Voltage regulated neutral

Not only willit "work" but our local utility does it when ONE of the THREE wires which comprise a service has broken.

If you have 120/240 volt service, the auto-transformer can compensate for any ONE of them being broken.

You worry too much. Just GROUND the center tap, call it NEUTRAL and enjoy your 120/240 "service."

I suppose, but why bother?

Sounds like something from the "third world."

Truse me, if the service being 240 rather than 120/240 is the only "protection" against someone stealing your power, consider your power has being gone already.

If the "thirf" is only stealing a "little" power, he can use things like a

240/120 volt motor as an auto-transformer.

| Assume I have a conventional 120-0-120V system but only the two live | wires are present. To get a neutral I put a center tapped | autotransformer between the wires. | | So far nobody has been able to tell me that this would work but nor | has anybody been able to give a reason why it wouldn't work.

It should work fine. Some companies make transformers just for this purpose.

| Now, if I have understood this correctly, the autotransformer has an | impedance which means that if I put a load between either leg and the | neutral the voltage will decrease. At the same time, the voltage will | increase between the other leg and the neutral.

That sounds right, to the extend you don't have voltage drop on the

240 volt lines coming into this. Ground the center tap and it will always be zero and the unbalanced load will just shift the whole system slightly to one side.

This is often done on three phase power arriving as ungrounded delta. It requires a more complex transformer to work (called a "zig zag").

| To compensate for this, I figured one might simply add taps to the | autotransformer and some electronics to control them. This sounds an | awful lot like a line conditioner. (I do not intend to regulate the | voltage between the hot wires, only to keep the hot to neutral | voltages roughly equal.)

Why do they have to be equal? Ground the center tap and then it is a neutral at 0 volts. The hot wires may vary, but as long as they are within the normal voltage tolerance, why worry that one goes up and the other goes down?

You could also use a (more expensive) isolation transformer. You'd still have the voltage drop, but then instead of the other side going up, the 240 volt connections would go down.

If you really, really want stable voltage, then you just need to go with a voltage corrector of some kind (there are several kinds).

| Would it be possible to build such a device? | | I'm well aware that adding a neutral wire would normally be much | easier and more economical. However, the lack of a neutral could have | certain advantages, like making the electricity less attractive to | steal. (Code and legal aspects need not be considered.)

Where would they be stealing this from? If I was going to tap into your power, I'd probably take the 240 volts and make my own neutral.

It would work. Ground the center-tap and call it 'neutral'.

Changing transformer taps normally requires the load to be removed (taps are 'break before make'). They *do* make 'load tap changers' which allow changing taps while under load. But these are more complicated devices, with two contactors and extra inductors to allow shifting the load from one tap to another without interrupting the current flow to the load.

With a properly sized autotransformer, the voltage variation shouldn't be too bad. How tight a regulation are you looking for?

Stealing 240V isn't much harder for a thief than 120V. Not sure you'd get much theft-protection for all your hassle.

daestrom

Thanks for your input guys!

Your're right, an autotransformer without taps is a lot simpler and will do.

/Clas-Henrik