Electronics > Repair
For those with experience in AC motors, what is the reason of this noise
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Ian.M:
The electrics are pretty much irrelevant at this point.  Its rotor assembly has  a bent shaft, and if the bend is between the bearings, its scrap.   If the bend is in the output shaft, it *may* be able to be straightened enough to get the runout down to something usable.    However as you suspect its been dropped, the grinding wheel is compromised*, you know its got bad bearings and it doesn't appear to have a guard and rest.  It is probably not economic to replace the wheel and bearings and make a guard and rest for it.

Before OSHA, HSE and other national workplace safety bodies mandated proper guards for fixed grinders, that pretty much enclose the wheel, their wheels catastrophically failing at speed (aka: 'grenading') caused many grinder operator deaths and serious injuries. .

* If a grinding wheel has had a hard knock, it may have an imperceptible crack in it which could result in its catastrophic failure when spun up or during use.  Any wheel that has been dropped or chipped should not be used and should be destroyed by breaking in half and disposed of.

Xena E:

--- Quote from: highcap on September 27, 2024, 08:21:12 am ---Thank you for all your replies! Unfortunately I don't have 3 phase power available here, just single phase 220v.

I took new pictures and measurements, I will try and answer all the above questions, here it goes:


* There is no start/run capacitors so those might have been externally, if any.
There are two sets of 3 wires each coming from the windings (let's call those wire sets).
Colors are Black, Yellow and White (white cloth turned to brownish partially).
One set of 3-wires winding was connected together, so all 3 wires making contact.
The power switch is a simple design which closes/opens its 3 contacts all at once.
The other set of wires which were connected to the power switch are measuring roughly 25 Ohms all in between.
If I were to unstuck the other 3-wire set, no measurement will happen when measuring wires in between within each set.
When measuring wires between the two sets, all reads roughly 12 Ohms, color to color only so they're consistent. (e.g. Yellow from one set measures 12 Ohms with Yellow from the other set).
*
My first test was the way it was setup and how it presumably ran before I got it: one set of wires was stuck together, and the other set had readings of 25-28 Ohms so I applied 220v onto it.

Video of winding measurements: https://youtu.be/tq2VeAgLLqs
Video of contact function: https://youtube.com/shorts/8i0wIpBRGIc

I attached a picture for those who can't open the videos.

Thank you all for chiming in, I'm excited about your answers!

--- End quote ---

As you have described this motor, with 12 ohms between each end of the three different coloured wires, it confirms it as a three phase machine as was previously said. The connection of the three wires together is star/wye.

Sometimes one bodge used to get these three phase motors to run on single phase was to connect the mains across two windings and place a capacitor between live and the other phase, this would cause a phase shift in the third winding, enough to start the motor off load, but it would only give poor torque and would overheat the windings if loaded.

If you want to restore this, and use it, I would recommend finding a VSD that outputs three phases from a single phase input.

They are available to run small motors like this.

I concur with Ians comments on the subject of safety...

Regards
X
gupa:
Hello, I would also measure the ohms against the motor frame if the winding is not punctured. But it looks good. Now practice. wires from one hole that go are number 1 plus color cables from hole no.2 are cables no.2 plus color.

Why am I writing this? In the triangle D, No. 1 of one color is connected to No. 2 of the other color. It is important to orientation the coils! No.

1 and three colors are connected to the star and on the other side there are connectors with No. 2 ends coils.

According to the flag, I took the liberty of looking for a reference to the theory in your language around this

https://ifrunze.blogspot.com/2013/08/pornirea-motoarelor-trifazate-la.html

Edit: also measure the switch if it has no connection to the frame. I would spray some oil on the mechanical parts.


He put the balls of the bearings in vaseline and lubricated them with lubricants during operation.

Edit:
That electric motor is very old, so I would reach for it. Touch classes are higher today. It is better to control everything with a voltage tester with light (neon tester) before touching the surface of a running electric motor.

Edit:
The frequency converter switches very high, these motors can handle it, but the test neon indicator is active on the frame. It is necessary to additionally ground and be instructed about the possible penetration from the coils to the frame.
Jeroen3:

--- Quote from: Xena E on September 27, 2024, 10:22:33 am ---If you want to restore this, and use it, I would recommend finding a VSD that outputs three phases from a single phase input.

They are available to run small motors like this.

--- End quote ---
This motor is too old to be run with a VFD without sine filter, the dv/dt of the switching will destroy the winding insulation. And buying a sine filter makes no economic sense for this thing.

If you want to run this motor you can convert it to single phase with a capacitor. It will be derated.

Remember, 220VΔ means 220VL-L between the phases, this old. In a lot of places it's replaced with 400VL-Lbetween phases and 230VL-N to neutral.
Maybe 220VΔ is still common in some other regions in europe, I know Amsterdam and Belgium still have some.
Xena E:

--- Quote from: Jeroen3 on September 27, 2024, 05:11:32 pm ---
--- Quote from: Xena E on September 27, 2024, 10:22:33 am ---If you want to restore this, and use it, I would recommend finding a VSD that outputs three phases from a single phase input.

They are available to run small motors like this.

--- End quote ---
This motor is too old to be run with a VFD without sine filter, the dv/dt of the switching will destroy the winding insulation. And buying a sine filter makes no economic sense for this thing.


--- End quote ---

That is a very good point, thank you for picking that up, I don't know the date  of this machine, but it may be that it is so very old, (pre 1950?) That it may have shellac insulation which could be destroyed.

The 220 volt rating is Delta, this motor has all winding ends available and if connected star could be run at ≈ 380 volts supply: this is often an arrangement used with small motors even more modern ones. Larger motors are often wound so that in Delta they are for 380/415 volt supplies.

Regards
X
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