Dual voltage consumer appliance oddity

[JT Smith]

TL;DR Summary

Appliance with a dummy switch to select between 120 and 240 volts. Why would they include a switch that does nothing? And what happens when you actually apply a different voltage?

I have a travel hair dryer that has a 120/240 voltage selector. There is also a speed switch (off/low/high) that controls both the fan and heat setting together. I wanted the high heat but lower fan speed and wondered if I could modify it to achieve that. So I opened up the handle part to take a look. I was surprised to find that the voltage selector button wasn't connected to anything. It's just a piece of plastic that can rotate.

Why would they do that instead of just saying "it works at either 120 or 240"? And what actually happens when used at different voltages?

I suspect that to achieve the low/high settings the speed switch is simply routing the current through the fan and heating element either in series or parallel. So wouldn't changing the input voltage from 120 to 240V make it run both hotter and faster?

 

[berkeman]

That's pretty funny. Can you link to product information and/or a datasheet? What regulatory certifications does it list in the User Manual? Does the AC Mains power cord go directly into the unit, or does it have a "wall wart" type power adapter? What does the power input label say?

 

[Baluncore]

Maybe brand recognition, and product loyalty, have been overtaken by switching power supply technology.

 

[Vanadium 50]

Marketing.

 

[Averagesupernova]

You presumably wanted more heat out of your hair dryer by lowering the speed of the fan. You could try it on the higher voltage. You may get more heat, at least for a few moments.
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Disclaimer: I shouldn't really need to explain right?

 

[JT Smith]

That's pretty funny. Can you link to product information and/or a datasheet? What regulatory certifications does it list in the User Manual? Does the AC Mains power cord go directly into the unit, or does it have a "wall wart" type power adapter? What does the power input label say?

It's this one: https://www.conair.com/en/compact-folding-handle-hair-dryer/124TLN.html?lang=en_US

The user instructions say very little about the voltage selection:
https://www.conair.com/on/demandware.static/-/Library-Sites-usConairShared/default/dw96860a04/Instructional Booklets/124TLN.pdf

The plug end has a safety device of some sort with "TEST" and "RESET" buttons, presumably to protect one from immersion accidents since not every place has GFCI. From there just two wires go into the handle at 120V AC. There are several warnings about shock danger and water but no mention of voltage.

I don't know how to crack the main body open without damaging it so I'm trying to sleuth how it works. I have to admit that I'm not highly confident. Peering inside I can see that there is a diode bridge arrangement which I'm guessing means the fan has a DC motor. I connected a couple wires with a jumper and was able to turn the fan on full blast without any real heat. That drew 7A. I don't think I can slow down the fan with a resistor. A light dimmer would be kind of bulky. The whole point was to have an inexpensive compact unit. Oh well, probably I should give up.


EDIT: I just noticed that there is a printed instruction booklet in the box. There they say that in 250V mode you can only use it in the low speed setting where it will in fact run at full speed/heat. And if you put it in high mode anyways what happens? Does the thermal fuse blow? Seems kinda kludgy.

 

[JT Smith]

You presumably wanted more heat out of your hair dryer by lowering the speed of the fan. You could try it on the higher voltage. You may get more heat, at least for a few moments.
-
Disclaimer: I shouldn't really need to explain right?

No, I want the heat it provides on full but with less airflow and less noise. Only 120V available anyway. I have a propane torch I can use but it demands more attention. A heat gun is another possibility I guess but they're also pretty darn hot.

 

[berkeman]

No, I want the heat it provides on full but with less airflow and less noise. Only 120V available anyway. I have a propane torch I can use but it demands more attention. A heat gun is another possibility I guess but they're also pretty darn hot.

Um, what are you trying to do?

 

[Rive]

TL;DR Summary: Appliance with a dummy switch to select between 120 and 240 volts. Why would they include a switch that does nothing? And what happens when you actually apply a different voltage?

Why would they do that instead of just saying "it works at either 120 or 240"? And what actually happens when used at different voltages?

As far as I know hair dryers of the 120V part of the world mostly has that beefy safety plug thing, which acts as a GFCI and maybe* as an overload protection too.

There they say that in 250V mode you can only use it in the low speed setting where it will in fact run at full speed/heat. And if you put it in high mode anyways what happens?

I think the overload will trigger the safety plug and so it'll stop working.

I wanted the high heat but lower fan speed and wondered if I could modify it to achieve that.

For a classic hairdryer that'll end with overheating. Heat guns are made to safely handle high temperature even if there is no direct temperature control (like in those cheap ones): a hair dryer will just soften up the chassis and lose safe insulation.

So - get a heat gun.

* I live in the 240-ish V part of the world so I'm not sure of the exact details.

 

[Vanadium 50]

I have a propane torch I can use

To dry hair? Man...that's hard core.

 

[JT Smith]

FWIW it's not for hair; it's for reducing the moisture content of pottery during throwing or trimming. It's a time saving tool mainly. The most commonly applied methods are:

- wait for it to dry under ambient conditions
- put it in a warmer place
- use a fan to provide air flow
- use a hair dryer
- use a propane torch
- use a heat gun

Probably one could think of other ways but those are the ones I've used or seen. I don't have a heat gun so I haven't given that a go but they seem less common. I guess the idea is that if you're going to go for a concentrated high heat approach you might as well do it without a cord. Fire is kind of fun anyway.

The thing about propane torches (and heat guns too) is that the have to be handled more carefully both in terms of applying the heat evenly and avoiding accidents. A hair dryer does the job quite well without those complications.

Since I have very limited space for tools I thought a compact travel hair dryer would be the best solution. Unfortunately they seem to all have this speed/heat combined approach for control. So it's an electronics puzzle that I thought, naively, I could easily solve. Now I'm not so sure. I wonder what the hair dryers with independent heat and fan speed settings have under the hood?

 

[Rive]

I wonder what the hair dryers with independent heat and fan speed settings have under the hood?

I think you would need to control the temperature instead of just heat or ventilation, and that's difficult if you start with a 30$ hair dryer.
Maybe a 206$ food dehydrator?
Used ones or ones without food grade interior will go cheaper.

 

[Averagesupernova]

I wonder what the hair dryers with independent heat and fan speed settings have under the hood?

Don't bet that there aren't controlling the heat as well when the fan is turned down.
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Or: Since the end goal is safety and if that means it's not dangerously hot on high heat low fan, then it will just be cooler on high fan.

 

[JT Smith]

I hear what you guys are saying about the need for a minimum amount of airflow for a given heat setting. But I know that what I'm after is possible since I've borrowed a friend's hair dryer that does what I want. And it's not some fancy high end dryer. She's had it for decades and told me it was cheap. There are dryers for sale like hers that I could buy. They just don't come with a foldable handle for compact storage. Maybe full heat and half fan speed would be a bad combination with mine. I wish I could easily adjust both heat and fan speed to find a good balance

EDIT: Amazingly I found an etsy listing for her model of dryer:
https://www.etsy.com/listing/589774...how_sold_out_detail=1&ref=nla_listing_details

 

[Baluncore]

When some feature of a plastic case is no longer required, it is cheaper to keep the feature, than to make a new set of water cooled injection moulds.

Maybe the next model will have shed the vestigial voltage selector.

 

[JT Smith]

Yeah I can see that. But they pretend it still is a feature. They instruct you to turn the dummy switch. And only one of the two fan/heat settings is available at 240V but they don't tell you that in the description, in the online instructions, or even on the box.

 

[DaveE]

Yeah I can see that. But they pretend it still is a feature. They instruct you to turn the dummy switch. And only one of the two fan/heat settings is available at 240V but they don't tell you that in the description, in the online instructions, or even on the box.

Because they have the switch, they have to tell you what to do with it, or users will be confused and complain. If they have to tell you about it, they'll want to make it a feature somehow. Consumer marketing 101: everything is good about the product.

As an aside, I was working in our EE lab once when a facilities tech wanted a 1/4W axial resistor, which we had a big cabinet with every 1% value. I read the part number pulled open a drawer and gave him a couple. Then he said "no, the one I'm replacing is brown and these are blue." My response was to say "sorry" while I got some brown ones for him. Quicker and easier than explaining that the electrons don't care. He was happy and I got back to work.

When some feature of a plastic case is no longer required, it is cheaper to keep the feature, than to make a new set of water cooled injection moulds.

Maybe the next model will have shed the vestigial voltage selector.

Yes exactly. Plus all of the other collateral stuff: instructions, packaging and ad photos, assembly methods, inventory control during the switch over, etc. That switch is cheap in the big picture. They'll go out of their way to shave tenths of a cent during the original design, but they don't want to revisit it unless they have to.

 

[JT Smith]

Because they have the switch, they have to tell you what to do with it, or users will be confused and complain. If they have to tell you about it, they'll want to make it a feature somehow. Consumer marketing 101: everything is good about the product.

As an aside, I was working in our EE lab once when a facilities tech wanted a 1/4W axial resistor, which we had a big cabinet with every 1% value. I read the part number pulled open a drawer and gave him a couple. Then he said "no, the one I'm replacing is brown and these are blue." My response was to say "sorry" while I got some brown ones for him. Quicker and easier than explaining that the electrons don't care. He was happy and I got back to work.

The dummy switch is one thing as it is relatively harmless. Like pretending to the tech that the color of the resistor mattered just to avoid the presumably exhausting effort of explaining it to him. It reminded me of reading that the "walk" buttons at some intersections don't actually do anything. On the other hand maybe the tech would have gotten it immediately. You'll never know. There are intersections I've been at where the temporary disabling of the walk buttons was labeled. It was very easy to read and understand. I appreciated that explanation.

What bothers me more in the case of the hair dryer is that the product functionality is reduced below typical expectations. If the blue resistors only worked in one direction but were not labeled as such wouldn't you be at least a little irked? Certainly "marketing" or "capitalism" or "whatever you can get away with means it's okay" can be used to explain that sort of behavior. But I don't accept it. It's not the way I'd treat a friend; it's the way I'd treat an enemy. Maybe that's the way it is in a world filled with snake oil. But it isn't ethical. It isn't moral.

 

[gmax137]

It reminded me of reading that the "walk" buttons at some intersections don't actually do anything.

I've been told the "Close Doors" button in elevators is a dummy. It just gives you something to do while waiting for the doors to close. I get it, people like to feel "in control."

 

[berkeman]

It reminded me of reading that the "walk" buttons at some intersections don't actually do anything.

I've been told the "Close Doors" button in elevators is a dummy. It just gives you something to do while waiting for the doors to close. I get it, people like to feel "in control."

 

[Averagesupernova]

Imagine the chaos that would ensue if bogus controls were put in places that would cause a little worry to those in the area. Nothing as crazy as wings falling off in the farside. I'm thinking more along the lines of "press button to initiate full wash down" outside of the restroom. How would that free up an otherwise busy public toilet?

 

[Tom.G]

That reminds me of an old joke:

At a military facility the word was out that a General would be taking a tour in a few days. This General was known to push buttons on control consoles to make sure they worked.

Now of course this was an opportunity that could not be ignored!

The General showed up for the tour as expected and saw a button labelled

"Push To Test."​

True to form he pushed the button and the legend lit up saying:

"Release To Detonate" ​

(this is one of those that really needs an additional punchline)

 

[JT Smith]

Is there a law analogous to Godwin's that predicts that some percentage of threads eventually evolve into jokes?

 

[sophiecentaur]

Nobody wants to be the straight man.

 

[gmax137]

Are there stats for how many threads each user has the final post? I'm not sure if a high score is good (provides a clear, definitive answer that needs no further discussion) or bad (nobody wants to continue the thread because they're tired or disgusted).

 

[JT Smith]

I'm pretty

Are there stats for how many threads each user has the final post? I'm not sure if a high score is good (provides a clear, definitive answer that needs no further discussion) or bad (nobody wants to continue the thread because they're tired or disgusted).

I'm pretty sure it's a bad thing.

Oops! :-)

 

[JT Smith]

Also, FWIW, I cracked the case on my cheap hair dryer in order to figure out the circuit exactly and to make a few measurements. I think I can simply solder in a 50ohm 100W resistor in series with the fan to achieve what I want. The question I can't answer for myself in advance is whether the hair dryer will simply overheat with that heat/airflow combination. But for $10 I'm going to satisfy my curiosity.

 

[Tom.G]

Better put that 100 Watt resistor external, in a metal box, with lots of ventilation holes!

Better yet, replace the hair dryer with one that HAS your desired functionality.

 

[Averagesupernova]

I think I can simply solder in a 50ohm 100W resistor in series with the fan to achieve what I want.

Seriously?

 

[Rive]

I think I can simply solder in a 50ohm 100W resistor in series with the fan to achieve what I want.

I think there must be some other, more proper ways to run a 12V DC motor from 120V AC mains...

 

[JT Smith]

I finally got around to finishing my hair dryer project. After completing the modifications I put it back together and discovered that what I had originally concluded about the "dummy" voltage select switch isn't exactly correct. The voltage switch *does* have a function. While it has no direct electrical connection it has a small plastic slot that interlocks with a plastic tab on the main speed/heat switch. This interlock prevents one from selecting both 250V and HIGH simultaneously. FWIW.

 

[JT Smith]

I think there must be some other, more proper ways to run a 12V DC motor from 120V AC mains...

Maybe. Like what? The original design is the motor (with a full wave rectifier) in series with a resistor. I just wanted a bigger resistor.