Exhaust fan motor

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aftershock

aftershock

Senior Member
Location
Memphis, TN
A resturant had the motor replaced on the exhaust fan for the kitchen last week.
One of our electrical guys was called out to hook it up. 220/v circuit, 110/v or 220/v motor depending on how the internal wires are connected.
The motor will run for about 10 minutes then shut down. We pulled the motor today to make sure it was configured for 220/v and after checking and double checking, it is configured correctly.

The belt does not seem to be too tight.
Im at a loss and can only figure the thermal protector for the motor is bad. I hate getting calls like this. The owner is going to exchange the motor for another one.

Any thoughts as to what I may have missed or could have further looked into?
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
There may be a problem that still is exsisting from burning up the first motor, since it has an internal overload switch I will assume that it is single phase, so phase loss should not be the issue, perhaps burnt contacts in the hood switch or contactor causing excessive voltage drop. Was the old pulley reused, or was a new one installed? If it is new it may not be the same diameter as the old one causing the fan to turn faster overloading the motor. Does the fan bearings turn free? Have you checked the amp draw of the motor versus the FLA rating on it? Plenty of things to check.
 
K

Kdog76

Senior Member
Location
The Dairyland State
Adjusting the shiv

Adjusting the shiv

I was on a trouble call recently same situation : replacing the motor of a rooftop hood fan/exhaust fan. Here's what i found:
1) replacement motor had same specs(e.g. hp, rpm's, voltage)
- only difference was new motor had a thermal reset button
2) pulley was reused from old motor
3) belt was reused/ in good shape

I got approx. 4-5 service calls saying same thing - motor runs fine for a while & then cuts out... had me scrathing my head for a while/ several days over a weekend w/ the owner saying if i don't come fix it they would have to shut the kitchen down. Here's what I learned!

The nameplate FLA on the motor is what the is thermal overload is set to. Some motors have a auto-reset built in, but this one had a push button that reset after the motor had cooled down. Most motors have a adjustable shiv, & there's more to it then adjusting the tension...The motor pulley you have MAY be what's called a variable pitch shiv - means you can spin the shiv more open or closed & that WILL determine the amps the motor is drawing... Like the previous post - if you can put your clamp-on ammeter and check your amps on EACH line & compare to your nameplate FLA, you will see you may be running high... Try opening or closing the shiv & recheck... I believe I had to open the shiv to drop the amps - but i forget... Anyways I was able to dial that thing to an exact amperage...

Next point is that an unloaded motor will not have the same amperage as a loaded motor - typically unloaded motor will not run at peak efficiency... My rule of thumb now would be to get that amperage to about 85% of FLA - and your motor can run forever w/o tripping the overloads at 85%.

Only hassle for me was to adjust the shiv I had to unbolt the motor mounting & take off the belt, spin the motor shiv open (if it's a two-part pulley that's threaded & adjustable just spin it open or close a little, lock it down, remount the belt & motor, & now check your amps. It's just what worked for me...
 
aftershock

aftershock

Senior Member
Location
Memphis, TN
hillbilly1 said:
There may be a problem that still is exsisting from burning up the first motor, since it has an internal overload switch I will assume that it is single phase, so phase loss should not be the issue, perhaps burnt contacts in the hood switch or contactor causing excessive voltage drop. Was the old pulley reused, or was a new one installed? If it is new it may not be the same diameter as the old one causing the fan to turn faster overloading the motor. Does the fan bearings turn free? Have you checked the amp draw of the motor versus the FLA rating on it? Plenty of things to check.
Click to expand...

The old motor is still on site and I dont remember seeing a pully on it, but I was not looking for it either. I will make sure I have an amp clamp next time I have to go back. It looks like they put a new belt when they replaced the motor and by checking the old ones on the roof, the size matches what was used before.

My guy told me that when he first arrived it looked as though someone hooked up one leg and was trying to use the ground for the other leg. Maybe trying to hook it up 110/v. Dont know if that would have damaged this motor in the way it is acting.

When I asked who installed the motor,, the only asnwer I got was "this guy".

I will see what I can find out if we get called back to hook up the second "new" motor.
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
agree... did trouble shooting on many and replaced many. 90% of the time, the belt tension/sheave adjustmemnt ends up incorrect.
Be sure you have correct overload or motor is thermal protected and check actual current vs. nameplate.
adjusting the sheave is a commonplace need on these installs.
 
K

Kdog76

Senior Member
Location
The Dairyland State
I agree... As far as 208 vs 240 volt, you should check incoming voltage coming in just to make sure - but the motor leads may be wired in the same for both 208 & 240.The FLA of the motor will depend on/change with the voltage. You can't change the voltage, but you can change the amperage on the loaded motor i.e. the sheave adjustment (And i've heard MOST motors like these will have that adjustable sheave. Only after looking at the motor leads or conductors going to the motor with the clamp-on would I say for sure & ruling out other mechanical possibilties: bearings, etc.
 
E

electric244

New member
I did this once. If its a hood exhaust it has no thermal or a very high thermal because the heat is too intense for it. Check the overload rating on the motor you pulled out.
 
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