Re: GM HEI (further measurements)

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Kevin,

I ran my un-cored GM coil with a 1 Vrms input signal and low-Z amp.

http://hot-streamer-dot-com/temp/GMCoilTest.jpg

At 1kHz I got 1.40 ohms but that was not purely resistive.

I swept the frequency from 10Hz to 20kHz and got:

http://hot-streamer-dot-com/temp/TekGMT2.gif

There is the peak at about 12.1kHz as shown by the input current.  Looks
like about 1.4 ohms at resonance.

So there may be significant variation in these coils.  Mine is made by
Wells for the same Cadillac engine.

Cheers,

	Terry


At 02:42 PM 1/18/2002 -0800, you wrote:
>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
>> >
>>
>>
>