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Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
Okay, I started building this thing on Saturday just for the hell of it. I had an old secondary wound with 36 awg wire 2.5" x 10" so I decided to cut it in half and make a small coil out of half of it.
It's got a half bridge of IRF450's and a voltage doubler all crammed into a computer power supply case. Secondary is 4.5" long with a 4" sphere on top. It uses secondary base feedback and runs at 500KHz with the topload. The sphere is too big and I'm thinking of replacing it with a small toroid.
I did manage to kill the fets after taking the video. In the last two pics it was running off ~75v on the variac. The secondary gets warm after shorts runs.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Tom540 wrote ...
Okay, I started building this thing on Saturday just for the hell of it. I had an old secondary wound with 36 awg wire 2.5" x 10" so I decided to cut it in half and make a small coil out of half of it.
It's got a half bridge of IRF450's and a voltage doubler all crammed into a computer power supply case. Secondary is 4.5" long with a 4" sphere on top. It uses secondary base feedback and runs at 500KHz with the topload. The sphere is too big and I'm thinking of replacing it with a small toroid.
I did manage to kill the fets after taking the video. In the last two pics it was running off ~75v on the variac. The secondary gets warm after shorts runs.
Beautifull litle "dildo". It's a pity that the FET based bridge topology is so fragile (I destroyed my IRF450 half bridge immediatelly after turned it on)...
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I really don't have a clue how you guys get out at all with these tiny primaries. Have you tried calculating magnetizing current? What are dimensions of your primary coil?
I wouldn't want it to be >3 amps for IRFP450's and from glance I'd use like 15 turns or more.
Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
I didn't calculate anything I just started slapping it together. I would have put more turns but thats all the wire I had in that size for the primary. I'll probably get some slightly thinner stuff and put more turns on it later after I replace the bad FETs.
I just ran out of the FGA40n60's I'm pretty sure they would be able to handle the 500KHz this thing runs at and they're much more heavy duty.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Tom540 wrote ...
A small update. I made a tiny tape toroid. I'm not really happy with the spark length and it arcs to the primary past 90 volts on the variac.
Put a protection plastic disk on your primary... you can use old LP - just cut a hole inside with some simple resistive wire based cutter (I've made one from old 30V 200W transformer, 20W 1ohm resitor in 5 minutes)
Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
Christopher Miles wrote ...
I am down to 3.5 turns and have not blown a FET yet in 2 years. This coil must have 100 hrs on it. It now is at the local power company still running demo's.
Could go down to 2 turns but the FET's start to cry a bit @
Use a big fat copper primary.........................was a bitch to bend the copper however.
Your fets are 48 amp lol. I was thinking about getting some 44n50's off ebay for this but since I didn't blow them why bother?
Speaking of the fets. it turns out I didn't blow them. I blew the ultrafast diodes. I didn't replace them I just cut them off and it works fine.
I think a big fat copper primary might be overkill for my 4.5" secondary, hehe. I do have some 10 awg solid strand wire. I could just have that wind around without a former.
Registered Member #973
Joined: Tue Aug 28 2007, 07:32PM
Location: Pittsburgh, PA
Posts: 66
reminds me of my topload
that primary cable on mine is insanely thick, and was a pain to make. Is it alright if i use stranded copper cable instead of copper pipe/solid copper wire?
anyway, you're ahead of me, i have yet to run mine past 40V on the variac. It works great with all 9 turns and the mosfets only get slighty warm, while giving 2.5" discharge from a needle point. I also use sec base feedback instead of antenna, i think it runs smoother. Mine runs at 330kHz, using a fullbridge of IRFP460's which you can see on the bottom right. For the topload i used flexible black hose covered in Al tape.
I've used down to 2 primary turns on some of my earlier tests, only to see the current spike up, the mosfets heat up, and the streamer length go down a bit. your primary seems very close to the topload, which might be why it has arced there.
Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
reminds me of my topload
that primary cable on mine is insanely thick, and was a pain to make. Is it alright if i use stranded copper cable instead of copper pipe/solid copper wire?
Yeah I think that is probably overkill. My primary is made from CAT5 2 twisted pairs paralelled.
anyway, you're ahead of me, i have yet to run mine past 40V on the variac. It works great with all 9 turns and the mosfets only get slighty warm, while giving 2.5" discharge from a needle point. I also use sec base feedback instead of antenna, i think it runs smoother. Mine runs at 330kHz, using a fullbridge of IRFP460's which you can see on the bottom right. For the topload i used flexible black hose covered in Al tape.
What size is your secondary?
I've used down to 2 primary turns on some of my earlier tests, only to see the current spike up, the mosfets heat up, and the streamer length go down a bit. your primary seems very close to the topload, which might be why it has arced there.
nice coil btw
Thanks, I was using 6 turns but the FETS seemed to get a little hot. I'm not too happy with the spark length considering I'm using a full wave doubler on this thing.
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Mini SSTC
2 twisted pairs paralelled.