FAQ - X-ray transformers
Posted: Wed Dec 04, 2013 3:14 pm
The x-ray transformer of yesteryear is the ideal fusor power source. By yesteryear I mean really old like 30 years or more old. They weigh from 50lbs to 200lbs They are found at the following locations.
E-bay - Rare
Hamfests - extremely rare
Dentists offices - closeted old spare.
Big cities - at X-ray repair facilities.
Remember they must be rather heavy iron core units and all are in oil. If you have to pay for one, make sure it works otherwise you will be the proud owner of a super massive door stop.
Such transformers, if very old, will have tube rectifiers which will most likely be blown (filaments bad) There are no replacements for these old kenetrons. Most x-ray supplies are set up as negative hot, which is ideal for fusor work. You will be forced to replace the tubes with modern high voltage rectifiers. (Another special quest in and of itself.)
Most all older x-ray transformers have a center tapped secondary that comes out to a screw lug that must be tied to ground through a current meter in order to work. You will have to find this key lug amidst what is often a field of screw lugs on top of the transformer case. Most all of this work means un-tanking an oily mess, letting it drain a bit and replacing the rectifiers as well as metering out the primary and secondary's, finding which lead goes to which external screw post. Sound tough? It can be a daunting task for someone with zero electrical knowledge. Thus, the limiting factor here is often age and experience or lack thereof.
Rarely, one half of the secondary is open or bad. You can still get full voltage though by using a single rectifier off the good half of the secondary. The resulting rectification will be half wave (60 hz) and not the full wave 120hz. Still, very serviceable. The primary of most all x-ray transformers demands 220 volt AC of the type normally only found in air conditioner outlets. Normal 120 volt iron core units are very rare and very old. It is even more rare to find a single coil secondary, but one of its ends will still be grounded.
Individual cases may vary, of course and adaptive and creative thinking by an adroit electrical minded person can often prevail where the average neophyte would fail.
One great advantage of the x-ray transformer is the output is easily taken from 0 to full high voltage using a simple variac, auto-transformer, on the primary input circuit.
This has been a broad overview with little key specifics, but should act as more of a warning than a how too. You are working with high voltages that can kill here and a lot of internal rewiring may be required with a special outlet or even a special electrical cable run from you breaker box. make sure you are up to the task before plunking down a lot of dough.
Image of a big 750lb monster attached 240v single phase, 60kv, 55mA
Richard Hull
E-bay - Rare
Hamfests - extremely rare
Dentists offices - closeted old spare.
Big cities - at X-ray repair facilities.
Remember they must be rather heavy iron core units and all are in oil. If you have to pay for one, make sure it works otherwise you will be the proud owner of a super massive door stop.
Such transformers, if very old, will have tube rectifiers which will most likely be blown (filaments bad) There are no replacements for these old kenetrons. Most x-ray supplies are set up as negative hot, which is ideal for fusor work. You will be forced to replace the tubes with modern high voltage rectifiers. (Another special quest in and of itself.)
Most all older x-ray transformers have a center tapped secondary that comes out to a screw lug that must be tied to ground through a current meter in order to work. You will have to find this key lug amidst what is often a field of screw lugs on top of the transformer case. Most all of this work means un-tanking an oily mess, letting it drain a bit and replacing the rectifiers as well as metering out the primary and secondary's, finding which lead goes to which external screw post. Sound tough? It can be a daunting task for someone with zero electrical knowledge. Thus, the limiting factor here is often age and experience or lack thereof.
Rarely, one half of the secondary is open or bad. You can still get full voltage though by using a single rectifier off the good half of the secondary. The resulting rectification will be half wave (60 hz) and not the full wave 120hz. Still, very serviceable. The primary of most all x-ray transformers demands 220 volt AC of the type normally only found in air conditioner outlets. Normal 120 volt iron core units are very rare and very old. It is even more rare to find a single coil secondary, but one of its ends will still be grounded.
Individual cases may vary, of course and adaptive and creative thinking by an adroit electrical minded person can often prevail where the average neophyte would fail.
One great advantage of the x-ray transformer is the output is easily taken from 0 to full high voltage using a simple variac, auto-transformer, on the primary input circuit.
This has been a broad overview with little key specifics, but should act as more of a warning than a how too. You are working with high voltages that can kill here and a lot of internal rewiring may be required with a special outlet or even a special electrical cable run from you breaker box. make sure you are up to the task before plunking down a lot of dough.
Image of a big 750lb monster attached 240v single phase, 60kv, 55mA
Richard Hull