Re: High frequency impedance of a neon sign transformer
Subject: Re: High frequency impedance of a neon sign transformer
From: jim.fosse-at-bdt-dot-com (Jim Fosse)
Date: Mon, 01 Apr 1996 22:49:16 GMT
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tesla-at-grendel.objinc-dot-com On Wed, 27 Mar 1996 11:01:40 +0700, you
>>From jim.fosse-at-bdt-dot-com Wed Mar 27 01:20 MST 1996
>I just received the used LCR bridge that I ordered 2 weeks ago. I
>grabbed the good secondary from my blown 15Kv 60ma neon that I
>dissembled last month. I measured:
> L = 8.29H
> Q = 2.6
> Rdc = 27K ohms
>The L and Q measurements were at 1Khz. The coil was "air core", that
>is it was not on the neon. Caveats: I've not had a chance to check the
>calibration yet and the biggest 1 yet. This was my first inductance
>measurement with an LCR bridge, so I may not have done it correctly.
>note: Q=Xl/R = 2*pi*1000*8.29/27,000 =1.93 at 1Khz, so I'm off on some
>more as I get better with measuring known values of inductors and
This weekend, I was trying to make some inductance measurements on my
neon transformer primary and secondary. I was using my Leader 740 LCR
bridge with a 60 Hz external frequency source instead of the 1KHz
internal source. I could not get a dip on the meter because it was
oscillating with a period of about 2 seconds. I then scoped my
excitation voltage: it was stable. I switched to 100Hz operation and
the period changed to about 0.5 seconds. I found it interesting to see
such a resonance condition happening with only 1 volt peak excitation.
Today, (I've been down all weekend with a cold, and have just gotten
the energy to connect a few wires:(
This showed up on both my 15KV 60Ma unit and my 15KV 30Ma unit.
Neither one says power factor corrected on the name plate, but I'm
wondering if they are.
I just pulled out my disassembled neon (Jefferson Electric 15KV -at-
60Ma) with a power factor correction cap. With the cap it shows the
oscillation, without the cap, no oscillation.
Without the PFC:
L = 5.71mH Q=0.056 at 60Hz
L~= 5.66mH Q~=0.014 at 100Hz note: the dip was very shallow
and hard to read, don't take this as a hard number. I'll redo when I
have more energy.
L = 5.77mH Q=0.77 at 1Khz using the internal source, good