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# Re: [TCML] MMC reference check.

```James,

The correct answer is somewhere in the middle.

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If you have 25 caps in series, then each will see 1/25 of the applied voltage.
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However, your transformer is putting out 15 KV RMS, or DC equivalent.  The peak voltage of the sine wave applied to the cap string will be at least 1.414 x the nameplate RMS voltage, or 21,210 nominal volts max across the string.  That works out to 848 volts across each cap, without any safety margin.
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Using 600 volt caps, you would need an absolute minimum of 35 caps in series, and I would use at least 25% more in each string to allow for transient spikes on top of the design voltages.  That will cut the effective capacitance of the string significantly.
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The TC environment is full of induced voltage spikes and primary strikes, and the caps are damaged by the maximum transient applied voltage, not the average, normal operating voltages.
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Most of the MMC strings I have seen used 15 to 20 2KV rated in caps in each string.  They can get expensive fast.  You can use fewer, but they will have shorter life time as the peak voltages across each cap increases.
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Dave

On 7/15/2018 8:42 AM, James Janota via Tesla wrote:
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```Ok, the old adage about measuring thrice make cutting nice comes to mind here. I have 25 942c6p15k-f in series. These are rated 600v each. Now my father in law who worked as an electrician for NASA and Inland Steel, said that my configuration won’t be enough for a 15kv NST. With my calculator it said 600x25=15000. But he said each one has to be rated for 15kv each. I don’t want a \$50. Firecracker. I also have 25 1M resistors, one for each cap.

```