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Re: Rotary Sparkgap


>I've reached the conclusion that the low-level Q I measure is 
>different from the powered-up Q. But it most certainly ddoes resonate
>at low-level, and at least three people here have encountered diffi-
>culties associated with resonances under normal running conditions.  
>I think the 360mA IS invalid. BUT, any resonance implies a higher
>current than the limited value into a resistive load. I have opened
>up a spark gap to well over the rated peak voltage and I know Ed
>Philips has too.

I'm sure I have also!
But is this due to the TC primary L and C or to the neon L and C?
I can't answer this right now, I tore everything apart tonight to measure my
neons.

>
>> If I remember correctly, the leakage inductance of a transformer is 
>> measured by shorting the secondary and then measuring the 
>> inductance of the primary.
>
>Shorting the primary should achieve the same end as shorting the 
>secondary IMHO. The idea of using a low-Z generator was to achieve
>exactly that.
NO, real world here! the secondary is so much BIGGER and futher away from
the core than the primary (of the neon) that it will have a much larger
leakage inductance than the primary will (both cases with the shunts removed!).
>
>> If you have an inductance bridge available (I don't) could you measure your
>> transformer, primary, secondary, and leakage? It would help some of
>> us-old-stumbling-EEs to get back to first principals;)
>
Just got 2 new consulting job in at work today, 1 RF key lock and 1 TV
camera remote with switching power supply, I'm trying to figure out how to
get an LCR bridge out of this:)

aside: related to resonant coils:

the card keys that you wave infront of a door lock to open them, are an
elegant design! the credit card size key contains a 3 turn coil with a cap
to resonate at 13.4Mhz. a 3 pin IC then uses the resonant voltage, 5 Vpp at
8", to run itself. It transmits it's key code back to the control unit, not
by a seperate RF path, but by loading it's 3 turn coil for a 0 and unloading
the coil for a 1. The control unit then uses the grid dip principal
(watching the current drain of the osc) to decode the data stream. Some one
went to a lot of thought to develop this technology!

>Looks like I have the same problems myself at times ;)  No, I don't
>have a bridge that can handle the beast. I reiterate that I think
>the resonant f idea (forget the Q one) is valid for finding Xl.
>BTW, the primary resistance is less than 2 Ohms. Total core sat-
>ration would spell death for primary fuses.
>
>Regards,
>Malcolm
>
>
Here is the 60hz data for the primary of my 3 neons:


Equipment       Simpson 260 VOM Doesn't measure AC amps!!!!!!!! 
                Amprobe Ulta    Clamp-on Ammeter 0-5A lowest scale
----------------------------------------------------------------------------
------------------------
                Franceformer
                120V    60Hz    450VA
                15KV            30ma.

                Primary DCR:    2 ohms

        Secondary open:

                115V    800ma   ->      381mH   I got different numbers here
each time I measured! 500-850ma
                105V    700ma           398mH
                95v     600ma           420mH
                87.5v   500ma           464mH
                60v     400ma           398mH
                37v     300ma           327mH   Hard reading below 300ma.

        Secondary shorted:

                115V    4.0A    ->      76.3mH
                95v     3.0A            84mH
                76v     2.0A            100mH
                32v     1.0a            85mH

        1/2 Secondary shorted:

                115V    2.0A    ->      152mH
                77.5V   1.0A            205mh

        other half shorted:

                115V    2.2A    ->      139mH
                110V    2.0A            146mh
                63V     1.0A            167mH

Notice the difference in readings! I bought this as a "bad" xformer I'm
still not sure. Makes a nice jacobs ladder tho.

----------------------------------------------------------------------------
-------------------------------

        Jefferson Electric

        120V    60Hz.   Cap. Va 500?
        HPF outdoor                     High Power Factor? Cap in parallel
with primary?
        15KV            60ma.

        Primary DCR     1.7 ohms


        Secondary Open:

        115V    4.1A    ->      74.4mH
        110v    4.0A            73mH
        83V     3.0A            74mH
        55V     2.0A            73mH
        25V     1.0A            66mH

        Secondary Shorted: 

        115V    3.4A    ->      89.7mH
        106V    3.0A            94mH
        75V     2.0A            99.5mH
        37V     1.0A            98mH

        1/2 secondary shorted:          both halves were identical

        115V    1.8A    ->      170mH
        55V     1.0A            146mH

this was also a "bad" xformer, notice the consistant readings. 

----------------------------------------------------------------------------
----------------------

        Gardner transformer

        120V    60Hz
        15Kv            60ma

        Primary DCR     0.7 ohms

        Secondary Open:
        115V    1.0A
                1.2A
                1.4A
                1.5A            kept moving with slight sizziling sounds!

        Secondary shorted:

        55V     7.5A            variac at 100%  oh oh!

        I then noticed the (cold) tar under one HV insulator and the small
blue discharge under the other HV insulator. This is the "good" xformer I
bought. I think I'll use it untill I get finialized and then switch to the
jefferson. I'll rebuild this one as an arc welder / battery charger. That
is: wind a new secondary for it of a few turns. Let's see? 900Va at 1 volt =
spot welder!

I suppose that I should reverse everything, short the primary and measure
the secondary. I try that tomorrow.


                        jim