is it possible? 1600W step-down transformer so tiny!

[Dave D]

Hi,

I've recently moved to London in the UK and brought along my trusty
cooker. It states that it requires 120V @60/1235 watts. After some
research on the net it was apparant that transformers that provide > 1000W
are at least the size of a shoebox and around $70-100. However, I later
came across a transformer sold by jWin which rates upto 1600W and is as
small as an average 100w transformer and costs about $10. You can see it
here - http://tinyurl.com/hra3r I called the shop selling them and they
confirmed the specs.... am I wasting my time? You get what you pay for
right? Any help would be much appreciated.

James

Take my advice- don't take chances with 240V supplies. It is far easier to
get a fatal shock from 220/240V than N American 120V supplies, although
ELCBs are very common now.. Using one of these cheap converters is dicing
with danger, if a short occurs and damages the converter, full 240V mains
voltage will be present in your appliance, and because there's seemingly no
earth on this converter, if there's a short to the oven's case you could be
killed- it's that simple. Even steam/moisture settling inside the oven could
bridge from live to chassis causing a shock hazard.

I can tell you by just looking at the picture that this converter is clearly
not intended for use with apparatus like ovens, and it doesn't appear to be
intended for use with earthed appliances. Either keep this converter for a
CD player or shaver, or send it back! I would even go so far as to say it is
not safe to plug into a UK wall outlet. It will require a UK 3-pin to
'shaver' style converter for starters, which are not intended to be used for
appliances drawing 5 Amps!


Incidentally, there's also the issue of liability should anything happen, is
it worth it?

Dave

 

[James Kelly]

Hi Dave,

Thanks for your reply. You sound like you know what you are talking about,
so I am going to take your advice and pack this thing up.... Some other very
helpfull folks have suggested the possibility of rewiring the upper and
lower elements in series to allow 220V or simply buying a 2nd and wiring in
series, but since my skills dont extend to this type of work, I dont have a
choice but to pack her away...sniff.....sniff..... I'm overwhelmed by the
support of this newsgroup though, people seem very keen to help. Thanks
again.

James.

 

[I.F.]

Hi Dave,

Thanks for your reply. You sound like you know what you are talking about,
so I am going to take your advice and pack this thing up.... Some other
very helpfull folks have suggested the possibility of rewiring the upper
and lower elements in series to allow 220V or simply buying a 2nd and
wiring in series, but since my skills dont extend to this type of work, I
dont have a choice but to pack her away...sniff.....sniff..... I'm
overwhelmed by the support of this newsgroup though, people seem very keen
to help. Thanks again.

James.

Sorry - the suggestion to wire 2 ovens in series was a bit of mis-placed
humour! If the heater thermostat on one oven opens while the other is
cooking, all the heater current through the oven that's on will flow through
just the motor on the oven with the open thermostat - the cloud of smoke
won't be coming from your pizza!

 

[Geoffrey S. Mendelson]

Hi,

I've recently moved to London in the UK and brought along my trusty cooker.
It states that it requires 120V @60/1235 watts. After some research on the
net it was apparant that transformers that provide > 1000W are at least the
size of a shoebox and around $70-100. However, I later came across a
transformer sold by jWin which rates upto 1600W and is as small as an
average 100w transformer and costs about $10. You can see it here -
http://tinyurl.com/hra3r I called the shop selling them and they confirmed
the specs.... am I wasting my time? You get what you pay for right? Any help
would be much appreciated.

It's not a transformer, it's a converter which is just a big resistor. In
order for it to work, it must disapate the electricity that would have gone
into the applicance. A worthless piece of junk.

Geoff,

 

[Travis Jordan]

It's not a transformer, it's a converter which is just a big
resistor.

A 1600 watt resistor? I think not. More likely an SCR methinks.

 

[Dave D]

A 1600 watt resistor? I think not. More likely an SCR methinks.

Agreed.

Plus, a resistor could only be used if the wattage of the appliance was
predetermined so the resistance could be calculated! It clearly isn't a
resistor.

Dave

 

[Dave D]

Hi Dave,

Thanks for your reply. You sound like you know what you are talking about,
so I am going to take your advice and pack this thing up.

I'm really pleased to hear that, James. If it's any consolation, you should
be able to find a safe and proper alternative, ie a new 240V oven, for not
too much cash- there's bargains to be had in this kind of appliance if you
look around.

At least you'll live to appreciate your Pizza!

Dave

 

[Rich Grise]

Yikes, ok so I bought it, its only $10 and I'll take the chance.... Any
danger though? Could this cause the convertor to melt/explode/catch
fire.....? Thanks again everyone.

From the look of the cooker, http://tinyurl.com/fpyjo , it won't like it
at all. The heating elements might be OK with it, but the raggedy
chopped-up waveform will probably confuse its controller.

So I'm going to recommend not even trying it, unless you can verify
that the adapter won't blow up your cooker. (or that the cooker
won't mind the waveform).

Good Luck!
Rich

 

[Phil Allison]

"Roger Hamlett"

Also, a 'cooker', that is rated at 1235W when running, will typically draw
many times this rating for a few seconds whenever the element switches on.

** What bullshit !

Heating elements use wire with an essentially fixed resistance value.

Won't change by more than few percent from cold to hot.

Never heard of Ni-Chrome ???



......... Phil

 

[Phil Allison]

"Gerard Bok"

My understanding is, that some of the cheaper '230 to 115 volt
converters' just contain a diode.

** Then you have no "understanding" of the issue.

Which indeed halfs the applied power

** Shame that a resistive load operating from DOUBLE supply voltage
requires the power to be reduced by a factor of FOUR !!

Using just a diode will supply the load with DOUBLE its safe power level.

MADNESS.



....... Phil

 

[JANA]

What you are describing is not a real transformer. It is a unit that is
employing a circuit that is using a device called a thyristor. This is a
solid state gate controlled dual rectifier. They are using a technique of
phase chopping to reduce the effective voltage, rather than stepping it
down. It can only be used with simple appliances such as hair dryers,
lights, and others that are non reactive loads. I would not use it with
anything that uses a power supply, or motor device of any kind. Sometimes
these units fail, and cause whatever the load is to be damaged.

If you want something safe and reliable, it is best to get a step down unit
that uses a real transformer. These are big, heavy, and sort of expensive in
comparison.

--

JANA
_____


Hi,

I've recently moved to London in the UK and brought along my trusty cooker.
It states that it requires 120V @60/1235 watts. After some research on the
net it was apparant that transformers that provide > 1000W are at least the
size of a shoebox and around $70-100. However, I later came across a
transformer sold by jWin which rates upto 1600W and is as small as an
average 100w transformer and costs about $10. You can see it here -
http://tinyurl.com/hra3r I called the shop selling them and they confirmed
the specs.... am I wasting my time? You get what you pay for right? Any help
would be much appreciated.

James

 

[[email protected]]

My understanding is, that some of the cheaper '230 to 115 volt
converters' just contain a diode.
Which indeed halfs the applied power

Auugggh! Noooooo!!!! Nooooooooo!!!!!!

The "DIODE CUTS AC POWER DISSIPATION TO SAME AS HALF ORIGINAL VOLTAGE
IN RESISTIVE LOAD" thread rears its ugly head yet again!!!!!!

I'm sorry I ever posted in this thread!!!!!!! In my defense I NEVER
used the word diode!!!!! Nor did I ever say "Root Mean Square"!!!! I am
innocent, I tell you, INNOCENT!!!!

Tim.

 

[Phil Allison]

"Travis Jordan"

Note that the power converter (it is not a transformer) isn't rated for
continuous use.

** At 1600 watts, it is rated for more load current than the OPs pizza
cooker at 1250 watts.

I'm not sure whether your cooker application
constitutes 'continuous use' - but if it does, prepare to be
disappointed.

** Very unlikely to be any problem.

The chopped sine wave produced by the triac (dimmer) has an * rms * value of
120 volts. However, the "average rectified " value is only 64 volts due to
the peaky waveform since 2/3 of the sine wave is missing ( conduction angle
= 66 degrees out of 180).

The OP's pizza cooker takes a little over 10 amps rms to operate - so
similarly, the "average rectified" current level is just over 5 amps.

The triac inside the "converter" has to pass 5.5 amps *average* current
with a voltage drop of circa 1.5 volts - so the heat dissipation is only
8.3 watts.

Easily managed by a modest heatsink.





......... Phil

 

[James Kelly]

Phil,

Just to confirm,( against the general consensus of the group) are you saying
that you think it will work and shouldnt pose any serious danger. (I of
course assume liability!). I might be willing to give this a go just to see
what happens..( wearing rubber gloves of course)!

Regards,
James.

 

[Phil Allison]

"James Kelly"

Phil,

Just to confirm,( against the general consensus of the group) are you
saying that you think it will work and shouldnt pose any serious danger.

** Nope.

(I of course assume liability!). I might be willing to give this a go just
to see what happens..( wearing rubber gloves of course)!

** The *peak voltage* of 310 volts, supplied by the triac, will could blow
the electronic timer inside to smithereens.

The peak of a 120 volt AC supply is only 170 volts - you see.


Like Harry said -

"...... do ya feel lucky - punk ? "





......... Phil

 

[Michael Kennedy]

Buy another identical cooker and wire the two in series.

hmm.. That sounds like a good idea.. you still have the 50/60 hz issue with
the timer but as long as that is dc it won't matter. I think you might not
even have any probs with it even if it is an ac timer.

Wiring them in series is very easy, but you will need to have 2 cookers and
run them both at the same time for everything to work.

- Mike

 

[Michael Kennedy]

Wait.. you'd have problems if this thing has a thermostat and shuts off on
one and not the other. It would draw all the current through the timer and
the electric moter and instant smoke...

 

[James Sweet]

What sort of things do you cook with a 1235 watt cooker???. That's nearly a
third of my electric kettle!!

You sure the rating is not 12350 watts which would be more reasonable. As
someone else hinted - get yourself a £29.99 800W 240V microwave, much safer
and more efficient!

12,350W? That would draw more than 50A at 240V and produce over 42,000
BTU's, that's enough to heat a small house!


1,235W on the other hand is perfectly reasonable for a cooker.

That said, these converters are not transformers, they're essentially
triac light dimmers and will only work for purely resistive loads, such
as an electric cooker.

 

[James Sweet]

I note that the unit doesn't appear to provide a ground
connection. This doesn't exactly give me warm fuzzies...

I've never seen any sort of portable cooker that had a ground connection
anyway, mine has a standard 2 prong cord.

 

[James Sweet]

Hi Dave,

Thanks for your reply. You sound like you know what you are talking about,
so I am going to take your advice and pack this thing up.... Some other very
helpfull folks have suggested the possibility of rewiring the upper and
lower elements in series to allow 220V or simply buying a 2nd and wiring in
series, but since my skills dont extend to this type of work, I dont have a
choice but to pack her away...sniff.....sniff..... I'm overwhelmed by the
support of this newsgroup though, people seem very keen to help. Thanks
again.

I wouldn't be so quick, the converters are simple and fairly robust.
They should be fused and will be perfectly safe to use.