Re: using an SS White x-ray transformer

Hi John,

>Original Poster: "John" <jbowers1-at-jnlk-dot-com>
>Hello everyone, first time to post here.  Here's my situation:  I have
> a 90 kV, 7 mA transformer from an older 1978 SS White x-ray
>generator and I want to readapt it for Tesla coil or other use.


In one word: forget it. The voltage is way too high and the current too
low for use as a TC power source. The high voltage (even at "only"
50kV) will give you lots of headaches trying to prevent corona (and
flash-overs between primary and secondary). The low current of
only 7mA will not allow you to recharge the primary cap in a suitable
amount of time. Remember, the ability to charge a cap in time "X"
(or make that: to obtain a certain breakrate) comes from the amount
of current the xformer can provide during this time. So, the stiffer the
PSU (i.e: <voltage and >current) is, the higher your breakrate can be.
Your transformer can only provide 630VA (90kV*7mA) and as it is an
X-ray transformer, it is (most likely) a pulse discharge xformer, which
is not meant to be used in continuous duty. Even a small NST (9-15kV
-at- 30-120mA) will give you better and easier service life than this
X-ray xformer (not to mention the weight).

>By the way, this transformer is set up kind of like a neon
>transformer:  one leg has a maximum of positive 45 kV-
>- the other leg negative 45 kV.

The reason for this is very simple. It is easier to insulate the
windings that way (to prevent disaster). The maximum voltage
above ground is "only" 45kV (the xformer is center tapped and
this center tap is grounded). If the secondary was wound as a
single unit, you would need to insulate it against 90kV above
ground and the insulation per layer (between the windings)
would need to be much thicker, as the potential (above ground)
increases as you add more winding layers.

As you went to some trouble to get this thing, I would search
for some used transformer oil (usually Shell Diala-X). If you
get lucky, you will be able to get it for free as xformer oil isnīt
re-used after a tear-down. You could (as Doc R. suggested)
make a nice loooong Jacobīs Ladder with it. You could also use
it for exploding wire/water experiments, but it will take ages to
charge a suitably sized capacitor (which wonīt be cheap or a
featherweight either). Somewhere in the X-ray unit, usually, due
to ease of construction, within the xformer box itself, you can
find a HV rectifier unit, which would be needed for those
experiments. You will need to design some current limiting and
xformer/rectifier disconnecting equipment, too. Otherwise the
rectifier will be shot in no time at all.


Coiler greets from Germany,