RE: Ignition Coil

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

Original poster: "Pete Komen by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pkomen-at-zianet-dot-com>

Hello Daniel,

I can't find Terry's controller e-mail on the Tesla Mailing List site.

The directory:

http://hot-streamer-dot-com/TeslaCoils/Misc/MarcMetlicka-STSG/Controller/

http://hot-streamer-dot-com/TeslaCoils/Misc/MarcMetlicka-STSG/Controller/
STSGcontroller.gif

Terry's schematic is in that file.  Sorry about the wrapped line.  I use a
32 ohm 500 watt resister across the output which is then routed to the 5uF
cap bank and GM HEI coil which are in series.

___________________________
               |                             _|_
               \                            ___       Cap
               /                              |
               \    R                       -at-
                /                            -at-        Coil primary
                |                            -at-
_________|________________ |


An oscilloscope is still down in my things-to-buy-someday list.  My first
paragraph was partly theoretical and partly based on observation of the
trigger working.

I'll post my schematic when I see if it works.  I tend to be slow building,
so 3 or 4 weeks before it's ready I think.

I am not familiar with a PIC controller.  I have learned about 555 timers,
differential comparators (and a little about other logic gates),
opto-electonics, what an IGBT is, and etcetera over the past 2 or 3 weeks,
but I am still pretty ignorant about electrical circuits.  OTOH, I figured
out the outside limits of current flow for a capacitor discharge through an
ignition coil (if the coil is 10mH).

I agree that the Cap should limit current about the time that the coil core
saturates.  A difficulty is that the driving voltage varies with the dimmer
control adjustment.  The optimum firing time should be determined by the
Tesla coil output, even though the best spark output from the ignition coil
is probably at peak voltage or perhaps a little earlier.  A scope would help
sooooo much.

Regards,

Pete Komen - The Land of Enchantment


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, September 06, 2001 12:18 PM
To: tesla-at-pupman-dot-com
Subject: Re: Ignition Coil

Original poster: "Daniel Barrett by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<dbarrett-at-clearcube-dot-com>

    Hi Pete!

> Original poster: "Pete Komen by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<pkomen-at-zianet-dot-com>
>
> Hello Daniel,
>
> While the Dimmer is driving at 60 Hz, the rising edge of the pulse is
> limited by the rise time of the triac, the inductance of the coil, and the
> voltage of the sine wave input when the triac fires.  At the limits of the
> dimmer control movement the triac is turning on when the voltage is low
and
> the coil does not output a good spark.  At the peak voltage of the sine
wave
> input  (near the middle of the dimmer control), the coil should see a
pulse
> of about 170v with a very fast rise time.
>
> My trigger driver (a near copy of Terry's published version), gives no
> sparks near the limits of the dimmer control and the best sparks in the
> middle of the range.
>

> Still working on a capacitor discharge ignition coil driver.


    Ok, that's consistant with my quick experiment last weekend (using a
dimmer modified so that the RC network that feeds the gate is driven by
connections to the hot and neutral wires and the coil is placed between the
neutral wire and the triacs MT1 terminal). Have you looked the that coil
current and voltage on the scope at all? I agree that the optimal firing
point is at the 90 degree points on the wave, but I'm wondering how fast the
ign. coil's core saturates. If, for instance, this occurs near the 120
degree point then most of the power between 120 degrees and 180 degrees
(when the triac cuts off) is going to waste as heat. I'd guess that there is
an optimal choice for capacitor value that would just barely saturate the
core and any capacitor larger than this value would *slighty* increase the
output power but drastically increase the heating in the coil. I hope to
have some time this weekend to play around with this.

    Do you have a schematic for what you have done?
    Where can I find Terry's schematic?

    I'll post anything I come up with next time I have a chance to play with
this. I'm thinking of using a PIC microcontroller to trigger the triac at a
precise time delayed from the zero-crossing as I noted a lot of
instabilities with the dimmer...
Best,
db