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Coil length to arc length ratio?

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LAN_403

nzoomed

Sun Mar 06 2016, 11:59PM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Is there any rule of thumb on the height of a secondary to the maximum arc length before you get too many hits to the strike ring?

Ive read that if the coil is too powerful for its size, that you will often see too many hits to the strike ring, yet i cant find any charts or data to use as a guide on the size of my coil.

My coil will be 72cm (28.5 inches) in length and im unsure what power output i will get from my pair of CM300 IGBT's, but i expect i will get at least 2m arcs from it if i can run it at 850 Apk, i believe i can push it easily to 1000Apk, as, my MMC should be able to handle this.

I think i would be happy with 2M arcs, but the longer the better, as long as my outlet can handle the power, and i will probably need a larger Variac.

So basically is my coil the right length? I think my coil is similar length to Loanoceans DRSSTC3, so i think i will be OK, but am still interested to know what rule of thumb to use.

Hazmatt_(The Underdog)

Mon Mar 07 2016, 01:27AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

if you want some hard data go to Stefan's Tesla Coil pages. I've looked at his data for a long time and it seems reasonable, and he has a lot of good information.

nzoomed

Mon Mar 07 2016, 09:44AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Hazmatt_(The Underdog) wrote ...

if you want some hard data go to Stefan's Tesla Coil pages. I've looked at his data for a long time and it seems reasonable, and he has a lot of good information.

OK, he has alot of info to read.

I cant find any charts, but he says he aims to get at least twice the length of the secondary in arc length, so thats pretty good going.

He also says that a smaller toroid below the main one seems to help primary strikes also.

KrowBar

Mon Mar 07 2016, 03:42PM

Registered Member #57401 Joined: Sat Sept 19 2015, 08:06PM
Location: Huntsville, AL
Posts: 10

You can get quite a bit of control over primary strikes by using the right breakout point. If you have a toroid with major diameter about the same as your coil length and then use a breakout point that extends up at an angle from the top of the toroid you can get arcs lengths of several times your secondary length. If you get primary strikes, use a longer breakout point and put some strike targets around your perimeter.

nzoomed

Tue Mar 08 2016, 08:09AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

KrowBar wrote ...

You can get quite a bit of control over primary strikes by using the right breakout point. If you have a toroid with major diameter about the same as your coil length and then use a breakout point that extends up at an angle from the top of the toroid you can get arcs lengths of several times your secondary length. If you get primary strikes, use a longer breakout point and put some strike targets around your perimeter.

OK, sounds good, so its not too big a deal then.

Fingers crossed for 2m sparks!

Hydron

Tue Mar 08 2016, 09:42PM

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

Your coil dimensions sound very similar to mine as well, and I got a bit over 2m without any worries (at ~750A, though I have run up to ~1kA).

As for a big variac, make a phase controlled rectifier with a couple of SCRs and you'll have all the power you ever wanted. I never bothered (have a 15A variac i got for a steal off trademe), but will probably do the same in the future.

If you want a suitable SCR module I'll happily send you one for free (got a good pile of them), but it'd have to wait till I'm back in Auckland in August.

Hazmatt_(The Underdog)

Wed Mar 09 2016, 01:13AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

try here

nzoomed

Wed Mar 09 2016, 09:06AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Hydron wrote ...

Your coil dimensions sound very similar to mine as well, and I got a bit over 2m without any worries (at ~750A, though I have run up to ~1kA).

As for a big variac, make a phase controlled rectifier with a couple of SCRs and you'll have all the power you ever wanted. I never bothered (have a 15A variac i got for a steal off trademe), but will probably do the same in the future.

If you want a suitable SCR module I'll happily send you one for free (got a good pile of them), but it'd have to wait till I'm back in Auckland in August.

That would be great thanks!

I think the variac is mainly used for power factor correction, am interested to see how other people address this issue.
I will get by with my 8A variac for statrers, i just think i will have to run my coil at a lower output or just ignore the variac and use with no power factor correction.

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