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SSTC 5 min questions

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ZakWolf
Thu May 30 2013, 10:06AM Print
ZakWolf Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
So I have a couple questions about Steve’s “SSTC 5 mini”

To begin, this is my first sstc. I tried building this sstc about a year ago today with no success, to many etching problems/ lack of experience made failure eminent.

schematic Link2
site Link2

Questions:

1. I do not own a variac so can I just “First light” at 120v ??? it doesn’t seem like a good idea to me. Can the sstc even function correctly if it’s fed 120v immediately?

2. Such a noob question but where would I place the switch to separate the interrupter from the driver so it can run in CW mode?

3. Lastly Steve says that C6 should be larger as it improves gate drive, what would be a better value ?

Thanks, hopefully I can get this to work properly
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Graham Armitage
Thu May 30 2013, 12:14PM
Graham Armitage Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I built this SSTC a couple of years ago, but modified the antenna input, but using a current transformer on the ground end of the secondary. Requires a small modification to the circuit but it works really well. I managed to get 19" sparks from the coil, but currents were pretty high and could not run for long without over heating.

You can run it directly on 120V but for first test I would not advise it.

I tried to run in CW mode once and fried the MOSFETS in spectacular fashion ! I would suggest you not try CW but play with pulse width to find what works best without overheating.

I used a 10uF non-polar electrolytic cap for C6.
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Physics Junkie
Thu May 30 2013, 03:43PM
Physics Junkie Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Don't run this coil cw. Since this is your first sstc, you really ought to get yourself a little 5A variac. If not, fuse it (5A) and make the interrupter external from the rest of the driver by using BNC jacks. Then you can use the PW to control the power.
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HV Enthusiast
Thu May 30 2013, 05:27PM
HV Enthusiast Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Just be careful with this coil. The half-bridge is connected directly to the mains with no isolation.

(As opposed to other SSTC single transistor coils that utilize a 24-30VAC transformer for power.)

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ZakWolf
Thu May 30 2013, 11:08PM
ZakWolf Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
Ok thats what I thought... hmmm well i dont think I can buy one now not with the cost of all the parts plus a small variac... could i use a rewound mot for like 50-80v AC? i dont want to go 100% on the first light.

I want to keep the interrupter so it starts on its own and i can mess with the output but i also want a CW mode

If i add the switch here and open it would that make the coil run in CW mode?
1369955276 3114 FT154415 Minisstcfnlsch
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Dr. Dark Current
Thu May 30 2013, 11:27PM
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Just use light bulbs in series while testing.
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Physics Junkie
Fri May 31 2013, 12:19AM
Physics Junkie Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Yes that would make it CW. But just so you know, if you exceed about 20-30ish VAC then you will blow your transistors in CW. I know from experience. I have two of these mini coils for CW but I use them to excite plasma tubes so I don't need much more than 20VAC input
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HV Enthusiast
Fri May 31 2013, 12:49AM
HV Enthusiast Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Keep in mind that when these coils are pulsed, they are usually done so at low duty cycle - say 5-10%. If you run CW, you are essentially operating the coil at 100% duty cycle.

Therefore, you can have 20 times the conduction losses and have quite a bit of heat dissipation on the MOSFETs when operating CW.
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Sigurthr
Fri May 31 2013, 04:48AM
Sigurthr Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597
My main 2.25kW SSTC is based on this coil and runs CW on full wave rectified and filtered 120Vac input regularly with run times over 5min. I used this design as a template and simply added a few additional safeties and upgrades like lower RdsON MOSFETS (FDL100N50F) and gate protection zeners. The main change I made was using a 12V version of the 74HC14 and a heavier gauge primary (gets hot!). It just takes a VERY solid half-bridge construction to handle the power safely.
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ZakWolf
Fri May 31 2013, 05:53AM
ZakWolf Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
awesome thanks everyone I think I answered just about all my questions

hopefully its a success
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