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Re: Dead xray transformer (fwd)
---------- Forwarded message ----------
Date: Fri, 27 Mar 1998 06:08:11 PST
From: Bill the arcstarter <arcstarter-at-hotmail-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: Dead xray transformer
Coilers,
I sent this message to hollmike-at-aol-dot-com regarding a dead xray
transformer. Perhaps someone else on this list would find it useful!
(I deal with medical xray equipment during my "working" hours!)
Our X-ray power supplies are rated at 20 to 60 KW. Input is 220-440
volt, single or 3-phase. We don't mfg them, but buy them from outside
vendors and integrate them into our product.
These units cost (typically) $10,000 - 20,000 new. Typical weights
range from 400-800 lbs.
The output is typically not a smooth DC - there are no output filter
caps. The output is a pulsed-DC in sync with the mains frequency. This
means that x-ray production is also pulsed, which is not a problem for
our application. Our camera system grabs the images in sync with the
radiation bursts, etc. Of course, the 3-phase units have a smoother
output.
Voltages are from 40-150KV, at currents up to 400ma.
Rectification is performed by either a vacuum-tube bridge, or a large
solid state diode bridge, like the one on my page:
http://www.geocities-dot-com/CapeCanaveral/Hangar/6160/electric.html
Note on that bridge - there are two separate 70KV bridges in series.
The large transformer has two separate 70KV windings, which feed each
bridge. This is done to ease the insulation requirements of trying to
build a single winding capable of producing 140 KV!
Now - We do use one model which is smaller - only 200 lbs or so. This
is actually a switcher - the input power is rectified into a large bank
of caps at 400-600 volts (depends on the line voltage). This DC is
chopped, etc, just like any switcher, except the output is 40-140 KV!
Also - I think these switchers don't have a very large or complicated
rectifier, as if the input switching is done properly, the output will
be mostly uni-polar. But I'm not completely certain.
>was meant to power the X-ray tube and has a control circuit attached
with all
>the caps etc(I warned him to bleed the caps before he even thought
about
$50K for an x-ray generator, eh? That seems high, even including the
tube!
Sounds like the great expense in that unit was the caps. Perhaps the
inspection process required a uniform (non-pulsed) or continuous-duty
production of x-rays?
I would think these caps might be useful for TC use. They are
certainly rated for a high enough voltage. But - are they pulse-duty?
Probably not, but perhaps the price is right!
> I am
>guessing that the control circuitry has failed and not the tranny
itself.
Our systems use a separate filament power control system. That is, the
power transformer is not current limited. However, the filament
temperature inside the tube only liberates a certain number of free
electrons, hence the tube current is limited.
Perhaps only this filament control is burned out on this NJ unit?? If
so, the rest might be useable.
>figure some HV switch or similar component failed(maybe a tube
rectifier if it
>is DC out). He said the replacement unit cost $50K. I figure the
tranny
>should be worth a lot if it is intact or repairable in a manner similar
to
>neon repair. I would not be opposed to unwinding it to half the
voltage
>output if necessary.
Also - our units are center-grounded, just like a neon. I'd expect your
supply to be the same. Thus - using one hot wire to ground would get
you down to 30 KV. IF it takes 240 volts in, then running it on 120 V
would get you down to 15 KV. You have arrived!
I'd say it might be useable! Since this is a 4KVA unit, you might not
even have to ballast it (much)!
If it is a switcher (look for a large 400-600 volt cap bank hooked
directly to the input mains) then it might be very hard to get going
again for TC use. (Depends on what is burned out)
Our non-switchers consist of a huge spiral-wrap of transformer steel,
just one single lamination (one strip, about 4 inches wide, about 4
inches thick, and about 1.5 feet in diameter! This is immense! If this
NJ unit is a non-switcher and you aren't adverse to rewiding it, you can
certainly build a pig-type supply out of the core, etc.
I think the key is to identify the voltage rating of the cap bank. This
might tell you if it is a switcher.
Go for it! But don't get yourself "kilt"!
-Bill the arcstarter
Starting arcs in Cinci, OH
http://www.geocities-dot-com/CapeCanaveral/Hangar/6160
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