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 100 kHz 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.

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.

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

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

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

Hi Mads,

thanks for providing all those great tools 🙂 i have noticed something, the specific dissipation is usually given in W/°C. On the form it’s °C/W. Is this a typo ?

btw. great quarantine vids from you 🙂 keep it up!

Hi fnordest

Thank you and it is not an error.

Thermal resistance (Rth) when given in data sheets are either Watt needed to raise the temperature by one Kelvin or degree Celsius the temperature rises by one Watt dissipation. Conversion from W/K to °C/W is to divide one by W/K dissipation factor. °C/W = 1 / (W/K). I only put this explanation in the good mmc capacitor list: http://kaizerpowerelectronics.dk/theory/good-mmc-capacitors/

Kind regards

Mads

Thanks fofr the quick reply.

I thought about using WIMA GTOMS04400 but now it seems they are not viable in this configuration. I thought i could get away with 1 String of 6 x 4uF but it seems that i have to put some strings in parallel.

From WIMAs datasheet the specific dissipation is 0.23 W/K and ESR around 5 – 10 mOHM at 80kHz.

At 1000Apk this would be around 15W power dissipation per cap. Might be a little bit too much.