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Unavailable small AC motor components

JHM

Apr 18, 2023
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Hello:

I'm at a loss with respect to a small motor I would like to fix/recycle.

It is the original Gefeg (ca. 1980) 220v/50Hz AC German made motor originally in a Unimat 3 lathe.

The original label was in very bad shape, barely visible.
I am posting one from a different unit with the same specs but (for some reason) different part number.

Being a small, rather noisy two speed (95/65W) 80% duty motor, it has been replaced by a smaller, quiet and much more efficient 12v/200W electronically controlled motor.

Now, after a thorough cleaning of decades old caked-in carbon dust and oiling of the bushings, it is almost ready to go.
But I am needing to replace two (essential?) parts: the condenser/line filter and the low speed speed diode.

The thing is that it would seem that both parts are no longer available.

The paper film condenser has these specs stamped on the plastic cover:

---
Brand: ERO
Model: F1740-325-5522

0.025uF X
+2X2500pFY
250V 4A

560-7 HPF
-25°/+85° C
RS7
D S 25/085/21
It has 5 cables -> 2x blue + 2x black + 1 ground
---

The diode reads:

---
BBC
DS 1.8
16A SI
---

This is very good quality electric hardware.
Even the switch works perfectly well after all these years.
All it took was the time/patience to take it apart, give it a good cleaning and there it was, as good as new.

You can't purchase this type of hardware anymore.
I would appreciate any suggestions as to how to get it running again albeit not necessarily on a two speed basis.

Thanks in advance.

Best,

JHM
 

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Minder

Apr 24, 2015
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I see it is an intermittent use motor?
The capacitor should be replaced with a AC motor run rated version, also if it has sintered bronze bearings instead of ball type they should be cleaned and ensured they are re-lubricated well, and also checked for wear.
Any 16a rated rectifier should work, if situated in N.A., then Digikey would be one source.
(The term condenser has been replaced for some decades now with Capacitor)
 

JHM

Apr 18, 2023
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Hello:

... an intermittent use motor?
Yes, according to the label it is.

... capacitor should be replaced with ...
Indeed ...

The problem is that paper film capacitors/line filters ceased to be manufactured quite a few years ago.
ie: they are not obtainable newly made.
What I have seen available (and for funny money prices) are old stock in limited ranges.
As such, they have probably been on-the-shelf for years and chances are that they are unreliable for use.

I have not been able to source a modern capacitor with the same spec/size and an outboard mount is not a suitable option.
Which is why I asked to see if anyone had been in the same spot and could suggest a workaround.

... if it has sintered bronze bearings ...
Yes, it does.

... they should be cleaned and ensured ...
Quite so.

Proper maintenance has been done on all parts of the motor, particularly on the bearings.
After cleaning the carbon residue from all nooks and crannies, the felt oil reservoirs were repeatedly flushed with SAE10 machine oil @~50°C till the excess started flowing out as clear as what went in.
Fortunately, there was no noticeable wear on the bearings.

After assembly, the motor spins very smoothly with no strange noises or noticeable radial play.

Any 16a rated rectifier should work ...
Of course.
If by any you mean a 220V/16A diode with a maximum size of 12.5mm x 12.0mm x 4.5mm.
The cavity to fit the capacitor and the diode is very limited.

... condenser has been replaced for some decades now with Capacitor ...
Indeed it has.
But you did know what I was referring to. 8^)

Please excuse me.
Not being my mother tongue, the command of the English language and technical terms I hold is rather poor.

Thank you very much for your input.

Best,
JHM
 

Minder

Apr 24, 2015
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Re-reading the OP I don't think the .025uF is a start capacitor, that is a really small value for the task.
But oil filled paper motor start caps are readily available, makes such as CDE , Cornell Dubilier etc
Oil/paper caps do not deteriorate like electrolytic do.
Is there any connection diagrams on the motor?
 

JHM

Apr 18, 2023
8
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Apr 18, 2023
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Hello:

... don't think the .025uF is a start capacitor ...
No, it is not.

It is an RF filter / interference suppression capacitor.
Similar to the one below but with three cables instead of five.

rf-filter.jpg

I have been advised that, besides noise suppression, it protects the carbons as it keps them from sparking.
Could well be: the original carbons are in perfect state with maybe 75% length left in them.

The ones in the attached photo are available on the German eBay as NOS, manufactured when West Germany still existed as state.
ie: before 1990. But I don't think it reasonable to pay ~ €15.00 for a 43 year old Entstör-Kondensator.

... connection diagrams on the motor?
No, not on the motor.
But I found one on the web some time ago:

rf-filter.jpeg
I'm afraid that I neglected to mention that this motor is as small as it is lacking in power. (95W max)
It is ~125mm long and ~75mm in diameter with the exception of the bulge/cavity holding the switch, diode and rf-filter.

This screen capture from an on-line advertisement gives you a good idea of the size:

unimat_motor.jpg

I have never seen a motor of this type/size with a start capacitor.

Thank you very much for your input.

Best,
JHM
 

Bluejets

Oct 5, 2014
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I have been advised that, besides noise suppression, it protects the carbons as it keps them from sparking.
Suggest new advisor, noise suppressor yes, commutator spark reduction, no.
 

Harald Kapp

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Nov 17, 2011
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Not exactly matching, not cheap either, but...
Instead of the 5 üin filter (left) you can probably use a 3-pin X/Y capacitor wired like this (right):
1681895523010.png

As for the diode: I understand you replace the 12 V motor by the original 220 V motor, right? so at 95 W current will be around 0.5 A, give or take.
Any diode rated >= 400 V, >= 1 A should work.AN 1N4007 with 1000 V / 1 A is at the lower limit, currentwise.
An 1N5407 is good for 3 A.
A P600M-E3/54 is good for 6 A, 12 times the rated motor current. With a surge current of 400 A this diode should easily take the inrush current of the motor.


See e.g. this selection table.
 

JHM

Apr 18, 2023
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Hello:

Not exactly matching, not cheap ...
Indeed ...
I am wondering if it is at all worthwhile to install this part again.

This motor will not be used on the Unimat 3 again, hopefully serving some other purpose.
eg: to drive a small diamond disk/wheel to touch up or put finishing touches on HSS lathe tools.

With all it's shortcomings, it is really well built and has survived the abuse usually dealt out bu Unimat owners for over 43 years.
Does not deserve to be a candidate for the recycle bin.

If assigned to more a diamond wheel, there would be two things to consider:
1.
The duty cycles would be short, I would be touching up an already formed tool, not grinding a blank.
With short duty cycles I may not have to worry too much about noise suppression.
Make sense?

I should also consider that a replacement filter will end up costing me over €30.00 (~€15.00+VAT+shipping).
As a reference: one of these motors can be obtained in very good condition on the web for ~ US$125.

2. As a sharpening tool, the motor's speed would have to be reduced considerably.
The best option may be via a suitable belt/pulley arrangement instead of a diode.
That said, keeping the motor as original as possible would be desired.

... replace the 12 V motor by the original 220 V motor ...
Hmm ...
The other way around.
The original motor (220V/50Hz - 95W) was replaced by a 12V/200W DC one.
Sorry if I was not clear.

Any diode rated >= 400 V, >= 1 A should work.
I have based my search for replacements on the especification of the original parts.
The motor left the factory with one of these:

u3motor_diode.jpg

ie: 1.7kV <- why 1.7kV?
German over-engineering? 8^)

I have been able to source the 1N5408 part which has the proper size and would be good for 1000V/3A but have not been offered the P600M-E3/54 by the chap at the shop, I'll have to check again and see if it is available.

Thank you very much for your input.

Best,

JHM
 

JHM

Apr 18, 2023
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... the issue of EMC, reason enough.
Yes, I can see your point.

The original part may still be viable.
I have cleaned it up and will test it.

If it holds, I'll install it. 8^)

Than you for your input.

Best,

JHM
 

JHM

Apr 18, 2023
8
Joined
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Hello:

If it holds, I'll install it.

Looking around the web for posts related to these motors, I came across an interesting recopilation of information regarding the different models used in Unimat lathes, from the early ones in the 50's to last the Unimat 3's built up to 1990.

According to the serial number on my U3, it was manufactured in 07/1980.

Unimat-3 motor is the most sophisticated ( electrically ) of all the motors Unimat ( Emco ) used.

As seen in diagram below. It uses a three position rocker switch to provide. Off, Lo-speed and Hi-speed functions.
It utilizes a diode to provide half wave rectification for Lo-speed. A feed through type X-Y capacitor to work in tune ( literally, it becomes an ; inductance, resistance and capacitance tuned circuit ), with the inductance of the field coils to help filter and smooth out the choppy half cycle of the rectifier ( diode ). Also, they included ceramic capacitors at each motor brush connection to provide for arc suppression (reverse EMF).

The motor from my U3 does not have ceramic capacitors at each motor brush.

At one point, the OP states:
There is no more real need to use a full XY-cap for noise suppression. If you open nowadays' coffee grinders, kitchen mixers, weed trimmers, vacuum cleaners and other brush motor driven appliances, you see small blockshaped capacitors containing the safe X-part only. So in your case an X-type suppressing cap (the modern and higher voltage rated variety is called "X2") will also do fine. A good electronics shop will be able to supply you with a 0.01 microFarad X2-cap, with must preferably be capable to withstand 275 AC Volts but at least 250 Volts AC. The "self healing" polyester foil types are the best quality on the market, in Europe they are called "MKT" types. A few dollars (as little as one or two) may get you such a part, whereas versions with readymade wires instead of soldering pins, may be slightly more expensive. Polypropylene film "MKP" types will also do fine, as long as the voltage rating is at least 250 volts AC. Since the X2-types have no ground connection lead and therefore don't need a third "ground" wire, there is only the need to attach the two remaining wires parallel to the motor itself. There are also brush motors that have their suppressing capacitor connected over the two brush holders. In that case the field coils also have a suppressing function ("inductances")

If this is correct, it would seem that I could use a 0.01 mF X2 275V AC capacitor connected in this manner:

Clipboard01.jpg
Image courtesy unimat.homestead.com

I'd appreciate an opinion from the forum on this.

Thanks in advance.

Best,

JHM
 

Minder

Apr 24, 2015
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What you show is a a Universal motor with a suppression cap across the brushes.
The motor will operate without it, just that it may emit electrical noise.
A high quality type should be used, ceramic etc.
 

JHM

Apr 18, 2023
8
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Apr 18, 2023
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Hello:
... Universal motor with a suppression cap ...
... motor will operate without it ... ... may emit electrical noise.
Yes, that much I know.
My question was more oriented to the X2 capacitor being enough.

Thank you very much to everyone for your input.

Best,

JHM
 

Bluejets

Oct 5, 2014
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My question was more oriented to the X2 capacitor being enough
X2 are mains rated caps , normally used in voltage reduction circuits.( places where non-isolated voltage reduction is used, such as say a mains operated daylight switch or pir detector, many others.........)
M referred to ceramic being more suitable to noise suppression however, the x2 would still work ( if you must).
 
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