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Registered Member #1034
Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154
I have been upgrading my DC resonant charging Tesla coil to run at higher power levels and now my four paralleled 8020 diode tubes that I use for a "de Quing diode" get overheated when I run the coil. The other day I decided to try using a solid state diode in place of the rather cumbersome vacuum tube rectifier.
I've seen web pages by other coilers who have done this by connecting the dequing diode between the dc smoothing capacitor and the charging choke so I figured I'd give it a try. The diode I used was rated for 30kv , 2 amps continuous, 8 amps surge. I ran the coil at about the 10 kva power level ( about 1 amp at 10kv) and it fried the dequing diode in less than a minute.
Now I'm thinking about expanding my array of 8020 diode tubes but this is going to be a pain because I will have to have a bigger cabinet for x-ray shielding and I might have to buy a few more of the tubes. Dose anyone have any ideas on how I can get a solid state dequing diode to work ?
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Was the diode very hot right after the failure?
Id suggest looking into some other types of HV diodes, preferably ones that are ultra-fast and avalanche rated (like the UF4007, but there are many others around). You can string them up provided you derate them by a good margin (maybe 50%). Still pretty cheap.
Of course tubes are very forgiving as im sure you know.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Steve Ward wrote ...
Was the diode very hot right after the failure?
Id suggest looking into some other types of HV diodes, preferably ones that are ultra-fast and avalanche rated (like the UF4007, but there are many others around). You can string them up provided you derate them by a good margin (maybe 50%). Still pretty cheap.
Of course tubes are very forgiving as im sure you know.
Steve, why would a de-quing diode need to be fast?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I used a big series string of 1N5408s with a 1000pF ceramic disc cap across each. The de-Qing diode actually outlived the rest of the coil.
What are you using for a charging choke? If the choke isn't working well, it could be saturating and pulling huge current spikes through your diodes. That would kill them, not to mention explaining why your diode tubes overheat.
Registered Member #1034
Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154
What are you using for a charging choke? If the choke isn't working well, it could be saturating and pulling huge current spikes through your diodes. That would kill them, not to mention explaining why your diode tubes overheat.
The charging choke is home made. It consist of about 2300 turns of 24 gauge wire wound on a bar shaped laminated core, 4 3/4" x 4 3/4" x 11" . The inductance is 6 Henerys.
I know why the tubes are over heating. They are rated for 100ma average current each and I'm using 4 of them in parallel. I'm probably drawing close to an amp though them at the power level I am running. That would be 250 ma each.
I think I will try a string of diodes like the ones Dr. Conner is talking about. The diode I fried is one I got off of Ebay and It dose not have detailed specs.
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Dequing diode for DC resenant charging Tesla coil
