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Re: [TCML] RF Ground and Brass

Hi Gary,

Lau, Gary wrote:
Hi Bart,

I don't believe that I have misinterpreted Terry's measurement. His measurement is consistent with mine, based on the current through my light bulb.  His post is at http://www.pupman.com/listarchives/2000/July/msg00478.html and is very clear:

It is not saying that this is base current. Terry says "secondary rms current". I can't tell which currents he's discussing (can you?).

I can't check the paper he wrote just now (a firewall issue at work);  I'll look at that this evening.  If you're looking at waveforms, maybe you're talking about peak currents?  Different storey there!

I'm talking about both actually. 10A peak, so 7A rms. Either way, not 350mA unless this figures in the off time between transfers (which makes no sense to me). Even with off times, there are still 7A rms bursts occurring. Say you pulse 7A rms at some duty cycle across a thin wire. Does this equate to some continuous low current value? If the current is large enough compared to the wire size, the wire size will heat quickly but cool slowly. The bursts over time raise the wire temps up until some equilibrium is reached. It's easy to assume no big deal, but is that true? If true on one coil, is it true on others? I would error on the side of a larger than assumed needed wire size.

This whole topic came up due to the ribbon. I agreed that "no, it's overkill" and stated what "I" used. I really don't care what anyone uses (that's up to them). But then I read 350mA base current and I know better (so I had to speak up). This is an area where Terry Fritz is probably the most experienced at.

Critical to this discussion are the answers to my questions of your measurements -
1) What size/power the coil are you talking about? and
My coil was my 8.5" coil. I'll try to digd up the measurements if wanted. It was one of those measurements to supply some info through an email question, so I'll have to dig through some of my TSSP emails to see if I can find it and whatever details I might have supplied.

2) Are you talking about peak current or RMS current?
Answered this above I hope.

As of recent, I've been looking to predict secondary base current as it
is directly related to output potential (something I'm looking to add in

Is RMS base current correlated with output potential?
Yes there is a relationship. Vtop = Ibase x sqrt(Lee/Cee). These relationships are all discussed in Paul Nicholson's document pn2511. I can hunt up the link if you like, but you probably already have this. Because Javatc uses these equations, it has the ability to knock out that Vtop potential, but I have to get the base current correct first.

  In a given coil, if you always had the same size bangs, the output potential would be the same from bang to bang regardless of BPS, but if you double the BPS, you would double (I think???  Certainly increase...) the RMS base current.

As bps is increased, the bang energy immediately begins lowering as it is a function of voltage over time, however, the power across the gap (j x bps) is increased up to a point then begins falling back down. How bps plays into rms base current I don't know. It may very well peak at the peak of j x bps or not.

Ibase(rms) = (Transformer rms output voltage x
I've also checked the above equation against Ibase(rms) = 0.707 * (sqrt(
2 * E_bang / Lee)) and it seems to follow well.

This sounds wrong to me.  Since you are talking about RMS current, the bang duty cycle or BPS directly affects RMS current, but doesn't appear in your equations.
I think your looking at this from a continuous current standpoint. Think about it from the start of the bang to quench. This is where the base current is found (and where the top volts and sparks are found). Your correct that there is more to this than mentioned. As I said, I'm just beginning to look at this and am nowhere near complete. Measurements will be made and if I'm successful with bps measurements, that will also help. BTW, I've built the little circuit and it works fabulous. Just need to work on mounting the fiber optic at the gap and I should be ready to start.

Take care,

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