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I've noticed this "feature" on a number of travel-oriented voltage converters - they either are meant to be used for small 50W loads, OR for larger loads up to 1600W. But you can't run a small load on the higher setting.

Here's an example of one which requires you to switch between the two:

enter image description here

Here's another which reads:

"1600 Watt Output for Personal Appliances or 50 Watt Output for Small Electronics"

I can imagine that the switch is physically engaging one of two coils, perhaps. But ... why? If it were left on the 1600W setting and someone powered a 50W item in that configuration, what problem would that cause? How do these devices actually work such that this design is important?

StayOnTarget
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2 Answers2

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There are two options- an autotransformer and a triac phase control with a fixed setting to yield the correct RMS voltage for appliances such as hair dryers which are more-or-less resistive loads.

The autotransformer is a 60Hz type similar to this one from B&H Photo in NYC:

enter image description here

It may seem small for 50W but that's because it's an autotransformer (meaning it really only has to deliver 25W) and also it's pretty crappy- it will run warm.

The 1600W portion looks like the below (my own photo)

enter image description here

This is the internal circuit of an ordinary phase control dimmer used for incandescent bulbs with the knob and pot replaced by a fixed resistor (maybe) and trimpot. This is a particularly horrible construction and is not only unreliable but likely rather dangerous- The springiness in the leads is what keeps the triac in dubious contact with the silicone insulator and heatsink.

Here is the curve of RMS voltage vs. conduction angle from here: As you can see, the conduction angle has to be ~65° and therefore peak voltage will be around 300V for a 230VAC mains vs. about 168V for a 120VAC mains.

enter image description here

If you run a 120V-only electronic device on the 1600W setting it could well be destroyed because it will see peak voltages well in excess of the rating.

There is very little need for either of these in 2021. You can buy compact travel dual voltage hair dryers and most electronics that would use the 50W setting is already universal voltage and only requires a plug adapter. I also would not want to try my luck with the hair dryer setting on a $500 CAD Dyson hair dryer.

Spehro Pefhany
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    Is the aposematic orange on that heatsink to remind the user that it is not earthed, so you got to unplug the device without touching it? – bobflux Nov 03 '21 at 20:18
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    @bobflux It was purchased for me about 15 years ago by an associate from a surplus place (Active in Toronto for those who remember the Queen Street Gorilla) as a fine example of utter disregard for safety and reliability. Most of the adapter things are unapproved and many are a bit dangerous (missing grounds being common). This one takes the cake though. – Spehro Pefhany Nov 04 '21 at 01:25
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    That has to be the sketchiest mounting I have seen on a mains connected product. Is it UL listed? – winny Nov 04 '21 at 08:07
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    @winny No. The beauty of every plug and voltage adapter I've seen is that they lack any safety or EMC approval markings whatsoever (save maybe a useless CE mark). After all, they are typically specifically stated as not intended for use in the country of sale ("for export only). One I bought at HK airport had the (locally useful) UK style plug taped off and the clerk extracted a pledge from me that it would not be used within HK. Since many of them allow a 3-pin US/Canada style plug to be inserted with the ground pin left open, they can't be approved even if they are well made. – Spehro Pefhany Nov 04 '21 at 12:24
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    I never imagined one can market a triac regulator for a "voltage regulator". Now that I know it is possible, I wonder how these people avoid jail time. – fraxinus Nov 04 '21 at 17:42
  • And people keep telling me those marks are not requirements and it doesn't matter! @fraxinus because most of the regulatory teeth involve financial consequences, which only are effective on businesses with assets. Seller is probably judgment proof. Sales location is probably "only a marketplace connecting buyers to sellers" like Amazon. – Harper - Reinstate Monica Nov 04 '21 at 17:50
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    I had the one in the top photo! complete piece of crap with lose connectors and running very hot. – Thomas Nov 05 '21 at 09:59
  • Which country is this even supposed to be used in? That won't fit in any of the common continental European sockets. – asdfex Nov 05 '21 at 11:37
  • @asdfex As I recall, it fit the old [Europlug](https://www.netio-products.com/en/glossary/type-c-electrical-socketelectrical-plug), and won't fit the more modern [Schuko](https://www.netio-products.com/en/glossary/type-f-schuko-de-electrical-socketelectrical-plug) recessed socket. Another older ["EU"](https://i.imgur.com/qkyeWDa.png) style plug that won't fit modern safer sockets. They have not been needed for many years since most low power electronics is universal input. – Spehro Pefhany Nov 05 '21 at 12:39
  • No, this is not Europlug compatible. It might fit the Italian dual-use type L, but not safely, because the contacts would be exposed. The power rating also doesn't match the Europlug limit. – asdfex Nov 05 '21 at 13:09
  • @asdfex Hotel shaver outlets? I actually have one of those things somewhere, but it's been decades since it accompanied me in travels. How new are the sheathed pins? As an ancient, they seem fairly "recent". – Spehro Pefhany Nov 05 '21 at 13:36
  • @SpehroPefhany Insulated pins were always part of the standard, at least since CEE 7 in 1963. – asdfex Nov 05 '21 at 17:12
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There is probably an auto-transformer for the 50W setting, which will convert 230V into 115V and work with most low power appliances...

And either a dumb diode or a phase cut triac for the 1600W setting, which will only work with resistive loads like a hairdryer. That will reduce power in a resistive load, but:

  • Peak voltage at the output is the same as the input, so if you connect a SMPS or transformer based power supply that only works on 115V and not 230V, it will blow. Even if it's a phase cut triac, you'll get a chopped up sine wave but the peak is still 230V...

  • If it's a diode, there is a huge amount of DC, so if you connect a transformer-based power supply, it will probably overheat.

bobflux
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  • A hairdryer also contains a fan motor – StayOnTarget Nov 03 '21 at 18:57
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    It can't be a dumb diode, if you do the math. More of a phase control. – Spehro Pefhany Nov 03 '21 at 18:58
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    @StayOnTarget, If the fan motor is a [_universal motor_](https://en.wikipedia.org/wiki/Universal_motor), then it will run on DC. – Solomon Slow Nov 03 '21 at 18:58
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    Most hair dryers have low voltage DC motors, which are run from a bridge rectifier and a voltage divider consisting of the heating coils. – Spehro Pefhany Nov 03 '21 at 18:59
  • @SolomonSlow I wasn't thinking about the DC but instead was referring to that fact that it wouldn't be a purely resistive load – StayOnTarget Nov 03 '21 at 19:01
  • Even if you chop a sinewave with a triac, you still get the same peak voltage – bobflux Nov 03 '21 at 19:41
  • You actually don't get the same peak, it's a bit less since the required conduction angle is <90°, but it's still way more than the 168V peak of 120Vrms mains. A half-wave rectifier with 240V in would result in double the design power of a 120V heater connected to it, with very unpleasant results most likely. – Spehro Pefhany Nov 03 '21 at 19:49
  • @SpehroPefhany how does the hair dryer work in "blow only" mode? Does it make a little bit of heat? (i always thought it did). – Harper - Reinstate Monica Nov 04 '21 at 17:55
  • @Harper-ReinstateMonica The cheap ones I've seen have [high and low](https://i.stack.imgur.com/glM2P.jpg) , no blow only. Ones like the Dyson are probably quite different- I think they use a BLDC 3-phase motor to get high enough RPM to have most of the noise ultrasonic. – Spehro Pefhany Nov 04 '21 at 17:59