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Can I use a DC foot pedal on an AC machine? Answered

I have an ancient Pfaff (German) sewing machine. The original foot pedal died in a plume of smoke. I bought a replacement electronic pedal and didn't notice that it says 200-240v. Oops! I'm in the US, so the machine has been running on AC. Will a European foot pedal work on it? The machine (from the back) plugs into an outlet in the wall. A separate cord (on the side) goes from the machine to the foot pedal. Modern machines usually use the same machine connection for both the power and the foot control.

If I try it on the AC machine, will I damage the machine? Aside from the motor, this is a strictly mechanical machine.



Best Answer 7 months ago

Germany of course also uses AC ;)
The elctronic ones should be just a simple regulator but the problem might be the power.
At just 120V your machine uses a motor that requires a few more in Amps, or milli Amperes.
Check the power rating of machine and the new foot pedal.
If the pedal can supply more Ampere (A) than what the machine needs it should still work.
You might have problems at low speeds and high work lods, like when doing thick materials.
In case it won't work or not good enough you can always try one of these:

If in doubt replace the plug for the machine or the entire cable with what you have from the broken one ;)


Answer 7 months ago

I tried it on a 1959 Signature. It works. There is a lot of humming in the 60 yr old motor, but that may be the motor's problem. I'll try it on the Pfaff next. Thanks so much for your input, downunder35m! Doing this stuff - with pretty much zero background - is intimidating. It helps to have someone to ask about it.


Reply 7 months ago

The humming might be result of the electronics.
A brushed motor does not like it if the AC is "chopped".
If the results are far better on a modern machine then I suggest to either get a suitable replacement motor or matching foot pedal.
Otherwise the humming motor might overheat under load.


Answer 7 months ago

Thank you, downunder35m! I looked at the bottom of the machine.
a-c / d-c
....................another area says: 55/28w
4700 min
I assume w = watts, but I don't know what 25-60c is.
Oh, and the machine says "made in Germany" Not 'West Germany". So it may have been made pre WWII.


Answer 7 months ago

Can you provide some images of the dead pedal?
I would say the replacement should be fine unless the machine would really require DC from the pedal.
Have not seen a Singer that requires this.

Jack A Lopez

7 months ago

At the risk of saying what others have said before...

A sewing machine motor is almost always a universal motor (UM), so it can run on AC or DC. Technically the choice is up to the machine designer, but almost every electric sewing machine out there runs on AC mains; i.e. plug it into the wall.

Strange that there is not an abundance of battery powered, rechargeable, sewing machines, like there is for other electric power tools, like drills, saws, etc.

Getting back to the motor, a universal motor is made to run at different speeds is by changing the voltage placed across it, voltage as measured in an RMS (root mean square) sense.

Moreover, there are a handful of different methods for limiting RMS voltage to the motor, for to make it run more slowly.

One way, an old way, is by putting a variable resistor (sometimes called "rheostat") in series with the motor. The old style style sewing machine pedal is essentially this, a resistor whose value decreases in proportion to how hard it is being stepped on. When not being stepped on, ideally it should be an open circuit; i.e. close to infinite resistance, so the motor stops completely.

One intrinsic, unavoidable problem with the use-a-resistor-to-decrease-voltage game, is the resistor necessary dissipates power. So it both wastes energy, and tends to make itself hot, or at least warm.

Another, newer way to limit voltage to a motor, is to use semiconductor switches, like a TRIAC, or MOSFET, to switch voltage to the motor, on and off very quickly, so a lower time-averaged voltage, or lower RMS voltage, results.

The advantages of these semiconductor based motor control solutions are numerous: smaller size, less energy wasted as heat, more reliable, cheaper, etc.

The only disadvantage is complexity. The resulting circuit is something too complex for most users to grok. But if he or she did not grok the old way (variable resistor) either, then it is not a big deal, especially if the new way is cheaper, and as reliable, or more reliable than before.

I found a page that shows us some pictures of an old, variable resistor, rheostat, style sewing machine pedal, side by side with one of the new TRIAC based ones, here:


Confusingly, this author uses the words "electric" and "electronic" to name these old and new style, respectively. Or maybe that is only confusing to me, because to me the words "electric" and "electronic" are almost the same word. Does the suffix, "-onic" imply newness or modernness? I dunno. I think I would call them rheostat vs TRIAC, or rheostat vs semiconductors, or similar language.

The final thing I was going to mention, is whether it is a resistor made of stacked carbon discs, or if it is a snappy little semiconductor, it is always wired in series with the motor.

Obvious, right? Maybe that is why when I looked all over, I only found one page, so far, authored by a sewing machine user who likes to draw circuit diagrams. No one else bothers with this, I guess because it is just so obvious.


And looking at those diagrams is very satisfying to me, because there is that symbol for a variable resistor, called "controller" by that author, always in series with the motor, and also in series with the plug to the AC mains.

Those diagrams are just so pithy, I am going to attach a copy of them to this post. I hope they post OK, since they're PNGs, and the Instructables editor prefers JPGs. If they get their pixels mangled, obviously the solution is to go view them on the original page where I got them from, linked above.