Re: [TCML] Help with high school Tesla coil

[John Forcina <forcijo10@xxxxxxxxx>]

>From those pictures of the driver it looks to be based off one of steve
ward's early drsstc driver designs.  I found this one here
http://stevehv.4hv.org/DRSSTC1/DRSSTC1OCDsch.JPG matches yours pretty
nicely.  However the coil you have does not have the over current protection
circuitry part of that schematic.  Basically in simple terms, the "BPS"
control on the remote control controls how many times per second the coil
turns on and off so lets say you have it set for 400BPS then the coil is
actually turning on and off 400 times per second.  The "On-time" also known
as duty cycle controls how long the coil is operating within your BPS
control.  For example if you are operating ast 400bps with a 200us On-time
then the coil will turn on for 200us 400 times per second.  I would set the
On-time knob as low as possible (for now at least).

On Wed, Nov 11, 2009 at 7:13 PM, Arnold, Mike <
marnold@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

>
> Thanks for your help, John. I know the students enjoy the Tesla coil and
>  I want to get it working again. Some of the students even seem to
>  understand its mysteries :^)
>
>  I've posted more images at http://collierhighschool.com/tesla/  If you
>  need closeups of specific components, I would be happy to take more
> photos.
>
>  I will try to get my hands on a scope, but I'm a little doubtful I will
>  be successful.
>
>  I do still think it has something to do with the timer not shutting
>  off.  It still fires sparks off.  I've included a photo of the dial for
>  the timer and, when I turn the dial, it feels a little funky.
>
>  I don't want to blow up expensive components in the process of trying to
>  fix it so I look forward to hearing your thoughts.
>
>  thanks very much,
>
>  Mike
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx on behalf of John Forcina
> Sent: Wed 11/11/2009 1:18 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Help with high school Tesla coil
>
> Hi, It looks like that is a drsstc and not a standard sstc.  We are going
> to
> need some more info on your coil in order to help you.  Can you post some
> pictures of the driver board along with the H bridge board and the dials of
> the remote control.  Your problem could be a number of reasons but for now
> im going to list some obvious ones.  You might have your "ON" time or duty
> cycle set very high meaning the coil will pull much more power then if it's
> set to a low duty cycle and you risk blowing your igbt's.  Another thing i
> can think of is the shootthrough on your igbt gates causing one igbt to
> turn
> on before the other is completly shut off and this will act as a direct
> short across your supply rails for a very short time.  By any chance do you
> have or does your school have a scope that you have access to because that
> will make debugging much easier.
>
> John.
>
> On Wed, Nov 11, 2009 at 10:02 AM, Arnold, Mike <
> marnold@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> > Our school has a solid state Tesla coil. I am attempting to get it into
> > working condition. It had a bad solder connection in the tuning remote
> > control. I have repaired the bad connection.
> >
> > Now the coil will spark for 1 or 2 seconds and then it trips the 20amp
> > circuit breaker. The coil only works (albeit briefly) if the burst rate
> > is high and the timing is high. The power cable gets warm in those
> > couple of seconds. (Not to influence responses, but I'm not positive
> > that the timing is working. It seems like the sparks burst without pause
> > -- da-da-da-da-da -- until the circuit breaks. I can definitely slow th
> > e rate -- da----da----da-----da.  I can see the pot for the timing and
> > it looks like it might have some cold solder joints.)
> >
> > When hooked up by itself, the low voltage transformer that powers the
> > control board does not blow the fuse.
> >
> > A photo of the board can be seen at
> > http://collierhighschool.com/teslacoil/board.jpg and I can provide more
> > photos if it helps.
> >
> > Any help would be appreciated.
> >
> > Thanks,
> >
> > Mike
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
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