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I'm trying to get to 40KV DC, the problem is I only have 16KV diode, and when I go over 17KV the current goes high faster on the primary, any ideas how can I separate the circuit , I tried 2 transformers and build 2 bridge rectifiers but the current goes high after 17KV,
I did that and somehow still the current goes very high at 17KV, maybe something else is wrong but I was guessing it could be diode likeage since they are rated for 16KV, I just wanted to know if there is a way to set it up since I can modified the transformer. and change the circuit layout, I just want to stick with the 16kv diodes because 40kv diodes are huge and expensive,
Well then I really think that something else is wrong, maybe your transformer is saturating etc.
Thank you, I though that would be the problem, so what I did was put tape between the core to have some airgap, and I still get the same results. could still be saturating?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
im going out on a limb here, so hopefully i wont look foolish.
I have 12Kv microwave oven diodes, (Used for ionocraft research off NST's) they have breakover protect when you go over the max Peak Kv by about 1KV, they really start conducting then on the reversed polarity phase... (avalanche!!!)
remember these 5kv plus diodes are made from sereised devices on silicon/epoxy/Aluminum Oxide, and often they use this overvotage trick to save themselves...
some use the SF or the 1Nxxxx diodes and hope for the best.... The SFxxxx's are better but 26 cents each, the 1Nxxxx are 1 cent or less.... Steve ward uses ths SF's:
I quote:
HV DIODE CONSTRUCTION:
The HV diodes are actually constructed from strings of small diodes wired in series. The particular diode I used (purchased from Newark) is the SF1600. It is a 1600V, 1A, 75nS Trr, avalanche rated diode. I went for 1600V as that was the highest available for the "cheap" diodes. The 75nS Trr is important for running at these high frequencies, so that recovery losses are not significant. The avalanche rating is especially important, and means that I don't have to worry about balancing the diodes. I series 40 of these diodes per each string, giving a 64kV diode. The diodes should only see about 40kv under normal conditions. I soldered the diodes on "perf-board" and then potted them with paraffin wax inside of some 1/2" PVC tube.
If this is not the cuase, there is one other possibility, with transformers like NST's when your rectifiying only half the sine wave, the opposite sine polarity tries to saturate, thus cuasing a non-symetrical flux patttern distorting the current draw and PF. In 1997, when didnt have HV diodes, i used a normal LV diode on the primary side and cuased all kinds of impedance problems. Such that i needed to monitor the variac/NST constantly.
This failure was a result of (foolishly) operating with a half-wave rectifier on the output of the transformer. I believe this may have caused saturation of the transformer. Always use full-wave rectification on your transformers!
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Bridge rectifier for 40KV
