# Frequency of AC for electronic devices

I was wondering why using different AC frequency makes some devises not working.

I found that I do not need to adjust frequency for using electric heat or electromagnetic wave such as ・rice cooker ・toaster ・stove ・light bulb ・TV ・radio

And for these appliance, I do not need to change the frequency but it will behave differently under different frequency. They are using motor. ・vacuum cleaner ・food processor ・fan ・fridge

For these appliance, I need to convert frequency. ・washing machine ・clothes dryer ・video tape recorder ・fluorescent light ・clock ・microwave oven

The thing I felt strange is that washing machine and clothes dryer also uses motor. Although, they cannot be used in wrong frequency. In electronic devises, why frequency matters? Is it related to clock frequency? And why there is a motor device that can be and can't be used in different frequency?

• All modern washing machines I’ve taken apart have VFD so they can be fed with 50-60 Hz without issues. – winny Feb 23 '19 at 8:00

Frequency matters if any of the following are true:

• If there is a synchronous or induction motor in the device. These run at or close to mains frequency so they will run 20% faster on 60 Hz than on 50 Hz. This includes motor driven mains clocks.
• If there is a transformer in the device it may be only rated for 60 Hz. 50 Hz transformers are slightly heavier and have different laminations.

A 60 Hz rated transformer can only be used on a 60 Hz system (with certain exceptions -- read further.) Whereas a 50 or 50/60 Hz rated transformer can be used on either a 50 or a 60 Hz rated system. Exception: If the energizing voltage does not exceed 83% of the transformers nominal voltage, the transformer can be used. Remember that transformers are simple ratio devices and the output will also be lower. Another important factor to remember is that the transformer`s capacity will also have to be derated at the same ratio of the applied voltage divided by the nominal voltage. Source: Schneider Electric.

Devices affected include microwave ovens and devices with larger transformers such as hi-fi systems, etc.

• If an electronic device uses the mains frequency for timing such as a digital clock or an old TV.
• If the device uses in-line inductors such as the ballasts on AC fluorescent tubes (as opposed to high-frequency driven) the impedance will vary. $$\ Z = 2 \pi f L \$$ where Z is the impedance and L is the inductance.
• If the device uses a rectified DC supply the smoothing capacitors have to be larger for 50 Hz supplies as the capacitor "top-up" pulses are less frequent.

• Universal motors don't care.
• Devices with variable frequency drives convert the mains to DC before chopping it back to AC. These don't care.
• Most electronic devices are DC internally so provided the PSU is 50 / 60 Hz capable there is no problem with them.

The answer probably depends on the specific appliance, but in general many appliances use the AC mains frequency to control their clocks. So in the case of the microwave oven (and the clock, of course!) that is probably the reason. Fluorescent lights typically include sophisticated switch-mode power supplies to generate the high voltage for the light; I would speculate that these are designed for a specific AC mains frequency. For other appliances, perhaps they are relying upon a specific motor speed (as determined by the AC mains frequency) and will not operate if they do not achieve that specific motor speed. But that's just a guess on my part.

In a past job I designed a home appliance that was sold into both the U.S. and European market, so we designed it to detect the AC mains frequency and adjust itself accordingly. I'm surprised more appliance manufacturers aren't doing this.