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Thread: exhaust hood

  1. #1
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    Mar 2013
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    exhaust hood

    if a belt is put on too tight can this cause permanent damage to a PSC motor?
    I got a call about exhaust hood not working, went to restaurant and found the belt was slipping and completely worn out. so I found a belt close in size and put it on and tightened up. The hood itself said belt size-AX27, it had a AX25 on it, all I had was a AX26 so i put it on and tightened it up and off I went. I mistakenly did not check amp draw at that point, which I should have. So five days went by and the restaurant called again saying exhaust fan comes on runs for a bit then shuts off. So I go see whats going and could tell the motor was overheating could barley touch it with my bare hand. So at that point I loosened the belt up just a tad and took an amp reading it was pulling 9 amps and RLA is only 7 and from what I understand motor should only be pulling about 75% percent of RLA or even as low as 50% . No matter how loose I made the belt it still would pull close to 9 amps. So now the motor is going to be replaced, but did I permanently damage the motor by having the belt on too tight? or is there something else going on here?

  2. #2
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    A belt that is too tight can wreck the bearings, but it generally won't cause high amp draw. Amp draw on a fan motor is usually a by product of how much air you are moving. If you are moving too much air, your amps will be high. If the motor has an adjustable pulley on it, you can usually open it up a little bit to slow down the fan and lower the amp draw, or you can obtain a smaller pulley to do the same thing. Don't try to slow it down by just loosening the belt, that will just eat up your belt and pulleys.

    It is also possible that the motor is going bad. They do that sometimes.

  3. #3
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    The motor could have already had issues. IMPORTANT!!! Hood exhaust motors should NOT have thermal overloads in them. You can purchase motors without overloads or any good motor supply house can remove the overload. As far as what you understand about a motor pulling 75% of rla, is wrong. The only for sure way to know what the motor should be pulling is to perform an air balance. The motor has an RLA, and also a SF (service factor) which is built in protection for voltage spikes. If a motor is running too little amps, it is not working. I have seen units with incorrect pulleys, with loose belt tension to keep from over amping. If this was the case with your motor, you wouldn't have known because you never checked. Oops!
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  4. #4
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    I seen quite a few overloaded fan motors caused by tightening the belt using the adjustable sheave. I hope you didn't do that!

    The motor should run at its FLA with no problems as long as it's also running withing it design temperature range, like 60ΊC or 70ΊC. A motor rated at 7.0 amps running at 9.0 amps is 29% overloaded and will definitely trip.

    The service factor is typically 1.10 or 1.15, which would allow for operation 10% or 15% over the rated FLA, and although it's best to stay withing the FLA, I've seen some 300-400 HP motors running well into their service factors all day long.

  5. #5
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    thank you for your info, just when I think im understanding things, even seemingly simple things i realize I know nothing hahaha. but seriously i really appreciate the responses. and no I didnt tighten the belt using the adjustable sheave, but now that its too late, im thinking I could have adjusted it to bring my amperage down enough to run with no problems. but dont really know for sure. next time im more prepared, thanks!
    Last edited by northeastbeast; 05-10-2013 at 10:03 PM. Reason: typo

  6. #6
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    By the way, Beast, I think I saw that guy in your avatar playing with Primus once a long time ago. I had forgotten about him until just now. Despite his gimmick of dancing around stage wearing a mask and a big chicken bucket on his head, he was one hell of a guitar player.

    Is he still around??

  7. #7
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    Quote Originally Posted by ammoniadog View Post
    By the way, Beast, I think I saw that guy in your avatar playing with Primus once a long time ago. I had forgotten about him until just now. Despite his gimmick of dancing around stage wearing a mask and a big chicken bucket on his head, he was one hell of a guitar player.

    Is he still around??
    Yes you definitely did because he plays with les claypool alot and they have another band, and yep hes still around his name is buckethead, and he is for sure a nasty guitar player, thats cool you recognized because hes kind of obscure not many know of him or care, same with primus for that matter, primus is my fav band of all time.

  8. #8
    Join Date
    Aug 2011
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    80 percent is what I put one at if the sheave has been closed or changed and over amp the motor and there is no baseline rpm to set the shaft speed to. Most stores I have balance never run at 100 percent of amp draw not even the new stores per drawing specs. I use thermal overload motors all day long in commercial exhaust fans except one one in particular and that is because they designed a different protection and the design eats thermal protected motors for lunch its hot and not in a good way they send us motors to stock just in case they need changing tho.

  9. #9
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    Quote Originally Posted by 2sac View Post
    Hood exhaust motors should NOT have thermal overloads in them. You can purchase motors without overloads or any good motor supply house can remove the overload.
    So, what protects the motor? Shouldn't they at least have a motor starter with the appropriate sized overloads?
    With your chrome heart shining in the sun, long may you run.

  10. #10
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    Quote Originally Posted by 2sac View Post
    The motor could have already had issues. IMPORTANT!!! Hood exhaust motors should NOT have thermal overloads in them. You can purchase motors without overloads or any good motor supply house can remove the overload. As far as what you understand about a motor pulling 75% of rla, is wrong. The only for sure way to know what the motor should be pulling is to perform an air balance. The motor has an RLA, and also a SF (service factor) which is built in protection for voltage spikes. If a motor is running too little amps, it is not working. I have seen units with incorrect pulleys, with loose belt tension to keep from over amping. If this was the case with your motor, you wouldn't have known because you never checked. Oops!
    Electric motor SF rating has nothing to do with voltage spikes, in fact has nothing to do with voltage, period.
    It's simply a built-in extra capacity eg: a 1hp motor with SF 1.15= 1.15hp output.

  11. #11
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    On single phase EF's we have had to take out the motors with thermal overloads and then install disconnects. I don't get it.
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  12. #12
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    May 2013
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    Quote Originally Posted by jamesbravo View Post
    Here you all guys have a great information about the kitchen exhaust hood.. I totally agree with your AMP sketch on a fan engine is usually a by item on how much air you are shifting. If you are shifting too much air, your amplifiers will be great. Have a great information..
    Wait, what?

  13. #13
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    Your amplifiers aparently not so great.

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