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400 to 480 VAC testing
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martincho:
I have to test a design with an input voltage range reaching at least 400 VAC and possibly 480 VAC.  Power consumption is about 250 W, so not a lot of current. 

Trying to figure out the most economical way to get there.  My first thought was to get a step-up variac (variable transformer) that can run off 240 VAC and get to at least 400.  They do exist.  Cost is about $2,000, which is fine.

Any other reasonable options?  Even used lab equipment would be fine.  I just don't have any part numbers to run a search.  For example, did companies like HP or Tektronix make such high voltage variable output voltage power supplies?

While I have 240 VAC single phase, I also have a digital phase converter putting out 3 phase for a CNC milling machine.  When I installed it I also installed a 4-prong twist-lock on the wall for any future application that could use this power.  I wonder if this might be the ticket?  Can I use two phases and get legit 480-is out of it?  I haven't thought this one through yet.  The device being powered is a switch-mode power supply rated for something like 300 to 500 VAC input.


Thanks,

-Martin
bdunham7:
The obvious way would simply be a 1:2  or 1:4 step-up transformer, with a variac in front of it if you like.

https://www.powervolt.com/group-ag-input-240-480vouput-120-240vpower-25-to-1500va-pd-164
NiHaoMike:
Perhaps get a transformer designed to provide 120V or 240V from 480V and use it backwards?

Might also work to use a microwave oven transformer (or two with secondaries in parallel and primaries in series) on a variac, add an end stop on the variac to prevent turning it up too much by mistake. It would also work for supplying 600V if there's a need later on.
jmelson:
"Step down transformers" were used in a lot of industrial equipment to run computers and general items from the shop floor 480 V mains.  These have jumpers to select the input and output range.  They can be connected in reverse to step up the voltage.  So, set jumpers for 480 to 240 V configuration, and then feed 240 to the LV side and get 480 from the HV side.  You can get one of these at a scrapyard for the metal scrap value.  Then, use a standard 240 V Variac to feed it.
Jon
Ground_Loop:
I have a 4 KVA 480-120 transformer running backward as a supply to several VFDs in my shop. I've been using it for more than 20 years without issue.
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