Re: Flyback questions

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

Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>" <scepp-at-mts-dot-net>

Hello Jan,

I've tickered with flyback circuits, about ten years ago.  I remember having
a DMM near it and it would give me erroneous readings just sitting there
with the flyback oscillator running,  come to think of it I cause an old PC
to malefaction every time I ran it near by, there's some powerful fields
coming off of those things.  The circuit I played with had two power
transistors , a wound center tapped primary and a extra feedback winding
also center tapped.  Anyway to find the ground pin just turn the flyback
upside down and look where the wires leave near the core of the transformer
(assuming it's an open design).  One will come out of the large rubbery,
hockey puck shaped coil, near to the core.  The other wire will probably be
right next to the core, these are extra windings for other TV circuits.
Another way is to use an Ohmmeter, one lead to the HV wire (note: this might
not work because some flybacks have big resistors and diodes inside them).
The other lead to test the bottom contacts and look for the highes
resistance.  BTW: the flyback is a single coil, not center tap grounded like
an NST.

These things are neat, I've run a ion motor and jacobs ladders from them.
Another neat trick is to make a handheld HV prod and do some wood burning.
I use to draw a name or pattern with a pencil on the wood, then zap it with
high voltage form the flyback,  the electricity burns itself in.   8-)

Shaun Epp
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, April 19, 2002 8:50 PM
Subject: Re: Flyback questions


> Original poster: "Jan Florian Wagner by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>
>
>
> > I finally got a xfrmr without a diode. It does indeed produce AC.
> However, one
> > end of the secondary is hot, and the other only has a few volts.
>
> Could be that the one end of the sec is grounded, and you get those "a few
> volts" from a feedback winding (also internally grounded)?
>
> > And this is a basic question I shouldn't have to ask, but if I am
getting AC,
> > my meter should read 1/2 of the true voltage or less on the DC settings,
no?
>
> Probably depends on the sampling freq of the DMM. And it won't be 1/2 of
> AC. Very likely jumps around between different values that are <<V_ac. (at
> least that's the case with the DMMs that I've come accross)
>
> Keep in mind that typical DMMs can not handle frequencies above a few kHz
> very well. Freq counter works ok there, but the error for voltage and
> current measurements will increase as the freq increases.
> (hmm, I would've thought that the "AC" setting will just rectify the
> AC input. That doesn't seem to be the case, though... Or? At least my
> DMMs screw up above 3kHz already, plus the piezo beeper starts to
> resonate)
>
> > And the meter should read nothing on the AC scale if DC is applied,
correct?
>
> Yup.
>
> cheers,
>  - Jan
>
> --
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