[Prev][Next][Index][Thread]
Re: PFC Formula (was: Re: Power Factor Correction weirdness?)
At 02:30 PM 02/10/2000 +0100, you wrote:
>Hi Terry,
>
>Comments below.
>
>> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>> I looked at my coils and the PFC caps I use and the basic
>>principle behind Adam's test seems to be a useful way of
>>selecting PFC cap values. Basically just correct for the
>>transformer's VA rating. In the non-linear operation of a TC
>>there are a few inaccuracies but they do not seem very
>>significant.
>
>[Snip]
>
>> 49.7uF where the actual value is about 60uF. Not exact but
>>close enough. Thus, I would propose the following equation
>>(unless everyone has been using it for years and I am the
>>last person on earth the figure it out ;-))
>>
>> Cpfc = ( Vo x Vi ) / ( 2 x pi x f x Vi^2 )
>
>Naw, your not the last person to find it. There will always be coilers,
>who enter the scene after you ;o)), so fear not ;o)). I have been
>using the same basic equation in my TC proggy. I think I "stole" it
>from Jim Lux´s website ;o) and I have seen it mentioned thereafter
>in some of the Richard Quick / R. Hull / TCBOR text files floating
>around on the internet.
Neat. I know a lot of people ask about cap sizes to use but I have not see
many equations about this. I guess I missed them.
>
>The only *problem* (which really isn´t one) is that this formula
>is for purely sinusoidal waveforms. Once you start squeezing an
>xformer, like we do in coiling usage, your waveform can become
>quite distorted, so the math won´t *truly* fit the real world. But as
>this has nothing to do with the output power of a transformer (i.e:
>it won´t increase your actual power throughput or spark length), it
>doesn´t really matter. It (PFCing) DOES allow you to actually draw
>more USEABLE power from a certain outlet as the fuse or c.b. no
>longer see an overcurrent situation (in certain "near-the-c.b.-limit"
>setups). However, it might (never thought about this until now) might
>contribute to a higher inrush of current the moment you flip on the
>main power switch. This, of course, only holds true for non-variac
>controlled setups.
If it weren't for PFC caps, my big coil could not run (coil and gap motor)
off 15 amp circuits. With them, my big coil can easily run at 13 amps
total. I think PFC caps reduce inrush currents but variacs are the
dominant part concerning that in most systems.
Another *problem* I can see, is if you run your
>coil at different voltages (via a variac). You can only determine
>(actually better: use) the proper PFC for a given voltage. In other
>words a 120V PFC will not be correct for those guys who will
>occasionally ramp the variac & xformer up to 140+V.
The input voltage divides out of the equation and should not make much
difference (Vo is a function of Vi). However, the gap firing may change
but over all it should work fine at any usable voltage.
>
>One last thought: I never quite figured out where to place a PFC:
>in front of, or behind the line filter? In front of the line filter
>would mean you would need to compensate for the line filter as
>well. I.e: it might not "PFC" as well as w/o the line filter. Placing
>the PFC behind the line filter would call for a cap that can take
>a kickback from the coil (voltage wise). I use the 2-3x figure (in
>my TC proggy) on AC voltages, which can lead to mighty big
>PFCs as they grow larger to accommodate for their higher
>operating voltage ;o(?)
The PFC cap must go directly across the inputs of the transformer. The
line filters are in front of them so they see lower currents due to the PFC
caps.
>
>Coiler greets from Germany,
>Reinhard
>
>
References: