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Old 09-04-2013, 07:40 PM   #1
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furnace blowers


fooling around with a pair of furnace blowers for basement ventilation. both are over heating on thermal overload. 1/2 and 1/3 hp split phase motors. I think I have to restrict air flow to limit current in the motors. which would be better, on the intake or outlet side? they are belt driven squirrel cage blowers. the 1/2 hp shuts down much sooner than the 1/3 hp.

any insight out there????

thanks,

bernie

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Old 09-04-2013, 08:56 PM   #2
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belts drives should not require any restriction. direct drives do. probably the motor bearings or blower bearings are seizing up.

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Old 09-04-2013, 10:33 PM   #3
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air is too free restrict the return adjust the belt so it it up full flush with the halves of the pully...check the amps adjusting the return
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Old 09-04-2013, 11:48 PM   #4
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too many variables to simply assume. how long have these systems been working without issue?

clean your coils, replace filters, change and tighten your belts.
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Old 09-05-2013, 10:00 AM   #5
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By checking with an amp meter you'll eliminate the guess work. If I recall I believe you'll find restricting discharge will reduce amp draw. If applicable, what gauge extension cord is being used and its length. Also correct belt tension can play a role in amp draw.

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Old 09-05-2013, 08:36 PM   #6
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Quote:
Originally Posted by yuri View Post
belts drives should not require any restriction. direct drives do. probably the motor bearings or blower bearings are seizing up.

pretty sure belt drives trip on
OL with no load on them yuri.
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Old 09-05-2013, 09:33 PM   #7
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thanks for the responses so far. I will try restricting the air flow and see what happens. will measure current with clamp on meter. the question is still do I restrict the output or the inlet air flow???
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Old 09-05-2013, 10:16 PM   #8
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belt drives not really, they have a centrifugal switch to disconnect the start winding and have enough torque and will get up to full speed w/o a capacitor. direct drives/PSC motors are different due to the sharp curve and design of the blower wheel. they won't get up to speed if they are not sucking against ductwork. try run a furnace w/o the blower door on and you see the difference. put the door on and you can hear it speed up. if they don't get up to speed they overheat.

I have seen lots of homemade autobody shop DIYers use an old belt drive w/o ductwork and they work fine. if you use a pulley over 3 to 3.5 inches and the belt is too tight it may overheat. try have at least 1" deflection in the belt and use a pulley under 3.5 inches.
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Old 09-06-2013, 12:36 PM   #9
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Restrict the outlet. If the pulley is adjustable, I'd try that first though. The motor/fan without any restriction on it (not installed in the furnace with duct work) is still adjusted for that amount of restriction. Without the restriction the adjustment of the pulley is allowing the fan to "try" and do more work than the motor is rated for. Reducing the RPM's of the fan blade will reduce the work thus the amps making the motor work less and stop overheating.

Last edited by old_squid; 09-06-2013 at 12:39 PM.
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Old 09-06-2013, 12:44 PM   #10
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Restrict the outlet. If the pulley is adjustable, I'd try that first though. The motor/fan without any restriction on it (not installed in the furnace with duct work) is still adjusted for that amount of restriction. Without the restriction the adjustment of the pulley is allowing the fan to "try" and do more work than the motor is rated for. Reducing the RPM's of the fan blade will reduce the work thus the amps making the motor work less and stop overheating.
That is true. technically it is gulping more air than it is designed for. same with the direct drives and they are more finicky/sensitive to that. I would open up the pulley until it is 3" or less and loosen the belt till it has 2" of deflection to reduce the load on the motor. most DIY exhaust fans guys use run a bit loose and sloppy and work good that way. once installed in ductwork we tighten em up and be more precise.
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Old 09-12-2013, 05:38 AM   #11
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Up and running, problem solved with all of your help. Loosened belt to about 2" and restricted air out flow. Ii do need to play with the amount of restriction, right now running with about 50% of the outlet covered by a piece of sheet metal. Quiet and cool motor, no shut down after an hr run.

again, thanks

bernie
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Old 09-12-2013, 11:24 AM   #12
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Yur Welcome and thanks for the reply.

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