Re: Fw: Primary RMS Current calculation

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

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

Hi Chuck,

At 11:49 AM 2/28/2001 +0000, you wrote:
>
>----- Original Message -----
>From: Tesla list <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Wednesday, February 28, 2001 2:22 AM
>Subject: Primary RMS Current calculation
>
>
>> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
>>
>> Hi All,
>>
>>         I have received a number of inquiries about primary circuit RMS
>> current and using MMCCalc for different types of capacitors.  MMCCalc
>displays
>> the current:
>>
>> http://hot-streamer-dot-com/TeslaCoils/programs/Mmccalc2.zip
>>
>> The RMS current is calculated using the formulas in MMCPower4.html.  The
>> equations for resistance of a single cap (Rcap) and power dissipated in a
>> single cap (Wo) can be used to find current by simply using Ohm's law.
>>
>> P = I^2 x R  ==>  I = SQRT(P / R)
>>
>> So the RMS current in a single cap (which is the same for a single string)
>> is:
>>
>> Irms = SQRT (Wo / Rcap)
>>
>> The Primary RMS current is simply that number multiplied by the number of
>> strings
>>
>> Iprms = SQRT (Wo / Rcap) x Nstring
>>
>> MMCPower4 is at:
>>
>> http://hot-streamer-dot-com/TeslaCoils/MMCInfo/MMCPower4.html
>>
>> Cheers,
>>
>>         Terry Fritz
>>
>Hello all,
>
>I have been thinking about another method for calculating rms current in the
>primary circuit (MMC and primary coil). Not being certain of its validity, I
>would appreciate  comments.
>
> Knowing the MMC value and the voltage it charges up to before spark gap
>firing, I would first calculate the energy in the MMC. Joules = 0.5V^2C to
>get a feel for what's going on.
>
>This energy moves back and forth between the MMC and the primary coil during
>oscillation.Since energy in a coil  is Joules = 0.5I^2L
>
>then    0.5V^2C  =  0.5I^2L  or I = V(C/L)^0.5  (peak current at the instant
>all energy is in the coil).
>
>I rms = peak I x 0.707.
>
>Of course getting two bursts of RF during each ac cycle (120/s in U.
>S.),each burst lasting several cycles of RF (if perfect quenching is
>achieved), and some loss of energy due to circuit resistance then the
>current over  one  second becomes problematical. So back to square one on
>rms, average etc. current in this area. .
>
>I would think that what the MMC has to put up with in terms of peak RF
>current and voltage stresses are of major concern since both are usually
>very large.
>
>Again please, if there are flaws in my reasoning, I would be most anxious to
>know about it.
>
>Regards  Chuck.
>

I think there is a problem due to that fact that our coils are "pulsed".
They spend 97% of the time idle and only about 3% of the time putting out
real power.  That seriously messes with the RMS calculations.  They
dissipate hundreds of thousands of instantaneous watts during the firing
cycle but spend the rest of the time asleep.

My big coil runs about 10 amps RMS in the primary but when I use you
formula I got 222 amps.  However, if you multiply 222 buy the ~3% duty
cycle you get sort of close so maybe this idea can be made to work with
more thought...

Cheers,

	Terry