Never heard of a Auto Transformer with Isolation.

Of course,
I was just emphasizing that there would be none.

 

If the OP is in N.A., the standard power system voltage has been 120/240 since the '50;s !
(120v-0-120v)

 

I agree.
Did you think I implied otherwise?

I thought so, but clearly, I was mistaken.

 

I have done exactly what was suggested in post #5 and it worked very well. There is a fair market foe autotransformers to adjust local voltages. Additional windings are the standard approach.
OF COURSE it is important for the users to understand that there is no isolation, and it is important to not overload any portion of the transformer. Thus the user must be aware of what they are doing.

 

I have done exactly what was suggested in post #5 and it worked very well. There is a fair market foe autotransformers to adjust local voltages. Additional windings are the standard approach.
OF COURSE it is important for the users to understand that there is no isolation, and it is important to not overload any portion of the transformer. Thus the user must be aware of what they are doing.

Has anyone found the specification for this transformer? Without a specification I would not hazard a guess as to the design operating frequency, the winding/winding and the primary to frame insulation breakdown voltages. I'm sure it would 'work' - at least for a while, but I would not sign it off as 'safe'

 

Has anyone found the specification for this transformer? Without a specification I would not hazard a guess as to the design operating frequency, the winding/winding and the primary to frame insulation breakdown voltages. I'm sure it would 'work' - at least for a while, but I would not sign it off as 'safe'

Could you post a picture of the whole transformer, with dimensions. That should verify if it is a mains-frequency transformer.
If so, it's probably 60Hz, as there are few countries that use 120V/50Hz.

 

Consider that the one view of the transformer that had markings included for the secondary: "100V, 7.5 A" .
That tells me that this is not a small weak transformer, but that it has a fair amount of power capability. 100 X 7.5=750 watts. And if we assume that the 100 volt side is a secondary, then the primary must also be able to handle 750 watts, and a bit more because efficiency is less than 100%.

OR this one could have been for the parts of Japan that use 100 volt mains.
The only concern I offer is about the polarity of that second winding.

Does the TS have an AC voltmeter able to measure up to over 200 volts AC???
Does the TS have a source of 120 volt AC available for a momentary test??
Is the TS able and willing to do a very short mains connection test??

 

The OP dwells where power Co. supply is 220v,
Hz = ?

 

OK, the challenge is a big one, which is to get the phasing of the two windings correct the first try. My guess is Pink to Black, with white and "sky blue across the 220 volt mains. If the TS has access to a 220 volt incandescent light bulb, put that in series with the mains feed and then measure the voltages across the windings. The bulb should be about half brightness. If it is full bright then the phasing is wrong.