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Re: Here comes the SCR based coil

I have used a small ferrite transformar from in a colour TV set to trig 
an scr. Some will work, some wont. also could consider using a 
Transformer from old switchmode power supply ( these are designed for 
pulsing), or perhaps a wideband 600R line isolating tranny. Also maybe a 
good idea to connect a diode across the tranny in opp. polarity to scr's 
gate to protect from reverse transients


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>Subject: Re: Here comes the SCR based coil
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>Original Poster: Eddie Burwell <eburwell-at-HIWAAY-dot-net> 
>
>At 06:53 PM 1/11/99 -0700, you wrote:
>>Original Poster: "Bill the arcstarter" <arcstarter-at-hotmail-dot-com> 
>
>>
>>Where'd you get the SCR gate trigger transformer? :)
>Mine were surplus from a motor drive circuit. I took the core and wound 
my
>own. Some ferrite toroids like line noise filters may work. Just make 
sure
>they don't saturate before you have completely turned the gate on.
>
>Check out http://www.mag-inc-dot-com/  
>I couldn't tell you what to get yet but I'm sure they would have it.
>
>
>>I suppose all coilers need is a supply of primary amp*turns at the 
>>appropriate excitation frequency...  
>>
>>How fast will your circuit run at this point?  What sort of output do 
>>you get?
>About 500pps max right now. I have been fighting some problem and 
learning
>the hard way about magnafier output transformers. It has been difacult 
for
>me to design a transformer with high coupling low inductance and a 
modest
>step up ratio. My most succesful transformer so far has been an 8" pipe 
tape
>wound with 180 turns of 4 mill poly and 1/2"x2mill copper tape. The 
primary
>was one turn of a 3" copper strap.  With this setup I could get 8" 
sparks.
>Kind of dissapointing. Some calculations based on the ESR of the 
resonator
>tell me that 180 turns is too many for a good impedence match. I cut 
back on
>the turns to no avail. The transformer by it self could produce 1.5" 
spark
>which tells me there is some loss going on somewhere since with 1KV in 
I
>theoretically could have 180K out. So with a little head scratching I
>realized that loading on the secondary will produce loading on the 
primary
>and thus more loss in the parasitics of the circuit. So I think I need 
to
>increase the L in the primary so that the parasitics are less 
significant. I
>also need to tighten up my wiring to minimize the parasitics.
>  The problem with increasing the L is that the primary resonant 
frequency
>can get low pretty quick! Especially with 2.5-30uF on the primary. I 
mean
>like 20-40Khz!  I think that is the route I'm going to take. I have 
like
>30lbs of #25 and maybe 10lbs of #14 and #16. I need to come up with a 
new
>resonator (third coil) in this frequency range. At first I was thinking 
of
>using a short squat coil to get a large inductance. Then I realized 
that
>self C is the bane of a maggie although at these frequencies it won't 
be as
>significant. Any thoughts on this are more than welcome.
>
>
>>Since the current pulse is such a step (as opposed to a sinewave) 
>>implies that substantial energy will be at frequencies far away  from 
>>the secondary's self-resonant frequency.  I'm not sure there's 
anything 
>>which can be done about that in your design.  This may be the limiting 
>>factor in terms of net arc length output!
>
>The BIG ??? diode in my schematic allows ringing. I'll see if I can 
post a
>waveform on my website.
>
>Eddie Burwell
>
>http://home.hiwaay-dot-net/~eburwell/
>
>
>


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