Help Needed Identifying Antique AC & DC Motor

Patina · Feb 21, 2019

I have an antique motor that I'd like to use to power an antique belt-driven drill press. I am not familiar with this type of motor. It has AC inputs on one side and DC inputs on the other side. When I apply AC to the AC contacts it does not rotate but just buzzes a little. The resistance between the AC contacts measures 38 ohms. Applying power to the DC side does not result in rotation either. I have tried "kickstarting" the motor while applying power but that did not work.

Can anyone help me identify this type of motor and/or give me some tips on getting it to run?

john.k · Feb 21, 2019

Have you applied DC to the brushes on the commutator?..........it may need quite high voltage.I think you would need to pull out the armature,and see how its connected to figure out what it is.As a general rule,each commutator bar will have a difference of 3 to 4 volts from the adjoining one,to limit sparking and arcing.So if you have say 40 bars,then it might be meant for 120v....i think it may be a teaching aid from a demonstration unit.

RustySparks · Feb 22, 2019

From the affixed labels, it looks like the DC (commutator) side runs from 110VDC, and draws .55 amps. I don't think the AC side (slip rings) would run as a motor, more likely it is an AC generator, putting out 70 VAC at around .3 amps, frequency not specified. Possibly used as a ringing generator in a telephone system.

iwananew10K · Feb 22, 2019

agree with RS....looks a lot like the little generator in an old hand cranked phone...the kind with the batteries.

Patina · Feb 22, 2019

RustySparks said:
From the affixed labels, it looks like the DC (commutator) side runs from 110VDC, and draws .55 amps. I don't think the AC side (slip rings) would run as a motor, more likely it is an AC generator, putting out 70 VAC at around .3 amps, frequency not specified. Possibly used as a ringing generator in a telephone system.

Interesting that the motor may be only able to run with DC... I have to admit that I have only tried the DC side with 35V since that is the highest DC supply I could find in my junk box. I'll put together a bridge rectifier to get 110V DC and report back.

I really appreciate everyone's expertise.

johansen · Feb 22, 2019

almost certainly a shunt wound motor generator. i would try applying 120vac rectified (100 watt bulb in series to protect it) and it should run. if not, is there any current flowing?

if you can get the shaft running it may self excite and supply both dc and ac, or not.

RustySparks · Feb 22, 2019

If used in a vintage phone system, everything runs off storage batteries to give battery backup. This motor generator not only acts to generate the 20 to 30 Hz (typical) AC ringing voltage, but also uses the shafts to drive reduction gear trains, which in turn drive cam operated electrical contact sets that interrupt the ringing voltage to phones, giving the on-off cadence we are used to hearing in phones. Also interrupted is the audible tones used to give busy signal and "ring back" (what you hear in your ear that tells you that the distant phone is ringing.)

Patina · Feb 22, 2019

I tested the motor with a rectifier and lightbulbs in series and it runs! It actually runs at a surprisingly high RPM. I measured it with my oscilloscope and got 7400 RPM. That seems a lot for a motor that does not have ball bearings.

Another related question: This motor has cups for providing lubrication to the bushings. Does this type of motor require grease or oil? There is no wick inside the cups.

RustySparks · Feb 22, 2019

No grease, not WD40, not detergent oil such as used in car engines. 3 in one electric motor oil would be fine, even though this is less than 1/4 HP. Also could use sewing machine oil, or oil for clippers if you have any of these around the house.

Patina · Feb 22, 2019

RustySparks said:
No grease, not WD40, not detergent oil such as used in car engines. 3 in one electric motor oil would be fine, even though this is less than 1/4 HP. Also could use sewing machine oil, or oil for clippers if you have any of these around the house.

Excellent. I will get the 3 in 1 electric motor oil and use that. Thanks for your help in getting the motor running and the historical information. It makes perfect sense that this motor was used in vintage phone systems because it does not only convert DC to AC but also acts as a motor to power the cams you described. If it were a dedicated DC to AC converter the shaft would not extend outside the housing.

JST · Feb 22, 2019

When you look in those oil reservoirs, I bet you find a felt wick that probably touches the shaft. May have a spring to push it down. Saturate the wick with oil, but no need to try to fill anything up.

Definitely no grease. Light oil.

jim rozen · Feb 23, 2019

You probably want to repair or replace that brush holder. It will run better after that.

TDegenhart · Feb 23, 2019

If the motor runs 7400 rpm, it probably is series wound. The standard central office voltage was 48 VDC. If in fact that it is as RustySparks mentions, a ring current generator, a 2 pole construction would yield 20 Hz at 1200 rpm, 4 pole - 600 rpm and so on. Use your oscilloscope the output frequency.

Tom

jim rozen · Feb 24, 2019

The cover nameplates show that it's 3300 TpM which is probably turns per minute or, converting to US
nomencature, 3300 rpm.

This might be a converter to supply ac power to equipment from a dc mains supply. If the output frequency
is around 50 or 60 Hz this is probably the original use for this. It's small but might power a small radio.

RustySparks · Feb 24, 2019

Assuming a two pole design for the alternator (slip ring side) and the motor powered and loaded so it turns at the nameplate RPM, 3300, this unit will output 55 Hz AC. Should be near the 70 volts indicated on the nameplate. Although this would not match the american phone system standards for ring current, 20-30 Hz at around 90 volts, it does fit into some other countries commonly used ring voltage and frequency. This motor-generator is obviously not intended for use in the united states.

Patina · Feb 26, 2019

TDegenhart said:
If the motor runs 7400 rpm, it probably is series wound. The standard central office voltage was 48 VDC. If in fact that it is as RustySparks mentions, a ring current generator, a 2 pole construction would yield 20 Hz at 1200 rpm, 4 pole - 600 rpm and so on. Use your oscilloscope the output frequency.

Tom

I measured the frequency and got 52Hz. I also bought some 3-in-1 electric motor oil today and I will try the motor on my drillpress soon.

Thanks everyone.

TDegenhart · Feb 26, 2019

3300/7400 x 52 = 23.2 Hz. Perfect for a ring current generator.

Tom

RustySparks · Feb 27, 2019

RustySparks said:
Assuming a two pole design for the alternator (slip ring side) and the motor powered and loaded so it turns at the nameplate RPM, 3300, this unit will output 55 Hz AC.

Patina said:
I measured it with my oscilloscope and got 7400 RPM.

Patina said:
I measured the frequency and got 52Hz.

TDegenhart said:
3300/7400 x 52 = 23.2 Hz. Perfect for a ring current generator.
Tom

So nameplate RPM of 3300, and a SINGLE pole alternator, would output 27.5 Hz.
This is very interesting. I am having trouble visualizing how a single pole alternator can be designed.
Can anyone share any insight on this? :willy_nilly:

OK, seriously now, I think it more likely that there is an error in measured RPM, and the actual RPM is more like 3120. Not sure how to measure RPM with an oscilloscope unless you have a special attachment.

Patina · Feb 28, 2019

I attached a small piece of reflective tape to the shaft and pointed a light at it. I then set up a light sensor connected to the oscilloscope. That way I would get a pulse for every rotation. I'm quite sure 7400RPM is right, it definitely sounds like a high RPM. Of course there is no load attached to the motor.

jim rozen · Feb 28, 2019

Patina said:
I attached a small piece of reflective tape to the shaft and pointed a light at it. I then set up a light sensor connected to the oscilloscope. That way I would get a pulse for every rotation. I'm quite sure 7400RPM is right, it definitely sounds like a high RPM. Of course there is no load attached to the motor.

How do you reconcile that with the nameplate speed of 3300?

Help Needed Identifying Antique AC & DC Motor

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