220 to 110 autotransformer being given away

micky forklarede den 16-12-2013:

In civilized countries with a modern electric system, we have 230v, allowing for using less copper/alu in the cables.

When we get equipment from backward countries with only 110v, we use an autotransformer to step down the voltage.

An autotransformer use less wire than a "normal" transformer, but does not give isolation between primary and secondary.

Leif

... with 230 and 400v in the house.

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Pretty useless in the shop here. Trade it for a dim bulb tester.

I think the description is faulty an autoformer with 240Vac winding and

120Vac winding doesn't make any sense. It would go from zero to 250 or so or zero to 140 or so. are you sure it only has one winding?

LOL! Thanks, I needed that today.

Of course, here in the US we should be happy that Edison LOST out regarding his DC distribution system. Wasn't Edison the one who invented the Electric Chair just to discredit his competitor [Tesla, Westinghouse]? He wanted to show how lethal these high voltages were, but alas, his first three testers died rather badly, inhumanely.

If it's an isolation transformer the numbers make more sense and it is very valuable on a bench.

We may end up with DC wiring after all. It is much easier to implement PV in a pure DC environment. Maybe 240Vac from the grid for the major appliances and locally generated 14/24VDC for lights and doodads.

Check whatever else is being offered by the guy.

I found a nice 120 to 220 transformer in a pile of garbage earlier this year, thought about, and couldn't think of a reason to bring it home, especially with that weight.

I dig a bit more in the pile, and find a sander, one of those ones with a sort of shovel part at the front for the sandpaper. So i bring that home, not really paying attention to it.

I get home, and I then notice the plug is wrong, and the label says it's for 220v.

There was a reason that transformer was there, it was for the sander.

Michael

A 240/120 Auto transformer is just a 240 volt winding with a tap halfway up. Very dangerous if you take your 120 off the top half instead of 5the bottom.

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John G

John G sendte dette med sin computer:

Why should that be dangerous?

Surely you do not rely on the which wire is live and which is neutral, and have the neutral connected to the cabinet or something?

Or are your insulation so bad it cannot withstand 240 volt to ground?

Leif

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All you say is correct BUT If you assume the 120 volts is just like the normalUS supply rhen you could get into trouble because connected to the top you now have 240 volts on one line and 120 on the other instead of Ground or near enough on one and 120 on the other.

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John G

"Leif Neland"

** Old US made items ( audio, radio TV etc ) have no connection to ground so the chassis floats at some mid voltage OR is linked to one side of the incoming AC line with a capacitor. The cap is usually either 0.1uF or 0.05 uF @ 400V DC.

The plug can be reversed so the user is supposed to find the way that links that cap to neutral and so brings the chassis down to a low voltage. This will result is less hum and noise in the sound.

If used with a auto tranny from a 240V supply, the cap ( aka " death cap" ) can bring the chassis to 240V or itself experience 240 VAC if the chassis is grounded by another item. 240VAC is more than such caps can stand and they often fail short.

With guitar amps, this situation is particularly lethal - hence the title "death cap"'.

FYI:

An auto tranny will deliver full AC line voltage on BOTH output wires simply if the neutral is not connected at the supply end.

... Phil

Yeah, but do you say "This is the neutral connection, I can touch this safely"?

Assume everything is "hot". Just like my father taught me: Check it is unloaded, and then treat it as if it was loaded.

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Leif Neland laid this down on his screen :

Yeah! But stop arguing. the facts are there. Some people don't know as much as you, you smart a..

There is too much "I did it it must be right" in this forum

When you are only guessing about the whole picture

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John G

So no voltage across the device connected.

Just as any device will have full AC line voltage on both inputs if the neutral is not connected in the wall socket. But no power.

Heck, if you have two/three-phase supply, and the ground is disconnected, you can get double or 1.7*line voltage. WITH power.

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don't forget you waste more iron in magnetics with that 50Hz stuff.

There was a picture and it clearly said autotransformer, no capital a, in big letters.

I'm in the US btw, if anyone thought otherwise.

Yeah, I've wanted one of those for a long time. I'm still alive so no harm done. ;-)

You are confusing autotransformers with variotransformers.

Actually, most variotransformers are also autotransformers, a subset with a movable tap.

Some variotransformers come with an isolation transformer, so you are relative safe as long as you only touch the hot circuit with one hand.

Leif

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It is a 240 volt transformer with a center tap. An autotransformer provides no isolation.

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