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Originally Posted by nsula_country

1.2 mfd vs 5 mfd? This is off 76% of a 5 mfd cap. Most caps are (+/-) 5%-10% tolerance. Change is good!

CT

X2

Originally Posted by Russ57

I would be careful saying a run capacitor's main job is to correct power factor.

I'd rather say the capacitor shifts the phase of one of the windings so that the voltage across the winding is at 90° from the other winding. The effectivly makes it a two-phase motor (when loaded).


Now if the proper capacitor is used......then the currents through each of the windings, when fully loaded, should be equal....and under those conditions power factor will be close to 100%.

I agree 100%. In a nutshell, this is what I was trying to explain, but it did not come out as cleanly as you described. I was thinking about the phase angles and the reactance the capacitor adds to shift the angle.

Thanks for the input. My wordiness probably confused some readers.

CT

I would be careful saying a run capacitor's main job is to correct power factor.

I'd rather say the capacitor shifts the phase of one of the windings so that the voltage across the winding is at 90° from the other winding. The effectivly makes it a two-phase motor (when loaded).


Now if the proper capacitor is used......then the currents through each of the windings, when fully loaded, should be equal....and under those conditions power factor will be close to 100%.

Originally Posted by iceage

Changed cap ,motor hummed, gave blower spin to get going, noisy as hell, bearings are shot, going to replace motor. Thanks all for help.

Motor runs hot on low mfd. cap. washes oil out of bearings, possible scenario.

Changed cap ,motor hummed, gave blower spin to get going, noisy as hell, berrings are shot, going to replace motor. Thanks all for help.

Originally Posted by Mr Bill

Yes checking amps is a good thing, but I never check just amperage until after I have check voltage.

Low voltage will make the amps climb... Then we find loose connections, and burnt wires, and well you know the rest.

CT

Originally Posted by Hwolfe

I would check your amp draw on your motor after replacing capacitor to insure condition of the motor.

Yes checking amps is a good thing, but I never check just amperage until after I have check voltage.

Originally Posted by B-Tech

^This

X3

Originally Posted by Hwolfe

I would check your amp draw on your motor after replacing capacitor to insure condition of the motor.

^This

Originally Posted by Mr Bill

Someone has been doing his homework, you are correct. I have seen numerous post here in my past years, that say "motors" have a 5%-10% tolerance. I have often wondered if the caps have a tolerance percentage, does this mean that the motor mfg. would say it ok for their motor designed for a 10 mfd. cap, to run at 9 mfd.? Maybe bypass a call to the distributor, straight to the mfg. would get you the correct answer, straight from the horse's mouth.

I'm unsure about the motors, but can investigate. Most run caps are (+/-) 10% tolerance. So if a motor requires a 10 mfd cap, the cap should read 9 mfd-11 mfd (10%). The motor designers should have this variance factored into the motor design. I would say it would be better to oversize a cap than to undersize it, but not more than 1 size up and only until the proper replacement can be installed.

Reasons:

Efficiency - A capacitor attempts to correct a poor Power Factor by adding Capacitance Reactance. Since a compressor or fan motor is an inductive device with Inductive Reactance, a capacitor will largely zero the reactances, resulting in a compressor or fan motor that runs cooler and uses less electricity. Oversizing or Undersizing screws with the Power Factor on a RUN capacitor.

Rules for Capacitor Replacement:

-Voltage must be EQUAL TO or GREATER than the cap being changed (ie, 370V)
-Start Cap must be (+/-) 20% of mfd
-Run Cap must be (+/-) 10% of mfd
-If the Start Cap is UNDERSIZED, the motor might not start.
-If the Start Cap is OVERSIZED, the high start current might burn out the start winding (Hard Start Kit ???).
-If the Run Cap is incorrectly sized, the Power Factor will suffer, resulting in lower efficiency, higher operating costs, and possible motor damage.

A failing cap can:
--reduce the speed of the motor, which
--increases the motor’s temperature
--causes bearing wear and insulation breakdown
-- increases overall noise

Basically the capacitor values posted on nameplates are engineered to be optimum for peak performance. replace with like part!

Run capacitors are there to correct the single-phase power factor. Three-phase is nearly perfect at 1.00 power factor, but sometimes capacitor banks are used to balance power factor in imbalanced systems.

Good luck!

CT

Originally Posted by nsula_country

Most caps are (+/-) 5%-10% tolerance.

Someone has been doing his homework, you are correct. I have seen numerous post here in my past years, that say "motors" have a 5%-10% tolerance. I have often wondered if the caps have a tolerance percentage, does this mean that the motor mfg. would say it ok for their motor designed for a 10 mfd. cap, to run at 9 mfd.? Maybe bypass a call to the distributor, straight to the mfg. would get you the correct answer, straight from the horse's mouth.

I would check your amp draw on your motor after replacing capacitor to insure condition of the motor.

1.2 mfd vs 5 mfd? This is off 76% of a 5 mfd cap. Most caps are (+/-) 5%-10% tolerance. Change is good!

CT

Depending on the age/condition of the motor, it may not be a bad idea to replace both the cap and motor. Customers get pissy when you have to go back a few months later to replace the motor. .02

Okay thanks, and agrred I do need to get some more van stock.

good point.....

next question....

why do you not have a blower cap on your truck????

yep.... change it all will be good..... well done lots of tecs would of changed a perfectly good motor... 1.2 is not close to 5 it should work.....

Probably.
See how it runs with the new cap, you might be too late!

Capacitor check on furnace.

I had looked at furnace with run cap for blower, unit was off on high limit. Did cap test and had 1.2 micro farads(cap rated for 5mfd) Cap wasnt bulged but my question is at 1.2 can I assume cap is at fault not blower? Even though it is not entirely open. Blower was hot. Didnt have cap in van at time so I will have to go back. Tested limit, when things cooled off and it was closed.