Re: ignition coil Plasma ball (how to get better results?)

I agree that SCRs work better, there is no doubt about that.  The problem
with that is that I have no SCRs whatsoever, and no money to buy them with.
I do however have LARGE quantities of 3055's.  I acquired these at no cost
to me.

I built this circuit and was getting some *unreal* results from just one
coil.  The problem is I can't find a power supply able to put out the
current I
will need for two of them.  Currently, I am using an old computer power
12V, 8amp wire.  I'm pulling 7, and with only one ignition coil I've been
able to
get sparks almost 2 inches long, thick, and white hot.  Too an earth
rod the "sparks" become an arc.

I had thought that a switching power supply would not last long in this time
RF conditioning.  I've placed a 100,000uF capacitor and a varistor across
supply between the PS and the driver circuit.  I don't have an accurate way
measure any RF kickback that might be occuring, but I ran this setup for one
FULL hour nonstop yesterday.  The 3055 ran cool all the time, as it is
on a VERY large heatsink.  In fact, the 555 got warmer than anything else!

Since it is easy for me to simply pull one 3055 out of the socket and put
one in, and that I have only used ONE for an hour nonstop, I think I will
with using them.

3055's, being rated at 15A, should be able to handle two icoils in
This should pull around 12-13 amps, correct?  Also, by placing the coils in
"anti-parrellel", won't I essentially be making the HV tap on one positive,
while the
other is negative, doubling the output voltages and potentially the length
as well?

Few more quickies :

I would like to go ahead and build a small tesla coil out of this, just to
say I did.
What recommendations for secondary size and primary size/type does anyone

What capacitor value?  Spark gaps, etc.

For those of you interested, I have the schematic and info to this page
at my page :

I do not have any pics of my new setup, they should be up tomorrow or the
next day.

>Commercial globes such as we manufacture use a flyback type running with an
>adjustable freq for tuning to the gas mixture.  The tuning range is usually
>only 1 kHZ wide for best display.  We never use style transistor circuits
>with flybacks, but, due to reliability issues, always use SCR type driver
>systems for ignition coil driver circuits which we use to trigger our large
>Marx impulse generators.
>Globe gases are typically neon, xenon, and krypton (at $13,000.00 per
>liter -- no misprint) blended in a gas manifold.
>-----Original Message-----
>From: Tesla List <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
>Date: Saturday, July 17, 1999 3:31 AM
>Subject: Re: ignition coil Plasma ball
>>Original Poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
>>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
>>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
>>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