The MMC capacitor
The MMC or multy mini cap was pioneeded in the late 1990`s it makes use of many easy and cheap to buy small axial capacitors in the range of 1.5KV to 2KV and with capacitance values around 0.015uf or above.
A "string" of capacitors is first wired in series to gain the requried voltage (our MMC uses a string of 16 x 1.6KV caps for a value of 30.4KV) now with capacitors in series there overall value is reduced by the multiple of the number of caps used, the way we get around this is to then wire multiple strings of capacitors in parrelle, each individual capacitor has a 10meg ohm across its terminals so that when power is turned off the capacitor will bleed it`s charge off.
A "string" of capacitors is first wired in series to gain the requried voltage (our MMC uses a string of 16 x 1.6KV caps for a value of 30.4KV) now with capacitors in series there overall value is reduced by the multiple of the number of caps used, the way we get around this is to then wire multiple strings of capacitors in parrelle, each individual capacitor has a 10meg ohm across its terminals so that when power is turned off the capacitor will bleed it`s charge off.
The image on the left is our finished MMC built up of 6 boards of caps, the picture on the right is a close up of just one MMC board it has the following values.
1 cap = 0.068uF at 1.9KV
1 string of 16 caps = 0.00425uF at 30.4KV
4 strings in parallel = 0.017uf at 30.4KV
The total value of the MMC can be changed just by adding or removing one or more boards of caps, this type of capasitor is almost indistructable, care must be taken to keep a reasonable space between the rows of caps, thses small axial caps are also "Self healing" they will continue to work even with minor damage.
1 cap = 0.068uF at 1.9KV
1 string of 16 caps = 0.00425uF at 30.4KV
4 strings in parallel = 0.017uf at 30.4KV
The total value of the MMC can be changed just by adding or removing one or more boards of caps, this type of capasitor is almost indistructable, care must be taken to keep a reasonable space between the rows of caps, thses small axial caps are also "Self healing" they will continue to work even with minor damage.
You can use the MMC calculator below to find the value and the number of mini caps you need by filling in the boxes above and the output figures will auto update. (MMC Calculator coded by Steve Bell see for more)
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