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OLTC Research and Experimentation

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DerStrom8

Tue Aug 05 2014, 05:49PM

Registered Member #3704 Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92

Hi guys,

I recently picked up some IGBT bricks at an electronics flea market and began thinking about OLTCs. I don't plan on building one any time soon, but I was curious where I might find some research for them. I realize they are probably outdated by now, considering the recent introduction of DRSSTCs, but I would be curious to read some documentation, if it exists. I know the basic theory of their operation and the overall diagram, but if anyone would like to share their own experiences and coils, I would appreciate it!

Regards,
Matt

GrantX

Wed Aug 06 2014, 02:06AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

There's a great deal of information on OLTC's spread across Steve Conner's site: http://scopeboy.com/tesla/

It's all mainly theory of operation, diagrams and photos of the physical circuits, but it seems to be enough to try building a small OLTC by yourself.

If you're interested in older exotic SSTC topologies you should have a look at SISG coils - They use SIDAC's and IGBT's to switch a very high input voltage (more than 10kV if you desire), so they operate in a similar fashion to a traditional spark gap coil. I've heard that the SISG modules are more efficient than a spark gap, so theoretically they can easily match the performance of a same-sized SGTC ("citation needed...").

DerStrom8

Wed Aug 06 2014, 02:11AM

Registered Member #3704 Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92

GrantX wrote ...

There's a great deal of information on OLTC's spread across Steve Conner's site: http://scopeboy.com/tesla/

It's all mainly theory of operation, diagrams and photos of the physical circuits, but it seems to be enough to try building a small OLTC by yourself.

If you're interested in older exotic SSTC topologies you should have a look at SISG coils - They use SIDAC's and IGBT's to switch a very high input voltage (more than 10kV if you desire), so they operate in a similar fashion to a traditional spark gap coil. I've heard that the SISG modules are more efficient than a spark gap, so theoretically they can easily match the performance of a same-sized SGTC ("citation needed...").

Thanks very much, that definitely sounds like some interesting reading! I saw a reference recently to a SISG but didn't know what it was.

Cheers,
Matt

Hydron

Wed Aug 06 2014, 05:39AM

Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208

You may also find some of the stuff Finn Hammer did to be of interest - google "Hammertone V-Twin" and search "BRISG" on 4hv for a start. Hit the video search option on google for a couple more videos of the coil, including the Palais de Tokyo installation.

GrantX

Wed Aug 06 2014, 10:42AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

Hydron wrote ...

You may also find some of the stuff Finn Hammer did to be of interest - google "Hammertone V-Twin" and search "BRISG" on 4hv for a start. Hit the video search option on google for a couple more videos of the coil, including the Palais de Tokyo installation.

I forgot to mention that! That Hammertone SISG coil is a work of art (and it has quite a cool sound).

DerStrom8: IIRC the BRISG coils had an IGBT brick in the SISG modules and used microwave oven transformers for power, might be a nice fate for your shiny new bricks :)

I read some references to the "Piranha" I and II SISG coils on the TCML which sounded like interesting beasts. Is there any information available somewhere? People were saying that the primary circuit was rather dangerous and naturally I really want to see some circuit specs and photos. :)

(If you can't already tell I've been interested in SISG coils for a while - I WILL build one, someday)

DerStrom8

Wed Aug 06 2014, 01:32PM

Registered Member #3704 Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92

Great leads guys, thanks a lot!

Unfortunately my bricks aren't exactly "shiny new". Also, after looking at the datasheet I'm not sure they'd be suitable for Tesla Coil operation, as the current rating is very low and the switching times are very high:

It did get me thinking about OLTCs though, whether I use it in one or not is a completely different matter.

Thanks again!
Matt

1407331979 3704 FT165228 1528598 829027357109164 1040129784330857895 N

EDIT:
Okay, now I've got what may be a stupid question, but has anyone ever used TRIACs to drive a small (low-voltage) tesla coil, or is it even possible?

Dr. Dark Current

Wed Aug 06 2014, 06:47PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

OLTCs have a problem of difficult tuning, usually you use 1 turn on the primary and tune by the capacitance.

The peak currents in normal-sized OLTCs are several thousand Amps.

The SCR is too slow for TC work, it just dissipates the energy in the tank cap and doesn't ring much oscillation.

DerStrom8

Wed Aug 06 2014, 06:49PM

Registered Member #3704 Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92

Dr. Dark Current wrote ...

OLTCs have a problem of difficult tuning, usually you use 1 turn on the primary and tune by the capacitance.

The peak currents in normal-sized OLTCs are several thousand Amps.

The SCR is too slow for TC work, it just dissipates the energy in the tank cap and doesn't ring much oscillation.

I had a feeling that was the case. Thanks a lot!

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