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LTSPICE Top load Voltage output

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zzz_julian_zzz

Sat Jun 09 2012, 11:53AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Hi,

I would like to know, what voltage on the topload we are looking in the simulator like LT spice? cause I am getting mine 250kV only on the top load, but my primary current reaches x3 of the max pulsed current rating of my IGBT.. Also, is there a length vs topload voltage basis in which there are certain Arc length we can expect from getting a simulation from spice? my older coil (build yr ago) reads only about 180KV on the topload on spice, but on actual, the sparks are 40 inches in length (from my 10 inch sec coil).. Is it really true that the length of 40 inch is in order of 180kV? ....

A little help over here please? =/
Thanks..

EDIT: I am looking for 6 foot arcs, what voltage am I have to Aim???

brandon3055

Sat Jun 09 2012, 02:20PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

I think current also plays a big part in spark length

zzz_julian_zzz

Sat Jun 09 2012, 03:10PM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

I think you're right. but then How can I increase the current on my Sec top load? I am getting only 2.4Amps.. =/ What would be the length of it?

Steve Conner

Sat Jun 09 2012, 03:18PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

What are you using to model the streamer loading?

zzz_julian_zzz

Sat Jun 09 2012, 11:14PM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

I'm using Terry's model,. here is the pics of my plot..
Do you think it will produce an 6 ft arc as expected? following all the parameters from JavaTC and inputed in LT Spice? =/

I read on the IL2 about 5 amps., but when I put the primary tank input from 315 to 650, I get 10 amps.. =/ how do we compute for the arc length vs these values we get? THanks

1339283680 3964 FT139695 Primary Readings

1339283680 3964 FT139695 Secondary Readings

Goodchild

Sun Jun 10 2012, 06:39AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Hehe I like how you you just jacked my simulation

Ive done a lot of sim work with DR over the past year and I find that the Terry model is accurate for simple simulations. A true simulation would vary the resistance and capacitance as the burst prolongs. However I find it to be useful enough for basic simulation. That 180Kv sounds about right to me. I think most people are mislead into thinking that Tesla coils produce millions of volts when in reality they don't even get close.

My thoughts on this were further confirmed when I had a chance to read about Steve Ward's "real" voltage measurements of the QCW with a HV Oscope probe. Finding that they turned out to be less than 70Kv for 4 or 5 footers. Given the QCW is a different beast.

From my understanding there is no set relationship between volts and distance. There is a lot more going on most of which I don't understand completely. I believe that it has a lot more to do with the dv/dt of the output. The relationship of voltage and time seems to be critical in the length and appearance of most sparks.

Anyway that's my thoughts...

zzz_julian_zzz

Sun Jun 10 2012, 02:47PM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

"Hehe I like how you you just jacked my simulation"

-Yeah you know who I am Idolizing.. =).. hehe,
DO you think Eric that the output on my simulation will put some 6' sparks from my 2foot by 6inch secondary coil with a primary 7 turns of 25 copper / .25 spacing 10" diameter. ?? IGBTs are in fullbridge MG100Q2YS51 brick.. 350V input, 0.3uf tank Cap

I know you can answer this cause I know you already simulate and did this =)
Thanks...

Goodchild

Mon Jun 11 2012, 01:15AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

zzz_julian_zzz wrote ...

"Hehe I like how you you just jacked my simulation"

-Yeah you know who I am Idolizing.. =).. hehe,
DO you think Eric that the output on my simulation will put some 6' sparks from my 2foot by 6inch secondary coil with a primary 7 turns of 25 copper / .25 spacing 10" diameter. ?? IGBTs are in fullbridge MG100Q2YS51 brick.. 350V input, 0.3uf tank Cap

I know you can answer this cause I know you already simulate and did this =)
Thanks...

3x the secondary length is going to be a tall order to fill with only those 100A IGBTs. In simulation however your original 180Kv sounds about right. I like how you are using a nice large tank cap though with that small secondary, a high impedance in my opinion is the way to go with DR because thermally it gives the IGBTs more time to dissipate heat with the same amount of average input power.

What is the fres of the system?

zzz_julian_zzz

Mon Jun 11 2012, 07:47AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Goodchild wrote ...

3x the secondary length is going to be a tall order to fill with only those 100A IGBTs. In simulation however your original 180Kv sounds about right. I like how you are using a nice large tank cap though with that small secondary, a high impedance in my opinion is the way to go with DR because thermally it gives the IGBTs more time to dissipate heat with the same amount of average input power.

What is the fres of the system?

Fres of the system is about ~90Khz,. A high Impedance system would make my tank current lowered, and so the Voltage i think. My changes would be make the Z approximately 15ohms. (by lowering the capacitance down to atleast .12uf and increase number of turns)
The idea of 0.3 uf vs the small secondary is based on the other coils i had researched.. You are probably correct on its capacitance overly high.. But I am afraid that the birdge current and also output voltage will go down and also the length of the spark.. =(

Do you also think that I should look for higher current rating IGBTs? I have here a MG5001US1 -single packed (2pcs) and MG400Q2YS60A -halfbridge packed(2pcs) but I am also considering the switching speed (frequency) that they can only handle.. =/

In my simulation, (and also looking forward in actual), I will put a full bridge of MG100... igbts on the switching bridge..
What can you suggest so that I can meet the 3x length spark of my secondary?
I read about your DRSSTC 2, and you used CM300 IBGT bricks, I would like the same length you have achieved =).. THanks IDOL!

Uspring

Mon Jun 11 2012, 11:36AM

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

zzz_julian_zzz wrote:

Fres of the system is about ~90Khz,. A high Impedance system would make my tank current lowered, and so the Voltage i think.

Primary voltage, i.e. the voltage the on primary cap is about Iprimary * Zprimary. So a higher Z will make a higher voltage rating of the cap necessary.
When the secondary gets out of tune, e.g. by a ground arc, primary current is limited only by the loss resistance in the primary tank and can shoot up severely.

Generally secondary voltage is roughly proportional to Iprimary*k*f*sqrt(L1*L2) so it is not a bad idea to go for higher L1. Streamer loadiing will reduce the voltage, though.

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