MMC calculator

MMC tank design calculator for SGTC, VTTC, DRSSTC and QCWDRSSTC Tesla coils. Results are guidelines to designing a MMC and should always be double checked in your final design! Most importantly is that voltage rating is the DC voltage rating, from experience this can used for good quality capacitors, AC voltage rating with frequency derating would be much lower.

Capacitor specifications are taken from data sheets at 100kHz and some values for peak current, rms current, ESR and dv/dt are estimates from similar capacitors and graph read outs.

Inputs are in green. Outputs are in red. Formulas used can be seen below the calculator.

Basic MMC configuration – List of good MMC capacitors
Capacitance uF
Voltage rating VDC
Capacitors in series
Strings in parallel
Price per capacitor
Results
MMC voltage rating VDC
MMC capacitance uF
Total capacitors
Total MMC price
Advanced options
MMC capacitor parameters
Peak current rating A
RMS current rating A
dV/dt rating V/uS
ESR rating Find correct ESR rating
for your resonant frequency
specific
dissipation factor
ºC/W
Tesla coil parameters – Examples are small, medium and large
Frequency kHz
Primary inductance uH
Primary peak current A
On time uS
BPS BPS
Advanced results
Primary impedance
Ohm
MMC Xc
(reactance)
Ohm
MMC Zc
(impedance)
Ohm
Energy
(single cap)
Joule
Power dissipation
(single cap)
Watt
Temperature rise
(single cap)
ºC 0-5 very good, 5-10 good
10-15 not good, 15+ bad
Actual values MMC rating
Peak voltage MMC VDC VDC
RMS current MMC A A
dV/dt for MMC V/uS V/uS
Peak current for MMC A A

Theory used

MMC voltage rating: MMC voltage rating = DC voltage rating * capacitors in series.

MMC capacitance: MMC capacitance = (single capacitor capacitance * amount of capacitors in parallel) / amount of capacitors in a string.

Primary impedance: Zprimary = SQRT(Lp / Cp).

MMC Xc, reactance: Xc = 1 / (2 * PI * F * C). F is frequency in Hertz. C is capacitance in Farad.

MMC Zc, impedance: Zc = SQRT(ESR^2 + Xc^2). ESR is the combined ESR for the MMC. Xc is the MMC reactanse from above.

Peal voltage MMC: DC peak voltage over MMC = Zc * primary peak current

RMS current MMC: Irms = 0.5 * primary peak current * SQRT(on time * bangs per second). Steve McConner.

dV/dt MMC sees: Actual dV/dt in V/uS the MMC sees = (2 * Pi * V * F) / 1000000. V is peak DC voltage over MMC and F is frequency in Hertz.

dV/dt rating MMC: dV/dt rating in V/uS = Primary peak current / MMC capacitance.

Peak current for MMC: Peak rating = capacitor peak rating * amount of capacitor strings in parallel.

5 Responses to MMC calculator

  1. Pingback: MMC calculator added to the online calculators | Kaizer Power Electronics

  2. Jay says:

    When you calculate dv/dt why do you use (primary peak current / amount of capacitor strings in parallel) * amount of capacitors in a string

    Why not use 2 x pi x Vpeak x Frequency

    It just really looks odd to me how you are factoring parallel capacitors into a dv/dt and that you are completely ignoring frequency.
    Perhaps my brain is missing some critical hunk of information.

    Thanks for any help.

  3. Mads Barnkob says:

    Hey Jay

    Thanks for pointing out that I did make a mistake in my calculator, the current dv/dt calculation is only the combined dv/dt value for the mmc which then was to be used in a equation.

    Kind regards
    Mads

  4. ESR Calc says:

    Hello Mads
    I’ve just trying to calculate a ESR of my cap and i have litle questions
    How to it calculated the capacitor Wim fkp1 has 10mOhm ?
    I added the data to the equation
    ESR = tan x (2 x x f x C)-1
    ESR = 0.0004*(2*3.14*10000hz*0.0000001F)^-1 = 0.06369 OHMA i thing so.
    ? what is wrong ?
    Could you contact with me ?

    Best regards Thomas

  5. Mads Barnkob says:

    Hello

    I can see that you are looking at 10kHz, the numbers in my table is given for 100kHz. The dissipation factor and ESR changes with frequency, so that could be the cause. There is also not that detailed information on WIMA FKP1 capacitors, WIMA gives a generic information that is widespread applicable for a large range of their foil/film capacitors and metallized film capacitors.

    Kind regards
    Mads

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