So I needed a way to automatically switch between 110 Volt and 240 Volt AC inputs and came up with the simple following

The theory being when 220 Volts is received then K1 is energized and the AC output is passed through as 220 Volts
When 110 Volts is received K1 does not get energized and is passed through the auto transformer to step up the output to 220 Volts.
It works as it should , but the problem I am having is relay chatter on 110 Volts , as K1 seems to want to operate down to 90 Volts!!! ( though the data sheet says 150 Volts ).
Any recommendations on how to solve this or pointers to a better way with a schematic would be appreciated .

Thanks

 

Look up the, "must operate" voltage for your relay. I looked one up and saw, "80%". Therefore, you can remove up to 44 volts and that relay will still work.
Put this in series with your relay coil.

 

Look up the, "must operate" voltage for your relay. I looked one up and saw, "80%". Therefore, you can remove up to 44 volts and that relay will still work.
Put this in series with your relay coil.

Thanks Man !
Will try this.

 

You should also consider what would happen if the relay fails to operate and you have 220V applied to the 110V winding. You might want to add some form of overvoltage clamp across the 110V primary.