Foreign Travel voltage converter (1500Watts 220V to 120V)

[Jacques Carrier]

Hi all fellow techs!!

I wonder what they put in those very small devices.It is certainly not
a real power transformer. Low power devices (50W) contain an
autotransformer.(I took one apart)

I think it might be some kind of dimmer (good only for resistive
loads).
Has anyone taken one of those gadgets apart??

Many thanks for your feedback.

Jacques

 

[Michael A. Covington]

It is either a circuit very similar to a light dimmer, or possibly just a
rectifier.

 

[Sam Goldwasser]

It is either a circuit very similar to a light dimmer, or possibly just a
rectifier.

A rectifier would cut the power in half compared to 230 VAC for a constant
resistive load. This is not what you want.

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[James Sweet]

A rectifier would cut the power in half compared to 230 VAC for a constant
resistive load. This is not what you want.

I thought the high powered ones were nothing but diodes? They're only good
for resistive loads, mostly they're made for irons and hair dryers.

 

[Sam Goldwasser]

I thought the high powered ones were nothing but diodes? They're only good
for resistive loads, mostly they're made for irons and hair dryers.

A diode would produce half wave rectified 230 V. This would cut
the power in half compared to using raw 230 VAC but would still
be twice the power expected by a 115 VAC resistive load.

For example: 115 VAC 1.5 kW space heater.

On 230 VAC: 6 kW.
On half wave rectified 230 VAC: 3 kW.

Either would result in failure very quickly.

Or, did you have something else in mind?

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[James Sweet]

A diode would produce half wave rectified 230 V. This would cut
the power in half compared to using raw 230 VAC but would still
be twice the power expected by a 115 VAC resistive load.

For example: 115 VAC 1.5 kW space heater.

On 230 VAC: 6 kW.
On half wave rectified 230 VAC: 3 kW.

Either would result in failure very quickly.

Or, did you have something else in mind?

I was thinking they had a chain of diodes and made use of the voltage drop,
guess I could be wrong though.

 

[Geoffrey S. Mendelson]

I was thinking they had a chain of diodes and made use of the voltage drop,
guess I could be wrong though.

The "converters" are just a big resistor. They really have very little use
except for things like hair dryers.

Your best bet is to:

1. If it has a "wall wart" bring the 120v with you and get a replacment
when you arrive. They are relatively cheap, and will fit the local outlets.
It's a lot easier to get an exact replacement if you have the original
in your hand.

2. Buy a transformer. Note that they are sold as xxx watt, but it's really
xxx VA on a good day if the moon is in the right phase. Expect to
use the transformer for half of it's rating.

If you come to Jerusalem, I can give you the name of a transformer
shop that will make what ever you want to specification. For example,
most transformers don't carry the ground through, I had a 250va
transformer (not auto transformer as most are) with the ground carried
through and a grounded core made up for my grounded tip soldering iron.

3. Think multivoltage/multisystem, when you buy things. Make your next
hair dryer a multivoltage one, etc. Buy in shops that specialize in
serving the 220 volt community instead of "travel shops".

Geoff.

 

[Sam Goldwasser]

I was thinking they had a chain of diodes and made use of the voltage drop,
guess I could be wrong though.

Let's see... Say 1.5 kW rating dropping from 230 VAC to 115 VAC. If half
wave rectified, that means it has to drop the peak voltage by about 100 V
(someone else can figure out exactly how much!) That means the adapter
dissipates or otherwise gets rid of several hundred watts. There
must be a mini-wormhole in there to dump the heat to another part of the
Universe.

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[Sam Goldwasser]

The "converters" are just a big resistor. They really have very little use
except for things like hair dryers.

Not really.

Think about what you just said for (1) variable load and (2) where the
heat goes.

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[Jacques Carrier]

Let's see... Say 1.5 kW rating dropping from 230 VAC to 115 VAC. If half
wave rectified, that means it has to drop the peak voltage by about 100 V
(someone else can figure out exactly how much!) That means the adapter
dissipates or otherwise gets rid of several hundred watts. There
must be a mini-wormhole in there to dump the heat to another part of the
Universe.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
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traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is ignored.
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Sam is right.Power must be eliminated!!

I was thinking about a simple 220V SCR dimmer adjusted to fire around 45
degrees on each positive half cycle of the 220V line input.I guess that could
give about the 1500W required by an hair dryer,a toaster,etc. which operate
normally at 120V.

I found one of those 1500W converters (very small) but I cannot crack it open
to peek inside........They cost about $20 in Montreal.

The 50W model costs only $5 .It is a simple autotransformer.(220V to 120V)

Many thanks for the replies.

Jacques

 

[James Sweet]

The "converters" are just a big resistor. They really have very little use
except for things like hair dryers.

They're most certainly not a resistor, a 1500W converter stepping 240 down
to 120 would be dissipating a tremendous amount of power.

 

[NSM]

....
| Sam is right.Power must be eliminated!!
|
| I was thinking about a simple 220V SCR dimmer adjusted to fire around 45
| degrees on each positive half cycle of the 220V line input.I guess that
could
| give about the 1500W required by an hair dryer,a toaster,etc. which
operate
| normally at 120V.
|
| I found one of those 1500W converters (very small) but I cannot crack it
open
| to peek inside........They cost about $20 in Montreal.
|
| The 50W model costs only $5 .It is a simple autotransformer.(220V to
120V)

That's correct. And the high power units use a triac - basically a light
dimmer preset to provide 1/4 power to a resistive load. The switchable ones
combine these two.

NM