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Registered Member #1641
Joined: Sun Aug 17 2008, 09:46PM
Location: Wimbledon, UK
Posts: 11
Hey all.
I have a heater for a project I am working on which is rated at 250W, 110V.
However, here in the UK, mains voltage is 110V. A 250W transformer is above my budget, so I am looking for other means of reducing the voltage.
My idea is to use a 240V, 400W dimmer switch. I will turn down the voltage until my (slow sampling) multimeter reads an average of 110V. Problem solved?
Obviously this wouldn't work for a computer/microchip, but is it OK for a heater?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Resistive heaters should be ok using a 'dimmer'
You could also use a 125 VA transformer that has two 120 Vac primaries in series and use it as an autotransformer (leave the secondaries un-connected) i.e. 2 x 120 Vac primaries in series, 240 Vac across both windings, 120 Vac from neutral to center-tap
Registered Member #347
Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106
Make sure you use a true RMS reading multimeter when setting the voltage. Cheap meters take an average of the rectified voltage, which is not an accurate measurement with highly distorted waveshapes like your dimmer will be providing. This would cause you to set a voltage that's too high, and you may damage the heater.
If you must use a non true RMS multimeter, you'll need to calculate what voltage to set on the dimmer's output to compensate for the inaccurate measurement. This voltage will be somewhat below 110V
Registered Member #151
Joined: Sun Feb 12 2006, 02:53PM
Location: Poland
Posts: 153
Many of transformers has primary winding divided (center tap), so if you don't need electrical insulation you don't need 230->115 transformer. You can simply find any 230V transformer that has divided primary and suitable power, no matter what secondaries it has, and use it as autotransformer.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
I would not recommend using a dimmer module because the phase angle control that it applies does not actually decrease the peak voltage!
If you run a 110V appliance off a "dimmed" 230VAC outlet you will still likely exceed the peak voltage level that the appliance was designed to safely operate from!
A 400W 240V dimmer would also likely overheat driving a 250W 110V load. This is because 250W at 110V represents more than twice the load current that 250W at 230V would do.
Registered Member #1641
Joined: Sun Aug 17 2008, 09:46PM
Location: Wimbledon, UK
Posts: 11
I think I'll stick with the dimmer switch. It is very small and compact, and means I can turn down the voltage to make it a variable heater. I will set it by making the input just over 1A - that will equal a power output of around 250W.
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Making 110V out of 240V
