Re: ignition coil Plasma ball
The NE555 can be configured as a variable duty cycle pulse width generator,
at less cost than the average pulse generator. It will work very well
driving an induction coil. Heat in the pass transistor can be due to a lot
of factors (not driving it hard enough to reach saturation, storage
time/frequency, or even breakdown conditions).
I would agree with Dr. Resonance on 3055's. Whatever you use to drive the
coil, will see a considerable inductive kick. The 3055 is rated at 80 volts
(if my memory is working) and the spike is on the order of 400 volts. Even
with damping diodes and snubbers, one will manage to kill a 3055 every now
and again (and the NE555 or driver transistor also).
A 2N3055 goes for about $ 0.50, a power mosfet will set you back about
$3.00. A high voltage bipolar power transistor will be $5.00 to $15.00. I
wiped out three parallel horizontal output transistors fooling with my
induction coil, at a cost of $7.35 each (more than once).
I've become a believer in high voltage power mosfets (with snubbers,
external dampers, and ferrite beads). One of the things I like about
mosfets is they can be used without any change in the drive circuitry. I
was burning up 3055's in a switching power convertor I designed. The N
channel To-3 case power mosfets plug right in as direct replacements (as
long as they are driven from a source of +7 volts or more). Power
dissipation, in my case, went from 8.8 watts, to 1.7 watts, and the mosfet
runs rings around the much slower bipolar.
I think you may have an error in your post to the list. A rep rate of 1
MHZ, is inconsistent with a pulse duration of 1 ms. You probably mean to
say: 1,000 cycle per second repetition frequency.
Tesla List wrote:
> 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
> 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
> Philip Mac Duffie