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Alex Yuan

Thu Mar 26 2015, 02:28AM

Registered Member #9614 Joined: Mon Jan 14 2013, 10:00PM
Location:
Posts: 44

For over a year I had issues making an account and today I decided to try logging in and it worked! :P

Anyway, hello everyone!

Here are my twin coils:

nzoomed

Thu Mar 26 2015, 03:09AM

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

Hi there, nice coil build!
Im working on a coil which will have similar specs to yours, im going to go to a 30AWG wire on 160mm pipe though as i think it will let me get longer sparks without striking the rail.

It took me a while for my account to get activated here too, ive only been on here less than a week :)

Benjamin

Thu Mar 26 2015, 04:06AM

Registered Member #54655 Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82

Hi nzoomed. I just got my account activated a few days ago too! I had a little bit of trouble but it works now.
I've built several sgtc's and a few sstc's and my best spark length was 40 inches with an sgtc at 1 kW! It's great to talk to other people who understand this sort of thing!

nzoomed

Thu Mar 26 2015, 04:26AM

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

Benjamin wrote ...

Hi nzoomed. I just got my account activated a few days ago too! I had a little bit of trouble but it works now.
I've built several sgtc's and a few sstc's and my best spark length was 40 inches with an sgtc at 1 kW! It's great to talk to other people who understand this sort of thing!

Ye it is, but TBH, im pretty new to all of this, most of my electronic experience has been valve amplifiers!
Ive wanted to make a tesla coil for some time and now ive got the resources and time to do so.

Mads Barnkob

Thu Mar 26 2015, 07:12AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Welcome to all the new members :)

That is a cute little set of twins you have built Ahyuan, nice and simple construction.

Uspring

Thu Mar 26 2015, 11:19AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

Hi Ahyuan, nice build.

I was wondering about your statement about reducing burst length at the end of your page. Did you do that in order not to hit the OCD? What is your burst length? I believe, that you should be able to get more spark length from your coil. My biggest one uses a CM300-24 half bridge running at 640V (1000A peak) and gets almost 7'. It's tuned in such a way, that the OCD just won't trigger, even for long burst length.

Alex Yuan

Thu Mar 26 2015, 02:55PM

Registered Member #9614 Joined: Mon Jan 14 2013, 10:00PM
Location:
Posts: 44

Thanks!

Uspring the max pulse width went down to around 120uS. After that and the sparks don't grow more. Before I needed about 180uS.
I know I can get more out of these coils, I'm open to suggestions!

Here's a video of it more in tune:

Sulaiman

Thu Mar 26 2015, 05:59PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Welcome Alex,
nice work, congratulations.

Uspring

Fri Mar 27 2015, 01:59PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

Alex Yuan wrote:

I know I can get more out of these coils, I'm open to suggestions!

Here some observations:

When you run your full bridge at e.g. 600V, you'll add 1200V to your primary tank caps every time you switch. After 7 switches, i.e. about 50us, you'll have charged your caps up to full voltage. This applies only, if there are no losses in the primary tank. Obviously, that is not the case, since you seem to be able to run 120us bursts without the OCD kicking in.

The biggest single reason for losses is transfer of energy to the secondary. That is, of course, intended, and well so. I'm a bit surprised, though, that this happens so fast. 50us is not much time and requires a lot of coupling in order to transfer energy fast to the secondary.
Another source of losses is parasitic primary resistance, e.g. in your winding, wiring or bus cap ESR. You can check that by removing your secondary and slowly increasing the variac voltage until the OCD is hit. The bus voltage at this time will tell you, how much voltage is lost in the primary. It should be a small fraction of the max voltage.

One of my favorite ideas is to store as much as possible energy in the primary tank. The primary is tuned to a low frequency, so that most energy transfer to the secondary will be deferred until the arc finally breaks out and pulls the secondary into tune. At this point the arc will be powered by the bridge and also by the energy stored in the primary tank.

This mode of operation requires a high Z primary, i.e. much primary inductance and less, although higher voltage primary capacitance.

Gregary Boyles

Tue Mar 31 2015, 01:15PM

Registered Member #9039 Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117

Hi Alex. Nice coils and nice sparks.

I am using the wire from the secondaries of MOTs, so my secondary coils don't look quite so 'sparkly'.

But they should still work OK.

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