240V-> 110V transformer - lighter with inverter techn?

Hi
Very "off the wall" question directed to our gifted electricals and electronics welders...
About 240V to 110V tranformers used with professional power tools here
in the UK - needed by law on building sites - which are heavy - my 3kVA one (?) weighs 19.5kg (43lb). These are "centred-tapped" (to Earth potential) - so see 55V between Earth and either "hot" wire.
Any "bright sparks" like Iggy - would it be possible to make a much lighter transformer using inverter technology?
Perhaps chop up the incoming 50Hz AC without rectification at thousands of Hz, put that through a much smaller and lighter transformer then rectify the output to an unsmoothed DC to run power tools?
As all wall sockets rated at 13A with 240V, power available = 240 * 13 = 3120VA - which would be a good capacity for this device.
???
Richard Smith
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here
13
110v transformers are NOT required by law on building sites in the UK. What the regulations call for is the lowest practical safe voltage, which is often interpreted as 110v. In fact a 240v source through a 30mA RCD is actually also acceptable, as is a 24v supply, which is even safer but hardly ever used !
AWEM
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You could make a smaller transformer using inverter technology, it would require a rectifier, high frequency inverter, transformer, rectifier, and low frequency inverter to make 50 Hz out of many kHz that inverters operate on, and then some sort of a filter to protect your tools from voltage spikes caused by high dI/dt inherent in inverters. Kind of expensive. I definitely do not consider myself to be very educated on the issue, but I would suppose that in the end you would not easily afford one. I would invest in a nbice dolly to drag that transformer around.
i

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message wrote:

and
here
you
Now THAT'S what I need, a nice Dolly to drag things around for me, she could also make copious cups of tea, and wipe my fevered brow when it all gets too much !
AWEM
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On Tue, 26 Jun 2007 09:49:26 -0500, Ignoramus11870

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber8137
Btw...it makes a pretty damned good base for a welding cart too. Lots of guys around here use these to make up welding carts and tool carts to drag around the back 40.
I think they are currently on sale btw
Gunner
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects. Lazarus Long
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I looked at them, did not get a feeling that they would actually hold up to 1,000 lbs of load. Though otherwise they are probably useful.
For myself, I made a wooden dolly out of 2x4's, 2x6's and 5" casters similar to HF 650 lbs casters. It did hold up to about 1,100 lbs load (diesel engine in crate). I use it all the time.
i.
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Iggy - help a poor simple guy like myself think this through from first principles.
Why rectify before high-frequency inverting? "Chopping up" the unconverted mains supply - you get say 10000Hz inverted frequency modulated at 50Hz... A teeny transformer would voltage-transform this??? Rectify the output, surely - as a series-would DC motor can run on low frequency AC (50Hz) but definitely not on kHz AC (induction and iron-losses would strangle the current and work to zero, wouldn't it?).
Then the power supply sees something that looks like a transformer - reactive (inductive) with no load, becoming increasingly "resistive" as tools draw power from the device.
???
I am sure my "scheme" is absurd - would you be as good as to explain it to me or point to information?
Richard Smith
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Richard Smith wrote:

This is simply the wrong group to ask, and Iggy has even problems driving an LED the right way. So do yourself a favor and ask that in an electronics group.
Nick
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driving an

electronics
Oh Nick, you are Iggy bashing again ! Leave the poor bloke alone <G>
AWEM
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On Wed, 27 Jun 2007 15:40:51 +0100, Andrew Mawson

Nick Mueller is lying again, my LEDs are driven just fine.
i
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Ignoramus8624 wrote:

Because they are driven around on a trailer? :-)
I know what *you* mean with "driving a LED just fine". And I remember well the current-limiting resistor "design" you use on your trailer. <G> Now you can call that "lying", I'll call it ignorance then.
Nick
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Nick Mueller wrote:

To prove what idiotic stinking liar Ignoramus is and what knowledge he has about electronics: <http://igor.chudov.com/projects/Homemade-Trailer-With-M105A2-Bed/08-Trailer-Electrical-Box/>
Iggy, you are just a huge asshole!
Nick
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remember well

<G>
he has

<http://igor.chudov.com/projects/Homemade-Trailer-With-M105A2-Bed/08-T railer-Electrical-Box/>
No need, Nick, to lower yourself to the gutter if you want to make criticisms. It only demonstrates a lack of vocabulary.
On that page cited by you he refers to a 500 ohm series resistor of half watt capacity running an LED off 12v. Now assuming a forward voltage drop of circa 1.7 volts for the led (not untypical) that gives 10.3 volts across 500 ohm, in other words the led and resistor are both passing approx 20mA, which is about right. Looking at dissipation in the resistor (I squared R) we have 0.0206 x 0.0206 x 500 watts or 0.212 watts - ie well within the rating. So what's the problem?
AWEM
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Andrew Mawson wrote:

What color?

The fact that you don't have 12V on a car's grid. It varies by more than 20%. Ignorant has been told that. But then, he wouldn't be Ignore-ant.
Nick
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than
Ignore-ant.
So if the voltage is up to 14, and any reasonable regulator should keep it below that, the resistor dissipation rises to 0.3 watts and the current approaches 25 mA - both within normal limits.
Just stop Iggy bashing and I might take you more seriously ! I don't know the bloke, I've never spoken to him or exchanged emails, but I'm sure he deserves being treated politely, and if you have issues with his designs (as I have had with some of his physical wiring layouts) just stick to factual suggestions politely phrased.
AWEM
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On Wed, 27 Jun 2007 17:27:49 +0100, Andrew Mawson

These are 30 mA LEDs, by the way, they are physically rather large.
The voltage may get to 14 volts, if I believe my voltmeter in the truck, it gets to about 14.3 volts or so. (going by memory).
All well within the specs of the limiting resistor.
i
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Andrew Mawson wrote:

The "brilliant" projects he's presenting speak for themselves. Or did you miss his electrical powered bicycle recently?

Not if he calls me a liar when in fact he is one.
Nick
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Gunner, consider trying slrn or other text based newsreader under linux. The nice thing about them is that you can read news from your machine while connecting remotely, over a bandwidth friendly text connection.
I have a somewhat messy killfile situation myself, as I read news from home and from my laptop, and the killfile on the laptop is not in sync.
i
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On Fri, 29 Jun 2007 08:43:28 -0500, Ignoramus19948

Im on dialup at home, shared DSL via wireless router at my RV in LA.
Ive tried all the various Linux newsreaders. Still far and away prefer Agent. So its Wine or nothing
But thanks
Gunner
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects. Lazarus Long
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On Wed, 27 Jun 2007 17:06:32 +0100, Andrew Mawson

A series resistor is not the most efficient way of powering a LED, because most power is dissipated in the resistor (80 percent or more depending on actual trailer voltage), where it is not doing anything useful.
But it works and in the context of trailer wiring (ie, no need to conserve milliwatts, like on battery powered devices), it is acceptable. Now, if I used a series resistor on a battery powered device, that would not be a good decision.
The resistors are well protected from mechanical damage, I wrapped everything snugly in insulation tape and they are covered by aluminum brackets.
if you look at this picture
http://igor.chudov.com/projects/Homemade-Trailer-With-M105A2-Bed/08-Trailer-Electrical-Box/08-Trailer-Electrical-Box-0006.jpg.html
you need to note that it is not how the resistors are physically placed when I installed this piece. It is kind of hard to explain, but I wrapped the bracket in insulation tape, then I bent the resistors so that they are close to the bracket, then wrapped everything in tape again.
i
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