Re: GM HEI (further measurements)

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

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

Hi Kevin,

I have a removed core GM HEI here and I get 200uH primary and 6.06H
secondary using a 1kHz hand held LCR meter.  It is possible that these
numbers vary a bunch from manufacturer to manufacturer.  

One needs to drive enough current to energize the core if they are in place
but I bet that gets messy since these are not designed for other than car use.

I'll set up the low-Z wide band amp and other toys tonight and see what I
get.  The top load or terminal attached to the high-voltage button affects
the resonant frequency a lot too even though the HV-winding does seem to
have a large natural capacitance associated with it.

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
>> >
>>
>>
>