Earth tapped transformers

[phil68]

Had a look at a Whirlpool Ice M/C today, the type that makes a block of ice that then slides onto a hot-wire cutting grid. The grid is powered at 20 volts from a step-down transformer. Now I think I've got a reasonable understanding of things electrical & even electronic -but what does the earth tapping part of the transformer do There was a live @ 230vac going in & the (I guess) 20vac live & neutral going to the cutting grid, but no neutral supply on the 230v side, just a cable going to earth from the windings

[frank]

This sounds like an autotransformer where the secondary winding is part of the primary winding so as to give increased current capabilities to the lower voltage side. Have a look here http://ourworld.compuserve.com/homep...h/autoxfmr.htm or do a search for autotransformers

[PobodysNerfect]

Had a look at a Whirlpool Ice M/C today, the type that makes a block of ice that then slides onto a hot-wire cutting grid. The grid is powered at 20 volts from a step-down transformer. Now I think I've got a reasonable understanding of things electrical & even electronic -but what does the earth tapping part of the transformer do There was a live @ 230vac going in & the (I guess) 20vac live & neutral going to the cutting grid, but no neutral supply on the 230v side, just a cable going to earth from the windings

As Frank says it is most likely an autotransformer. They are cheap, but not particular safe, as there are no isolation between primary and secondary side.

A standard autotransformer (step down) is shown here.

A________________C
{
{
{
{________D
{
{
{
B_______{


If you have 130V between A-B, 20V between C-D and B is live and A neutral, then all is good and it will not kill you if you
touch C or D.

If, on the other hand, you connect the live to A and neutral to B, then C also will be live, and it is not safe to touch C or D. This
possibility you can of course eliminated if you connect B to live and A to earth. Normally this would cause no trouble, but I am not sure if it is permitted to use earth as neutral in this way.

Also, if the connection to A is open (blown fuse (fuses are not allowed here)) then again you have an unsafe situation.

Saludos cordiales,

Jan

[PobodysNerfect]

Sorry, my drawing went to hell.

I hope all know how my transformer was supposed to look.

Jan

[Steve Wright]

phil68

In the US many codes require the secondary of transformers be grounded.

The primary and secondary are individual curcuits. You have to check phase to phase to get accurate readings.

Steve Wright CM

[bernard]

Hi

Here,s some helpful info on whirlpool ice machines.

www.truetex.com/icemachine.htm

Regards Bernard

[frank]

Good link Bernard but his methods for re-charging the unit -