Sewing Machine Motor Speed Contol Wiring?

[Yorkie]

An odd title for a thread on a vintage radio forum perhaps!

I've just embarked on the total restoration of a 1936 Ecko AC77 and it comes as no surprise that the field coil is open circuit. The easy option would be to get the filed coil re-wound, but I'd rather have a go at that myself. My present thoughts are to make a winder using a sewing machine motor and foot control to control the winding speed, and a calculator/cam-operated micro-switch to count the turns, though for a field coil that will run into thousands of turns, the usual way from what I've read is not to count turns but to weigh the wire off the old coil, and to wind on a similar weight of wire, then check the resistance, adding or removing turns as necessary. I haven't even removed the field coil from the speaker yet, but I know it should be 2,000 Ohms.

I've just bought (cheaply!), a job lot of sewing machine motors and foot speed controllers, but the chances are that the controllers won't marry up with the motors. They're all described as in 'good condition' but I won't know what that means till I get them. (I haven't counted them but I guess there are half a dozen motors and three or four controllers).

Using a sewing machine of any kind is way outside my skills portfolio so I haven't a clue how the motor and controller marry up and connect to the mains. (All of the motors have different input plugs at their entry point - some with three pins, some with four). I assume that the foot control plugs into the mains, and the output from the controller plugs into the motor, but that's just an assumption of my part which could be mistaken. (No doubt modern ones are different in design from vintage ones).

I guess my query is premature, but I'm assuming that I'll have to try to mate up one of the controllers to one of the motors using a terminal bock or whatever. I'm also assuming that any controller will work with any motor provided the two are married up correctly. I've attached a pic I've plucked off the net of the circuit of a controller, but I've no doubt that there are myriads of them.

I wondered if anyone has any experience of how the controllers and motors are coupled and if I'm on the right lines - mains into the controller - two wires out (plus maybe an earth) to the motor.

I'm out of the country from tomorrow till next Saturday, and though I'm taking my i-pad, wi-fi will be a bit iffy, so if I don't respond to any posts for a few days, it's 'cos I can't get connection.

Any advice would be appreciated, (except of course: "get someone else to wind the coil"!).

[Nick]

Welcome to the coil-winding club, David!

The controller schematic you provided is the absolute basic triac-based phase angle power controller - it should work with most sewing machine motors - the circuit is electrically noisy as it's not a "zero-crossing" controller, i.e. it switches current mid-phase creating EMI.

I would use a micrometer to measure the diameter of the wire, then work out how much you need of that diameter for 2Kohms, and the weight of that.

A useful table can be found at http://www.engineeringtoolbox.com/wire-g...d_419.html. If you look at the diameter on the Brocott's site (http://www.brocott.co.uk, that'll give you numbers you need to calculate the weight for a given gauge and length.

Measuring the length that you are winding is nigh on impossible, so do it by weight - if you have a set of digital kitchen scales, these are accurate to 1/10 gramme, so stick the spool on the scales and watch the weight drop...

One thing I've found when doing the DAC90A output xfrmr etc is that the feed spool must be extremely free-running, preferable on good bearings as any "jerk" at all will snap the wire. I have known people to use the bearings from the read/write head of an old VCR for this - works very well...

[Refugee]

I am making a transformer winder and its first job will be a PDA transformer for a scope.
It is based on a food mixer and has a turns counter that uses a paper end sensor from an old printer coupled to a vintage Nixie tube batch counter that has a programmable mains relay output.

[Nick]

... coupled to a vintage Nixie tube batch counter...

Anything. Anything at all, with nixies in it is cool...

[tiv48]

the very early ones just used a rheostat connected to the foot pedal.
a later one I looked at used a thyrister rather than a triac still without zero mains switching .
maybe an idea to use a lamp dimmer made for inductive loads?
Rob t

[Refugee]

Are they not universal motors?
That would explain the thyristor. Perhaps 110V DC with a triac for the US model.

[Yorkie]

Thanks for your input guys.

At this stage - not having received the controllers or motors, while I don't think any are a 'matching pair' I'm assuming that one or another controller will fit one or another motor. Primarily, I just wondered whether what the wiring arrangement of motors/controllers is - i.e., if the controller plugs into the mains, and the motor is fed by a flex from the controller, or whether the mains first goes to the motor and down to the controller. I know that sewing machines generally have a light fixed on a bracket on the motor, so that must come straight off the mains. I guess I'll have a better idea when I open the parcel in a week or two.

All good harmless fun!

[tiv48]

on the few I have looked at the mains goes to the controller then the controller to the m/c.
Rob t

[ex 2 Base]

Hello David, re the sewing machine motor and foot controller, well we have 4, yes four Bernina machines and a lot of spares as well.these are not the latest machine but all have a resistor in series with the motor.The motor is a series wound type with two carbon brushes, not easily reversed but possible if one needs to use the motor for other uses. Some have wire wound resistors others have a block of some material (maybe hard carbon)with wipers either side,but still in series with the motor, both type are foot switches. When needed I wind motor contactor coil on my lathe and maybe you could do the same, its not easy to regulate the tension on fine wire. I made a block of wood with a reed relay mounted on it and a plastic disc attached to the lathe chuck, the disc has very small magnet attached to it. Now as the chuck rotates the reed switch opens or closes. I bought a large calculator and modified the pcb so that the equals key is connected to the reed, incrementing as the chuck rotates. I think I have got the details correct, I seem to remember some thing peculiar about it, I made the set up several years ago, but it works well. It won't work at high speed (reed contact bounce) but it allows me to layer the turns in a neat orderly manner. I also made a foot switch for the lathe, such that I can turn it off quickly if necessary.I haven't used it a lot but its handy when needed and is easily stored. If you need any more details let me know.Ted

[Yorkie]

Thanks for reading my post Ted, and for your comments.

Yes, to use a calculator as a turns counter, you just fit a switch across the = contacts, then to start counting, you press '1' then the + button to make '1' a constant, then each time the = button is shorted, it increments by one. You can try it on a calculator of course. 1 + + then with each press of the = button, it counts upwards. I've already added this to my hand wave wound coil winder (yet to be use in anger!), but of course it's impossible to wind a field coil of many thousands of turns by hand. With fine wire obviously the speed won't be very great or it risks breaking the wire, but rather than use a reed relay and magnet, I think a micro-switch and cam will reduce the chance of contact bounce. Time will tell! (The other option would be a mechanical one, using a 'tally counter' operated by a cam. Cheap enough and originally used on the 'Morris Gingery' hand wider.

As I said earlier, it's not so much the number of turns that's relevant, but the weight of wire, which correlates to the resistance for each gauge of wire. I won't know until I've removed the field coil what gauge of wire was used. At this stage, I'm concentrating on re-building the power supply which is on a separate chassis from the rest of the radio. All stripped down ready to de-rust and re-spray the chassis and rebuild it. (It's the first time I've tacked a valved radio that's older then me!).

Incidentally, back in 2007 Gary Tempest wrote an article in the BVWS Bulletin which you can download off internet. Google: "Making a Coil Winder (mostly from the junk box)" The article has a lot of useful info about winding field coils. (Gary designed and built a CMOS IC turns counter using an interrupted light beam).

(Back bedroom is now full of stuff to go to Hornsea Rally Ted - all neatly labelled and priced up! Have you booked your table?).