High Voltage High Current Supply Ideas

[hmour]

Hi everyone,
I need a high current hv supply (around 60kv at 20ma ideally) for a couple of projects.
I initially looked into buying one but the cheapest ones cost around 2500usd  which is way outside my budget.
Since i have an ee background and some experience with hv i decided to check some diy options out.
I initially looked at flyback transformer array supplies but those seem quite delicate and i've never worked with more than a single flyback.
My current best idea is using 4 MOTs in series to drive a 2-stage full-wave CW multiplier. However i'm not sure this will function properly and i would happily avoid it for a better/safer alternative.
Does anyone have any suggestions?
Thanks in advance

Note: I am aware of how dangerous these voltage/current levels are.

[klugesmith]

If you are using MOT's at 50 or 60 Hz, the capacitors for CW multiplier will need to be huge.
I bet the commercial 1200W HV supplies (outside your budget) use a high frequency transformer, followed by voltage multiplier with expensive HV doorknob capacitors.

A brute force path for you might be to get a line frequency (or high frequency) X-ray transformer, bigger than those for dental imaging, and rectify the output.  Note that all x-ray transformers for medial imaging are designed for very small duty cycles, and must be derated a lot for continuous operation.

[rikkitikkitavi]

I am not sure there is a "safe way" of producing 20mA at 60kV.

Even if the current itself is likely not dangerous there will probably be energy stored in capacitors.

Question:
What ripple is acceptable?
What duty is desired ?

I was thinking of a switching high voltage transformer => voltage multiplier, say operating at 30 kHz.
Say the switching transformer generates around 5kV feeding the multiplier.

You still need a lot of high voltage parts such as diodes and caps, and rated for the power and duty.
But yes, it is still a lot of EE work behind this.

60kV 20mA 100% duty is a lot, and as Klugesmith points out that even if a X-ray transformer produces in this range, it is not for continous duty.

It will also be difficult to find line frequency transformers for this range, because 60kV means a lot of insulation is necessary => larger transformers and then you dont build them as 1-2 kVA transformers but rather 3 magnitudes larger.

Maybe , maybe if you find a potential transformer somewhere? But they are normally rated < 1kVA.

[huntergroundmind]

Alternative and relatively cheap and simple way of building such power supply is to make transformer with number of well insulated secondary windings which produce say 5kv individually. Each secondary is followed by bridge rectifier or voltage doubler. Outputs of those rectifiers giving f.e. 5-10kV  are connected in series to give output you want. The secondaries don't need to be on one ferrite core. They can be a few individual cores, forming few transformers. Their secondaries "just" need to be insulated for full output voltage from core and primary. This approach gives you advantage of smaller capacitors, compared to CW, as the more stages, the more voltage drop when loaded for given value of capacitors. Here you have 1 or no stages, bridge rectifier . At the same time you keep high self-resonant frequency of secondaries, so you can run it at high frequency. which could be hard in case of using one big winding. It is actually used in some X-ray units, and tv flyback transformers (with half wave rectification just diodes "placed along" split winding).

[klugesmith]

Yes on that idea -- several isolated HV secondary windings that are individually rectified and then connected in series.  I have some commercial supplies that work that way, all of them with high frequency ferrite cores.
One is from a little dental x-ray generator.
Two are the cathode and anode tanks from a 125 kV Bennett x-ray generator, like the one pictured here:
https://www.xraypartsdepot.com/e30040-c

Discussed at 4hv.org here: https://4hv.org/e107_plugins/forum/forum_viewtopic.php?p=1&id=166826#post-166826
I'm sad to report that 10 years have passed since then, and I have never energized the transformers except with high current at 60 Hz to measure core saturation.

[rikkitikkitavi]

Here is a guy who built a HV supply,albeit at lower voltage but considerably more power inline with the proposed design of multiple HV converters stacked

https://www.eltem.fi/thor.htm

The link is actually a cornucopia of HV info.

[JoeBusic]

Transformer cascade. 4x 15kV should be good. If it's AC you're going for.