Help please with PWM sewing machine pedal

Ummmm ..... PWM controls are for DC motors for the most part. When used on AC motors, they will cut speed by some amount just by being in place. Moto rs are funny things. They draw rated current even when throttled, which is why VFDs are preferred for AC motors. Not so much the control heating up as the motor heating up if fed with a PWM device.

Yes. There are some featherweight motors that are both AC or DC - but it wi ll run better on AC.

Peter Wieck Melrose Park, PA

I've seen designs - but not the actual product - of cheap motor controls that can provide only half the power at full throttle. This is because the phase-controlled device is an SCR without any pre-rectification and conduct for only half of each AC cycle.. Maybe you have one of those.

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** SCR speed controls for AC/DC motors are brilliant things - cos they allow for back EMF feedback as well as very low speeds.

The feedback keeps the speed steady with varying loads - while trigger speed controls built into drills use triacs and give no such benefit.

The sewing machine foot controller is likely a triac type - which is a form of PWM too.

..... Phil

I bought one of those for my wife almost 60 years ago. She still uses it for all her sewing. I bought a complete rebuild kit a few years ago and still have the leftover pieces. The biggest problem is lint and dust collection, but you have taken care of that.

Have you actually tried sewing cloth with the machine. My wife seldom operates it at full speed. Sewing with the machine is an art, not a race.

And the foot control is a wire-wound resistor with a slider.

Paul

Yeah, I do sew with it. That's why I bought it. I have a larger machine that is really heavy and a real chore to set up. That little featherweight is a joy to use. It is supposed to be able to sew leather but the motor stalls. Looking online for information about this machine I found out all sorts of folks collect them and actually use them a lot. I also found a zig zag attachment that I use when patching holes in my work shirts. Eric

Simple: connect it up without the controller to see how fast it goes. Didn't know zigzag adaptors existed for ancient machines Some early electric machines are quite slow.

NT

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** Some Singer models use that and others have triac controllers.

One I saw recently had an "air controller" - model 6233.

Yep, the foot pedal fed compressed air to the machine via a rubber tube.

Not sure how that activated a triac circuit.

..... Phil

Wife has trouble patching denim with hers, if more than 2-3 layers thick. Original motor is not powerful enough. She has to help the machine by hand. Paul

My mother hated those. She would have me install one of the carbon pile type, because it gave a smoother control. I would save the old ones and add a few extra disks to them to return them to like new condition. The wirewound controller changes speed in steps, not in a linear fashion. I also replaced old motors when they no longer had enough torque for thicker material. She sewed six to ten hours a day, and wore out eight commercial grade machines.

--
Never piss off an Engineer! 

They don't get mad. 

They don't get even. 

They go for over unity! ;-)

Leather is much easier to sew with the specialised needles, which have a sharp triangular point.

CH

Damn. I once sewed 12 layers of denim with my oldest one, 1960. It struggled but got there.

NT

Did you mess up the timing of the motor by chance? The angle of the brushes makes a huge difference.

maybe? How's the motor run with no speed controller?

The brushes are sleeved and fit in only one way. About the only other 'unusual' possibility is that Eric has a Euro version - which has flat paper caps in the motor. They should be REMOVED and NOT REPLACED!

Peter WIeck Melrose Park, PA

It's only somewhat related to this, but I have a precision drill press with a real goofy looking manufacturer supplied speed controller. I called them up about something unrelated and and issue of weird bursts in speed came up. You'd have no load on the motor and it would randomly start to race.

The suggested fix was to open the speed controller and cut out a bridge rectifier that turned the AC output of the triac speed controller and just let the motor get AC.

It worked fine after that. I'm not sure why they added a bridge recitfier in the first place, or why removing it made a difference but it did. The motor is pretty similar is size to a sewing machine motor, and the standard universal motor type deal. The whole controller is cobbled together looking so I can't even tell if they added the rectifier or the OEM did.

I'm sort of tempted to try the drill press with a properly designed industrial speed controller (Dart Controls), with and without the bridge rectifier to see how it behaves.