220V to 110V adapter without transformer?

Most 220V to 110V travel adapter use a transformer, making it very heavy. Is there something that is transformerless? Perhaps some sort of switching
circuit?
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peter wrote:

What do you want to power? There are lightweight "hi power" travel adapters - which just have a rectifier and a fuse inside. They are suitable for a lot of 110v kit, eg electric frypans, waffle makers, etc.
If what you are powering is an external power supply, it is often lighter (and cheaper) to replace it with an 110v equivalent.
One thing to consider is to travel with a 12v inverter, which can produce mains voltage from a car socket. You could add a lightweight 12v SMPSU to suit. Thus giving you a few hundred watts of the appropriate mains voltage, wherever you are.
-- Sue
-- Sue
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Unfortunately, that doesn't work. Usually it will result in some combination of smoke, sparks, and a bang;-) If you take 240V RMS and half-wave rectify it, you will end up with an RMS voltage of 240/sqrt(2) = 170V. This will run a 120V appliance at exactly twice it's power rating, and whilst overloading it in this way, also stress its insulation to twice its design voltage.
To get the power rating right, you would need to half-wave rectify and then let only alternate pulses through by some other means. You still have the peak voltage problem, and a peak current which is 4 times the design rating.
I built a switcher to solve this problem some years back. I use a pair of MOSFETs to switch the mains. What I do is switch off during the middle portion of each positive and negative going cycle. (IIRC, the switching angle is 43/137 degrees to produce 120V RMS from a 240V RMS sine wave, but that's actually quite a bastard to work out with integral calculas, although going the other way is easy.)
This has a number of benefits. The higher voltage part of the sine wave is removed, reducing the excess stress on the insulation of the 120V product (although it's still higher than when running on 120V RMS sine wave). It also keeps the instantaneous peak current as low as possible, although the power factor will only be 0.5. It also draws power only from the portion of the sine wave which is under- utilised by the very many power supplies which only draw current near the peaks, so although it generates a nasty harmonic current, it's cancelling out the nasty harmonic currents most other loads generate!
In my case, this runs a 1050W 120V frying pan on 240V mains, and is a big improvement over the transformer which we used to lug around.
--
Andrew Gabriel
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Andrew Gabriel wrote:

Erm, IME, it works rather well - I've got a US waffle iron in the kitchen that has run for well over 10 years on an adapter that consists solely of a power rectifier in a box (I opened the box to see what was inside, out of curiosity..).
Of course I don't make waffles all that often ;)
I did modify things a little by running an earth wire to the metal case of the thing. As supplied, it was two pin.
I'd replace it with a UK one, if I could find one that made such large waffles. It heats up quickly, too. ;)
Doubtless, in time, the thermostat contacts will burn out, or the element fail.

Yep, I'm not disputing any of that. But all that is in this particular "hi power travel adapter" is a rectifier. I even checked its part number to make sure that is wasn't something special.
I'd assumed that all these "hi power" adapters had the same arrangement. However, I have only opened this one to see.
-- Sue
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peter wrote:

They're a triac light dimmer circuit with a fixed, they work only for resistive loads.
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What travel appliance does not work on both 110 V and 220 V? Anything intended for travel should operate on any voltage from 90 to 265 VAC.
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That is the current norm in modern switcher manufacturing practice.
Also, I would add that most auto switch through that entire range just fine. In the past, one would have to set a switch depending on the region.
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I had a AA charger that says 110 to 240 V. It works perfectly in the USA. Last time I traveled to a 220V country, the charger overheated and the plastic shell started to warp. The batteries were damaged -- their plastic covers peeled off. Good thing I noticed it before it did more damage. Amazingly, it still worked when I bring it back to the USA.
Even though it was out of warranty, I asked the manufacturer to replace it, and they did. Since then I am afraid to plug anything bought in USA into 220V, even if it says 110-220V. Admittedly, that charger was not a very well known brand.
This time I'm bringing a panasonic camera (usa version) to europe. The charger also says 110 to 220V. I suppose it should be safe to use, and I don't want to carry a 50W 220V to 110V transformer. But if there is a light weight device to step down 220V to 110V, I would feel safer using it. Maybe I can also bring my scary AA charger for other use...
BTW, the high wattage voltage reducer all say "resistor network" in their product descriptions, but people responding to this thread say they use diodes, which make sense. Could it contain a diode and a resistor? Light dimmer (triac) also sounds feasible, but it would produce spikey waveform, probably not suitable for transformer use.
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I use a Panasonic camera battery charger (supplied with the camera) regularly here on 235v. I've never had overheating problems - and it worked on 110v in the USA last summer.
--
From KT24 - in "Leafy Surrey"

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charles wrote:

Modern stuff with switchmode power supplies is usually designed to cover the full range from 120 to 240V. This wasn't nearly as easy to do with magnetic transformers common in the past.
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wrote:

Most modern switchers work from about 85V up to 265V. Most run easily down to 90V, and that is the goal since Japan uses 90 Volt system, AND the end of the line voltages can be lower than that.
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On Sat, 14 Jun 2008 16:02:24 -0700 ItsASecretDummy
| wrote: | |> |>charles wrote:
|>> |>>> This time I'm bringing a panasonic camera (usa version) to europe. The |>>> charger also says 110 to 220V. I suppose it should be safe to use, |>> |>> I use a Panasonic camera battery charger (supplied with the camera) |>> regularly here on 235v. I've never had overheating problems - and it |>> worked on 110v in the USA last summer. |>> |> |> |>Modern stuff with switchmode power supplies is usually designed to cover |>the full range from 120 to 240V. This wasn't nearly as easy to do with |>magnetic transformers common in the past. | | | Most modern switchers work from about 85V up to 265V. Most run easily | down to 90V, and that is the goal since Japan uses 90 Volt system, AND | the end of the line voltages can be lower than that.
Japan uses 100 volts. End if the line can be 90 volts.
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I used a Sanyo automatic 120/240 VAC NiMH charger in the UK recently with no problems. Cheers, Roger
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----------------------------
wrote:

I used a Sanyo automatic 120/240 VAC NiMH charger in the UK recently with no problems. Cheers, Roger
I have used a Panasonic 120/240 NiMH battery charger on 240V (New Zealand ) with no problems. I took it to Italy as well.
--

Don Kelly snipped-for-privacy@shawcross.ca
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