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  1. #1

    Commericial exhaust fan over amping with new motor...

    So we changed out the motor in this exhaust fan. It is a Loren Cook 100R2B. We replaced the motor with the exact one that was removed (Dayton 5K601). It is 1/3 hp 115v 1725 RPM. The amp draw was within the limits when we installed the new motor. So today that new motor won't run, its only humming and then shutting off. It was drawing something like 40 amps. This is about 2 weeks after we originally replaced it. So we went back and threw in a brand new Dayton 6K778 that we had laying around, basically the same motor as the 5K601. It has full load amps of 6.6, but no matter what we do, we can't get it to draw less than 7.1 amps or so. The bearings, shaft and wheel of the fan all seem to be in good condition. The belt is brand new, tension is correct, and is aligned straight. There are no restrictions in the duct at all. We adjusted the pulley on the motor to slow it down as much as possible. But it still draws over 7 amps.

    Is there anything else we can check? Change the motor pulley size? Any other ideas?

    We've changed countless motors on exhaust fans and have never had any issue like this.

  2. #2
    Join Date
    Jun 2006
    Location
    Charlotte, NC area
    Posts
    87
    It appears the fan is trying to do more than 1/3 hp worth of work.

    Are you sure the new motors are the same RPM as the original?

    Do you have more info on the fan? The 100R2B does not ring any bells.

    You said there are no restrictions. Was there a restriction before you changed the motor the 1st time? If so that may be the problem. Fan HP is proportional to the CFM3 so if the air flow went up the fan HP may have gone way up. The solution may be to put the restriction back or slow the fan down.

  3. #3
    Join Date
    Jun 2011
    Posts
    11
    I think he means an ACRU B100. The RPMs sound a little high to me. Also, I think that motor may be oversized. That seems to me like it's one of their smaller units, and they usually put 1/6 to 1/4 H.p. motors in the little guys. I don't think the Dayton was the original motor. call your local distributor and double check the specs on it.

  4. #4
    Join Date
    Aug 2006
    Location
    st.petersburg,fl
    Posts
    802

    Lightbulb

    A couple of things .....

    I've had acouple of motors bad right out of the box so remove belt and check amp draw if still high and you have verfied wiring you hava a bad motor...

    Check rotation if running backwards you will draw higher amps..

    and last if all is correct open your sheave a turn or two, if open all the way swap to next smaller size sheave, and recheck amps, if this works for you check balance of hood cause if you have too much make up it will cause your smoke to roll out from under hood...

    Hope this helps....
    Isn't sanity just a one-trick pony anyway? I mean, all you get is that one trick, rational thinking, but when you're good and crazy, well, the sky's the limit!

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,270
    Quote Originally Posted by hvac n-j-near View Post
    It appears the fan is trying to do more than 1/3 hp worth of work.

    Are you sure the new motors are the same RPM as the original?

    Do you have more info on the fan? The 100R2B does not ring any bells.

    You said there are no restrictions. Was there a restriction before you changed the motor the 1st time? If so that may be the problem. Fan HP is proportional to the CFM3 so if the air flow went up the fan HP may have gone way up. The solution may be to put the restriction back or slow the fan down.
    Do not over look this important point. Scroll blowers draw more amps when unrestricted. Less air movement increases the rpm and decreases the amps.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  6. #6
    Join Date
    Apr 2006
    Location
    Phila.
    Posts
    38
    double chech rotatation wrong direction will cause higher amp draw. I know, been there done it

  7. #7
    My experience with these exhaust unit are when I turn up the speed the amp draw actually comes down. I usually install 1550 rpm with 1/2 hp motors. It was unusual when I found this out, but now I know. Just adding my experience to help good luck.

  8. #8
    Join Date
    Apr 2010
    Location
    southern california
    Posts
    535
    Quote Originally Posted by Rootytootie View Post
    My experience with these exhaust unit are when I turn up the speed the amp draw actually comes down. I usually install 1550 rpm with 1/2 hp motors. It was unusual when I found this out, but now I know. Just adding my experience to help good luck.
    Increasing the speed of the fan will require more hp and more amps. Check the ductwork and grills. Static pressure could be the culprit.

  9. #9
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,330
    Quote Originally Posted by w00derson View Post
    So we changed out the motor in this exhaust fan. It is a Loren Cook 100R2B. We replaced the motor with the exact one that was removed (Dayton 5K601). It is 1/3 hp 115v 1725 RPM. The amp draw was within the limits when we installed the new motor. So today that new motor won't run, its only humming and then shutting off. It was drawing something like 40 amps. This is about 2 weeks after we originally replaced it. So we went back and threw in a brand new Dayton 6K778 that we had laying around, basically the same motor as the 5K601. It has full load amps of 6.6, but no matter what we do, we can't get it to draw less than 7.1 amps or so. The bearings, shaft and wheel of the fan all seem to be in good condition. The belt is brand new, tension is correct, and is aligned straight. There are no restrictions in the duct at all. We adjusted the pulley on the motor to slow it down as much as possible. But it still draws over 7 amps.

    Is there anything else we can check? Change the motor pulley size? Any other ideas?

    We've changed countless motors on exhaust fans and have never had any issue like this.
    We will start off with what tag shows. It's a upblast centrifugal
    exhaust, belt drive, 1/6hp motor, and 18" square.

    So you now have a 1/3hp motor over amping.......why? You are doing to much work.(Assuming everything is wired right)

    I would get the right motor back in there. Since it's under 5hp, you have an adjustable sheave. Put the sheave to about 2 turns open, that's normally where you will find them from factory. And then check amperage, rpm of driven sheave, and airflow. And then move on from there.

    Do you know what you need to move...cfm wise?

  10. #10
    Join Date
    Jul 2003
    Location
    Massachusetts
    Posts
    288
    what is your incoming voltage?

  11. #11
    Join Date
    Aug 2006
    Posts
    2,583
    Exhaust fan motors should have a Service Factor of at least 1.25. Once I was told this, my repeated failures went away. BTW I noticed that a lot of OEM fan motors don't even mention S.F.
    Also I recently saw a lot of problems with the smaller A and 3L belts causing EF problems. That's why I switched to Opti-Belts.

  12. #12
    Join Date
    Nov 2000
    Location
    Memphis TN USA
    Posts
    6,945
    1st when the wheel turns backwards, you will know. The manager comes running out cussing because you fill his store up with smoke. Done that

    easiest way to mess up speed- change belt width done that

    The high service factor comment is a good one too. Had a cheap boss that bought cheap motors. Then we had to replace them mcuh too often.
    If the superheat ain't right it ain't charged right.

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