Electric Motor Guru Needed

bird dogger

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There’s been a nice little motor in my project shelf for years while waiting for an application. Don’t know or can’t remember what it was off of. It may have come with its “run capacitor” but I’m not sure….and can’t find it if it did. Most likely, I rescued the motor off some outdated equipment heading for the scrap dealers 20 years ago or more.

The motor is a nice compact 1/3 HP PSC (permanent-split capacitor) type. There is no centrifugal switch, so the start winding stays energized with the capacitor full time. The thermal protection fuse can be seen wrapped up on top of the field windings. I’ll have to cut loose the motor leads to trace them back to see how they are configured. I want to add to and bring out both start winding leads anyway to make the motor reversible.

Permanent Split Capacitor Motor Stator.JPG PSC Motor Nameplate Data.JPG Run Capacitor Size 300mfd.JPG Yellow arrow points to capacitor value.

The question of the day: Notice the nameplate data listing the capacitor value of 300mfd (micro farads)!!! That seems unbelievably high for a permanent run capacitor in such a small motor?? Most are normally in the 10mfd to maybe 50mfd. Multiple cap’s could be parallel connected to add up to 300mfd but the bank of cap’s could be as big as the motor almost. There is no “decimal point” stamped in the nameplate value, either.

Does anyone know what application or motor of this type would require such a large run capacitor?? There seems to be no single capacitor of that size listed as a motor capacitor, oil filled.

Could a smaller cap be used instead without an excessive increase in current draw to the start winding? I’m sure starting torque would be reduced. I’d hate to let the magic smoke out of the start winding.

Believe the motor to be circa 1970s. I found a similar motor for sale online….listed as used. But there’s no pic of the capacitor and I’m betting they don’t even know that it requires an external capacitor to properly run.

Any and all ideas welcomed!!
 

North Idaho Wolfman

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I have several electric motors here that all take a cap that big.
 

Bee-Positive

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The GE 5KC motors are outdated (1940’s???) and GE no longer makes fractional HP motors, they farm them out. Doing a quick search I couldn’t find that exact model #. It's late and I'm tired.

The rating is probably the starting capacitor. Start capacitors will typically have a much higher capacitance rating than run capacitors (100 to 1600 µF vs. 5-100 µF).

Nameplate RPM is 3,000, higher than a typical 1,750 motor so maybe it needs the 300 MFD (µF) to get up to 75% speed. You could go +10% if you buy a new cap, maybe a little lower depending on what you're using it for.

Just my WAG.
 

bird dogger

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This one has the capacitor and the capacitor does indeed show 276-324 MFD.


View attachment 151941
Dustball, Thanks for the great response! I need a new search engine as I could only find one picture online of the motor…..and with no capacitor included.

The link in your post definitely shows it to be the exact same motor. And definitely a standard “electrolytic” start capacitor. Apparently, this motor was designed to get by with using this type of capacitor versus an oil filled “run” capacitor.

Sourcing this as a replacement will be easy….and cheap. However, the pics show something else that caught my eye and piqued my memory. For some reason, I’m sure I’ve seen that same mounting bracket for the capacitor shown. I’m betting the missing capacitor and bracket is lurking in a dark corner in a box of goodies here somewhere. The question is….where? LOL!

Lastly, there seems to be enough evidence in those pics to piece together exactly how the capacitor was connected to that motor’s windings. That should help to keep the magic smoke locked up inside. We shall see, once the new bearings arrive and the capacitor is found.

Your post has checked all the boxes!!
 

bird dogger

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I have several electric motors here that all take a cap that big.
NIW

I do too. But I’d bet (well….almost bet :ROFLMAO:) that they’re all “capacitor start” motors with a centrifugal switch that disconnects the start capacitor almost instantly once the motor is almost up to full speed.

This motor is a permanent capacitor run motor….meaning there’s no centrifugal switch to take the capacitor and start winding out of the circuit once the motor is up and spinning correctly. This type keeps the start winding and capacitor energized as long as the motor is energized. Normally, an electrolytic capacitor can’t take the heat buildup in that scenario. They then require a “Run Capacitor” that is usually oil filled.

But maybe that rule doesn’t apply for these fractional HP motors? Here’s a pic of its rotor without any centrifugal switch mechanism.
IMG_4702.JPG

When I get the new bearings and find the wayward capacitor, I’ll report back on its health.
 

bird dogger

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The GE 5KC motors are outdated (1940’s???) and GE no longer makes fractional HP motors, they farm them out. Doing a quick search I couldn’t find that exact model #. It's late and I'm tired.

The rating is probably the starting capacitor. Start capacitors will typically have a much higher capacitance rating than run capacitors (100 to 1600 µF vs. 5-100 µF).

Nameplate RPM is 3,000, higher than a typical 1,750 motor so maybe it needs the 300 MFD (µF) to get up to 75% speed. You could go +10% if you buy a new cap, maybe a little lower depending on what you're using it for.

Just my WAG.
Bee-Positive that’s interesting info, thanks! And it jives with my questionable memory of where this motor came from. This motor most likely came out of some equipment we scrapped at work (power company) back in the ‘70s or real early ‘80s.

Yes, it is a start capacitor….but it’s also more technically the "run capacitor" since it doesn’t have a centrifugal switch to remove it from the circuit. See the pic above. That’s what had me thinking it seemed unusually high valued for this motor. But Dustball’s link above with the pictures proved it must be engineered to work in this application.

It is a two-pole motor so nominally 3600 RPMs. A four pole motor is nominally 1750 RPMs,….etc. You might be right on your correlation between MFD and speed requirements. Your guess is as good as mine...or better! LOL!!
 

Bee-Positive

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I agree, Dustball nailed it.

I noticed the description in the link states “General Electrtric HP1 RPM 3500 V – Modele 5KC19SG331X”, Electric is misspelled, Model is misspelled, and HP is listed as 1 HP but the nameplate show 1/3 HP. Not a big deal but I’d be pissed if I thought I was getting a 1 HP motor. The misspellings are probably just a French/Canadian thing.

Notice the pully for a flat belt, these were typically use for HVAC fans and such. I’ve seen 1/2 HP KC motors on air compressors too.
 
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Bee-Positive

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I have several electric motors here that all take a cap that big.
Side Note: I just noticed…

When I open OTT and look my first post without logging in – the time of day for shows 9:59 PM. When I log in and look at my post it shows 12:59 AM – which is the correct time. Time zones, DTS? What do I know, I’m new to this forum stuff.
 

North Idaho Wolfman

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Side Note: I just noticed…

When I open OTT and look my first post without logging in – the time of day for shows 9:59 PM. When I log in and look at my post it shows 12:59 AM – which is the correct time. Time zones, DTS? What do I know, I’m new to this forum stuff.
Yes times are local to you when you're logged in, if you are not logged in then they are native to where ever the server is.
 
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