An auto transformer has no isolation between the primary and secondary windings, correct? This unit here says "205voc cw auto transformer 60hz" on it yet I don't see any connection between the windings except outside the core between the leads leading to the starter and capacitor. Is this some sort of special type or is there an internal connection I can't see?

Any fun ideas I could use this for?

 

The other side and a better shot of the label.

 

It is a combined step-up transformer, ballast, ignitor for some exotic lamp, like mercury vapor or sodium vapor. It is not isolated primary to secondary. It has multiple taps on the primary side for various line voltages.

 

How are they not isolated? Where is the connection? Even the schematic on the label only shows the capacitor connecting the 2 sides?

Forgive my ignorance, I'm new to this.

 

To me The schematic shows a connection between both windings? It is possible this is intended to be made externally?
A resistance check would show it.
Max.

 

the capacitor is probably connected to a seperate isolated winding, like a sola constant voltage transformer, hleps regulate the output of the transformer, but not connected to any external circuit except the cap.

 

How are they not isolated? Where is the connection? Even the schematic on the label only shows the capacitor connecting the 2 sides?

With or without the ignitor in the circuit?

 

Doh! Why didn't I think of that? I just checked, they are not connected. It's like 2 auto transformers in 1. The only connection is through the capacitor. When it is hooked up the yellow wire on the primary side is used with the ignitor along with the red, blue and white/red wire from the secondary. The remaining black/white on the secondary is the one connected to the capacitor. So I could use this as an isolation transformer, right? How would I figure out amps and voltage outout? I guess I can just hook it up for voltage but what about amps?

 

Look up the current for a 250 watt High Pressure Sodium bulb and that is the output current available.

 

No, not 2 auto transformers in 1, it's a multiwinding isolation transformer - when not used for it's intended purpose.

 

There are current ratings on the label for different voltages. Would I be correct in assuming I could count on the same current if I used the same taps as the rated voltages?

 

Those are the input current ratings.
I would actually have to think to decide if 1 amp into the lowest voltage tap would cause 1 amp to arrive at a higher voltage tap without overheating the copper wire used to wind the higher voltage taps.

I think, "no".
You will have to limit yourself to the maximum current labeled for the higher voltage tap.

 

Look up the current for a 250 watt High Pressure Sodium bulb and that is the output current available.

The secondary current available will depend on what the resultant voltage (winding) is selected to be used, and then conform to the estimated Va rating based on the original load.
I should add also the wire gauge of the secondary used.
Max.

 

The secondary current available will depend on what the resultant voltage (winding) is selected to be used, and then conform to the estimated Va rating based on the original load.
Max.

Sorry. I was assuming the original configuration to determine the secondary output current. When the concept changes to, "How do I use this for an auto-transformer?" the intended secondary current is only a reflection of the input capabilities.