Re: ignition coil Plasma ball

Pulse width is THE critical parameter when driving an ignition coil with a
low voltage (i.e. 12V).. You have to leave the power on long enough to get
the current through the coil high enough (that I = V/L *delta T thing) so
that you have a reasonable amount of stored energy (L*I^2/2).. A typical
coil current is 5A...

You can see that doubling the time makes the energy 4 times greater, so it
has a very large effect.  The HV impulse comes when the transistor turns
off (BTW, a 3055 won't last too long with 400 V across it... every time you
run it it gets a bit more thrashed... or, it just avalanches and acts like
a 100V zener, and dissipates a fair amount of energy and, more important
limits the output voltage) (Use an ignition transistor like a 2n6062 (I
think that's the number) with a BVceo of 400V, or a horizontal output
transistor (A radio shack part) with a BVceo of 700V)... both of these are
TO-3 packages, BTW).

In a V8 car application,  running at 6000 RPM (100 RPS), the pulse width is
about a millisecond.  (PRI = 2.5 mSec)

Capacitive discharge ignitions don't rely on the slow ramp up of current
and then the Ldi/dt to get voltage.. They charge up a (typically 1 uF) cap
to around 400V and just dump it into the coil.  400V doesn't take as long
to get the coil current up to 5A.

> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: ignition coil Plasma ball
> Date: Thursday, July 15, 1999 6:11 AM
> Original Poster: Philip <shadow42-at-totcon-dot-com> 
> Before I have tried many times to get a ignition coil based plasma ball
> to perform. I do beleive ive found what I was doin wrong and will pass
> it along. I am now useing a pulse generator to do my work instead of the
> 555 of the past. Here are my system specs.
> Coil - Ford standard coil 12v
> Pulse gen - Systron donner 100a
>    settings
>                Repetition rate - 1mhz
>                Pulse delay - 10us
>               Pulse width - 1ms
>               Base voltage - 3v
> Power source - 12v sealed gel cell battery
> Transistor - 2n3055
> Heatsink - 12x5" all finned stock
> Globe used - 5" commercial globe (gas content unknown)
> I found that adjusting the pulse width was more critical in the
> performance than the repetition rate. Amplitude setting was set about
> 3v. 3055 never became warm during operation. I have a digital cammera
> but it will not photograph the plasma ball well. I tried and tried. I
> even fittled with exposeure time to no avail. I need to get out the real
> cammera. Hope this helps someone. My original photos are at
> http://hv.hypermart-dot-net/pb.html.
>    Philip Mac Duffie