How many watts do you want to drive?
It is all to do with waveform. Mains voltages waveforms are sinewaves, and all appliances will run if the waveform is sinusoidal. Transformers change the voltage but keep the waveform the same, so all appliances will work through a transformer if the voltage is correct.
However transformers are big and expensive, and lots of appliances will work on non-sinusoidal waveform. Heaters will work with any waveform. The makers of the plug-in adaptor have used that to make a circuit that switches the power on and off, so that the RMS output voltage is about right. However it might not even be a symmetrical waveform, so there might be a large DC voltage on the output. A transformer connected to the output of an adaptor like that won't work.
The output voltage of an adaptor like that might well be nearly 220 V with no load, for several reasons. Either the switching device needs some load to work, or there is an alternative current path that bypasses the switch, but cannot provide much current, like a high value resistor or a capacitor.
The most important reason why you can't measure the voltage without an appliance connected is that you need a true RMS voltmeter to measure the voltage whether or not there is an appliance connected. Cheap voltameters do not give the true RMS voltage of non-sinusoidal waveforms.
If you're going to ask us what the solution is in the UK, it would be nice to know which country you are from.
It might also help to tell us what appliance you are trying to run, as that could help with a solution. Different types of power supplies react very differently to non-sinusoidal waveforms.
250 VA for 420W ?If it was me I would just use a common 250 VA power transformer with a 120/240:xx winding setup. You can find lots of them on line for a few tens of dollars or less price wise.
Just use the 120/240 primary windings in a center tapped autotransformer configuration to get the proper voltage. The transformer only has half the working load to deal with this way so it can be smaller and cheaper.
I think the cheap and simple adapter is simply one rectifier diode. It passes 220V half the time to a heater so the heater gets an average of 110V.
Many products will blow up if you use it.
You are correct, I was wrong. I remembered a very cheap lamp dimmer that uses one rectifier.Wouldn't that still give twice the power that the 110 V device would produce on 110 V? Twice the voltage would give 4 times the power, so twice the voltage for half the time would give you twice the power.
You got a 1K watt power inverter for less than $10? No wounder it did not work.ii) Probably a SMPS (a plug type).
Yep transformer set up in a voltage bucking configuration only has to carry the power of the relative input to output voltage difference.
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metal halide, mercury vapor, or high pressure sodium lamp. They have power taps on the primary windings for 277, 240, 208, and 120 volts and make excellent buck boost auto transformers! You can probably get a used one, or possibly several of them, from a local electrical shop that services street and parking lot lights for next to nothing.
Otherwise the only fix for being a cheap ass is spending money, spending time learning, or spending time scavenging.
What exactly are you powering anyway?
What is the appliance?
If the appliance is so cheap, you could just stand back and try it on 220 V.
The problem with things like this is that a simple Google of 240 Volt to 120 Volt starts by bring up: 240 Volt to 120 Volt Adapter, 240 Volt to 120 Volt Converter and finally 240 Volt to 120 Volt Transformer. The naming conventions can get confusing and many times I have seen what they call Transformer to be an inverter.
I think the cheap and simple adapter is simply one rectifier diode. It passes 220V half the time to a heater so the heater gets an average of 110V.
Many products will blow up if you use it.
Nice info RCinFLAMany computer power supplies and switcher mode wall wart
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transformer.
You got a 1K watt power inverter for less than $10? No wounder it did not work.
I'm waiting for the REPLY...
hi Ron,
bit confusing, in my understanding adaptor = converter. But, in what way are they diff in your case?
What would you still like to know? We pretty much covered the subject.
Ron
Hi tcmtech, thanks for the answer. I really didn understand the diff b/w a transformer and auto transformer, for this application. I can well use a transformer, what advantage will i have if i use auto transformer? i know it is used to decrease the max kV of the output. But i can do that even using a transformer with 1:1 turns ratio.
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