Re: Designing for high Power Factor

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Robin Copini by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rcopini-at-merlin-dot-net.au>

Hi Richie,

 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
ballast
I am very interested in improving power factor in my system.

 Best Regards

 Robin Copini




Tesla list wrote:

> Original poster: "R.E.Burnett by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<R.E.Burnett-at-newcastle.ac.uk>
>
> 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
> components.
>
> 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
>     calculated.)
>
> 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:
>
> www.staff.ncl.ac.uk/r.e.burnett/async.html
>
> 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 !
>
>                                                         Cheers,
>
>                                                         -Richie,
>                                                         (Newcastle, UK)