Mains Voltage Adapter

[Electroenthusiast]

I bought some appliances that which work for 110v. But power supply in my place is 220v. So, there's a need a need to convert 220v to 110v.
I found that the dealer had two types of converters/adaptors.
i) Stepdown Transformer (a satellite box type).
ii) Probably a SMPS (a plug type).
The latter one, as the dealer said it only works for heater appliances - like Food Warmers, Coffee Pots, Irons, Hair Setters etc., Moreover, the transformer type was costlier than my appliance cost (for same power rating).

So i bought the 2nd type of adaptor since it suited for my application. The dealer didn't give me much information about it. He said that i can not test this type(type ii) of adaptor with multimeter. So, he didn check the adaptor, and i brought it home just like that. But back in my home, i measured the o/p voltage of the adaptor, and found that to be around 55v/60v. Connecting it to the appliance did not make the appliance work.
So, here are my questions:
1) Why SMPS type/type ii can only be used for heaters only? I had also heard abt a diode circuitry(only for resistive - i guess), which can help in convert 220 to 110, anyone with the circuit pls?
2) Why adaptor voltage can only be checked when app is connected?
Anyone from UK? because they would have undergone this.

 

[colin55]

How many watts do you want to drive?

 

[Diver300]

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.

 

[Electroenthusiast]

How many watts do you want to drive?

Exactly 420W, but my adaptor is rated for 1kW (I couldnt get a lower wattage one).

 

[Electroenthusiast]

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.

I forgot to mention that some of the dealers had only 20W/50W(and no higher wattage adaptors) plug-in adaptors. I guess that's what you are talking about, Because the dealer said that one i bought was a sort of built-in SMPS.

 

[tcmtech]

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.

 

[Electroenthusiast]

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.

250 VA for 420W ?
I checked out for transformers, they were about $25 - $30, which is impracticle for my purpose. I use it only once in a while, else i can get a new one for 220v mains at that cost.
The appliance is a 35$, and i dont wanna spend more than 10$, in that case it's more sensible to return it back.
Thnks...

 

[tcmtech]

Yep transformer set up in a voltage bucking configuration only has to carry the power of the relative input to output voltage difference.

Read up on auto transformer principals if you want to understand the how and why specifics.

The other option is to find a common universal voltage type ballast transformer for a 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?

 

[Reloadron]

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.

When I lived in Italy for a number of years I had the transformer from hell as we called it. It ran my US Refrigerator, all 18 cubic feet of it as well as all my US spec appliances. All my Italian appliances ran off the 220. The transformer was a 10 KVA unit. That thing ran the entire villa.

What I knew I had was 120 VAC, 50 Hz. and a nice sine wave. The fridge lived on the 50 Hz but the compressor would have freaked out with a modified inverter sine wave as well as some other devices.

Yes, a transformer cost more and yes, they are heavy but yes, you know exactly what you have. What I did not need was a Chinese made inverter, running in Italy to power US specification appliances.

Ron

 

[Diver300]

What is the appliance?

If the appliance is so cheap, you could just stand back and try it on 220 V.

 

[audioguru]

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.

 

[Diver300]

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.

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.

 

[audioguru]

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 are correct, I was wrong. I remembered a very cheap lamp dimmer that uses one rectifier.
The cheap adapter probably uses a simple triac circuit (like in a lamp dimmer) to make a symmetrical mess of the sine-wave:

 

[RCinFLA]

Many computer power supplies and switcher mode wall wart power supplies for chargers will run on 120v or 240 vac. There are adaptors that are just plug to socket changers that allow a two spade prong 120v plug to be connected to the European 220 vac. You get direct connect so what you plug in gets 240 vac. You have to be careful on their use to be sure what you plug in can take 240 vac. Again, these are fine for a laptop power supply that works on 240v or 120 vac. The primary determiner is the voltage rating of their power supply's filter electrolytic caps after the input rectifiers. How do you tell, first look at the label for input voltage. If it is relatively large and heavy it is an old power transformer based wall wart and will not work. If it is relatively thin and light it is likely a switch mode power supply and will likely take the 240vac. But check the label to be sure. The old transformer based wall warts actually cost more to manufacturer these days then a switch-mode power supply so you rarely see the transformer based wall warts supplied with new equipment.

Next level is the triac based power converter. As shown in Audioguru diagram they trigger at a partial point on the sinewave where the voltage is lower. Not all devices like these converters. An AC syncronous motor like a refrig compressor would not like these converters. An electric motor with brushes, like an electric drill, hair drier blower, will work with these converters. Heating devices are okay with the choppy waveform. They can also create RF interference to radio/TV equipment. They need a minimum load to cause the triac to conduct and latch on. Once the triac is triggered on, the triac is latched on and turns off at zero current crossing. This is why you cannot just measure open circuit, unloaded voltage with a high impedance DVM. Even with a load you need a true RMS meter. Most inexpensive DVM are AC averaging which will give an incorrect reading of the non-sinusoid shaped waveform. All triac have about 1.5 to 1.8 volt of drop across the triac. If you draw a heavy load like a hair drier they can get very hot. A 10 amp hair drier times 1.5 v triac voltage drop produces up to 15 watts of heat to dissipate by triac. This is quite a bit of heat for a small packaged converter to dissipate to surrounding air.

The last is the power transformer. Relatively small wall wart sized transformer are only good for 10 to 20 watts which is good enough to run an electric razor or charge a phone. You can get bigger and bigger transformers, for higher and higher cost, that will handle whatever wattage (actual VA) you want. A 2 kVA auto-transformer will cost you several hundred dollars and weighs about 25 lbs. An auto-transformer wiring configuration allows a transformer size of half the size of a full isolation transformer.

 

[4pyros]

ii) Probably a SMPS (a plug type).

You got a 1K watt power inverter for less than $10? No wounder it did not work.

 

[Electroenthusiast]

Yep transformer set up in a voltage bucking configuration only has to carry the power of the relative input to output voltage difference.

....
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?

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.

The second type using ballast transformer seems to be nice.

What is the appliance?

If the appliance is so cheap, you could just stand back and try it on 220 V.

An Hair Stiffener(/whatever you call it) from US, rated for 110V/420W. Usually gets heated up in 30s. And used to work well there.

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.

hi Ron,
bit confusing, in my understanding adaptor = converter. But, in what way are they diff in your case?

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.

Yes AG. Maybe thats why i couldn measure the voltage. I hope it did nothing to the appliance. Hope it works back well when it is connected to 110v.

Many computer power supplies and switcher mode wall wart
.....
transformer.

Nice info RCinFLA

You got a 1K watt power inverter for less than $10? No wounder it did not work.

I'm not sure what it is. But, the dealer said it's SMPS, and i also confirmed it with another dealer too.

 

[Electroenthusiast]

I'm waiting for the REPLY...

 

[Reloadron]

I'm waiting for the REPLY...

What would you still like to know? We pretty much covered the subject.

hi Ron,
bit confusing, in my understanding adaptor = converter. But, in what way are they diff in your case?

The point I was making is that different manufacturers use different terms. That when shopping for a solution make sure the device selected will do the job needed and pay attention to output wave shape. If you require a sine wave make sure you get a transformer.

Ron

 

[Electroenthusiast]

What would you still like to know? We pretty much covered the subject.

Ron

Ya.. but was waiting for answer for this:

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.

 

[tcmtech]

Google is your all knowing friend.

What do you need me to explain?