Sewing machine motor as a Nipkow disc motor?

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Sewing machine motor as a Nipkow disc motor?

Postby aussie_bloke » Mon Jun 25, 2012 2:18 pm

G'day all.

Just bought from the Dapto markets yesterday an old sewing machine motor from I guess the 1940s era, it's an Australian made Wernard 240VAC 0.38A AC motor. Anyhow these sewing machine motors have a few leads coming from them, this particular one has AC mains in lead, an adjacent lead that goes to a two prong female plug, and at the back two little black leads. This motor was obviously designed to be speed controlled with the sewing machine pedal. I have connected a cord to the mains input and powered it up on my variac but no response. I guess it must have an interlock system in which it must be connected to a sewing machine to operate and so perhaps that two prong lead has to be shorted though not sure. Anyhow any of you on here familiar with the general schematic layout of a sewing machine motor? I need to know how I can get this motor powered up and effectively speed controlled and if possible synchronized with sync circuitry? Any help would be much appreciated. Here below are some photos of this motor:
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Postby gary » Mon Jun 25, 2012 4:04 pm

It looks pretty similar to mine Troy, even that bracket at the front is identical (I have taken that off). Mine doesn't have the junction box and cable yours has though - just 2 short wires coming out of the motor. When these are connected to the mains it runs fine.

I haven't pulled mine apart to check but most sewing machine motors are meant to be universal type motors and so will run on DC as well as AC - I haven't tried that either yet but I will because well... I am not lucky enough to own a variac... :roll:
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Postby aussie_bloke » Thu Jun 28, 2012 7:59 pm

Nice motor you have there, certainly does look similar with the exception of the wiring arrangement. I bought my variac from Jaycar for $230.

Anyhow I have gotten a hold of a schematic of a typical sewing machine motor control setup which is similar to my motor setup and have found that the cord coming out of the motor at the front goes to the motor speed pedal and the two smaller wires that come out the rear are branch off wires from the mains to power the sewing machine's light globe.

I have attached the schematic for anyone who needs one for reference when using sewing machine motors for their projects.

I am now wondering what was used in those sewing machine pedals to control the speed of the motor, was a high wattage potentiometer used or a mini variac?
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Postby Steve Anderson » Thu Jun 28, 2012 10:20 pm

aussie_bloke wrote:I am now wondering what was used in those sewing machine pedals to control the speed of the motor, was a high wattage potentiometer used or a mini variac?


Usually a fairly high wattage rheostat of 20W or so rating, after an extended period on her machine my mother would complain about the heat. A variac would have been far too expensive and probably too large even if only 60W or so. I also remember the pedal itself weighed almost nothing, no transformer in there!

Today, I would guess a Triac, basically a light-dimmer.

As these were generally universal brushed motors (akin to earlier power-drill motors) I would think that running them off DC would be the way to go, controlling 50Hz for NBTV use seems laden with problems. But beware of the volts!

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Postby Harry Dalek » Thu Jun 28, 2012 10:47 pm

Steve Anderson wrote:
aussie_bloke wrote:I am now wondering what was used in those sewing machine pedals to control the speed of the motor, was a high wattage potentiometer used or a mini variac?


Usually a fairly high wattage rheostat of 20W or so rating, after an extended period on her machine my mother would complain about the heat. A variac would have been far too expensive and probably too large even if only 60W or so. I also remember the pedal itself weighed almost nothing, no transformer in there!

Today, I would guess a Triac, basically a light-dimmer.

As these were generally universal brushed motors (akin to earlier power-drill motors) I would think that running them off DC would be the way to go, controlling 50Hz for NBTV use seems laden with problems. But beware of the volts!

Steve A.


Steve i recall using a light dimmer for motor control it melted after a while last time i ever tried that ..worked till it got hot ! :wink:
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Postby Steve Anderson » Thu Jun 28, 2012 11:04 pm

Yes, not surprising really. A light-dimmer deals with a resistive load* (which does vary between hot and cold), but a brushed motor will produce a whole bunch of inductive pulses of significant voltage and they need VDRs, Varistors or whatever to protect the Triac.

Next to a spark-gap transmitter a brushed motor generates more interference and inductive pulses than anything I can think of. Maybe a vibrator (no giggles please) the sort used in valve car radios years ago is another contender.

Steve A.

*Except those designed for fluorescent tubes.
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Postby gary » Fri Jun 29, 2012 10:33 am

Nice motor you have there, certainly does look similar with the exception of the wiring arrangement.


Well I would assume the wiring arrangement WOULD have been similar before some one cut it off. I suppose the point being you should be able to just hook up your variac to the 2 wires that go to your motor itself to run and (roughly) speed control it.
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Postby Klaas Robers » Sat Jun 30, 2012 7:25 am

I think this is the same type of motor J.L. Baird used for his televisor. As well Denis Asseman used it for his Televisor replicae. It will run on 220 V AC 50 Hz, but I experienced also on about 48 volt DC. And the motor runs smoother on DC.

You may place the Nipkov Disc imediately on the spindle of the motor (Direct Drive). Then apply a variable DC voltage to the two wires that run into the motor and increase the voltage gradually, until the correct speed is reached. First think of 40 to 50 volt. No difference in + and -.

And 50V DC is not lethal.....
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Postby holtzman » Sat Jun 30, 2012 8:14 am

I used this kind of motor in my 60 lines 1500 rpm project. I bought a cheap dimmer rated 600W and it worked well, the triac did not get hot at all. The problem was the adjustment was too crude. So I replaced the original potenciometer by some resistors plus much lower resistance pot, and it worked well.
The motor was geared down a lot by means of a belt drive. There was some amount of slippage, as my pulleys were not toothed and the belt was overloaded.
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Postby aussie_bloke » Sat Jun 30, 2012 12:55 pm

Thanks for the responses all in regards of this motor.

So far I have shorted the output lead that goes to the speed control pedal and have powered the motor from the mains lead connected to my variac and it works very well and the speed of the motor varies according to the AC voltage coming out of my variac. The motor seems to not turn till I reach (I think) around 100-120VAC. Anyhow the motor does seem to have a funny electrical smell to it when I run it for a few minutes at mains voltage of 240VAC, just wondering is that a bad thing???

Anyways will try running it off DC as well, just got to build a variable DC power supply that can easily output (I guess) 40-100V and a decent amount of current flow to the effect of at least 0.38A which is the motor's current rating. Just wondering, for DC power to this motor, will the current drawn be the same as AC or will it be more or less???
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Postby gary » Sat Jun 30, 2012 4:10 pm

That will probably be the smell of burning dust on the commutator due to arcing brushes, which, of course, is quite normal.

The current drawn will be mostly due the resistance of the coils (good enough for calculation purposes using good old ohms law).
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Postby aussie_bloke » Sat Jun 30, 2012 8:03 pm

I powered up the motor again to 240VAC and noticed through a small gap in the top there was a bit of a spark show at the rear of the motor which is of course is what Gary said.

I decided to pull the motor apart and see if it was all good inside anyhow and found at the rear where the copper striped commutator was it was quite filthy covered in what I assume to be magnet dust or some kind of metallic dust. So I cleaned it up and put it all back together again, fired it up and it showed a great improvement, the smell being less intense and the arcing spark show less prominent and the motor runs smoother too. :)
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