Harbor-Freight 3 in 1 Motors?

[Richie B.]

On the nameplate you have 300 and 35 uF. The 300uF is the starting capacitor and the 35uF is the running capacitor.

Thank You! I am a millwright by trade; wiring a house is pretty much the limit of my electrical capability.

So, if I were to get a 300uF 250/300v cap and a 35uF 250/300v cap, I would have a set of run/start caps for emergencies??? Or is there some critical difference between a run and a start capacitor???

 

[compsurge]

The caps I linked earlier should be good for starting capacitor. They are rated for 125VAC (again, the voltage rating is just what the capacitor can handle - higher will be fine, but likely cost more). If you need a running capacitor, you change the filters on those site's search pages for 35 uF and you should be good (they even label motor run vs motor start capacitor).

Both caps should be similar in physical size to that they are replacing so they fit in the motor's housing. You don't have to be perfect on the match, but get as close as you can. I don't know what the OEM motor spec for tolerance is, so get as close to the nameplate as possible +/-%.

Here is a sample run capacitor that should work:
http://www.mouser.com/ProductDetail/Cornell-Dubilier/SFP24S35K375A/?qs=JlSiUoO6twkxQypibr45LQ==
http://www.mouser.com/ProductDetail...=sGAEpiMZZMv1cc3ydrPrFyAEDdQ02CGeTFmI6u1kbkY=
http://www.mouser.com/ProductDetail...=sGAEpiMZZMv1cc3ydrPrF8gMTJ0uZsYNKiIhvdTDv4A=
Here was the search: http://www.mouser.com/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371?P=1z0wqr8

These are capacitors from only one site. Hopefully you are armed with enough knowledge to make an educated purchase now. If in doubt, post it!

 

[wa5cab]

Richie,

The short answer is "yes". However, if you are only going to run the motor on the 120 V line, as Compsurge wrote you will probably pay more for the capacitors. But, If the motor happens to be reconnectable for 240 V, then you should buy the 250 to 300 volt rated ones. The next owner might decide to reconnect for 240 (I would) and not knowing that the motor has 120 V capacitors in it, do some damage when they quickly fail.

The difference between a start and a run capacitor is two-fold. The start capacitor will generally have a much higher capacitance. But it is rated only for intermittent operation. Once in a while the specification sheet will be detailed enough to show the duty cycle, which will be something around 10%. Meaning for example 10 seconds on, 90 seconds off. The run capacitor will be lower capacitance but still about the same size. It is rated for 100% duty cycle (continuous operation). Which is why it will be as large as the start capacitor but with around a tenth of the capacitance. However, if you just pick one that the catalog says is a start capacitor and one that it says is a run capacitor, and if the listing shows HP ratings, match that, too, then you'll be safe,

Robert D.

So, if I were to get a 300uF 250/300v cap and a 35uF 250/300v cap, I would have a set of run/start caps for emergencies??? Or is there some critical difference between a run and a start capacitor???

 

[den-den]

Capacitors on a 120v motor need to be rated much higher than 125 volts. Normal household voltage (120 is the "rms" value) actually has a peak voltage about 160v; and spikes can go higher than that. Using a capacitor rated for 200 volts will give you much better service.

 

[John Hasler]

Capacitors on a 120v motor need to be rated much higher than 125 volts. Normal household voltage (120 is the "rms" value) actually has a peak voltage about 160v; and spikes can go higher than that. Using a capacitor rated for 200 volts will give you much better service.

He wrote "125VAC". That means that it is designed for operation on the AC line and designed to take the peak voltage it will see there.

You would not want to use a 125VDC capacitor on the 120VAC line.

 

[Richie B.]

That brings up another question: Are capacitors polarity-sensitive??? If I have two wires coming out of the motor for each capacitor, does it matter which side of the cap gets which wire???

 

[John Hasler]

That brings up another question: Are capacitors polarity-sensitive??? If I have two wires coming out of the motor for each capacitor, does it matter which side of the cap gets which wire???

The AC-rated capacitors used in induction motors are unpolarized.

Electrolytic capacitors used in electronic circuits are polarized. They have "+" and "-" signs identifying the leads and say DC on them. If you try to use one on a motor it will explode.

 

[Richie B.]

I guess my next question is where is a good place to order a pair of 300uF/250v Start caps and 35uF/250v Run caps??? Amazon does not list anyone selling the 35uF caps, and the Mouser caps list minimum quantity:32...

I'm not into electronic parts suppliers; the only catalog I have here is from Grainger, and they don't list the 35uF/250v Run caps...

I'm also in an industrial-challenged area; if there's an electronics supply facility around here, they're well hidden...

 

[wa5cab]

Richie,

As John implied, the answer is "no". It does not matter which of the two wires goes to which of the two terminals.

The majority of electrolytic capacitors made are polarized or polarity sensitive, and are marked with the polarity (+ and/or -). However, the motor start capacitors made today are all electrolytic, and non-polarized. And certain electrolytic capacitors made for other type service are also non-polarized. Perhaps the most common application would be in solid state audio power amplifiers.

The run capacitors may or may not be NP electrolytic. 50 years ago, they weren't (they were oil filled), but that could have changed. I'll have to look into that.

Robert D.

That brings up another question: Are capacitors polarity-sensitive??? If I have two wires coming out of the motor for each capacitor, does it matter which side of the cap gets which wire???

 

[wa5cab]

That's correct. "VAC" instead of just "V" implies RMS of a sine wave. And when used in the voltage rating of a component, it also implies a safety margin appropriate to the typical service the device is intended for. The actual peak to peak voltage rating of a Start capacitor for use on the 120 VAC line is probably around 300 V.

Robert D.

He wrote "125VAC". That means that it is designed for operation on the AC line and designed to take the peak voltage it will see there.

You would not want to use a 125VDC capacitor on the 120VAC line.