Capacitor Value

[sam am I]

Haven't looked/googled it but might anyone know off the top of their head about what value(s) the cap would be used for this motor?

It runs a direct drive hydraulic pump I guess, co-worker just left it with me the other day asking if I knew....I don't!! The cap (lost I guess) connects to the two loose black wires in second photo.

Thanks much in advance

 

[Scott Danforth]

I would go with a 500-600uf or so for the motor start cap for a 1hp motor. the run cap is about a 30uf

 

[sam am I]

So, not knowing which I need and it appears this motor only runs one cap, is it a "run" or a "start" cap that the motor uses? Sorta where I've been scratching my bald head, run or start.....

 

[harringtondav]

An A/C motor needs a start cap. Not all require a run cap. From what I've heard run cap motors are more efficient and pull fewer amps under load.

 

[sam am I]

An A/C motor needs a start cap. Not all require a run cap. From what I've heard run cap motors are more efficient and pull fewer amps under load.

So it's most likely a start cap?

I found some (legit?)YouBoob info, on values and such

https://www.youtube.com/watch?v=OMd9QkinXz4

https://www.youtube.com/watch?v=gdDBbdVImTs

 

[harringtondav]

So it's most likely a start cap?

I found some (legit?)YouBoob info, on values and such

https://www.youtube.com/watch?v=OMd9QkinXz4

https://www.youtube.com/watch?v=gdDBbdVImTs

If you only have leads for one cap, I'd say it's a start cap. I can't help with the values. Anytime I've had to change a cap the capacitance, and if I was lucky, the p/n were on the bad cap. I'd go with SD's recommendation. He knows his scat.

The bad start caps I've changed caused the motor to hum when energized.

 

[sam am I]

If you only have leads for one cap, I'd say it's a start cap. I can't help with the values. Anytime I've had to change a cap the capacitance, and if I was lucky, the p/n were on the bad cap. I'd go with SD's recommendation. He knows his scat.

The bad start caps I've changed caused the motor to hum when energized.

Yes, just those two black leads is where the cap was.........I'll try/start with something around the 400/500/600MFD(start cap size) , if after the motor starts, the cap then gets switched out (centripetally, etc), it would then have to be a start cap, and we guessed right.

If it(the cap) stays electrically in circuit (and the switch out circuit isn't broke, crossing fingers), it has to be a run cap and a 500MFD should smoke as seen in video #1 above @ 6:24...Would then go back to a 10MFD'ish run cap at that point.

Xc = 1/(2*pi*f*c)

= 1/(2*pi*60hz*500uf)

= 5 ohms

@ 120Vrms (340Vpp)/ 5 ohms

= 24 amps

i^2*R = P

= 2900W

= lets smoke out

 

[harringtondav]

Look at either end of the armature shaft, probably the power shaft end. The start cap disconnect switch will be there. Centrifugal as you note. I had to replace the start cap on my radial saw. The start cap contacts were bent and the cap stayed energized during run. It finally failed, but it took a many, many hrs before it did. No smoke. Just humming.

Bending my contacts back was neurosurgery. I put my VOM leads across the contacts. When I finally saw line voltage I knew the switch was opening properly. ....Also, thinking you know this, but I have a cheapo capacitance meter. But your VOM set on ohms is a good fail/no fail check. Short the cap terminals to discharge. Connect the ohm meter. If good, the resistance will slowly increase. YouTube shows the details with expected max resistance based on cap capacity.

 

[sam am I]

Will do and tyvm, all good things to check out.

 

[sam am I]

Yup, start cap........55MFD not luck, 150MFD no luck BUT a 300MFD(uf)got her to kick over, once at speed the cap disconnected.....Thx again HD and SD.