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Re: Peak Primary Current

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi again Mark,

At 02:48 PM 4/15/2005, you wrote:


I'm back from a 2 year hiatus from the list.  I could not handle the
"List" e-mail volume and had to quit and follow you guys in the

I don't think the archiving is working right now... Must tell Chip......

I now have finally created a 2nd inbox for "List" e-mail and
can still get my work done and follow you guys as well.  I have stored
up some subjects to discuss and this is the first which may be obvious
to you, but not to me.

I have used many different wire combinations for my primary wiring
thinking that the primary wiring was a major resistance in the circuit.
Interestingly, no matter what I do with the primary wiring, I see no
change in the performance of my coil.  I have tried the following for
the primary wiring #18 ga, #14 ga, (2) #14 ga, #14 ga 20 KV, (2) #14 ga
20 KV, #12 ga, #8 ga, and 1/4" tubing(a real pain to set up).

Interesting!! See this:



Looks link the link is broke... :-(, but Gary measured a bunch of primary configurations for AC resistance.

I have run (2) coils with my primary and power suppy(Note I am using DC
resonant charging so I have one extra degree of freedom than you AC guys
and can pick my tank capacitor independent of the power supply).

My small coil resonates and 383 kHz and runs great with an 18 nF
capacitor(18 to 24" streamers).
My medium size coil resonates at 100 kHz and runs with a 34 nF
capacitor(48 to 60" streamers).

In both cases, I charge the capacitor to 20 kV.

It takes 1/2 cycle to empty the capacitor - 1.3 uSec for the small coil
and 5 uSec for the medium coil.

Using I = Cdv/dt, I get 277 amps for the small coil and 136 amps for the
large coil(Have I made a math error?).

We need to know the primary inductance, and then finding the peak current is easy. but your calcs should be fine too.

These values seem absurd for my wire sizes.  How can I be moving this
level of current?

You have 20,000 volts behind it!!! 20kV will pump 2000amps into a 10 ohm resistor!!

Also, note Peak current is dropping as the coil size
increases because the frequency dropped faster than the capacitor
increased in size.

I think you're going to tell me that the spark gap creates such a large
loss that the capacitor is significantly discharged during the first
cycle and does not recover until the next re-charge period.

Spark gaps waist a lot of power, but not too bad at the beginning for the firing cycle.

I tried to measure primary current with an isolated CT and got 88 amps.
This is obviously not accurate because resonance only occurs for about
40 uSec(383kHz coil) until we reach the first notch and quench.  I'm at
460 BPS so charging occurs for 2200 uSec.  During charging available
current is absolute max about 200 to 250 mA(documented by
studying/measuring power supply capability and typically only ~75

Sounds like a cool system!! We can help getting the measurement stuff figured out so all should be in perfect agreement. need to know more details like inductances and other general coil data to pin things down.



Straighten me out, please.