50kV Supply

[Chris Giles]

All true.

Excellent work! I appreciate Richard's comment about the diodes not being a limiting factor and also that Spellman would have been designed to have a very low % ripple which is not necessary. Given it is a charge pump circuit i think the factor determining how much power it can supply is the capacitance of the capacitors in the stack (i.e. can be estimated from the charge CV^2/2)

Joe, I'm sure anyone else trying to rig this up would appreciate any further details on the driver and/or the pinout etc of input to the Spellman HV stack, especially for those not so expert.

BR
Chris

[Joe Gayo]

The multiplier is 10 full bridge stages with 2100pF caps.

Use the excel sheet on this page to calculate regulation and drop: http://www.voltagemultipliers.com/html/multdesign.html

(But in reality I've done the work already, 75kHz drive frequency gives the least voltage drop and maximum power)

[Richard Hull]

75khz may heat the ceramic caps a bit and reduce the full power duty cycle run times, but it is rare you would need tremendous full power runs.

40kv @ 10 ma is 400 watts. In Tesla work, it was found that the higher the spark interrupt rate, ceramic capacitors would drop in capacitance as the silver deposition (plate electrodes) on the titanate ceramic faces would be blown off in spots, but that arc shock excitement in the primary circuit was horrid and sharp. In a modern switcher this should be less of an issue, but heating is certainly expected in high power filtering at high frequency.

Richard Hull

[Nicolas Krause]

Thanks for the note about this supply! The price was right, and I picked one up and will hopefully put it to good use with a bit of work in the future.

[Rex Allers]

So this HV multiplier is a 50N06 = 300W out.

I have a Glassman ER series 60N05 supply so also 300W.

I'll have to wait to get the one I ordered but I wouldn't be surprised if they are about the same design except 10 multiplier stages for the 50 kV vs. 12 stages for the 60 kV.

Here are some pictures of the 60 KV one I examined.

I made these notes when I was looking at the innards of the 60 KV multiplier.
-----
Glassman ER60N05 (or) ER60R05 negative

60KV @ 5mA (=) 300W

12 stages so ~ 5KV input (each phase)

all Caps 2000 pF 7.5 KV
room for double (parallel) caps on 1st 6 stages

1st two diodes (ground end of multiplier) are
RVT 1500 -- 15kV, 50mA, 100nS

rest of diodes (46)
apparent random mix of 3 parts
S56A, S57B
and a few S59A

Never found full PN or specs on these diodes
Since these are probably lower rated than the two input diodes,
I'd guess these may be 25 or 30 mA rated.
-----

This doesn't change anything said so far but might add a bit of info.

If Joe is pushing it to 700 W out, that's 700/50 = 14 mA. That would be below my guess of 25 or 30 mA rating for the diodes, but not as much margin as most HV multiplier designs I have looked at.

[Dennis P Brown]

Interesting pictures. Those are tiny caps compared to my 8 stage unit (20 kV/0.1pF door knob caps and 100 ma diodes.) I just used a 1500 volt, 60 Hz MOT so, certainly not in the class of continuous power like those units with their very high driver frequency but certainly my unit was a dangerous bear (a bit too; I ran it to full power all of once before setting it aside.) Quarter power from the P.S. to the stack equaled 45 kV. I still have the breast - it is in a vertical plastic cylinder tube (clear) and was filled with oil (since drained.) If I get brave, I could still revive my deuterium accelerator but just don't have a use for that monster, either. I prefer fusors (which is slated for reconstruction using a new, four-way cross and 70 kV power supply (single transformer - not a multiplier.)

[Rex Allers]

Dennis, not sure what you meant to type but those door knob caps surely must be a lot more that 0.1pF.

[Richard Hull]

I agree! maybe in the nano farad range like .002uf = 2nfd = 2000pf. They are just too big to be .1pf. I don't know if I have ever beheld a .1 pf cap.
Normal capacitance between nearby wires might be in the .1pf range.

Richard Hull

[Dennis P Brown]

Oops; you are both correct. I should have typed 2000 pF. Thanks for catching the mistake!

[Chris Giles]

Please could someone let me know if these units come with the High Voltage transformer or are just the HV multiplier? I can't find the pic which Joe posted of it(?). I found the pics which Andrew S posted of a similar complete unit here and that has the HV transformer on the main PCB, not cased with the multiplier.