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Generators & Electric Motors General Discussion

GE Electric Motor - 5KC45PG4FX


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  #1  
Old 10-10-2019, 02:18:52 PM
kruss77 kruss77 is offline
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Default GE Electric Motor - 5KC45PG4FX

I'm struggling to find ANY information on a GE electric motor model number 5KC45PG4FX. Specifically, I'm looking for the capacitor specification for it. The motor powers a centrifugal blower on a large commercial shop heater that has never worked. The motor would start, then slow and speed-up (surge) repeatedly until it blows the capacitor. I'm a little unsure if there's something wrong with the motor itself or perhaps just has the wrong capacitor in it.

A photo of the replacement capacitor I bought for it (exact specification as the one I took out of it) is attached along with the specification plate from the motor.

I hope some of the experts here can push me in the right direction to get this thing going.

Ken
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  #2  
Old 10-10-2019, 04:29:47 PM
Power Power is offline
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Default Re: GE Electric Motor - 5KC45PG4FX

That is a common 3/4 hp 1725 RPM motor. I would just replace it. They are cheap enough.

If you want to waste time on it, first check incoming voltage under load. Make sure motor is wired for that voltage. If incoming is 115, and motor wired for 220- well, Bob's your uncle.

When you are sure it is correctly wired for voltage, put an amprobe on it, and confirm amp draw is within nameplate rating.

Check motor and fan bearings are not binding, or incorrectly assembled.

Let us know what the problem was.
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Old 10-10-2019, 04:37:37 PM
Vanman Vanman is online now
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Default Re: GE Electric Motor - 5KC45PG4FX

Hi Ken, welcome to the ‘Stak.

I’m not familiar with GE model numbers, but that certainly appears to be a capacitor start motor. That being the case, it does appear that you have the correct type of capacitor, a start cap, not a run cap.

On this type of motor, the capacitor and start winding are only designed to be in the circuit during starting, ~several seconds at most. There is normally a centrifugal switch which cuts out the starting circuit when the motor gets up to around 75% of running speed.

From your description of “surging”, it sounds to me like the motor is successfully accelerating up to this speed, and the centrifugal switch is cutting out the starting circuit, but then the motor is not able to carry the load, so the motor loses speed until the centrifugal switch recloses, and the cycle repeats until the capacitor overheats and fails.

There are a few possible reasons for this, but the most likely is overload. Belt too tight, bearings dry or worn such that something is dragging, or perhaps someone installed the wrong pulley, trying to speed up the blower. Unlikely there is actually anything wrong with the motor itself.

Centrifugal blowers take a LOT more hp to drive when the speed is increased even slightly. Hp required varies as a cube function of driven speed. They also take more power when they are not working against pressure. So if this installation was designed to operate against a certain static pressure, and now it is running free air, the motor will be overloaded.

Lastly, low line voltage can also cause the trouble you’re having. The torque developed by an induction motor varies with the square of the applied voltage. So that’s something else to think about and check.

Good luck, and let us know what you find.

Edit, posted at the same time. Good point about making sure that the motor is connected for the correct voltage. On half voltage a motor will only make 1/4 it’s rated torque and hp.

I would not just replace the motor without first proving that it is bad and not able to be simply repaired. A new motor will be lower quality than an old one, and will not resolve any other problems, should they be present. That would be known as the “shotgun” approach. Throwing parts at it until you happen to replace the faulty one.

Keith
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Old 10-10-2019, 06:21:31 PM
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Default Re: GE Electric Motor - 5KC45PG4FX

Looking at the pic of the motor I'd say early 70's. Hmm,,, 'the blower never worked'. Makes me think the motor was a replacement and likely undersized by at least 50%. Find the data on the system and the blower and that'll tell the story. Put up a few pics of the system for us to chew on.
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Old 10-10-2019, 06:59:38 PM
kruss77 kruss77 is offline
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Default Re: GE Electric Motor - 5KC45PG4FX

When I say 'never worked', I probably should have been more clear. I was told it worked once, but after having been "repaired" by someone years ago it never worked properly after that. That's why I'm wondering if they perhaps put the wrong capacitor in it back then.

Attached is a photo of it in it's current state.

I've pulled out just the motor & blower housing to use to move air through my workshop. Now I'm trying to get the motor to work properly.

Ken
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Old 10-10-2019, 07:13:38 PM
kruss77 kruss77 is offline
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Default Re: GE Electric Motor - 5KC45PG4FX

Quote:
Originally Posted by Vanman View Post
...or perhaps someone installed the wrong pulley, trying to speed up the blower. Unlikely there is actually anything wrong with the motor itself. Keith
It does have a rather large pulley on the motor. Larger than I would have intuitively expected.

Quote:
Originally Posted by Vanman View Post
Centrifugal blowers take a LOT more hp to drive when the speed is increased even slightly. Hp required varies as a cube function of driven speed. They also take more power when they are not working against pressure. So if this installation was designed to operate against a certain static pressure, and now it is running free air, the motor will be overloaded. Keith
It was one of those hanging garage/factory heaters with no ducting on the incoming air side, so I'm assuming using it as a shop blower to move air around my workshop would be essentially the same as when it was hanging from the ceiling in the factory (same realative static air pressure?).

Ken
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Old 10-10-2019, 07:15:06 PM
kruss77 kruss77 is offline
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Default Re: GE Electric Motor - 5KC45PG4FX

Drive motor pulley it came with.
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  #8  
Old 10-10-2019, 10:02:17 PM
Steve Dawkins Steve Dawkins is online now
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Default Re: GE Electric Motor - 5KC45PG4FX

The motor pulley looks to be about the same size as the motor. The original motor pulley was probably smaller, and got replaced with a larger one to increase air flow, possibly overloading the motor. I would recommend replacing it with a smaller pulley. That will reduce the load on the motor. What is the diameter of the blower wheel pulley?

As previously mentioned, check to make sure the motor lead connections match the line voltage. Speeding up and slowing down under load is a classic symptom of a capacitor start motor that is wired for 230 volts with 115 volts supply voltage, or the motor is overloaded. Under these conditions, the motor will start with the extra torque of the start winding and capacitor. When it gets up to speed and the centrifugal starting switch disconnects the start winding, the motor will slow down. When it slows to the point that the centrifugal switch engages the start winding and capacitor again, the motor will speed up and the process will repeat itself. This is very hard on the starting capacitor, and will eventually cause it to overheat and burn out, which is probably what happened to your capacitor. You will probably be able to hear the starting switch click in and out as the motor slows down and speeds up.

Refer back to post 2.
- confirm the motor is correctly wired to match the incoming line voltage.
- put a clamp-on ammeter (Amprobe) on the incoming line to ensure the motor amps are within nameplate rating. If they exceed nameplate, disconnect the belt, and see how many amps the motor draws unloaded. If the motor runs fine and doesn't overheat, it is probably overloaded when running the blower.
- reduce the motor pulley diameter until the amps are within nameplate rating. (This is assuming that the blower shaft turns freely.) You can buy adjustable sheaves (pulleys) that will allow some adjustment of the belt to change the blower speed.
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Old 10-10-2019, 10:46:35 PM
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Default Re: GE Electric Motor - 5KC45PG4FX

Looking at the size of those pulleys and the size of that blower, I think that it is trying to drive it way too fast. Big blowers like that run really slow, or take a lot of power. You could get an adjustable sheave for the motor, allowing you to dial in the load to suit the motor.
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Old 10-10-2019, 11:19:54 PM
kruss77 kruss77 is offline
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Default Re: GE Electric Motor - 5KC45PG4FX

Quote:
Originally Posted by Steve Dawkins View Post
What is the diameter of the blower wheel pulley?
The blower wheel pulley is 7" in diameter.

Quote:
Originally Posted by Steve Dawkins View Post
As previously mentioned, check to make sure the motor lead connections match the line voltage.
I checked this several times. I even switched between 110v & 220v wiring to test the motor. Both wiring configurations yielded identical results. Attached is the wiring diagram I used.

Quote:
Originally Posted by Steve Dawkins View Post
Speeding up and slowing down under load is a classic symptom of a capacitor start motor that is wired for 230 volts with 115 volts supply voltage, or the motor is overloaded.
It's only a 3/4 hp motor with a big 5" pulley on it tiring a fairly large fan. Is it possible that it's just overloaded? Also, I quadruple-checked the wiring each time against the wiring diagram attached and would be very surprised if it were still wrong on the motor.

Quote:
Originally Posted by Steve Dawkins View Post
Under these conditions, the motor will start with the extra torque of the start winding and capacitor.
Yes! Each time it did this the motor really 'lurched'. Incidentally, I tested the motor using a 2" drive pulley and it did the same thing, except that the cadence of the surging was a lot faster.

Quote:
Originally Posted by Steve Dawkins View Post
When it gets up to speed and the centrifugal starting switch disconnects the start winding, the motor will slow down. When it slows to the point that the centrifugal switch engages the start winding and capacitor again, the motor will speed up and the process will repeat itself.
Yes, that is exactly what it did.

Quote:
Originally Posted by Steve Dawkins View Post
This is very hard on the starting capacitor, and will eventually cause it to overheat and burn out, which is probably what happened to your capacitor.
Yes. Initially, when it started 'lurching' I would just shut it down right away. But the last time I just let it go until it just shut down by itself. Found that the capacitor was fried.

Quote:
Originally Posted by Steve Dawkins View Post
You will probably be able to hear the starting switch click in and out as the motor slows down and speeds up.
Yes, I do recall hearing a "clicking" each time.

Quote:
Originally Posted by Steve Dawkins View Post
Refer back to post 2.
I will do some further testing.
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  #11  
Old 10-11-2019, 01:50:53 AM
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Default Re: GE Electric Motor - 5KC45PG4FX

5/7 x 1725 = 1232 rpm, if you had a powerful enough motor. I’d expect a blower like that to run something more like 400 rpm.

2/7 x 1725 = 493 rpm. Closer to reasonable. What does the motor do with the belt off of it? Does it and the blower turn freely, even with the belt on?
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Old 10-11-2019, 07:41:39 AM
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Default Re: GE Electric Motor - 5KC45PG4FX

Quote:
Originally Posted by Vanman View Post
What does the motor do with the belt off of it?
In the process of working on all this I never ran the motor by itself. I'll let you know after the replacement cap arrives.

Quote:
Originally Posted by Vanman View Post
Does it and the blower turn freely, even with the belt on?
Everything rotates freely. I even opened the motor up to clean it and remove all of the varnish from the bushings and re-lubricate everything. It all rotated even better after that.
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Old 10-11-2019, 11:36:14 AM
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Default Re: GE Electric Motor - 5KC45PG4FX

At this point, I'd say an amperage test is in order. If you don't have access to a clamp-on ammeter, you can buy a Kill-A-Watt meter at Home Depot for around $30. It has many functions other than amperage. The frequency function is especially useful for checking/adjusting the 120 volts output of a portable generator to ensure the engine is running at the proper speed for the generator to produce 60 Hz.....if you have a generator.

If you go the Kill-A-Watt route, just bear in mind that the maximum amperage for it is 15 amps. If your motor is severely overloaded and drawing more than 15 amps, it may damage the Kill-A-Watt.

As Vanman mentioned, it would be a good idea to run the motor without the belt. I would do this first when checking the amperage. This will give you a base line of what the motor draws unloaded. If the amperage exceeds the nameplate rating without a load, the motor is defective.
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Old 10-12-2019, 08:39:39 AM
Joe Romas Joe Romas is offline
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Default Re: GE Electric Motor - 5KC45PG4FX

It's also possible the blower pulley has been replaced with a smaller one too
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Old 10-12-2019, 07:09:31 PM
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Default Re: GE Electric Motor - 5KC45PG4FX

I have a furnace blower powered by 1/3 up split phase motor. 4" motor pulley, 6" blower pulley. This is free standing for shop use. I had to reduce the air output area by half to stop motor overheating. They must have a load on them. I will try to attach photos.

Last edited by BernieTech; 10-13-2019 at 09:17:06 PM. Reason: correct spelling
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Old 10-12-2019, 07:50:34 PM
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Default Re: GE Electric Motor - 5KC45PG4FX

Trying the pics again.
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Old 10-12-2019, 09:33:32 PM
Mark Dieckmann Mark Dieckmann is offline
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Default Re: GE Electric Motor - 5KC45PG4FX

First off,try to run the motor without the belt. As stated take amp readings if possible. Second that motor is likely designed to be in the air stream, cold air return of the furnace it came out of, and will likely overheat fairly quickly and possibly shut off on thermal overload without the air stream cooling it. Next I would think that the pulleys are running the blower too fast as mentioned before. Probably 500 RPM max on the blower. Last, that blower is intended to be in a furnace with ductwork creating static back pressure as stated before. In free air it moves much more air so more work is done, more HP required so it becomes overloaded. The combination of no cooling air, excessive speed and no back pressure are all overloading the motor. You can try smaller pulleys, and blocking off the air flow coming out of the blower by approximately 1/2 and may get it to work. It would be best done with an amp meter so you know how much load is on the motor. In the end you may not be happy with your fan's output and decide to go buy a fan designed for what you are doing.
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Old 10-25-2019, 07:58:33 PM
kruss77 kruss77 is offline
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Default Re: GE Electric Motor - 5KC45PG4FX

Thanks for all the excellent help, gentlemen.

I finally got the replacement capacitor as well as a smaller (2") drive pulley and will be getting back on this this next week.

I'll let you know what I find.

Ken
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Old 11-11-2019, 12:29:01 PM
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Default Re: GE Electric Motor - 5KC45PG4FX

Ok, FINALLY got back on this, and found that it was in-fact the very-large pulley size that was blowing the capacitor (as many of you suggested).

I installed the new capacitor and switched-on the motor without a belt on it (no load. It ran just fine with no problems at all. So I installed a new 2" pully I purchased (probably similar in size to what it was originally designed to run with), installed the belt, and voila! It ran just fine with no problems!

Thanks to all for the kind assistance in diagnosing this problem. Simple-enough to those of you familiar with these types of matters, but sufficiently complex for someone like me with no real experience resolving issues of this sort. I'm a lot smarter now, though, thanks to you guys!

Here's a "link" to a video of the motor running with the new pulley installed.

Ken
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