Re: Help for MOT SGTC
Patric, Mon Aug 19 2013, 07:00AM

Sorry, it must be this circuit:

Re: Help for MOT SGTC
Dr. Dark Current, Mon Aug 19 2013, 04:16PM

Hi, this is a voltage tripler, so you can use just 3 caps on the output. The resistors are not necessary as the caps contain 10Meg bleeder resistors.

Re: Help for MOT SGTC
Patric, Tue Aug 20 2013, 10:13AM


Thank you for the hints!
Is current limiting necessary when using it in a SGTC?

Re: Help for MOT SGTC
Feathers, Sun Sept 01 2013, 01:47AM

Current limiting is necessary with an MOT.

You can use either a resistive or inductive ballast.

For a resistive ballast, its: (line voltage)/(desired current)=(ballast resistance). Then poke around your hardware store for a hot water heater of that resistance, stick it in a bucket of water, and you're ready to go.

This will however burn off tons of power thats doing nothing usefull.

Many use an inductive ballast to increase the impedance of the transformer's primary circuit. It is common to use another MOT as an inductor to do this. Some short the secondary, some remove it alltogether, but the idea is to run the primary in series as an inductor.

Re: Help for MOT SGTC
Patric, Sun Sept 01 2013, 08:17AM

Thank you!

Re: Help for MOT SGTC
redruM69, Wed Sept 11 2013, 02:57AM



I beg to differ. A well tuned MOT powered SGTC does not require ballast. MOT's do have shunts in them to limit current when shorted, albeit not for an extended time. I'm running dual MOT's unballasted, no tripler, no filter. The transformers only get warm to the touch after several minutes of run time:

Re: Help for MOT SGTC
Patric, Wed Sept 11 2013, 07:48AM

That is fantastic! How do you make your spark gap? It must be very small, with only two MOTs.

Re: Help for MOT SGTC
redruM69, Thu Sept 12 2013, 03:06AM


Its an asynch rotary. Gap size is about 2mm (x2 for each side).

Re: Help for MOT SGTC
Patric, Thu Nov 21 2013, 08:02PM

Thank you very much, it is all clear now for me! The capacitor is the only thing that bothers me. What value is optimal? I think 10 to 20nF is enough for me. I have several choices:
http://www.ebay.com/itm/200844654385
http://www.ebay.com/itm/190931420792
http://www.ebay.com/itm/190855218801
http://www.ebay.com/itm/200963004770
Can you please help me once more? I will use two MOT's with AC.

Re: Help for MOT SGTC
twist2b, Fri Nov 22 2013, 05:03AM

redruM69! I had seen your work before browsing youtube I didn't know you were on 4hv haha. that is an awesome system you got there. Did it cost you a lot?

Re: Help for MOT SGTC
redruM69, Fri Nov 22 2013, 06:34AM


Thanks!
The spun aluminum toroids, and the 942c caps were the expensive bits. The rest is trivial stuff. A lot was just junk that I collected over time.
On Halloween I had it on display outdoors. Streamers occasionally peaked around 6ft! Not bad for a 5.25" coil!

Re: Help for MOT SGTC
Dr. Dark Current, Fri Nov 22 2013, 09:47AM

Has anyone mentioned the charging inductor, which is required in a DC-powered SGTC?

Re: Help for MOT SGTC
Patric, Sun Nov 24 2013, 07:22PM

Please can someone give an opinion about those capacitors? I'll be very grateful!

Re: Help for MOT SGTC
redruM69, Mon Nov 25 2013, 06:15AM


The first one, no idea. As for the other 3, I've messed with doorknobs in the past. The old surplus ones are hit or miss, most often miss. They aren't pulse rated and usually dont work. If you are going to use doorknobs, try to find TDK or Murata pulse rated ones. I've had some success with those in the past.
Have you considered building an MMC with 942c series caps?

Re: Help for MOT SGTC
Patric, Mon Nov 25 2013, 06:41PM

Caps are so (...) expensive! But thank you!