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Jrz126

Mon Aug 14 2006, 12:23PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

Well I ordered 200 caps (0.68 uF and 1200V) based on MR Ward's recommendation. They are being delivered today. I think there must be a Murphy's Law that no matter when you order a package, it will always be delivered on a monday. So you sit around all weekend waiting for it.

What are some things to keep in mind while trying to do a low inductance layout?

Steve Ward

Mon Aug 14 2006, 03:25PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Muahaha! Now this coil can become the largest OLTC when its ready

.

For the MMC, since its "only" 2400V, you can rely on the PC board material to insulate just fine. So, what im envisioning is a large 2 side PCB, set up very similar to your current MMC, where each side of the board is one of the termination points. Now you just have to series 2 caps before connecting them to the board. I would suggest putting 2 caps sitting parallel to each other, so they form a upside down U shape (the leads connect the 2 legs of the U). That should be the most space efficient, and keep the inductance down. You could probably find some way to put caps on both sides of the PCB like you did with your current MMC. Anyway, careful thought is required to minimize the inductance on a 100 cap MMC bank!

If you want, i can draw a picture of what i was trying to describe.

Jrz126

Mon Aug 14 2006, 11:54PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

I think I understand what you are talking about. Now how would attach the caps to the front side of the pcb? I could drill a hole for the one lead to go through, but there isnt an easy way to secure the second one.

Also, I may need to use more than 1 double sided PCB. I can only fit 82 caps on a 6x9" board. =14.7uF

This is definitly going to be a challange...

Jrz126

Wed Aug 16 2006, 06:28PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

I think I might try to use some of these

to mount my capacitors. The plug will be mounted on the PCB so that it is only conducting on one side of the PCB. Then I'll stick the leads of the capacitors (2 caps, one on each side of the board) into it and solder them in.

It'll be pretty complicated and a PITA since I will be trying to cram as many caps as possible onto this board. But its the best idea I can come up with at the moment.

Will the stray inductance have a significant affect on the output of my TC? It'll be alot of work to build this low inductance cap bank, and if I'll only lose 3-4" of spark from building a simpler design, then I'm ok with that.

Also, Is it possible to operate a microcontroller near a tesla coil as long as it is well sheilded? I'm thinking about building a microcontroller based SCR powersupply, and I'd hate to go through all of that work and have it screw up once I start making streamers.

Marko

Wed Aug 16 2006, 06:44PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Will the stray inductance have a significant affect on the output of my TC? It'll be alot of work to build this low inductance cap bank, and if I'll only lose 3-4" of spark from building a simpler design, then I'm ok with that.

It's not about the output, but rather your ability to put most of inductance you have into the primary.

Using2 primary turns would cut your surge current in half, reducing losses havily and allowing you to use lower coupling.

Also, Is it possible to operate a microcontroller near a tesla coil as long as it is well sheilded? I'm thinking about building a microcontroller based SCR powersupply, and I'd hate to go through all of that work and have it screw up once I start making streamers.

You can build a 'solid state variac' easily from 2 SCR's adn few other components:

Steve Ward

Wed Aug 16 2006, 11:17PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Provided the uC is electrically isolated and in a shielded box, it might just work

. Id really suggest just finding some other controller IC thats made for what you want to do. uCs and tesla coils together just dont give me a good feeling.

As to the inductance in the cap bank. Basically, it will add to your primary inductance. This normally doesnt matter, but if you only have 1 primary turn to start with, your leakage inductance could be a good % of the primary inductance. What this does is lowers the overall coupling coefficient to the secondary coil. You might be able to make up for that with raising the primary, but at some point, the coils will arc over. If arc over is your limitation, then to get the maximum coupling, you need to have the least leakage inductance in circuit as possible.

I think if you stick with the idea of a double sided PC board to construct the MMC, you will do just fine.

Jrz126

Thu Aug 17 2006, 07:19PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

Well the parts are ordered for the cap bank. Hopefully it wont be too time consuming. I think I might go with a 2-turn primary so I can get away with less caps.

Where can I get/make some high current inductors for currentlimiting? Whats a good inductance to shoot for?

I'm testing my SCR rectifier using a 19Vrms AC input from a transformer as my AC input. I'm getting ~34 volts out. When I try to connect up my oscope probe, the output drops to ~10-15 volts. I checked the voltage between my probe ground and the SCR power supply with my DMM and its reading ~30 volts.
anyone know whats going on here?

Jrz126

Thu Aug 24 2006, 12:19PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

I recieved my banana plugs from the ebay auction a couple days ago. I was kinda surprised by the size of the box.
It turns out that they are individually packaged.
Yep, there were a total 479 in there (should have been 500).

I think I might be able to get 120 caps (there's 200 in that box) onto a 6x9" board

.

I'll try to post some more tonight.

Marko

Thu Aug 24 2006, 12:27PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Lol for bannana plugs

Why don't you just solder the caps to piece of copper clad boaqrd or prefboard?

I don't get why you nees a ton of bananna plugs (exscept for increasing overall inductance)?

Jrz126

Thu Aug 24 2006, 01:09PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

Thats the plan. I'm going to have 60 on each side of the board. The problem is trying to attach the lead that doesn't go through the board. This is where the banana plugs come in. With the banana plugs and some plastic insulators, I'll be able to have the lead stick through, but it will still be attached to the front of the board.
I dunno if that makes sense but I'll try have some pics up later tonight or tomorrow.

Oh, and I'll only need 60 of the plugs, but the auction was for 500. I only paid $26 for them.

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