Re: DC power

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

Original poster: "Kevin Ottalini by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ottalini-at-mindspring-dot-com>

> Original poster: "Chris Swinson <exxos-at-cps-games.co.uk>
>
> Kevin,
> > >>>(in reference to http://www.mindspring-dot-com/~ottalini/)
>
> I took a look at it, thats one of the designs I have tried. Though I have
> not tried a 10K resistor mine was a 200K.
>

OK, using a 200K series resistor with a DC supply is not going to work
very well.  This limits the MAX current to .060A or 60ma which may be
the typical maximum for an NST driving a neon tube but that isn't the
maximum that is seen with AC (or DC) TC applications.

The purpose of the resistor is to protect the rectifier diodes not the
transformer.  Take a look at the Max surge current for your diodes
and limit the current relative to that and the maximum sustained
power you want to run.  Try 40K or 20K ohms to begin with.

Remember that the higher the resistor value the greater the I^2R
losses (and greater heating too) ... take a look at:
    http://www.mindspring-dot-com/~ottalini/tc/losses/losses.pdf

How are you checking to see that the rectifier is functional and
operating properly? Do you have an HV probe or HV meter of
some kind?  You could have bad or improper diodes.

Also, it would help all of us (to help you) if you draw a picture or
take a photo of exactly what your system looks like now and the
values of the components.  Debugging Tesla coils long distance
is a remarkably difficult task when minor things like the gauge of
the hookup wire you are using can make a significant difference.

>
> The coil was run and tuned and working with AC. I wouldn't have thought DC
> would change that much. Sure has proved me wrong in many respects now. I
did
> check the archives out a few weeks ago for DC information, Though I am
still
> at a loss ( bad pun there ? )
>

Brian Basura converted his AC system to DC with success and minimal
changes (added the rectifier bridge and a resistor) and the tuning and
performance at the same BPS rate was about the same.

I went to look for his web site with the description of what he did but
the site was down or moved.

>
> I tried 200K resistor, with and without spark gap, spark gap on its own
and
> yesterday a NST secondary. All of which didn't really do anything.
>
> It is variable speed. higher the speed the better so far. Though I dare
not
> run my gap to fast as it might fly apart. The output went from sparks to 1
> flame like arc at high BPS. pushing it more made it arc a bit further
though
> it started to pulse on and off.
>
> Chris

At low RPM (<2 BPS) and long dwell times, DC coils tend to power arc
(fire multiple times at a single gap presentation).  Also, as with AC,
keeping the spark gap cool with a reasonable air flow is important.

You don't need to run the rsg at high speeds ... although I don't know
what it looks like (maybe take a pic?) or how many poles it has so I
don't know what BPS you are trying to run at.

If you try to run the RSG at a speed that is faster than the recharge rate
of your tank cap you will get an odd stuttering discharge sound but
really never get more BPS.

It takes real power to run a DC coil at more than a few 100s of BPS ...
remember that in AC systems you are typically running at 60 BPS
or 120 BPS.

I definitely know that small NST DC driven coils are simple to build
and a lot of fun, although with limited power the sparks will be much
more discrete (zap, zap, zap) than the 60Hz sizzle that we normally
hear with AC systems.  My friend Mike down in Southern California
has been running a very basic 60ma rectified NST driven coil for
several Halloweens and it's quite impressive (and scary for the
kids!) for such a simple little system.

Kevin