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    This comes from our Tos:
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    There will be enough sites where automotive questions can be discussed :
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    Bertus
     
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