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In my country we have 220V system. I have a fan that is rated 220V 80W with 3 speeds, but even the lower speed is too fast and noisy. Since a fan is basically a simple AC motor I figured I could reduce the voltage in order to make it slower.

So I connected an old 220-110V 50W adaptor and so far (30 minutes) it works and at max speed it runs very silently and efficiently. The adaptor which I'm monitoring very closely is running at ambient temperature.

My question is: am I doing it wrong? is there any danger? Thanks.

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  • Possibly. Is the fan motor running excessively hot? Jan 10, 2018 at 21:45
  • I disconnected the adaptor. It started to run hot. The fan was OK.
    – Danita
    Jan 10, 2018 at 21:45
  • Going to a lower frequency could be a problem depending if it is a shaded pole motor, the frequencys are not listed.
    – Ed Beal
    Jan 11, 2018 at 3:12
  • generally ok. you should start it on high to reduce long current spikes.
    – dandavis
    Jan 11, 2018 at 4:33

1 Answer 1

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There are a few different types of voltage adapters, some of which are probably safe, and others will destroy the fan because the output contains a DC component. Check which type you are using.

  • Transformer: Transformers produce a pure sine-wave (other than esoteric Sola- type constant voltage transformers) AC output which is unlikely to damage the fan unless the fan stalls and overheats due to lack of air circulation. Since the rating of your adapter is 50 W, it is probably a transformer. Check also that the fan does not draw more than 2 A maximum, or it would exceed the capability of the transformer.
  • Diode: For resistive devices such as clothes irons, some adapters contain just a silicon diode. The output is pulsating DC, which is likely to destroy the fan or even cause a fire.
  • Thyristor: Triac and SCR devices do not really reduce voltage but slice the AC waveform into smaller pieces. Some are designed specifically for use with small shaded pole motors, as used in most ceiling fans. A danger with some controls not intended for use with motors is that the "chopped" waveform may not be equally balanced and have a DC component, with possibility of slow overheating, not immediately apparent, so perhaps a greater danger.
  • Series inductor: It is possible to use a simple inductor or "choke" to slow a fan, which should be safe, but the value of the inductor would depend on the current draw of the fan.
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  • what kind of voltage adapter would just use a diode?
    – dandavis
    Jan 11, 2018 at 5:56
  • I can confirm the 220-110 adapter is a transformer.
    – Danita
    Jan 11, 2018 at 11:20
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    @dandavis, Cheap adapters for running 120 VAC devices such as travel irons used a single series diode to reduce the average voltage to a bit less than half. These adapters would destroy transformers in radios and other devices, possibly setting them on fire. See electronics-tutorials.ws/diode/diode_5.html for details. Jan 11, 2018 at 16:33

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