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Re: Designing for high Power Factor
Original poster: "Robin Copini by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rcopini-at-merlin-dot-net.au>
Count me in on this, I can vary my cap in increments of 0.01uf from 0.05
to 0.09uf and use a variac to
I am very interested in improving power factor in my system.
Tesla list wrote:
> Original poster: "R.E.Burnett by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Hi guys,
> Original Poster: "Mike Doyle" wrote :
> > How would one go about designing a high PF system?
> Maybe I should have explained this power factor thing better, but I
> didn't want to make my original reply too lengthy. I have been looking at
> AC resonant charging behaviour for some time, but have been delaying
> presenting my findings here until I was sure they were valid for both 50Hz
> and 60Hz countries.
> In a system using a separate power transformer and external ballast, it is
> possible to achieve a power factor of 0.85 or better for a wide range of
> rotary speeds by careful choice of the BALLAST and TANK CAPACITOR
> Rather than considering the ballast and tank cap values separately, I
> believe we should really work with them as a pair. It is not the actual
> ballast and capacitor values which are important. Instead it is the
> resonant frequency, and characteristic impedance of the charging circuit
> which define its behaviour.
> The resonant frequency of the charging circuit essentially defines the
> charging profile of the tank cap after each bang. It controls all of the
> timing related stuff like Power Factor, and response to various break
> rates. For any chosen rotary firing rate there is a natural frequency for
> the resonant charging circuit which gives best power factor.
> The characteristic impedance of the charging circuit defines the power
> throughput aspect of its behaviour only. Resonant frequency changes with
> the product LC, and the impedance is proportional to L/C, so it is
> possible for us to control each of these things separately by manipulating
> the ballast and tank cap values together.
> Eg. Double L, double C, to halve Fres and leave Z unchanged,
> Double L, halve C, to double Z and leave Fres unchanged.
> If the resonant charging circuit is designed such that it has the correct
> natural frequency, then the values of the ballast and tank capacitor can
> be tweaked together to set the characteristic impedance and achieve the
> desired power throughput.
> Therefore I propose the following design approach:
> 1. Choose the desired rotary BPS,
> 2. Find the optimum resonant frequency for the charging circuit,
> (this fixes the LC product and guarantees good power factor at
> the chosen rotary speed.)
> 3. Adjust characteristic impedance to get desired power throughput.
> (this fixes L/C, so values for ballast L and tank C can now be
> Using these L and C values will provide the desired power throughput at
> the best achievable power factor. (Like biggest spark for minimum
> current.) (It's difficult to get a PF better than about 0.93 because of
> the current waveform is not a pure sinewave.)
> There is more information about this at my web site:
> Be sure to click the link at the bottom for externally ballasted supplies.
> This stuff is kind of heavy going, but I am planning to develop a simple
> computer program to do all of the clever stuff. I was inspired by Bart's
> excellent MMC Designer, and realised that there really is not much
> information about designing AC resonant charging circuits.
> The program will ask the user to input the chosen rotary speed in BPS and
> the desired power throughput in Watts. It will then calculate the ballast
> inductor and tank capacitor values necessary to achieve the specified
> power throughput at the chosen BPS, with good power factor. I'm still
> working on this, and will be asking for some people to volunteer as Beta
> Testers shortly ;-)
> If there is much interest on this list, I will try to go through a
> "Design Example". Something like "What ballast and cap values would give
> 10kW at 371BPS with a PF of 0.9 ?" I think that correct design of the
> charging circuit is very important, however I don't want to bore the
> socks off those who don't really care about this stuff, and get along just
> fine without it !
> (Newcastle, UK)