Re: SG electric control Idea - opinions wanted

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Original poster: "Sean Taylor by way of Terry Fritz <twftesla-at-qwest-dot-net>" <taylorss-at-rose-hulman.edu>

Hi Cory -

> Hello again,
>
> i have an idea: it is my understanding SCRs and TRIACs
> arent fast enough switching and dependable enough to
> handle TC spark gap replacement...  it is also my
> understanding that a single MOT is not useful as a TC
> trannie because it doesnt have near enough voltage for
> a reasonable gap, ide like to change this:
>
> My idea involves using a Triggered gap that uses a car
> coil to trigger powered by a dimmer switch to adjust
> the degree of the cycle it fires at.
>   this way you could have a  1" spark gap which would
> be MUCH easier to quench then a 1mm spark gap.
>

I don't know about 1", but true, it can be very wide.

> secondly my idea involves using a Power TRIAC or
> simple transistor in series with the big ugly mot that
> is on all the time except a short ammount of time it
> turns off all current draw from the MOT shortly after
> the TC is done resonating,

A triac or SCR won't turn off until current goes to 0 - no way to change
that.  A FET or BJT would have to be used to interrupt the current.  BUT
when the current is interrupted, a large spike of voltage may occur, similar
to that in an ignition coil. That is if the semiconductor is on the primary
of the MOT.  If it were placed on the secondary, it would be fairly
difficult to prevent the RF noise from most likely destroying the device,
not to mention the high currents present in the spikes.  I'm not saying it
can't be done, but as someone said in a previous post, it would cost a small
fortune for the semiconductors needed.

> i have been told was about 30 cycles, according to my
> speedy calculations that is only about 2 degrees of
> the AC cycle.  so almost DIRECTLy after the trigger
> electrod fires the tranny is basically turned off
> untill the next cycle has begun and passed up some of
> the lower voltage components of (like 120-600V) it.
>
>
> problems this may encounter:
> - making a module to turn off the triac at the right
> time
Not really so much of a problem . . . fairly easy to detect a low current
and turn off a device (not a triac as mentioned before)

> - protecting your car coil from the dangerous aperage
> of tha tank cap, anyone know how this is done?
Not really much of a problem either.  It has a fairly high inductance, and
will be hard to destroy - they are typically used to 20 to 30 KV, I think.

> - low voltage = reduced primary tank energy :-/
>
> why this would be good:
> - beginners who dont have NSTs available ( i live in a
> pretty large city but i cant find a single one!  then
> again im also not really willing to buy one new )
> - MOTs are Free!
> - NSTs are very fragile i hear...
> - MOTs have good charging current- i forget the
> equasion to the time it takes to charge a cap (mabey
> somone can remind me) but i am pretty sure current is
> involved.. faster cap charging might = more BPS

I=C*dv/dt   current through the cap is equal to the rate of change of
voltage times the capacitance - more current, quicker charge times, granted
you have the voltage to draw the current.  Just need to pay attention to cap
size, supply current/voltage . . . I think that it is best to have an LTR
system, and just fire at the peaks of the AC cycle . . . I think others have
found this as well.

> - More efficient?
>
I think that you are thinking along the right lines - the spark gap is
probably the most lossy part of a TC.  As soon as I get out of school, I
wanna do a lot of work in experimenting with the spark gap, like different
types, methods, etc.  I would also like to try rectifying the output of the
hv tranny before going to the cap.  all sorts of fun experiments!


> just an idea,
>
> Cory Roussel
> G1206


----------------------
Sean Taylor
The Geek Group
G-2 #1204
Because the geek shall inherit the Earth! (c)
www.thegeekgroup-dot-org