Re: Micro coil help Re: Micro coil help

Tesla List wrote:
> Re: Micro coil help
> >From dknaack-at-rdtech-dot-com Sat Dec  7 00:05:47 1996
> Date: Fri, 6 Dec 1996 12:30:00 -0600
> From: David Knaack <dknaack-at-rdtech-dot-com>
> To: "'tesla-at-pupman-dot-com'" <tesla-at-pupman-dot-com>
> Subject: RE: Micro coil help

> >You need to determine if the transformer self-limits under short circuit
> >conditions. My initial "guess" would be that it won't. The easiest way
> >would be to place a 1000 ohm 10 Watt resistor directly across the output
> >and measure the voltage developed across the resistor. If your
> >transformer "limits" current to a relatively low value (say 10 MA), you
> >should only see about 10 volts developed across the resistor. If you see
> >substantially more, then you may need to externally limit current with a
> >series inductor. Keep looking for that neon! :^)
> Tried above setup, it does not self limit ( but it sure does get warm! :).
> On a transformer like this one, what can I use as an inductor?  If I want
> to use a resistive limiter, what resistance should I use?
> Again, thanks for the input!
> I dunno what I would do without it!
> David Knaack
> South Texas


No problem - glad to help! I re-read your previous post, and it's not
clear why the output of the transformer would have been directly shunted
with a 0.01uF cap if there wasn't an internal rectifier of some type. It
also sounded like the unit may have been used to drive an electric
fence. Electric fence drivers usually have some associated pulse
electronics to drive the fence with intermittent high voltage pulses. Do
you have any other information about the unit?

Anyways... back to your questions:
Assuming your transformer outputs about 1200 Volts at 6 MA (from your
previous post), and you may be able to push it to 10 MA if you only use
it intermittently. This means that you need to restrict the primary so
that the transformer will not draw more than about 10-12 VA. Although
connecting an inductor in series usually results in better performance,
it may be simpler to use a resistive ballast in this case, since the
inductor size will be quite large. 

Since you're running off the 120 volt mains, you want to restict the
input current to the transformer to about 0.1 Amp or so, which will take
a series inductance of about 2.5-3.0 Henries, or a series resistor of
about 1000 - 1200 Ohms rated at 15 Watts or better. 

Good luck, and safe microcoilin' to ya', David!

-- Bert --