Re: [TCML] Primary selfC

["DC Cox" <resonance@xxxxxxxxxxxx>]

It's very low because this is only isotropic capacitance.  A normal
capacitor has two plates and this is similar to a single plate capacitor
with the second plate being ambient ground.  I would suspect it's only 3-4
pF if even that high.

I never use ribbon due to corona.  Take a 5 sec B&W 400 ASA exposure and you
will see what I mean.  I did with earlier coils and the photos almost scared
me.  High level of degradation on the sec coil.  Perhaps for occassional
operation it's ok, but I would not make a commercial unit with sharp edged
ribbon.  Corona much less for copper tubing.

Dr. Resonance

On Fri, Jul 25, 2008 at 7:50 PM, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:

> Hi Gary,
>
> I'll await Paul's reply also. I personally just looked at the ribbon coil
> as "similar" to a rolled capacitor given it's geometry both in conductor and
> shape. It may or may not be correct to look at it this way. The value
> surprised me, but the numbers came out as they did. My initial gut instinct
> told me the capacitance would be very low, the resonant frequency would be
> in Mhz, etc.. (like anyone else), but then I started thinking about basic
> variable air plate capacitors. This is similar. I may need to do a math
> check or have someone else check my math, but the numbers showed a somewhat
> significant capacitance. I'm not sure what to think of it either.
>
> However, I am in the process of building a ribbon primary (cut the
> standoffs this week using 3/8" thick Garolite). Maybe this next week I can
> test it myself (assuming my honey-do list is short).
>
> Regards,
> Bart
>
> Lau, Gary wrote:
>
>> Hi Bart,
>>
>> Until Paul can speak to my earlier question, I think you're subscribing to
>> the same false intuition that I and many, many others apparently do.
>>
>> For a secondary coil (where we are more accustomed to discussing Cself),
>> the value of Cself is not affected by the number or turns, the spacing of
>> the turns, the diameter of the wire, or the dielectric between the turns.
>>  All that matters is the geometry of the overall cylinder that contains the
>> coil.  Try it with your favorite simulator!  No doubt the same is true for a
>> primary coil as well.  This is why Paul was suggesting modeling the primary
>> as a free-standing disk - the shape of the flat spiral primary.
>>
>> I whole-heartedly agree - it sure does seem that the relationship between
>> turns would be a dominant factor in Cself, but apparently it is not.
>>
>> Regards, Gary Lau
>> MA, USA
>>
>>
>>
>>> -----Original Message-----
>>> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
>>> Behalf Of bartb
>>> Sent: Thursday, July 24, 2008 9:59 PM
>>> To: Tesla Coil Mailing List
>>> Subject: Re: [TCML] Primary selfC
>>>
>>> Got to thinking,
>>>
>>> Didn't rolled caps have 2 metallic sheets rolled up? If so, then 1/2 the
>>> value, so 3.2nF and 940kHz. Chris, you can verify by measuring Fres and
>>> back calculating C from L.
>>>
>>> Bart
>>>
>>> bartb wrote:
>>>
>>>
>>>> Hi Paul, Chris,
>>>>
>>>> It might be more accurate to look at the total length of the ribbon
>>>> and width to determine area and treat it as rolled capacitor separated
>>>> by 1mm, using air as the dielectric, and determine C as one would with
>>>> any flat plate capacitor, but in this case, as a "rolled capacitor".
>>>>
>>>> C = 0.2248*k*A*(N-1)/(d*x)  (in pF)
>>>>   where
>>>>    k = Dielectric constant (1.0006 for air)
>>>>    A = Effective plate area in square inches (length x width)
>>>>    N = Number of conductive plates (3 for a rolled cap)
>>>>    d = individual dielectric film thickness (.03937" in this case)
>>>>    x = number of stacked sheets of dielectric between plates (1 in
>>>> this case)
>>>>
>>>> I think Chris is looking at about 6.4nF for the ribbon primary. So
>>>> he's probably correct to ask the question given the very low tank
>>>> capacitance. Primary C may be much higher than expected (a good deal
>>>> of area at about 557 square inches). Should be able to verify by
>>>> inserting a signal to the primary as one would with a secondary and
>>>> looking in the range of 470kHz assuming inductance is about 18uH.
>>>>
>>>> Regards,
>>>> Bart
>>>>
>>>> Paul Nicholson wrote:
>>>>
>>>>
>>>>> Chris Swinson wrote:
>>>>>
>>>>>
>>>>>
>>>>>> Does anyone know how to work out , or know of an online
>>>>>> calculator for crunching primary Self Capacitance ?
>>>>>>
>>>>>>
>>>>> Does JavaTC not give the Cdc of the primary?  If not,
>>>>> use JavaTC or FANTC to work out the self capacitance of a
>>>>> disk.
>>>>>
>>>>> Then, divide the Cdc by two to get an approximate effective
>>>>> capacitance.
>>>>> --
>>>>> Paul Nicholson
>>>>> --
>>>>>
>>>>> _______________________________________________
>>>>> Tesla mailing list
>>>>> Tesla@xxxxxxxxxxxxxx
>>>>> http://www.pupman.com/mailman/listinfo/tesla
>>>>>
>>>>>
>>>>>
>>>> _______________________________________________
>>>> Tesla mailing list
>>>> Tesla@xxxxxxxxxxxxxx
>>>> http://www.pupman.com/mailman/listinfo/tesla
>>>>
>>>>
>>>>
>>> _______________________________________________
>>> Tesla mailing list
>>> Tesla@xxxxxxxxxxxxxx
>>> http://www.pupman.com/mailman/listinfo/tesla
>>>
>>>
>> _______________________________________________
>> Tesla mailing list
>> Tesla@xxxxxxxxxxxxxx
>> http://www.pupman.com/mailman/listinfo/tesla
>>
>>
>>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla