I have a situation which I'm not sure how to handle. I've purchased an appliance from US. This appliance is powered by electric motor (175W) and then I realized I cannot use simple step-down converter because they usually convert 220v 50hz to 110v 50hz, but in electric motors the frequency matters. Of course, such voltage/frequency converters exist, but they usually in kW range industrial grade converters with price tag ten fold of the price of the appliance. So, I'm thinking about taking 220v 50Hz AC to 12v DC converter and connecting it to 12v DC to 110v 60Hz converter, like pure sine or something. Does it make sense? Would it work? is there any better solution which wouldnt break a bank?
In case my solution is good to go, how to calculate the wattage of each of parts I will use? For example, 175W it is nominal power draw of the motor, but it has spikes, so I guess, 300W output will be ok, maybe 350W. Then what wattage AC to DC I have to use for the DC to AC converter to produce 350W output given the power efficiency is not 100%?

EDIT001: The appliance is WorkSharp Ken Onion Edition Knife & Tool Sharpener, hope it helps

  • \$\begingroup\$ That would work, sure, but 110V 50Hz will almost certainly also work, and be much cheaper, unless the appliance is particularly sensitive to speed. \$\endgroup\$
    – Hearth
    Jan 18, 2019 at 16:10
  • \$\begingroup\$ I dont understand what damage could be caused to the motor once it powered by 50hz instead of 60hz. Sure it will affect speed, but lower speed would (wouldnt?) affect current in the motor? Huh maybe Im just trying to solve a problem which is not really a problem? \$\endgroup\$ Jan 18, 2019 at 16:15
  • \$\begingroup\$ The lower speed may lead to higher current in the motor, yes. But I doubt that will be a major problem; it may shorten the lifespan of the appliance or cause it to heat up a bit more as it operates, but I wouldn't feel unsafe using it. I may be wrong on this, though--it depends on a number of factors, and I could just be completely wrong, too. \$\endgroup\$
    – Hearth
    Jan 18, 2019 at 16:17
  • \$\begingroup\$ well, I will be happy to find out that I can just use a simple step down, but lets wait and see what others have to say :) \$\endgroup\$ Jan 18, 2019 at 16:19
  • 2
    \$\begingroup\$ but in electric motors the frequency matters It depends on what type of motor is used. Also, the appliance might still "just work". If it would be a (mechanical) clock which uses 60 Hz as its timebase, sure then at 50 Hz it will be useless. A lawnmower might simply run a bit slower at 50 Hz. Yes converters exist but the device must be a really special one if you can justify a voltage+frequency converter for it. \$\endgroup\$ Jan 18, 2019 at 16:23

3 Answers 3


It depends totally on your appliance motor.
If the motor is a universal motor (it has brushes), then the frequency is much less important. In this case a simple 220/120 transformer will work just fine providing it can support 2A at 120V.

If the motor is a 60Hz AC synchronous variety you will lower both the speed of the appliance motor and increase the losses in the motor (so it gets hotter).

Since you gave no idea of the appliance or motor type it's hard to judge what might be the effects of a lower operating frequency.


Since you now have given more information, I would suggest that the frequency (50 or 60Hz) will have ABSOLUTELY NO impact on the tool.
The manual shows that this is a speed adjustable application. These types of motors are almost always a 'universal' brushed motor with a phase controlled speed adjustment.
Today we start to see BLDC motors used in some tools, but this does not appear to be one of those (they have an SMPS power supply).
As I said, IMO all you need is a 220/120 voltage convertor and your tool will work fine.

I would recommend that you buy a voltage convertor that clearly supports your 175W load (though I didn't see this power rating in the manual). Don't buy a 'travel adapter' as many are based on an autotransformer and can be very hit an miss in terms of reliability.
Something like this is ideal. No bells and whistles and clearly just a transformer (though this one is an autotransformer it's ideal for double insulated tools).

enter image description here

  • \$\begingroup\$ since I have no idea of the motor type. the appliance is WorkSharp Ken Onion Edition Knife & Tool Sharpener \$\endgroup\$ Jan 18, 2019 at 18:18
  • \$\begingroup\$ indeed the manual does not mention power rating, but it written on the tool, 115V 1.5A. Thank you, will use one of these simple step downs. \$\endgroup\$ Jan 19, 2019 at 9:33

Since excitation current depends on V/f ratio and inductive impedance, you must consider the 60/50 ratio of higher excitation current of running it at 50 Hz when trying to match the 120V 60Hz rating for no-load excitation current.

If you wanted the same RPM, then you need a 120V 60Hz inverter.

If you just wanted to use a transformer at same power capacity and slower RPM , then you can either use 50/60 * 120V = 100V for same excitation current and full rated power of the motor P=V * I = Torque * RPM

Since the current is the same for no load at lower RPM but same V/f ratio your more torque can increase but less RPM yet same "product" = Power

If you use 110V or 120V @ 50Hz then excitation current increases. ( higher V/f) and may risk overheating if you applied the rated torque at a higher V/f ratio than expected.

It might be cheaper to just change the motor and anything else voltage dependent or replace the appliance.

If it is a vacuum motor then consider replacing the motor at a repair shop. Might be $25 plus labour or DIY online purchase $15.


Chances are about 99.9% that this is a "Universal" motor, the same kind found in most portable power tools and small appliances. It will care about voltage, but not frequency because internally the motor converts the AC to DC and is technically a DC motor.


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