Re: mysterious coil failure / M and k Measurement (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 31 Oct 2007 07:02:14 +0100
From: Kurt Schraner <k.schraner@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: mysterious coil failure / M and k Measurement

The safety concerns, regarding the circuit at Bart's site:
http://www.classictesla.com/download/M_and_k_Measurement.gif
can be eliminated, using a downstep transformer (i.e. Vout=6...12V; some 
Amps), inserted between the mains AC line and the rest of the circuit. And 
voltage may optionally be adjusted, by using a variac. This allows much 
quicker measurement at different taps of the primary.
BTW, I'm also taking the measurements without the RC combination accross the 
secondary.

Regards, Kurt


Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Mon, 29 Oct 2007 13:04:46 +0000
> From: "Lau, Gary" <Gary.Lau@xxxxxx>
> To: 'Tesla list' <tesla@xxxxxxxxxx>
> Subject: RE: mysterious coil failure (fwd)
>
> One doesn't need a signal generator or scope of any kind to measure
> coupling.  You need only know the primary and secondary inductance,
> and perform the measurement described at
> http://www.classictesla.com/download/M_and_k_Measurement.gif
>
> I've not found it necessary to include the RC network across the
> secondary.  The wording is confusing with "Take concentric readings
> from meters."  I think what was meant is to take both primary current
> and secondary voltage measurements at the same time on separate
> meters.
>
> Regards, Gary Lau
> MA, USA
>
>> From: resonance <resonance@xxxxxxxxxxxx>
>> To: Tesla list <tesla@xxxxxxxxxx>
>> Subject: Re: mysterious coil failure (fwd)
>>
>>
>>
>> You need to check your coeff. of coupling and usually keep it below
>> 0.12 for most classic spark gap coils.  Some of my coils run best
>> with greatest spark output at .08 to 0.1 range.  A local Univ. or
>> tech college with a storage scope and sig gen can help you do this.
>> The equations and procedures are in the Tesla List Archives.
>>
>> If your coeff. of coupling is producing a "double hump" then your
>> coupling is too tight, energy is being wasted, and your coil will
>> hit HV peaks at two points --- sometimes not at the end of the sec.
>>
>> This produces tracking and eventually destruction of the coil.
>>
>> Also, be sure to always sand both interior and exterior of any
>> coilform prior to winding.  Also use some small acrylic baffles
>> approx 6-8 inches down from each end in the sec.  Silicone into
>> place with GE Silicone II  --- available at most hardware stores.
>>
>> Dolph's AC-43 has much greater anti-tracking properties than
>> polyurethane, and it's price is reasonable if you consider the
>> amount of repair time that is required when a coil fails.
>>
>> Dr. Resonance
>>
>> Resonance Research Corp.
>> www.resonanceresearch.com
>>
>>
>> ----- Original Message -----
>> From: "Tesla list" <tesla@xxxxxxxxxx>
>> To: <tesla@xxxxxxxxxx>
>> Sent: Sunday, October 28, 2007 8:03 PM
>> Subject: RE: mysterious coil failure (fwd)
>>
>>
>>
>> ---------- Forwarded message ----------
>> Date: Sun, 28 Oct 2007 19:50:56 -0400
>> From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
>> To: Tesla list <tesla@xxxxxxxxxx>
>> Subject: RE: mysterious coil failure (fwd)
>>
>>
>> Thanks guys,
>>      I don't think it was a shorted turn, there is no carbon on the
>> inside but there is a tiny black spot on the outside (I don't use
>> end caps on my coils, is this bad?).  I attach my RF ground by a
>> copper strap, soldered onto the end of the bottom turn, I think it
>> arced from the sharp edge of the strap to the wire above it (turn
>> 2).  This occurred underneath of the several layers of electrical
>> tape coated with polyurethane insulation on the bottom.  One other
>> detail I forgot to mention, I set the coupling as high as I could
>> get it that night to make up for decreased performance
>> from wind and humidity, so that may have contributed.  I'll sand her
>> down and rewind the bottom and see if it works again, thanks guys.
>>
>> Scott Bogard.
>>
>>> Date: Sun, 28 Oct 2007 11:07:40 -0700
>>> From: tesla@xxxxxxxxxx
>>> To: tesla@xxxxxxxxxx
>>> Subject: Re: mysterious coil failure (fwd)
>>>
>>>
>>> ---------- Forwarded message ----------
>>> Date: Sun, 28 Oct 2007 11:01:32 -0800
>>> From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
>>> To: Tesla list <tesla@xxxxxxxxxx>
>>> Subject: Re: mysterious coil failure (fwd)
>>>
>>> Hi Scott,
>>>
>>> Yes, the glowing spot is either a shorted turn or carbon track. It
>>> may be a shorted turn and easy to fix if right on the bottom, and
>>> "if" it is like the very bottom turn, it's probably too much power
>>> for too long a period. I've had this happen on my 4" coil even with
>>> low coupling. If enough power is provided, it can cause extensive
>>> heating a greatest heating on the bottom of the secondary (highest
>>> current). If you were to continue running it, a nice little fire
>>> will begin. If it's a shorted turn, you'll have a nice black carbon
>>> ring around the entire turn. Real easy to fix obviously.
>>>
>>> Take care,
>>> Bart
>>>
>>> Tesla list wrote:
>>>> ---------- Forwarded message ----------
>>>> Date: Sat, 27 Oct 2007 22:10:06 -0400
>>>> From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
>>>> To: tesla@xxxxxxxxxx
>>>> Subject: mysterious coil failure
>>>>
>>>>
>>>> Hey guys,
>>>>      I was running my 6-in MOT coil tonight for my little cousins,
>>>> and it
>>>> died and I cannot figure out what is wrong.  The spark gap fires
>>>> fine, I did not adjust anything, it just died between runs, and
>>>> won't arc except to a grounded rod (it acts like it is badly out
>>>> of tune, but like I said,
>>>> I adjusted nothing).  The only thing different I notice, is that
>>>> there was
>>>> very high humidity, and I could see a tiny spark at the base of the
>>>> secondary.  It isn't arcing to anything, it is just a glowing
>>>> spot, that melted through the electrical tape insulation.  I'm
>>>> stumped, I guess I'll
>>>> tear the insulation off of the bottom of the sec' coil and see if
>>>> anything
>>>> is amiss, but I've never had a failure like this before.  The only
>>>> other possibility is that somehow my ballast malfunctioned, but I
>>>> don't think so.
>>>>
>>>> Scott Bogard.
>>>>
>>>>
>> _________________________________________________________________
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>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
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