I want to get a transformer with 277V output so that I can run European ballasts and kWh meters (as well as 277V-only American ballasts). But no matter how hard I search, I can't find a transformer that is 120 to 277V, it is always 277V to 120V or an HVAC control transformer with 277V and 120V inputs and 12 or 24V output.
I could obviously use a multi-tap ballast for this, but I plan on running this continuosly, so I am then left with a ballast that I don't need that is wasting energy and has a high no-load current with no lamp connected.
I also read that you shouldn't backfeed a transformer, because you get a higher inrush and twice the primary current, with only half of the current capability.

If anybody can find me a real 120 to 277V transformer, it would be greatly appreciated.

You can get one of these, if you only need a 275VA unit, there's a 500VA unit too but it's out of stock and the other vendor I found requires a quantity of 500 and a lead time of 20 weeks. The attached datasheet indicated it's designed for lighting applications such as ballasts, drivers etc. Should have enough head room to run lower wattage cobraheads too.

https://ballastshop.com/120-277-275va-ic-thomas-research-products-step-up-autotransformer/
https://ballastshop.com/120-268-277-500va-ic-thomas-research-products-step-up-autotransformer/

Thanks! But what the heck is the 268V tap for?

Yeah I wasn't sure either, maybe for situations where you have higher than normal line voltage.

I want to get a transformer with 277V output so that I can run European ballasts and kWh meters (as well as 277V-only American ballasts). But no matter how hard I search, I can't find a transformer that is 120 to 277V, it is always 277V to 120V or an HVAC control transformer with 277V and 120V inputs and 12 or 24V output.
I could obviously use a multi-tap ballast for this, but I plan on running this continuosly, so I am then left with a ballast that I don't need that is wasting energy and has a high no-load current with no lamp connected.
I also read that you shouldn't backfeed a transformer, because you get a higher inrush and twice the primary current, with only half of the current capability.

If anybody can find me a real 120 to 277V transformer, it would be greatly appreciated.

As far as I understand, you can actually run a transformer in reverse too as long as you don’t exceed the maximum power load rating. This means that even though 277V to 120V step down transformers have a 277V primary and a 120V secondary, you can still use them as a step up transformer with a 120V primary and a 277V secondary. I have used such transformers to run 18W SOX low pressure sodium lamps on North American 277V F20 preheat fluorescent tube series choke ballasts in conjunction with FS4 starters as an affordable magnetic ballast solution for running 18W SOX low pressure sodium lamps and not having to rely on Fulham Workhorse electronic ballasts.

Not power, amperage. If you exceed the maximum amperage on either side...  (except with a transformer)

But what I am concerned about is that the transformer’s VA rating would go down and the inrush current would go up. Plus, pretty much every transformer and a lot of documents says you shouldn’t back feed it for those reasons.

This is one of the reasons I'm glad we're in 240V land. With a Variac I can run pretty much anything that will work at 50Hz, and for 60Hz stuff I have an inverter that runs from our 32A DC bench supply.

  What u need is a Industral transformer. 
   
   U need to keep in mind the VA of transformer is going to remain the same.   I have some british fluorrscent fixtures
 And they have no problem running on 60 Hz  except for ballast with capacitor connected the lamp in seires.  As current will shoot up.   But most British/EU gear will run normally fine on
60hz 240 volt.  I still recomend that u keep  voltage at 240 volt
 U can still have problems with some ballast cooking on 277V
  Far as USA 277 volt  gear yes Use 277 volt.   I found mine at habitat restore few years ago i got lucky there.   

   Depending on what u want to run with step up
But keep in mind  if u put  in 100 watt load on  transfirmer
 Primary side will see 1 amp as u have to factor in the transformer losses.   .83 A cuurent x 20 percent transformer loss.   Then  secondary  side  it goimg to be  240 volt   .41  amp
 277 volt would be a bit lower  ..36   

 Anyway  I hace 120/240 volt to 240/480 volt step up
    Soon i will have it set up as 240 volt in and 240 Volt out
   This will allow me to ground one side of 240 volt transformer
  This will result me a true 240 Volt  that way Ria can plug in her Tea Kettle 

 

Keep the following information in mind as well when considering inductive choke ballasts:

“If you have 240V 60Hz between two phases the ballast and Lamp will work.
The problem is the frequency, which is 20% higher than it should be which results in a higher AC resistance. To compensate that, you may use a higher voltage. For example:
220V/50Hz=4,4
X/60Hz=4,4 |*60Hz
X= 60Hz*4,4

X=264V.
You need around 260V for the Ballast and Lamp to operate properly.
The capacitor should be disconnected, as it is made for only 220V 50Hz and not for 260V 60Hz that result in a lower AC resistance (capacitor will be overloaded).

It is possible to use the Lamp like this, but it's not ideal.
For this purpose, you need an (Auto)transformer.
The best way would be to use a device that has a 110V input and a 220-230V/50Hz output. We call this "Frequenzumrichter" in German, I don't know the english word, sorry.

By the way, in Germany we have the same Problems when dealing with US stuff because our frequency is around 20% lower than the frequency used in USA. => if we would step down the voltage to 110V, we would overload the chokes, so we have to use a lower voltage to compensate for the lower ac resistance of chokes.”

This was sourced from another thread about using a European ballast in Canada.

@ funkybulb - Our kettle is 3kW, will your system handle that..?

I have access to an 240V circuit with 15A at my disposal, and very easily too.  That should be more than enough to run Ria’s tea kettle which is a resistive load, so for that, frequency doesn’t matter.

The problem is with inductive loads, frequency does matter, and when running stuff on 240V 60Hz, because as the original poster that WWHIDUSA quoted said, things run differently because of the lower voltage per square root hertz on a 60Hz supply. This has the consequence of HID lamps being underdriven, and 50Hz electricity meters under registering electricity usage. Because of this I have thought about more DIY alternatives like winding my own transformer by cutting off the high voltage secondary of an old microwave oven transformer and winding roughly 260 turns of wire on it to run 240V 50Hz equipment properly on 120V 60Hz.

Be very, very, VERY careful with microwave oven transformers. They have seriously injured and even killed people.

https://www.youtube.com/watch?v=FBeSKL9zVro

I am perfectly aware of the dangers of the original high voltage winding, but without that, it is just a big transformer, perfect for rewinding with your own turns of wire. I have no intention of ever playing with an MOT it its original high voltage form.

Yeah, I think if he was planning on rewinding it the only hazard would be to make sure that the capacitor inside the microwave is fully discharged prior to removing the transformer. There should be a bleeder resistor fitted to it which will discharge it if you leave it unplugged for a day but it's best to wait a day and then either discharge it with a well insulated resistor or a well insulated screwdriver across the terminals to ensure it's discharged.