Run -vs- Start Capacitor

[Cliff Rohrabacher]

If I put a start capacitor on a little fractional HP motor (the kind on a generic blower fan) and the motor really needs a run Capacitor will the motor start and run but at merely some fraction of it's rated performance?



Yes It's Aprilaire and their horribly incompetent engineering again.

My other Aprilaire dehumidifier has died. The capacitor on the blower fan burst. The printing on the brust cap is mostly unintelligable.

All I got from it is
"VAC 5/60"
and after some fudged out print "70t"
RK SFA3747 17
None of which is at all helpful for replacing the thing.


I had a start capacitor that I put on it and the blower. The motor limps along. I'm guessing this'll wreck it, if I let it go that way.

[Rod Sheridan]

Hi Cliff, the issue is that start capacitors are intermittent duty, run capacitors are continuous duty.

Any oil filled capacitor will be suitable for run capacitor service......Rod.

[Cliff Rohrabacher]

Ya think it shouldn 't matter the Voltages so long as it's not too small?

I'm looking at this from Granger for about $5.00
http://www.grainger.com/Grainger/items/2MDV2
Motor Run Capacitor
MFD Rating 3
Voltage 370
Hz 60/50
Shape Oval Height (In.) 2 11/16 Width (In.) 1 1/4 Depth (In.)
2 Terminals 4-blade Quick-connect Insulated
Temp. Range (C) -40 to 70
Construction Hermetically-sealed Aluminum Case with Terne-plate Cover
Standards cULs Recognized (E224674)


(http://www.grainger.com/Grainger/items/2MDV2)
It’s cheap about $5.00

[Rod Sheridan]

Hi Cliff, if it's a 120 volt fan the 370 volt capacitor will be fine.

Can you find out what the capacitance was on the old one?

That will be critical..............Regards, Rod.

[Cliff Rohrabacher]

Naaah AprilAire Tech hasn't got any stats on it at all other than they "think" it's a run capacitor.

I'm going to run with that metal can cap.

[Rob Russell]

I'd let one of the EE's chime in, but I wouldn't use a start capacitor as a run capacitor regardless of the voltage rating of the cap.

[Chris Padilla]

Being an EE but not too familiar with motors, I had never heard of "run" and "start" capacitors so Google to the rescue! :)

http://dnr.louisiana.gov/sec/execdiv/techasmt/ecep/hvac/d/d.htm

[Rick Christopherson]

It isn't the type of capacitor that is important, but the size of the capacitor. You need to determine the size of the capacitor. The only difference between a run-type and a start-type is how long they can sustain the power before popping.

[Cliff Rohrabacher]

It isn't the type of capacitor that is important, but the size of the capacitor. You need to determine the size of the capacitor. The only difference between a run-type and a start-type is how long they can sustain the power before popping.

Sounds like it calls for a capacitor with a lot of capacity.

In speakers and Amps I'd call that headroom

[John Daugherty]

I just went through this same thing with my grinder. The capacitor busted. My advice would be to take it into a motor shop. They should be able to tell you what you'll need to get it going.

Funny thing when I handed the guy to blown capacitor he said "you know what's wrong with it?" I said the capacitor popped. He said "nope, it's Chinese junk" He told me that he had seen several thing from china with the wrong capacitor in it. He had me fixed up and out the door in about 5 min. for around 15 bucks including tax.

[Kerry Verne]

I ran into this when my Delta DC motor died. In their infinite wisdom/'thriftiness' they could fit a start cap in the wiring box on the side of the motor, but a run cap was bigger and more expensive. It ran fine for two years before it died, so another start cap may last you just as long.

[Matt Stephenson]

Check to see if it has synchronized blue running lights in an inward starburst pattern. It may very well be a FLUX Capacitor. If this is the case, and I'm just going from memory here, it should require something north of 1.21 Jiggawatts.

[Ron Bontz]

Well don't feel alone on this one. My Delta shaper also has the run and start cap in the same box as the reversing switch. I ran into a problem with physical size. Originally just needed a run cap. Put a new one in, a little bigger, wasn't careful, two connectors touched, and suddenly I had to repair a switch connector and now am waiting for a new start cap. I contacted the maker of the motor, WEG, they were very helpful but ultimately Grainger, very nice folks, is trying to obtain the capacitors from the motor company. Delta/BD service did not seem to even want to do much except replace the whole motor to the tune of $630.00 and don't even list the capacitors for it. You can bet I'll be covering that switch with a non conductive barrier. :o