I am moving to Poland this summer and would like to take my two HEPA air filters with me (it really helps with my breathing, especially when the air is so polluted in the region). However, they are rated for 120V at 60Hz while the only reasonably priced transformers change the voltage to ~120V, 50Hz. I am not sure what else to do because I have have severe breathing issues and even my skin reacts to something there (hard to figure out what this is). A 50 to 60Hz transformer would be more expensive than ordering a new filter from the UK (I can't seem to find these filters anywhere in Europe except on amazon.co.uk), which I would like to avoid doing.

Will a ~50W motor (120V, 60Hz) accept 120V, 50Hz power without issue, especially since this is in a fan, which ought to keep it cool?

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    That is why I plan to use a transformer to get ~120V power. The voltage is very easy to deal with. Frequence is NOT so simple (or at least cheap, anyway).
    – user39525
    Commented Jan 27, 2016 at 13:11
  • I edited the question to make this more clear. But why would I need 220V? A tranformer will drop the voltage down to 110-120V very cheaply.
    – user39525
    Commented Jan 27, 2016 at 13:13
  • @JonathanReez a transformer is a device that plugs into the 220 V wall socket and uses that electricity to provide a 120 V socket, into which a US appliance can be plugged. This allows one to power a 120 V appliance from a 220 V socket.
    – phoog
    Commented Jan 27, 2016 at 13:27
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    Isn't this a question for electronics.stackexchange.com? Commented Jan 27, 2016 at 14:27
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    @IAmJulianAcosta I suppose it has already been asked and answered there, but it is also relevant to travel and ought to be represented here, too. Thefact that the OP is moving to Poland, however, suggests that thisquestion ought to be on expatriates. An expat is more likely to have experience with this, anyway, as voltage transformers are bulky and inconvenient for travel.
    – phoog
    Commented Jan 27, 2016 at 14:36

3 Answers 3


The answer is unfortunately not as simple as stated by CMaster.

If the device contains an AC motor directly driven by the mains voltage, reducing the mains frequency will indeed cause the motor to rotate slower, but it may also overload the motor. It is difficult to easily explain the physics behind this, but basically, a motor needs a larger magnetic core to run on a lower AC frequency. If the magnetic core is not large enough, it might saturate during the AC cycle (with is longer if the frequency is lower), cause a significant current increase and finally the motor to overheat. Electrical motors are also often cooled by a fan attached to the motor shaft, so reducing the rotation speed of the motor may lead to insufficient cooling of the motor block itself.

The issue with the physical dimension of the magnetic core also applies to transformers. If the device contains a transformer designed for 60Hz, it may overload if operated on 50Hz.

Without knowing the exact design of your device, it is impossible to answer your question. If you won't risk the device to break or in worst case overheat and catch fire, your only reasonable option is the get a confirmation from the manufacturer, that the device can be safely used on 50Hz mains.

  • Although I agree with your assessment: that asking is best, I would like to say that the way UL and CE requires over engineering many devices probably work at both. Additionally the way manufacturing works it is likely that all magnetics (motors and transformers) work at both frequencies, and have wiring for both 120V and 240V (most motors are wound differently, so the voltage is less likely to be compatible than the frequency)
    – Sam
    Commented Jan 27, 2016 at 17:20
  • @Sam Hence why I will certainly have a transformer to drop the voltage, but was unsure of the frequency!
    – user39525
    Commented Jan 29, 2016 at 18:27
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    @zagadka314 Who says that the engine won't dissipate a few hundred watts more heat if connected to 50Hz mains? Commented Jan 29, 2016 at 19:17
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    @zagadka314 Please feel free to ruin your expensive equipment if it is more important for you to nitpick on my wording as a non-native English speaker. If you believe to understand the physics and know what will happen if you run an electrical motor at a lower frequency than what it was designed for, why do you ask here at all? And just to repeat what I already wrote in my answer: If the magnetic core of the motor saturates during the AC cycle, it will draw a much higher current (several times higher is not unrealistic) and hundreds of watt of extra thermal energy is a realistic problem. Commented Jan 30, 2016 at 14:31
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    @zagadka314 You are of course right that reducing the voltage will mitigate a potential overload due to lower AC frequency, but you cannot deduct a general rule from the table you are linking to. As you can see on the web page, it applies only to a few specific motor models from this manufacturer. For other models, you are referred to the engineering department for further advice. Commented Jan 30, 2016 at 22:16

Your fan, or its power supply, should have a label on it indicating the acceptable power inputs. You should find something like:

  • Input AC 120-240V 50-60Hz

This gives the range of voltages and frequencies that are acceptable. If it says "50-60Hz" then you are OK at 50Hz. (Or any other range that includes 50Hz, but other ranges will be very rare.)

If it says something like:

  • Input AC 110-130V 60Hz

then you are not OK. As a rule it will be cheaper to buy a new unit than a frequency converter. However you may be able to get an alternative power supply for the unit.


If the system is simple enough, it shouldn't be a problem. The motors will work, just spin slower. If there's more complicated electrics going on, or slowing the speed of the fan will effect the actual role of the device, then you might have bigger problems.

Edit: While this answer covers "does it run", other answers have shown that there additional (potentially safety related) concerns. Please see them.

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