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johnt · Joined: 08 May 2008 Posts: 4 Location: UK

Hi. I have an electric desk fan that is too powerful on its low power setting.

I'd like to buy a box to reduce the mains voltage further still, in effect to create a dimmer switch so that I can turn a dial to get the fan blowing as little as possible. Is this possible? It's quite a small fan rated at 23W 230V, so it should behave like a light bulb if connected to a dimmer right?

Thanks, J

AlanE · Posted: Fri May 09, 2008 1:48 pm Post subject:

johnt · Joined: 08 May 2008 Posts: 4 Location: UK

Yes, you're right. Have a look at the detailed response halfway down this page, which I just found [url]http://forums.dealmac.com/read.php?6,2575455[/url]

So, do you have any other suggestions?

Thank you, J

AlanE · Posted: Fri May 09, 2008 7:34 pm Post subject:

I would think the only way would be to reduce the input voltage somewhat, but NOT too much, because of the inherent risk of either not starting which would then cause motor to burn out.

What you need is a variac which is a variable transformer. You could then reduce the voltage, but preserving the mains waveform, and see the effect.

Some fans have resistors in them which is ok but you will need to ascertain resistor value using variac first.

The principal behind using lower voltage is simply whilst the motor tries to reach its design speed because of the lower power applied, and the resistance to the motor turning due to the fan, motor effectivly runs slower.

johnt · Joined: 08 May 2008 Posts: 4 Location: UK

Right - thanks. So it could conceivably be tried with a UK - US 110 V adapter, and if the motor doesn't turn then switch off asap presumably?

AlanE · Posted: Sun May 11, 2008 9:36 am Post subject:

If I get a chance later today I will see what effect running the fan I have at 110Volts.

I'll also let you know approx voltage that fan will start at.

johnt · Joined: 08 May 2008 Posts: 4 Location: UK

OK, so I bought a UK -> US 110V AC step down converter rated at 45W from [url]http://www.beststuff.co.uk/mw_mw2p045_voltage_convertor.htm[/url] - £7 cheaper than maplin and free delivery too.

My 23W fan starts up, is obviously performing about 10% of what it would do at 230V, is whisper quiet, and blows just enough air under my laptop to keep it cool. I've raised the laptop off the desk with a few short mugs. It might be nice to have a bit more power, I reckon 140 V would be ideal, but I don't know what the voltage/current curve looks like.