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4hv.org :: Forums :: High Voltage
<< Previous thread | Next thread >>   

Xray Transformer Overvoltage

Author Post
Tue Jul 11 2017, 07:59PM Print View
Registered Member #61674
Joined: Mon Jul 03 2017, 04:01AM
Posts: 15
So I just bought a dental xray head on ebay. Its a 100kV head, but I was wondering if you could double the input voltage (240v) to double the output voltage (200kV). I will obviously ballast it, especially when overvolting it. I have seen people do it before (Andy/Photonicinduction), but I was wondering if any modifications will be required.
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Tue Jul 11 2017, 11:50PM
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1501
On x-ray equipment, the nominal kV value (which means the number printed on nameplate, invoice, and users manual) is typically peak, not RMS.

Why do you think the design would have a 100% margin against core saturation? Are you planning to use an AC frequency higher than normal?

Why do you think the design would have a 100% margin against HV insulation breakdown? I bet core saturation will get you first, but insulation failure only needs to happen once & you have a brick (well, maybe a half-brick).

It seems unusual for dental x-ray heads to have output voltages. Are you trying to make high-energy x-ray photons? 2x voltage on tube filament will probably burn it out very quickly.

Please let us know how your experiments work out. Watch out for that ionizing radiation!
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Wed Jul 12 2017, 04:19AM
Registered Member #61674
Joined: Mon Jul 03 2017, 04:01AM
Posts: 15
I am not interested in generating Xrays. Simply a high voltage nut whom likes arcs. I am simply going to use it on 60cy mains 120v. I was just wondering if you COULD overvolt it with a ballast inline for current regulation/control to obtain higher output voltages.
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Wed Jul 12 2017, 07:58AM
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 2800
As noted by klugesmith, the manufacturer will not have used a magnetic core larger than neccessary, so using 60 Hz it is unlikely that you will get even 20% headroom,
but if you increase the frequency (e.g. x2 = 120 Hz) then you can increase the ac voltage proportionately without saturating the core,
however, the hysteresis (heating) losses will be proportional to frequency, so very efficient cooling, or a low duty cycle is required.

To test the insulation of your transformer, use it as a flyback transformer,
you do not need to use high power, just enough to 'power' losses and your probe.
At these voltages the easiest 'probe' is a variable spark gap using large spherical electrodes.
radius (mm) > (kV)/3
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Sat Jul 15 2017, 10:21PM
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5232
And jumping from 60 Hz AC to 120 Hz rectified AC via full bridge will cause primary reactance problems in which the primary wont limit its own current as intended.

But you can increase frequency with a timer driven full-bridge if your willing and know how.
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