Hi,

So I've got this rotary floor sander I've got to fix. When I opened it I noticed someone had fixed it before and 1 of the capacitors had swollen. I've been told it had been working for a long time before the capacitor broke. I assumed the silver one was the run capacitor and the blue broken one was the starting capacitor so I ordered one with the same capacitance (big white one), which apparently is way bigger than the original.

Motor:

Capacitors:


When I hooked it up the motor just buzzed for a second before tripping the breaker. Not knowing what was going on and not being sure how the motor was supposed to be wired, I took it apart. It has 5 wires, and as expected, the 3 thicker colored ones are the 2 windings, which measured about 1 and 2.9? ohm. I was pretty sure the other 2 wires were the centrifugal switch, but doing a continuity test while turning the motor gave mixed results.

After taking it apart I noticed there was dried glue or enamel between the windings and on the top of the gearbox. Part of the centrifugal switch has molten but after reinstalling it in the motor it's seems to be working normal.

Windings:


Gearbox:


Centrifugal switch:


After knowing how the motor works and rewiring it, it still keeps tripping the breaker when testing it. Does anyone have any idea what might be going on and how to fix this?

After rewiring:

 

First did you fit motor start and motor run rated capacitors?
If the centrifugal sw is dodgy, you should be able to spin the motor in either direction at the point of switch on, if it goes into run, then the centrifugal sw is faulty.
Max.

 

On the pictures of the winding I can't tell if I am looking at dark spots, almost black or if it is just how the lighting played out. When a motor is made the winding is made with magnet wire which is coated. Then a good motor goes through an impregnation process which forces a resin into it. It looks to me like the resin has been cooking off from heat. Rotary floor sanders place a large load on the motors, this can generate excessive heat and start to break down the varnish. Not knowing what the coil resistance should actually be makes it hard to identify shorted windings. Even when known you really want a good quality DLRO (Digital Low Resistance Ohmmeter) to measure the stator resistance. Shorted windings would cause a circuit breaker to blow assuming the capacitors and wiring is correct.

<EDIT> I see Max was here. That would be a very good motor type guy. </EDIT>

Ron

 

Hi,

So I've got this rotary floor sander I've got to fix. When I opened it I noticed someone had fixed it before and 1 of the capacitors had swollen. I've been told it had been working for a long time before the capacitor broke. I assumed the silver one was the run capacitor and the blue broken one was the starting capacitor so I ordered one with the same capacitance (big white one), which apparently is way bigger than the original.

Motor:
View attachment 189608
Capacitors:
View attachment 189619

When I hooked it up the motor just buzzed for a second before tripping the breaker. Not knowing what was going on and not being sure how the motor was supposed to be wired, I took it apart. It has 5 wires, and as expected, the 3 thicker colored ones are the 2 windings, which measured about 1 and 2.9? ohm. I was pretty sure the other 2 wires were the centrifugal switch, but doing a continuity test while turning the motor gave mixed results.

After taking it apart I noticed there was dried glue or enamel between the windings and on the top of the gearbox. Part of the centrifugal switch has molten but after reinstalling it in the motor it's seems to be working normal.

Windings:
View attachment 189626View attachment 189627

Gearbox:
View attachment 189620

Centrifugal switch:
View attachment 189624View attachment 189622

After knowing how the motor works and rewiring it, it still keeps tripping the breaker when testing it. Does anyone have any idea what might be going on and how to fix this?

After rewiring:
View attachment 189623

View attachment 189628

I would say the Brown wires are the Switch, and the Red,Green,Yellow are the Start and Run windings, the highest resistance is the Start, which goes to the capacitors via the switch, the lower resistance goes across the mains with common to Neutral.

With your readings of 1 ohm and 3, that sounds way too low, probably burned out..

Start capacitor is around 10 -22uF, run capacitor 3-10uF..depending on wattage of motor..

 

I would say the Brown wires are the Switch, and the Red,Green,Yellow are the Start and Run windings, the highest resistance is the Start, which goes to the capacitors via the switch, the lower resistance goes across the mains with common to Neutral.

That's exactly how I wired it. But the fact that the resin has started boiling away and the windings having multiple dark spots makes me believe it has burned out.

The motor is 1100W, 220V.

 

Have you confirmed the valid operation of the centrifugal switch?
You can get evidence of winding overheat without turn to turn short..
Max.

 

Yes, the switch stays closed but I don't know if it will open when the motor spins up. I'll know if it works if I can get the motor to start, but when connecting it, the breaker instantly trips.

 

It will do, at 3 Ohms on 120V that's 40 Amps...the windings are too low in resistance...