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Best way to go from AC to DC motor in a sewing machine? Answered

So my wife's sewing machine motor died recently and it costs 115 dollars to fix it which is just about the cost of the machine.  I have a 12V, 100W scooter motor that I can adapt to the machine pretty easily.  The problem is that the old motor was AC.  The machine has some nice features so I wanted to run the DC motor with the AC that the machine outputs.  My plan was to use a full bridge rectifier on the AC output and then a simple voltage divider to get the max voltage to 12V.  What I am wondering is if this will work.  I know normally you would use PWM but then things are more complicated.  Will the 120 Hz ripple affect the motor?  Will my method put a lot of strain on the DC motor?  Will this even work?  Thanks.



Best Answer 8 years ago

There only seems to be one firm in the world makes sewing machine motors. When Lizzyastro's machine died, we bought a new motor on ebay for 20 USD, stripped it, and dropped it back into the old case. Job done.

Using a voltage divider just won't work.

If you HAD to do it, you would put the nearly 120 volts into a 120V/12V transformer, then a rectifier. I'd probably still put some capacity in there, but not too much or you will end up overrunning the motor, and someone will curse you.

Doug Paradis

8 years ago

The first question would be is the scooter motor suitable to run the sewing machine? Is its rated horsepower and speed similar to the old motor? Some
motors obtain horsepower by running at very high RPMs. How did the foot pedal
of the sewing machine control the motor speed? Would your conversion be
compatible with the foot petal?

If you want to keep the machine, the best solution might be to search for
an old beater sewing machine on craigslist or at a thrift shop and strip off the motor. If you are lucky you might find a machine superior to the one you have now.


8 years ago

Really it should be fine to feed it rectified bouncy dc. Really its best to rectify and smooth, then run pwm, but if thats too complicated it should work. The reason its hard on the motor is because you're not running the motor at its rated voltage for a majority of the time, this is when you get less bang for your buck. PWM is better because it delivers 100% voltage 100% of the on time.