Urema Esslingen with a wiring problem

[Klassiker]

I recently bought a very old cleaning machine, and as expected the wiring was in a very poor state. It was fitted with a plunger switch which kept sticking, an obsolete plug, a two-core cable and all the internal wiring had crumbling insulation. Nevertheless, when the switch cooperated, the motor would run. I decided to replace as much of the wiring as possible, fit a new toggle switch, and add an earth connection to the casing. I have completed all the work, but when I flick the switch, the motor doesn't run and just emits a buzzing tone. I can turn the spindle by hand, so it isn't a mechanical blockage. My best guess is that the motor is OK but I have made a mistake with the connections. Does anyone have any tips what I should check? Here are some photos of the motor for those who understand these things.

Thanks in advance!

 

[HectorLooi]

Does the motor have a starting capacitor? If it has one, check if the capacitance is within specs. A weak capacitor is unable to spin up the motor.

Also, check that the rotor is centred properly. If the rotor is off-centered, or if the housing is not securely tightened, the imbalance in the magnetic field can pull the rotor against the stator and cause it to seize and hum.

[Klassiker]

On 12/3/2023 at 3:07 PM, HectorLooi said:

Does the motor have a starting capacitor?

No, it's a very simple shaded pole motor, as far as I can make out, but then I know next to nothing about electrical devices. This type of motor seems to produce very low starting torque which fits well to the problem I'm seeing. The stator is a really close fit into the housing, so no adjustment there. There are two opposing pointed grub screws which locate the stator, but tightening them doesn't move the stator within the housing any appreciable amount. The points just dig deeper into the laminations. The rotor bearings are a close fit into machined cups into the housing. No adjustment there either.

I removed the rotor and checked again for any possibility of fouling, then reassembled, and it is trying so hard to run! The spindle will make several slow revolutions, then stall. It seems to be freeing up slightly with each new attempt though. My grease-monkey brain is saying either the voltage in the coils is too low, or the friction in the bearings is too high.

I wanted to change the roller bearings, as I thought the were too noisy and a bit sloppy, but they are EXTREMELY tight on the spindle. I gave up and just added more grease. I don't think so, but possibly I have damaged the bearings, or the bit of extra grease is dragging too much. As I say, with each attempt, the rpm is a bit higher at first, but then it dies off and stalls. I'm guessing when the windings are cold, the resistance is lowest, and so the motor turns until the coil warms up a bit. Failing any better suggestions I will flush out the grease and add some light oil.

The other possibility is that the new switch I fitted is robbing voltage somehow. Maybe it's the wrong rating or it was damaged by my soldering to the terminals? This is the switch:

Contact resistance < 20 mOhm.

Or, I have damaged a part of the windings, or my soldering is not good enough???? I cannot smell anything burning or giving off fumes, and nothing seems to get hot either.

 

[HectorLooi]

Is the wiring of the stator coils original?

I'm not sure if this is a shaded pole motor. I don't see any shaded coils and slots in the laminaions.

Let's get Prof @LittleWatchShop to advise you.

[Klassiker]

6 hours ago, HectorLooi said:

Is the wiring of the stator coils original?

How can I tell? It all looks very old indeed. That's all I can say, but I'm otherwise clueless. Happy to post more pictures to aid identification and diagnosis.

[Kalanag]

Is it this type of motor?
https://www.ebay.de/itm/145427114248

[HectorLooi]

I don't know. Other watch cleaning machines use carbon brush motors. They have better torque and speed control.

[Kalanag]

Here is the slot in the pole:

[LittleWatchShop]

Switch is unlikely the problem. Bypass it to prove.

I suggest you remove the earth ground that you added and see what happens.

[HectorLooi]

Ok. That is a shaded pole motor. Check that the welds of the copper shaded loops are still intact.

[Klassiker]

16 hours ago, Kalanag said:

Is it this type of motor?

Yes, exactly. At least, that shows the motor housing from an identical machine.

10 hours ago, LittleWatchShop said:

I suggest you remove the earth ground that you added and see what happens.

I will try this tomorrow.

10 hours ago, HectorLooi said:

Check that the welds of the copper shaded loops are still intact.

Not sure what to look for here, but I will check for anything wich appears loose or broken, and post pictures.

[Kalanag]

6 hours ago, Klassiker said:

Not sure what to look for here, but I will check for anything wich appears loose or broken, and post pictures.

There should be welded copper loops in the stator slots like shown in the pic.

Edited December 6, 2023 by Kalanag

[Klassiker]

Problem solved! In my attempts to remove the roller bearings I had displaced one of them very slightly (about 0.5mm) and they were binding a little when I closed the housing up tight. I reseated it firmly. Now everything is running very freely, and the motor has no problem getting up to speed. The bearings are noisy, so I think a replacement is due at some stage, but I'm just happy to have the machine running for the time being. Now to find out if it actually cleans watch parts!

Many thanks to all those who tried to help so far. If anyone has any more questions about the machine or wants to add their own knowledge, please feel free to continue the topic.

Edited December 7, 2023 by Klassiker

[LittleWatchShop]

1 hour ago, Klassiker said:

Problem solved! In my attempts to remove the roller bearings I had displaced one of them very slightly (about 0.5mm) and they were binding a little when I closed the housing up tight. I reseated it firmly. Now everything is running very freely, and the motor has no problem getting up to speed. The bearings are noisy, so I think a replacement is due at some stage, but I'm just happy to have the machine running for the time being. Now to find out if it actually cleans watch parts!

Many thanks to all those who tried to help so far. If anyone has any more questions about the machine or wants to add their own knowledge, please feel free to continue the topic.

Lol...Occam's Razor.  Good job!