# Re: [TCML] Power Factor Correction

```So if using several NST’s in parallel… The PFC will not be a straight calculation.
The DC resistance will be significantly lower.
So be sure to get the accurate measurement…
In javaTC I was given a value of 700 uF…
In teslamap it came up with 3 F

> On Dec 3, 2016, at 2:51 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:
>
> Hi Ron,
>
> I remember trying to meter the mains current with my coil running and try
> various PFC cap values, looking for the lowest drawn current.
> Unfortunately, particularly when using a static spark gap, the mains
> current varies wildly from moment to moment.  I was utterly unable to
> experimentally determine if one value was better than another, although it
> was clear that current with a PFC cap was lower than without.   I think the
> takeaway is that the optimal value is by no means critical, as if you were
> trying to hit some kind of resonance.
>
> Regards, Gary Lau
> MA, USA
>
> On Sat, Dec 3, 2016 at 5:32 PM, Ronald Reeland <ronreeland@xxxxxxx> wrote:
>
>> Hi:
>>
>> I have been researching adding an A.C. power factor correction capacitor
>> across the 120 volt primary of a 15,000 volt, 30 milliamp secondary neon
>> sign transformer for a spark gap Tesla coil application.
>>
>>
>> It appears that the power factor of an ordinary transformer without a
>> built-in correction capacitor is 40 to 50 %. That means that the input
>> volt/amps is around twice that of a "perfect" power factor of 100%. Of
>> course we can never achieve a perfect 100%.
>>
>>
>> But it appears a person can attain a 90% or greater power factor thus
>> reducing the primary input current draw by calculating an approximate value
>> of correction capacitor.
>>
>>
>> Here is a  power factor correction capacitor formula that I found on the
>> web and in Brent Turner's book;  "The Tesla Coil Book", how they work & how
>> they are built" :
>>
>> PF Capacitor=  "corrected kVA" x  (10^9 divided by 2TT x Frequency x
>> primary volts^2) or in a more compact form : C=kVA (10^9/2TT f e^2).
>>
>>
>> There is a partial chart in Brent's book titled" PF-Corrected Transformer
>> ratings" and complete charts on the web for various transformer output
>> volts and current. It appears that the "corrected" output kVA is one half
>> in some instances and 55% or so in other cases.So if I have computed the
>> formula properly, a 15,000 volt, .030 amp transformer requires a 46 ufd
>> A.C. capacitor across the transformer primary. This is based on the charts
>> "corrected kVA" of .250. (The un-corrected kVA would be 15,000 x .030 or
>> .450 kVA.)
>>
>>
>> 1. I am asking for confirmation that all of above is true and that I
>> manipulated the formula properly.
>>
>> 2. I assume that since the formula deals with secondary output, the
>> lowered kVA is reflected in the 120 volt primary input and the current draw
>> there is reduced in proportion.
>>
>> 3. Also, is the formula a starting point for adjusting the capacitor value
>> higher or lower with an A.C. ammeter in the primary until the lowest input
>> amperage is achieved?
>>
>> 4. I also assume the secondary must be under load while fine tuning the
>> power factor capacitor value.
>>
>> 5. I have some 56 ufd, 250  volts A.C. motor-run capacitors (EPCOS brand)
>> that I would like to try.
>>
>>
>> Any help or corrections to my assumptions would be greatly appreciated.
>>
>>
>> Thanks,
>>
>> Ron Reeland
>>
>>
>>
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>>
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