Re: Newbie Questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 20:58 24/04/03 -0600, you wrote:
>Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><jtf-at-dejazzd-dot-com>
>
>Stephen Conner wrote:
>
> > The base bias resistor is probably too big even for 12 volts.
> > ...... That would mean using a 20 ohm resistor, ....So you ought to put an
> > extra emitter follower in.
>
>Stephen....your reply helped a lot. Added an emitter follower, (still used 
>the 100 ohm
>base resistor) and the spark doubled in length to 1/2 inch. Changed the 
>base bias
>resistor to 22 ohms and gained another 1/4 inch, for a total of 3/4 inch. 
>The spark was
>screaming :-) Then it all stopped :-( Guess the NPN transistor smoked. 
>Didn't have the
>time to measure current, before it fried.
>
>Need to buy more transistors. LOL

Don't buy 2N3055s, they suck for this application. You're trying to 
generate a hi-voltage spike by turning the transistor off suddenly, but the 
2N3055 can't take more than about 70-100V before it dies. A specialized 
high-voltage switching transistor like the BU208D ought to work much 
better. Note: The BU208D is easy to get over here in Europe but might be 
rare in the US. Maybe someone else could suggest an equivalent?

You can find a couple more ignition coil drivers at 
http://www.powerlabs-dot-org/ My favourite one runs straight off the 120V line 
and uses a SCR instead of a transistor. It gives pretty impressive results 
when driving 2 ignition coils, but could be a bit dangerous.

Steve C.