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  1. #1
    Join Date
    Dec 2006
    Posts
    1

    Changing a ac motor to dc motor for blower

    Anyone ever attempt to replace a ac Blower motor with a dc controlled motor. I recently added ac to an exsisting warm air furnace. When we installed the ac we also changed the single speed (belt drive unit) to a two speed ac motor. The problem I have, while trying to increase air volume a larger pulley was installed. The two speed motor was lagging when it started, the amps were peaked out. So we tried a larger 1 hp 2 speed ac motor with cap start. This unit is ok, However when the fan starts the motor has a kick to it, this can be heard all throughout the house. So my next thought was a dc motor, They start smooth and stop smooth any thoughts from anyone.

  2. #2
    Join Date
    Dec 2001
    Location
    Chicago, N/W burbs
    Posts
    8,004
    Variable frequency drive for the motor to allow it to ramp up and not start with such a kick, also referred to as a soft start. Not cheap but less expensive than converting to a DC motor and the rectifiers and all that mess.
    R2B4BTU

  3. #3
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,741

    Thumbs down

    don't know if you could find a belt drive motor like you are talking about, if you did cost would be way high.

  4. #4
    Join Date
    Dec 2004
    Location
    Grand Rapids, MI
    Posts
    613
    what brand of furnace and what year was it installed ? dan

  5. #5
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    dc

    you might get lucky with a 1-h.p.variable speed motor
    with the proper controller to ramp up speed slowly,

    make sure the amp draw is within specs.

    if it fails to work properly it WILL be an expensive experiment!

  6. #6
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,963
    Quote Originally Posted by Airmechanical View Post

    if it fails to work properly it WILL be an expensive experiment!
    You got that right all the VS stuff is a big seller right now until a few HO have to replace those VS motors "out of warranty" and the word about the cost gets out to there buddies, it will probably kill the VS stuff in about 5 to 10 years. Heck I went into the supply house the other day and just asked what one sells for for a particular unit heck I thought he was giving me the HO price and that included installation.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  7. #7
    Join Date
    Jul 2006
    Location
    Seattle, WA
    Posts
    103
    What I've heard is that GE is buying a west german motor that is virtually bullet proof and what is normally failing is the brain box on the end, which costs much less than the whole assembly.

  8. #8
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,903
    Any residential furnace with a belt drive blower is probably 20+ years old and a good candidate for replacement. Do not blow hundred of dollars on a piece equipment which probably sends half of its heat up the chimney. (<= 60&#37; AFUE when new and properly tuned)

  9. #9
    Join Date
    Dec 2001
    Location
    Chicago, N/W burbs
    Posts
    8,004
    Actually, you could rig a 2 pulley drive system.....or an adjustabl variable pitch that would adjust itself according to static pressure. Lennox did it in the 70's. Worked great, that's why they still make it....Oh, wait, they quit it.

    Bah...........nevermind.
    R2B4BTU

  10. #10
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    It is probably cheaper to replace the furnace with a new one that has a variable speed drive motor in it.

    An add on frequency drive would also work. You can get one on eBay if you know how it works and how to wire it up.

    You could also add all the parts from a new variable speed drive furnace and "pimp" yours, but that will be way more expensive than the first option- replacement.
    Proper Prior Planning Prevents Piss Poor Performance

    "There is hardly anything in the world that some man cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey. It's unwise to pay too little.
    When you pay too much, you lose a little money -- that is all. When you pay too little, you may lose everything, because the thing you bought was incapable of doing the thing it was bought to do.

    The common law of business balance prohibits paying a little and getting a lot -- it can't be done. If you deal with the lowest bidder, it is well to add something for the risk you run. And if you do that, you will have enough to pay for something better."

    John Ruskin


  11. #11
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,963
    Quote Originally Posted by otto View Post
    Actually, you could rig a 2 pulley drive system.....or an adjustabl variable pitch that would adjust itself according to static pressure. Lennox did it in the 70's. Worked great, that's why they still make it....Oh, wait, they quit it. Bah...........nevermind.
    Hey Otto what about a gear drive like a timing gear drive on a race car?
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  12. #12
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by seaeagle2 View Post
    What I've heard is that GE is buying a west german motor that is virtually bullet proof and what is normally failing is the brain box on the end, which costs much less than the whole assembly.
    In 13 years of working with equipment that has GE variable speed motors, I have never found one where the motor itself was bad, only bad modules.
    Back in the ICM1 days the module was part of the motor housing, so you had to replace the whole thing.
    Unfortunately it seems that many equipment distributors only stock the whole motor and module assembly, especially the ones that are relatively new to offering VS equipment.

    In my area Trane and Carrier are the only ones I know of that have done the smart thing and stocked unprogramed modules and load the program for the specific equipment when you go in to pick it up.
    If more government is the answer, then it's a really stupid question.

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