Re: Triggered spark gap resistors

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

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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