DC Motor Fan Heater
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  1. #1
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    DC Motor Fan Heater

    Hi

    This one is puzzling me. I have a 1930s underdash heater with the original 6V motor and fan. I have taken it all apart to clean, paint, pressure test etc and its all ok.

    I did do a bench test and didnt notice what is coming.....

    Now its all installed ... and working the fan is spinning the wrong way and not pushing the air through the matrix. I did take the fan blade off the shaft and must have inadvertently installed it the wrong way round.

    Easy fix you say ... swap the wires over on the supply changing the polarity

    It still spins the wrong way ??


    I know the fix is to dismantle it all and turn the fan over ... but its hell of a job now it is all installed and full of water

    Ideas welcome

    Mal

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    Official RnS Addict brading's Avatar
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    Think you will have to take it apart and put the fan on the right way. Due to the fan blade design when fitted the wrong way round it will possibly push a little bit airflow but no where near the same as when fitted the right way.

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    if you fit a blade the wrong way round, it's efficiency will possibly change, but the air direction won't....

    think of the blade pitch as a stud thread... turn it round, it'll still screw into the bolt hole by turning it the same way.

    swapping the motor wires, if it's a fixed magnet motor, will make it spin in reverse.... and should blow the air the other way....

    did you strip the motor? if you put it back together with the magnets moved (180 degrees perhaps) relative to the motor brushes, then that would reverse the motor too.....

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    If the motor was stripped did you fit it back with the end plates swapped round? in effect putting the armature in upside down. That would make it spin backwards. Whatever, it is going to be a strip down again.
    If it's got tits or tyres, its gonna be trouble

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    Yeah I think its a strip down. What a PITA

    The motor was taken apart, cleaned and put back together the same way. The blade is held on with a brass screw so there is a chance I put it on backwards. Its now sucking from the matrix instead of blowing air through it. It was blowing through originally when I tested it before strip down.

    The puzzle for me was the reversing of the polarity did not change direction. I guess I have something to learn about motion,field, current in older design DC motors

    Mal

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    If it's a conventional type fan, like a rad fan, the orientation won't affect the direction of the air, only the strength of air movement if the blade profile is shaped. Only the motor rotating the other way will change the air direction....... Is it a magnet motor? Or is it like an dynamo with coils instead of magnets?

    How many wires are connected to the motor?
    Last edited by thisYup; 30-06-2020 at 13:49.

  9. #7
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    Quote Originally Posted by thisYup View Post
    If it's a conventional type fan, like a rad fan, the orientation won't affect the direction of the air, only the strength of air movement if the blade profile is shaped. Only the motor rotating the other way will change the air direction....... Is it a magnet motor? Or is it like an dynamo with coils instead of magnets?

    How many wires are connected to the motor?
    Its a two wire motor. I think its a very basic magnet motor. The blades are metal and very spoon like. When I bench tested it when I got it I do recall it blowing air through the matrix. Now it is definitely sucking and putting the warm air on the bulkhead.

    I am using a 12v to 6v voltage dropper but that shouldn't make any difference


    Mal

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    if they are spoon shaped that might be the issue... reversing the wires on a basic magnet motor will reverse the rotation, but the cup of the blade might be why it doesn't 'seem' to be blowing the other way, as it's acting more like a paddle steamer, rather than a propellor ....

    you'll still have to reverse the motor connections as the air is moving the wrong way...

    do this.... make a simple 2 blade fan out of a bit of paper, imagine it turning and the direction the air will blow. flip the fan and do it again, with the same rotation the air will go the same way....

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    It uses the electric current to make the magnets, changing the polarity of the wiring also changes the polarity of the magnet therefore it spins the same way however you connect it. Had the same issue with an old heater I installed on my hot rod. Founda new permanent magnet motor that fitted perfectly ( Kenlowe fan motor).

  13. #10
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    Quote Originally Posted by rovertenrod View Post
    It uses the electric current to make the magnets, changing the polarity of the wiring also changes the polarity of the magnet therefore it spins the same way however you connect it. Had the same issue with an old heater I installed on my hot rod. Founda new permanent magnet motor that fitted perfectly ( Kenlowe fan motor).
    That makes more sense. It was the reverse of the polarity that I was struggling to understand - I think it will be a take the fan off and turn it round job for now.

    Mal

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