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Large DRSSTC: choosing secondary impedance

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Uspring

Tue Apr 29 2014, 03:01PM

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

The remaining ZCS frequency is close to primary fres. You probably excluded that.

Can't wait to see Odin throw sparks.

Kizmo

Fri Jul 25 2014, 04:12AM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Allright guys.

New space wound secondary is now finished and measured. Here are some numbers:

- 1300 turns
- 93.4mH calculated
- 0.67mm wire
- 0.58mm between turns

Measured resonant frequency without "streamer" was 63.3kHz. Calculated whole system capacitance is 67.67pF and reactance at resonance 37.1kOhm

With 4 meter metal rod as fake streamer the resonance peaked at 56.3kHz. From there i get 85.544pF capacitance and reactance of 33kOhm

Now i just need to wait ~1 month for darker nights. Right now its as dark as it gets.

1406261540 599 FT162582 10489957 333613276793534 592506322530913947 N

Mads Barnkob

Mon May 09 2016, 12:22PM

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

I wanted to elaborate on the small tables that you often find about width:ratio to power levels for Tesla coil secondaries.

I assumed only secondaries of ratio 4:1 to 6:1, with different wire sizes and always a toroid topload that follows the rule of major diameter = secondary winding length, minor diameter = secondary coil diameter.

So far it does not contain any surprises, the general design thumb rules does however land around 50K.

Uspring

Wed May 11 2016, 08:52AM

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

If you "magnify" a secondary, e.g. double all dimensions, inductance and top load will double, resonant f will be halved and Zsec will remain constant.

I believe, Qsec, i.e. secondary Q with arc load, should remain equal for different coil sizes. Since arc load increases for more power, Zsec should decrease (somewhat) for higher power coils. A badly chosen Zsec can be compensated for to some extent by more primary turns. That involves longer rampup times and more losses in the primary winding, though.

Kizmo

Wed May 11 2016, 01:42PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

It is hard to say if the new secondary somehow runs better than the old in terms of power vs spark output but the heavy epoxy coating and space winding did make it very resistant to flashovers and racing sparks. I have had lot of them while experimenting and so far there is absolutely no damage at all :)

Oh btw, here is a small video i made a while ago about how the coil was made:

Mads Barnkob

Tue May 17 2016, 08:48AM

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

Uspring wrote ...

If you "magnify" a secondary, e.g. double all dimensions, inductance and top load will double, resonant f will be halved and Zsec will remain constant.

I believe, Qsec, i.e. secondary Q with arc load, should remain equal for different coil sizes. Since arc load increases for more power, Zsec should decrease (somewhat) for higher power coils. A badly chosen Zsec can be compensated for to some extent by more primary turns. That involves longer rampup times and more losses in the primary winding, though.

I was looking for a difference in desired impedance, not to seek out the optimal design, but to discover the boundaries of "usable" secondary coil construction.

I would like to add the loaded secondary Q, maybe a few different loads, then compare those Qs to a extensive list of q=1/k for k between 0.1 to 0.25 or so, for each of the listed configurations. Does it make sense?

"badly" chosen as you state, is only in regard to designing low impedance primary circuits for highest possible primary peak current in the shortest amount of time, so the sheet might also have to take into account(separate files to avoid additional 150 tabs) if you build low impedance, high current, short ontime expensive coil systems or high impedance, lower current, long ontime less expensive coil systems.

Uspring

Tue May 24 2016, 03:06PM

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

Mads Barnkob wrote:

I would like to add the loaded secondary Q, maybe a few different loads, then compare those Qs to a extensive list of q=1/k for k between 0.1 to 0.25 or so, for each of the listed configurations. Does it make sense?

Arc loads used to derive secondary Q are unknown territory. They change with power input and also during arc growth. Hard to tell, what is sensible without any measurements.

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