Re: GM HEI (further measurements)

["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>

Terry:
            Ok, I removed the core and interestingly the peak only shifted
slightly to ~18.4kHz.  I checked from 1kHz to beyond 2 MHz and there
is one much smaller peak at about 117kHz, but that's it.

I replaced the cores and the frequency dropped right back to 13.5kHz.

I trust this setup and have used it for more than 4 years testing
HV transformers of many different types, and only have problems
with extremely low resistance primaries (under 1ohm) ... and built
an outboard fet driver to fix that, but I guess this was a little
unexpected (I thought the frequency would be much higher).

OK, so I re-measured the inductances.

Without the core (1kHz)
Primary: 155.3uH
Secondary is 2.7H

Much lower inductance which is what I expected.

I replaced the core and repeated the measurements.
Primary: 2.6MH
Secondary: 15.8H

Both slightly lower, which is exactly what I would expect
with the cut E cores.

Any thoughts?

Kevin


----- Original Message -----
From: "Kevin Ottalini" <ottalini-at-mindspring-dot-com>
To: "Tesla list" <tesla-at-pupman-dot-com>
Sent: Friday, January 18, 2002 2:01 PM
Subject: Re: GM HEI


> Terry:
>     I just measured the resonant frequency of the "GM" coil I have here.
>
> This particular one is a Niehoff GM replacement model PT226 for
> a '76 Caddie 500 cid engine.
>
> With the core, the primary inductance is ~2.8mH at 1kHz and
> the secondary is 17.22H at 1kHz.
>
> I drove the primary directly with a 1vpp sinewave.
>
> The peak output is around 13.5kHz, but the response is quite
> broad, from 3kHz to about 20kHz with only a small roll off.
>
> I used a siggen that can drive low impedance coils, but it
> didn't appear to be working very hard, so I measured the
> primary resistance and it was a very nice 58ohms at 1kHz.
>
> The secondary resistance was ~544Kohms at 1kHz.
>
> Since I'm using only 1V for drive, I was able to use my Tek scope
> directly to see the output waveform amplitude and envelope with
> the sweep function.
>
> I haven't removed the core yet, but if you need measurements
> with the core off let me know.
>
> Hope this helps.
>
> Kevin
>
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Friday, January 18, 2002 11:29 AM
> Subject: Re: GM HEI
>
>
> > Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> >
> > Hi Rocky,
> >
> > I have a schematic of my GM coil setup at:
> >
> > http://hot-streamer-dot-com/TeslaCoils/Misc/GMHEI/sch.gif
> >
> > Bob also sent me some data that I will post in awhile.
> >
> > Measuring the frequency of GM coils is a bit tricky since you cannot
> > separate the primary and secondary coils.  You pretty much have to
connect
> > up the secondary with terminal and all as you want it and then stimulate
> > the primary to find the frequency.  A signal generator (perhaps with an
> > audio amplifier) can drive the cored or uncored primary and then an
> antenna
> > probe to a scope should be able to find the resonance.  One can then put
> in
> > a primary capacitor, disconnect the secondary connections, and tune the
> > primary to the frequency.  These coils are harder to tune since you only
> > have one primary inductor tap.  You have to vary the primary capacitance
> > for tuning.  I added or subtracted 0.1uF caps and ended up with 1.7uF.
> >
> > Cheers,
> >
> > Terry
> >
>
>