Obit voltage doubled / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Obit voltage doubled

1 2 next

Move Thread

LAN_403

Reaching

Thu Feb 23 2006, 12:37PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

Hi, i have a few Questions about Voltage doublers.Now that my Marx generator is performing very good (29cm Sparks from a 11Stage marx, 30kV per stage,

) i have had many failures regarding the charging powersupply. i run the marx with a zvs driver and a flyback transformer. the internal flyback diode is the problem. i already destroyed 5 flyback diodes so the flybacks are running all on ac now.

now i want to build something more robust.
i want to build a voltage doubler for my 10kv 20ma obit to get 28kV dc. i ordered 200x 1n4007 diodes. i wanted to wire 2x 50 diodes in series for the hv diodes. the capacitors are 30kv 590pF, i hope thats enough.

now i want to hear what do you think about it , are the capacitors big enough? can the diodes withstand the voltage (underrated,overrated?)

Marko

Thu Feb 23 2006, 01:58PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

50 diodes in series is about enough for that voltage, but for 50Hz capacitors are way too small.
Best idea is to stack (lots) of beer bottle caps or make some ov heavy glass, at 50hz you cannot notice dielectric losses, in all cases it would be ten times bigger than marx itself.

You need a couple of nF to get some voltage boost as marx draws a lot of power.
Maybe its best idea to use 1Ns as replacment for flyback diodes (here only small filtering capacitor is needed as frequency is high) and you get nice HV DC.

If you can find two obits they can be seriesed in order to give expected power...

Reaching

Thu Feb 23 2006, 02:48PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

a marx generator does not need lots of power, 2mA is enough to load it relatively quick. and i cannot use 1n diodes to rectify the high frequency of a flyback.

yeah, and seriesing obits is a bad idea, i tried it and fried one due to the overvoltage.

i have a couple of the 590pf 30kv doorknobs, i can parallel 2 or three to get the needed capacitance

Self Defenestrate

Thu Feb 23 2006, 03:34PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

That sounds fine. I would suggest putting your multiplier under oil, or atleast the diodes. How many caps do you have left?

Marko

Thu Feb 23 2006, 04:24PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

2mA is lots when we have only 50Hz of frequency, If you don't have enough knobs (doubt two 500pf are enough) some bottle caps can help to make q&d doubler

You will have to wait for long before caps reach 28kV and fire if capacitance in doubler is low.

And I think that at such small power 1Ns could do the rectifying (in old TVs selenium rectifiers used are not too fast either but they do the job quite well). Seleniums are limited with very small current (few mA at most) with 1A of current 1N4007 will surely not burn out but they may suffer (some) switching losses, fast reaction is not really needed here.

I never tried hooking bunch of 1Ns to flyback, but I have hundreds of them and maybe I could try it, also have some new HV selenium rectifiers that also work very well.

Or some stronger valve diode may be good idea (in old TVs they were hooked directly to flyback), and you need 6V supply for filament.

obit is not a bad idea but large capacitances are needed before it can build up voltage and fire fast enough

vasil

Thu Feb 23 2006, 04:56PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

So, we finally found a good way to distroy the internal diode in the flyback secondaries.....

Dr. Shark

Fri Feb 24 2006, 09:21AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

There is a guy on ebay in germany selling 15kV diodes which are fast enough for flyback frequency. I suggest you get some of those and forget about the Obit thing. Looking at a MOT tells you that you need uF's, not nF's for a doubler at 60Hz.
On the other hand, if you just want to lash up something quickly, I guess you could get about 5W through that kind of doubler arrangement, so if you think thats enough give it a try.

Marko

Fri Feb 24 2006, 11:51AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Normal 1N4007 should work with some heating, steve ward did similar for his 1,5kW supply and CW with series of some faster diodes and losses have practically gone.
I used 1Ns in SMPS applications and they are not bad at all, in large arays we can just have few wats of dissipation in full load...

Doubling obit output could be done with llots of capacitance (doesnt need u, but maybe tens to hundreds of nF) and this is hard to acheive for that voltage.
Some huge LDPE rolled caps may be the most compact solution, but thas unneeded and huge work...

williamn

Sat Feb 25 2006, 05:09AM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

The serries 1n diodes will work just fine for the 50hz. I used a 10KV cascaded output obit and serriesed strings of 4007s for another project(cw multiplier). Since I only needed the dielectric to withstand 20KV I rolled my own capacitors. I used the thick PE sheets that people use for overhead projections, 20mil worth if I remember correctly (two 10 mil sheets). I ended up with each cap having something like 8nf. I just taped the whole mess up and popped each one in a PCV tube, no oil. They worked forever, until I gave away the obit and threw the caps away anyway.

Marko

Sat Feb 25 2006, 12:20PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

im talking about 50khz (not hz) for diodes, they get some losses at high frequencies but it doesnt matter for much.
There can also be found cheap diodes with more voltage rating and faster than 1N4007, and can be used for good halfwave or fullave rectifier for high frequencies...

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob