Speed control for motor salvaged from vintage electrical sewing machine

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How can I slow down a 240V brushed AC sewing machine motor for use as a bench drill with a cheap hand-operated speed controller instead of a foot pedal?

A cheap lamp dimmer should work on a brushed AC motor, but speed regulation under changing load will be poor, so an SCR-based controller is the better solution [#21683330][#21683332] The recommended circuit uses a TIC106D SCR to apply pulsed DC to the motor, with the motor placed below the SCR so the back EMF provides feedback and helps stabilize speed [#21683332][#21683336][#21683338] This type of controller can run a brushed motor at about 70% or more of full AC speed, and it is especially suitable if you need a simple knob-controlled bench speed controller [#21683338] It is mains circuitry, so it must be treated with great care, and the SCR metal tab may be live/anode [#21683332][#21683335] The inductor and capacitor for interference suppression can be the hardest parts to source, but they may be salvaged from old switched-mode power supplies [#21683338] If you want an off-the-shelf alternative, a variable transformer would work well but is heavy and expensive [#21683333]

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Light dimmer may work as a cheap speed controller
#1 21683329 15 Oct 2019 18:19

Michelle OBrien Michelle OBrien

Anonymous

Light dimmer may work as a cheap speed controller
Post #1 21683329 15 Oct 2019 18:19

I have an ac motor taken from a vintage Singer electric sewing machine - 240v 50Hz 60W.

The motor's drive shaft rotates powerfully but far too fast for the purpose I have in mind , which is to power a drill. So I need a speed controller for it, one with a knob that I can operate by hand from a workbench (NOT a foot pedal).

Can anyone please recommend a simple, ready-assembled speed-control module for the motor that does not cost a bomb? Would an electric light dimmer switch suffice to control the speed of the motor?

Michelle O'Brien
SE London, England
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Dimmer or wire-wound resistor for motor speed control
#2 21683330 16 Oct 2019 14:55

David Ashton David Ashton

Anonymous

Dimmer or wire-wound resistor for motor speed control
Post #2 21683330 16 Oct 2019 14:55

Michelle what sort of motor is it, do you know? If it is a brushed AC motor you can certainly use a dimmer on it. If it is a small shaded pole motor (no brushes) then a dimmer may not work well. Dimmers are cheap and you'd certainly not have much to lose by trying one (effectively they are a pulse width control).Sewing machine motors usually have a variable resistor in the foot pedal. If you can find a rotary wire-wound variable resistor of the same value (and a fairly hefty power rating) that would do the job as well.
#3 21683331 17 Oct 2019 00:56

Michelle OBrien Michelle OBrien

Anonymous

Post #3
21683331 17 Oct 2019 00:56

It's a brushed AC motor , David - when it is running you can see the little sparks from the brushes through the air vents.

Michelle
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SCR speed regulator with back-emf feedback
#4 21683332 18 Oct 2019 01:52

David Ashton David Ashton

Anonymous

SCR speed regulator with back-emf feedback
Post #4 21683332 18 Oct 2019 01:52

A dimmer should work ok for a brushed motor, Michelle, but there is a better way to do it.I found this circuit on Aspencore's sister site Electroschematics.com:https://www.electroschematics.com/rotative-speed-regulator-borer-driller-controller/
By putting the motor below the SCR (TH1) the back emf of the motor gives some feedback and stabilises the speed. I've built one of these and they work very well.. However....1. You will have to build this yourself, which you didn't seem keen on2. This is mains circuitry and can be very dangerous to work on. You need to be VERY careful.I'd try a lamp dimmer at first and see how that goes. If that does not give the results you're looking for try something like this. A lamp dimmer will control the speed but the speed regulation at differing loads (which you'd get with a drill or drill press) would not be very good.The above circuit looks like it was lifted from Elektor magazine. I have the full set of Elektor on PDFs so will see if I can find the original article, which may have a PCB design as well. I also have an old book with a similar design. I've never seen this type of circuit available commercially (thinks, maybe I should start producing them
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#5 21683333 18 Oct 2019 06:31

PeterTraneus Anderson PeterTraneus Anderson

Anonymous

Post #5
21683333 18 Oct 2019 06:31

A variable transformer would work well, but is both expensive and heavy.Old brushed motors often worked as well on DC as on AC. You want much slower speed, so try your motor on 12V DC. If it works OK, you could use a variable low-voltage DC supply as your controller.
#6 21683334 18 Oct 2019 15:32

Michelle OBrien Michelle OBrien

Anonymous

Post #6
21683334 18 Oct 2019 15:32

David, that circuit from Electroschematics that you posted here (rotative-speed-regulator-borer-driller-controller) looks like it could very well fill the bill. Thank you.
I might try to assemble the parts and build it. Do you have access to a handy list of components and maybe even a photograph of the built circuit. That would be of considerable help.
Michelle
#7 21683335 18 Oct 2019 17:47

Alan Winstanley Alan Winstanley

Anonymous

Post #7
21683335 18 Oct 2019 17:47

The PE/ Silicon Chip speed controllers are very elaborate and high power, the cct mentioned above looks like a circuit scanned in from somewhere else but it should fit the bill. Note the metal tag of the TIC106D thyristor may be live (anode) and a lot of extra care is needed with insulation.New Singers are nothing like the old ones, I've found.- Alan W
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#8 21683336 19 Oct 2019 00:02

PeterTraneus Anderson PeterTraneus Anderson

Anonymous

Post #8
21683336 19 Oct 2019 00:02

The Electroschematics controller uses a TIC106D silicon controlled rectifier SCR to apply pulsed DC to the brushed motor.
Elektor archive circuit found and shared privately
#9 21683337 19 Oct 2019 13:33

David Ashton David Ashton

Anonymous

Elektor archive circuit found and shared privately
Post #9 21683337 19 Oct 2019 13:33

Michelle I found the circuit in my Elektor archives. It is from the July/August 1983 issue. The July/August issues used to be called "Summer Circuits" and usually had 100+ small projects like this. it's got an explanation but no PCB, parts list etc.
As it is in PDF form I can't post it here but I have sent you a private msg (don't like displaying my email to all and sundry) with my email in it, if you reply to that then I will email you the PDF and, when I have access to a scanner next week, another similar circuit from a book I have.Cheers // David
SCR controller gives brushed AC motors partial DC pulses
#10 21683338 19 Oct 2019 13:41

David Ashton David Ashton

Anonymous

SCR controller gives brushed AC motors partial DC pulses
Post #10 21683338 19 Oct 2019 13:41

Peter, Michelle yes because it's a SCR not a Triac you only get positive DC pulses, not the full AC. However, brushed AC motors don't mind DC and get up to 70% or more of full AC speed when run like this. If you're really finicky, you can put a full wave rectifier before the circuit so it can run full speed, but I've found it is not necessary and I've built a couple of this type of circuit.Usually the most difficult bits to source are the inductor and capacitor used for interference suppression, because they have the full mains power through / across them. But you can often salvage such components from old switched-mode power supplies. Michelle, I'm sure I'd have suitable bits for this, it would take some time to post them to you though....
#11 21683339 19 Oct 2019 14:54

Michelle OBrien Michelle OBrien

Anonymous

Post #11
21683339 19 Oct 2019 14:54

Will do, David, and thank you. Your help on this and on other questions that I have raised here from time to time is hugely appreciated.

Michelle
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Topic summary

A vintage Singer electric sewing machine motor (240V, 50Hz, 60W) with a brushed AC design produces excessive speed for use as a drill power source. A simple, cost-effective speed control solution is sought, preferably with a hand-operated knob rather than a foot pedal. A standard electric light dimmer switch can be used to control speed on brushed AC motors, as it functions via pulse width modulation, but may offer limited speed regulation under varying loads. An alternative is a specialized speed regulator circuit using a silicon controlled rectifier (SCR), specifically a TIC106D SCR, which applies pulsed DC to the motor and provides better speed stability through back EMF feedback. This circuit, originally published in Elektor magazine (July/August 1983 issue) and available on Electroschematics.com, requires careful assembly and mains safety precautions. Other options include using a rotary wire-wound variable resistor similar to the original foot pedal resistor or powering the motor with a low-voltage DC supply (e.g., 12V DC) to achieve slower speeds. Variable transformers can also control speed but are heavy and costly. Components like inductors and capacitors for interference suppression may be salvaged from old power supplies. The discussed solutions emphasize safety due to mains voltage involvement and the need for proper insulation, especially around the SCR's metal tag (anode).
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Speed control for motor salvaged from vintage electrical sewing machine

Speed control for motor salvaged from vintage electrical sewing machine

How can I slow down a 240V brushed AC sewing machine motor for use as a bench drill with a cheap hand-operated speed controller instead of a foot pedal?

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