Electrical gurus, sander help?

[Lil Foot]

I have two of these Delta Strip/Disc sanders.
1/4Hp, 1 PH, 60Hz, 120V, 2.5 A
Both have developed the same problem- on startup, they just hum, and need assistance to get rolling- just a couple of flicks with the fingers is enough. After they start, the run great.
They seem to need assistance more on initial starting, then on subsequent starts they usually start on their own.
Shafts on both spin freely.
I assumed run/start caps were bad, but at Grangers today the cap I brought with me tested fine on their equipment.
Opinions?

 

[Lil Foot]

There is one of these caps on eboy coming out of Canada for $57- a lot to spend if not the problem.
(or even if it is the problem)

 

[Henro]

There is one of these caps on eboy coming out of Canada for $57- a lot to spend if not the problem.
(or even if it is the problem)

Well, if the start capacitor is good, and the wires are good going into the motor then chances are you have an open start winding In the motor.

An OHM meter could be your friend here.

OR… there is probably a centrifugal switch that removes the start winding from the circuit when the motor gets up the speed. You could also have a problem with that switch. Check the contacts and the mechanism. This might be the most common reason for issues like your experiencing if the capacitor is good.

 

[DustyRusty]

You might have a low voltage problem coming from the pole. Ask your electric supplier to check the voltage.

 

[Sidekick]

Could be corrosion in the power switch not letting the full start current surge through. I find the Delta products use very cheap switches.

 

[GreensvilleJay]

OK, silly me but...did you try them in different receptacles ? Might be 'bad' breaker,loose wiring in panel ?

I actually had one phase go low once. Called Hydro they 'fixed' something,problem solved.

 

[Flintknapper]

Well, if the start capacitor is good, and the wires are good going into the motor then chances are you have an open start winding In the motor.

An OHM meter could be your friend here.

OR… there is probably a centrifugal switch that removes the start winding from the circuit when the motor gets up the speed. You could also have a problem with that switch. Check the contacts and the mechanism. This might be the most common reason for issues like your experiencing if the capacitor is good.

^^^^^


This.

 

[mikester]

can you replace the motor brushes?

 

[Henro]

can you replace the motor brushes?

It’s a single phase AC motor so it’s unlikely there are brushes…

 

[Lil Foot]

No brushes, no centrifugal switch.
Line voltage 120 to 122. (and no other low voltage symptoms on anything else)
Lots of different outlets, and two different sanders at two different homes 150mi apart, two different power companies.
I will check switch, but I kinda doubt it- not much corrosion out here.
Motor starts 100% reliably without the belt in place.
I think it is just weak at start up.
It is basically a sewing machine motor.

 

[Henro]

No brushes, no centrifugal switch.
Line voltage 120 to 122. (and no other low voltage symptoms on anything else)
Lots of different outlets, and two different sanders at two different homes 150mi apart, two different power companies.
I will check switch, but I kinda doubt it- not much corrosion out here.
Motor starts 100% reliably without the belt in place.
I think it is just weak at start up.
It is basically a sewing machine motor.

So it looks like everything is pointing towards the start winding in the motor. Do you have an ohm meter? If so, you can easily determine if the start winding is open or not. An open start winding would not provide any additional torque for motor rotation on start, and would measure infinite, or very high, resistance.

If the start winding were partially shorted, this would also reduce the amount of starting torque it develops. This is more difficult to determine with an ohm meter measurement because you don’t know what the resistance should be to begin with.

 

[chim]

I have two of these Delta Strip/Disc sanders.
1/4Hp, 1 PH, 60Hz, 120V, 2.5 A
Both have developed the same problem- on startup, they just hum..............................

Obvious explanation - they don't know the lyrics.

Sorry, couldn't resist

 

[Flintknapper]

So it looks like everything is pointing towards the start winding in the motor. Do you have an ohm meter? If so, you can easily determine if the start winding is open or not. An open start winding would not provide any additional torque for motor rotation on start, and would measure infinite, or very high, resistance.

If the start winding were partially shorted, this would also reduce the amount of starting torque it develops. This is more difficult to determine with an ohm meter measurement because you don’t know what the resistance should to begin with.

^^^^^^
Again....correct, and the path that should be taken to troubleshoot the issue.

 

[jaxs]

Having two with same problem (unusual problem at that) points to poor design that will reoccur if you fix them. Being somewhat a gearhead myself I realize it's hard to resist the challenge of figuring out what's wrong instead of just tossing them. If you aren't convinced cap is good look for a cheap one with same rating and cobble it in temporarily to see if that fixes it. I agree $50 is steep even if that fixes it but at least you will know.

I miss Radio Shack

 

[Lil Foot]

Switch has no resistance, no voltage drop.
Start winding checks 50 ohms.
Did find one of the spade terminals on the switch was loose, crimped it down and re-attached.
(no obvious signs of heat or arcing)
Right now it is starting 100%.
We will see after it sits overnight or longer.
If the problem persists, I guess I'll just learn to live with it.
Both sanders are low hours, but old. (20+yrs?)

 

[jaxs]

Switch has no resistance, no voltage drop.
Start winding checks 50 ohms.
Did find one of the spade terminals on the switch was loose, crimped it down and re-attached.
(no obvious signs of heat or arcing)
Right now it is starting 100%.
We will see after it sits overnight or longer.
If the problem persists, I guess I'll just learn to live with it.
Both sanders are low hours, but old. (20+yrs?)