[TCML] Another MMC question.

[Barton B. Anderson]

Hi Scott,

Temperature rise = power dissipation x thermal dissipation factor (TDF).

TDF for this cap with various lead spacing can be determined as 
1250/lead spacing(mm). A constant I stumbled across a long time ago 
while evaluating Terry's test data.

Power dissipation = bps x discharge energy x capR / (capR+3). I used 120 
bps for this chart.

Discharge energy = 0.5 x (CapValue) x 
(pow((CapFireVoltage/CapPerString),2));

CapR = TANd / (2 x PI x CapValue x ResFreq); I used 200 kHz ResFreq for 
this chart.

CapFireVoltage = RMSVoltage x sqrt(2);

TANd = ResFreq/110000; Constant (110000) over a range of 50kHz to 
400kHz. TANd is the dielectric loss factor or the dissipation factor.

Irms = NumberOfStrings x sqrt(PDissipation/CapR); Just something else to 
look.

The values in the chart will be accurate for this particular cap type. 
Other caps will vary a bit on the temp rise but shouldn't be too far off 
the mark if of similar construction and dielectric. It is all based on 
Terry's testing. But if your trying calc temp rise for other caps which 
are different in construction and material, then testing would need to 
be done. The factors I have found which help me over the range of 
frequency and lead spacing were only available following testing and 
then evaluation of that testing (occurred several years ago).

Take care,
Bart





huil888 wrote:
> Hello Bart -
>
> How were the "temperature rise" values determined for this chart? As a 
> purely calculated value, it seems like you'd need to know the 
> dielectric loss factor for the cap, the operating frequency, the 
> thermal mass of the cap, etc.
>
> Terry Fritz' original test setup used an RF power supply to pump 3.5A 
> at 350 KHz through the cap, and then measured the temperature rise 
> after 15 minutes. Terry's test setup can be seen at:
>
> http://www.hot-streamer.com/TeslaCoils/MMCInfo/GeekCaps/GeekCaps.htm
>
> Terry's formulas for determining the power handling capability of an 
> MMC are at:
>
> http://www.hot-streamer.com/TeslaCoils/MMCInfo/MMCPower4.html
>
> I'm just curious how the temperature rise info was obtained, for use 
> in calculating the temp rise for other types of capacitors.
>
> Regards,
> Scott Hanson
>
>
>
>
>
> ----- Original Message ----- From: "Barton B. Anderson" 
> <bartb at classictesla.com>
> To: "Tesla Coil Mailing List" <tesla at pupman.com>
> Sent: Wednesday, December 12, 2007 9:14 PM
> Subject: Re: [TCML] Another MMC question.
>
>
>> Hi Michael, All,
>>
>> I deleted that old MMC Cap Chart. I created another chart in the way 
>> "I" would do it for the 0.15uF CD cap which is so common. The chart 
>> is good only for that cap. I basically added Vp and Temp Rise for a 
>> given transformer type and then added combinations to meet the value 
>> for Resonant, Static LTR, and SRSG LTR.
>>
>> Basically:
>> The higher the voltage rating = the better the cap.
>> The lower the Temp Rise = the better the cap.
>>
>> For a given NST type, I stopped when the MMC met or exceeded 2.5 x Vp 
>> and if the temperature rise per cap in degrees centigrade was below 2 
>> (when both conditions were met). In all cases, the temp rise is 
>> either "good" or "excellent". It's the standoff voltage really that 
>> is of the most concern with this particular chart.
>>
>> Like I've said in the past, I don't use charts, but for those that 
>> prefer a chart to get "as near as possible to stated LTR sizes", this 
>> one should help (and if you can't understand if the string combo is 
>> good or bad, then just ask the TCML). Due to the single cap value 
>> (0.15uF), the "nearest" mmc value must be used. The old chart didn't 
>> really explain that. With this chart, the value you see is the actual 
>> value of the mmc. Just something I noticed while going through 
>> numbers on the old chart.
>>
>> http://www.classictesla.com/download/mmc_cap_chart.pdf
>>
>> This chart is 60Hz only. If there are "any" 50Hz coilers desiring the 
>> same, just let me know. It's no big deal (but please ask while it's 
>> still fresh in my brain).
>>
>> Take care,
>> Bart
>> _______________________________________________
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>> Tesla at www.pupman.com
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>>
>
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