Re: but all the transformers do it

--- In CAD_CAM_EDM_DRO@egroups.com, jmw@c... wrote:

> (Disclaimer: I know I'm electronically impaired.)Why isn't it the
> case that all transformers are not isolation transformers? The wire
> in the primary and secondary coils is insulated -- and so isolated

--

> right? Don't the sparks only cross the divide via induction?

(Talking

> plain vanilla single phase VAC here.)
>

You are correct. Most transformers (except autotransformers) are in
fact "isolation" transformers. Any multi-winding transformer will
allow you to re-establish a ground on the secondaries. Typically
isolation transformers are those breed of transformers that do not
change the voltage (turns ratios are the same primary to secondary)
but allow you to re-establish a new ground on the secondary (or not
if desired). If you just hang a bridge across the AC line you can
get the high voltage DC you need (160VDC) but its real easy to have a
condition where circuit ground on the electronics could be the AC hot
leg! As long as you really know what you are doing and don't try to
hook up a piece of equipment that is grounded to another reference
you can get by with it. Televisions and a lot of consumer equipment
do not have 60HZ transformers and you have to use special precautions
when you are connecting test equipment to them.

All you have to do is get your 70 volt transformer and let the
secondary of that be your new ground. If the transformer has other
windings you can use them to power the low voltage circuitry. There
are some interesting things you can do with multiwinding transformers.
You can tie two windings together in series and get a sum or
difference of the AC voltage depending on wheather they are in phase
or out. You can't measure phase with an ohmeter and the output
current is only rated for the smallest of the two windings because of
wire size. SO if you can find a transformer with the correct primary
rating you can play around with secondary windings to get various
outputs.

Parting Note. All transformers have loss evidenced as heat. Using
more than one transformer will just decrease your effiency and
increase the heat and weight. I once used two 120VAC to 28VAC
transformers back to back (28VAC tied to each other) to build a quick
Isolation transformer...worked but man was it inefficient!