On Thu, 2 Feb 2017 12:52:28 -0800 (PST),
wrote:

On Thursday, February 2, 2017 at 3:30:12 PM UTC-5, wrote:
I was looking at the commercial isolation transformers and they are very
costly, so I decided to build my own. After all, all they are is a
transformer with a power cord on the primary and an outlet (and fuse) on
the secondary. And I already have an enclosure to put it in.

I'm looking at a bare transformer to use as an 120v isolation
Transformer. (120v in, 120v out). The transformer primary is 480 / 240.
The secondary is 240 / 120.

This is for single phase 60 cycle AC. (U.S. power).

Will it work if I connect the 240 lugs on the primary to 120 volts, and
use the 240 lugs on the secondary to obtain 120 volts.
Electrically, this makes sense, but I am not 100% sure, so I thought I'd
ask.

Also, this Transformer is rated at 750 va.

Using the calculator chart on
http://www.rapidtables.com/calc/elec...calculator.htm
750 va should give me 6.25 A output. (Which should be enough amperage
for anything I need to test on my bench).

However, since this transformer was intended to be used at 240 / 480 on
the primary, will it still give me 750 va (6.25 A) on the secondary if I
run it on 120v?

Thanks

My read on this is that the transformer converts input to 1/2 voltage on output. This
means that connecting 240 on the input side will result in 120 on the output side (similarly 480 == 240).

You need a 1:1 transformer not a 2:1 as described here.

Dan

Note: If the transformer you have has multiple windings or taps, it may be usable as a 1:1
transformer. How many connections are there?

In case I was not clear.

Primary is labeled 240 or 480 v
Secondary is labeled 240 or 120

What I want to do is connect 120 volts to the primary winding intended
for 240.

Then use the secondary winding intended to be for 240. This would be
1:1, except I'm running 120 volts into windings made for 240volts.