Re: Hot Primary

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

Original poster: "Gregg Adams by way of Terry Fritz <twftesla-at-qwest-dot-net>" <network-at-nexband-dot-com>

Thanks bert I will give these suggestions a try.  It might take me a while
to upgrade some of the components but I need to do something or risk burning
something up.  I just wrapped a new 6" secondary so there's one part
finished.  I'll see if I can resolve some of these issues through your
suggestions.  Wish me luck!

Thanks again Bert



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, July 04, 2002 1:53 PM
Subject: Re: Hot Primary


> Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<bert.hickman-at-aquila-dot-net>
>
> Hi Gregg,
>
> I did a quick estimate for primary current in your system, assuming your
> main gap is firing at 12 kV. Your primary inductance is around 3.2-3.3
> uH, and your bang size is about 3.6 Joules. This means that your peak
> primary current may be as high as 1400 - 1500 amps! Your tank circuit is
> also operating at a relatively high frequency (~350-400 kHz), so the
> skin depth of the copper tubing in your primary winding is only a bit
> over 4 mils. The above combination certainly explains why your TC
> primary gets hot.
>
> Some suggestions:
> ================
> 1. Replace your existing secondary a longer one using a finer wire
> gauge. This will increase its inductance and voltage handling
> capability, while also lowering its operating frequency. [Even better,
> consider using a larger diameter coilform to further increase
> inductance, power handling capability, and reduce operating frequency].
>
> 2. Combine the new secondary with a toroid that has a relatively large
> outer diameter for additional topload C. For example, if you made a
> 4.25" diameter secondary winding 28" long using 24 AWG, and topped it
> with a 22" x 5" toroid, the combination would drop your secondary
> frequency to about half its present value. The longer secondary also
> makes it easier to handle more power or longer sparks.
>
> 3. The previous changes will now permit you double the number of turns
> on the primary, halving your peak primary current (which, at 700 amps,
> is STILL fairly high for a coil this size). BTW, making the same changes
> but using a 6" diameter coilform will drop your secondary frequency to
> around 130-140 kHz, permitting you to tune at 8 primary turns, and
> reducing your peak primary current to a more reasonable 500 amps.
>
> 4. While most of your losses are still coming from the primary spark
> gap, you may also want to consider migrating to 3/8" copper tubing to
> further reduce primary losses.
>
> Hope this helped and best regards,
>
> -- Bert --
> --
> Bert Hickman
> Stoneridge Engineering
> "Electromagically" Shrunken Coins!
> http://www.teslamania-dot-com
>
> Tesla list wrote:
> >
> > Original poster: "Gregg Adams by way of Terry Fritz
<twftesla-at-qwest-dot-net>"
> <network-at-nexband-dot-com>
> >
> > To all who responded to my question, thanks and here's the specs on my
coil:
> >
> > Secondary: 4.25" / 22 gauge / 22 inches in length
> > Primary:  flat sprial / .25inch copper tubing / tapped at 3rd round out
> > Power supply:  dual MOT's with voltage doubler(12kv) / not sure on the
> > amprege
> > Tank cap:  .05uf -at- 12kv / 2 strings of 6 geek caps(.15uf -at- 2kv) I have
more
> > just not hooked up.
> > Spark gap:  ARSG / 10k rpm angle grinder w/6 inch disc and 4 contacts
> > Performance: 40+ inches
> >
> > My primary is getting hot enough that you can't leave your hand on it
for
> > more than a few seconds.  Also, I'm having to run alot of topload now.
> >
> <SNIP>
>
>
>