RE: Triggered spark gap resistors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ted Rosenberg by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Ted.Rosenberg-at-radioshack-dot-com>

Hello Jon: Thanks for the background info. Even I can follow your thread.
I would offer that Marc, Terry and everyone else who has gotten into this
triggered gap discussion, has repeatedly stated with emphasis, is that
unless you are using an LTR cap and unless you have a safety gap set and set
conservatively, you are indeed asking for trouble, NST-wise.

But since an LTR cap lets you take advantage of the "automatic" 120 bps, and
safety gap adjustment and correct setting should be routine, then I see no
real reason to be overly concerned (unless the builder is just plain
careless or sloppy).

Safety First

Ted

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, November 01, 2001 12:44 PM
To: tesla-at-pupman-dot-com
Subject: Re: Triggered spark gap resistors


Original poster: "Jon Tebbs by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jgtebbs-at-eos-dot-net>

Hi Ted, List,

Terry's suggestion of the _series_ resistor placement probably came from
an off list exchange I had with him several months ago. At the time I
was doing some independent testing of the triggered gap idea and
confirmed Terry's measurements of 28 Amp spikes at each firing of the triac.

I tried using a series _ballast_ resistor since it has been common
practice in the automotive application for many years, either in the
form of resistance wire in the harness or a firewall mounted ceramic
power resistor. I cannot say whether GM has used or is currently using
ballast resistance with the HEI coil. Any wrench twisters who can
comment here?

This ballast resistance resulted in _smoother_ operation, not a great
amount but enough to warrant it's use. The trigger arc sounds less
harsh, the dimmer has a little more adjustment _range_ and the trigger
point in reference to the sine peaks shows a bit less _jitter_. The
current spikes were much tamer as I recall, on the order of 16 Amps.

Since probing this trigger design with a scope and Pearson CT, I've seen
that the triac as a trigger driver leaves a _lot_ to be desired. Jitter
is quite broad, I've measured upwards of 2 mSec. If this is used with a
resonant matched cap and improperly set or no safety gaps, there exists
a real potential for _missed_ firings and we all know what that means.

Wealze, if my memory is correct, I believe you reported that you
modified a dimmer with the _third_ lead brought out and found the jitter
greatly improved? I'd like to compare notes with you as I have not been
able to confirm this. Feel free to contact me off list if you wish.

Hope this helps explain the _why_.
-- 
Jon G. Tebbs
<jgtebbs-at-eos-dot-net>





Tesla list wrote:
> 
> Original poster: "Ted Rosenberg by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <Ted.Rosenberg-at-radioshack-dot-com>
> 
snip

> I followed Marc's and Terry's original insertion point and quickly had a
> super hot resistor pair. I contacted Terry as Marc was 'out of pocket' as
we
> say in TX. Terry suggested an alternative location (across the HEI as
> opposed to across the 120V) which worked and the resistor pair was no
longer
> a toaster. But then, (and I really cannot recall why) I think there was
> another exchange between Terry and myself and the last position of the 8/8
> ohm pair was in line (series) with the HOT side of the HEI.
> 
> Now, does the resistor pair "do something?" I have NO clue what-so-ever.
> Marc has since stated that they wound up being used in the first place "by
> accident." (His words) And no one else has done any evaluation of this
> strange issue.
> 
snip

> Safety First
> 
> Ted
> 
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Wednesday, October 31, 2001 10:32 PM
> To: tesla-at-pupman-dot-com
> Subject: Triggered spark gap resistors
> 
> Original poster: "Paul Arrowsmith by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <p_t_arrowsmith-at-hotmail-dot-com>
> 
> I am about to build a triggered spark gap as per the excellent
instructions
> posted by Ted, except for a few changes as I will be using 240V 50Hz here
in
> 
> Australia.
> The very low value resistance across the output of the fan speed
controller
> does seem severe to me and I am concerned about putting a near short
circuit
> 
> on the output of the dimmer. I saw that there was a lot of posts about
this
> but did not catch any resolution to this problem.
> Can someone please update me on the correct resistor value and position in
> the circuit.
> Thanks in advance, Paul A.
> 
> _________________________________________________________________
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