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*To*: tesla-at-pupman-dot-com*Subject*: Re: ballast formula*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Fri, 23 Feb 2001 16:19:26 -0700*Resent-Date*: Fri, 23 Feb 2001 16:42:07 -0700*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <PwQuKB.A.W4B.LVvl6-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com> Tesla list wrote: > Original poster: "James T by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jamest2000-at-att-dot-net> > > Hi Deano, > Thanks for the response. That is just what I was looking for. I think i > need those drawings to > figure out the mean length. > Whenever you get a chance to scan those pages would be great. There should > be a clickable email > next: > mailto:jamest2000-at-att-dot-net > > I think the MU(permaebility) should be around 60,000. Does that sound right? > > Thanks James > > Tesla list wrote: > > > Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>" > <deano-at-corridor-dot-net> > > Hi James, > > I have an old text book with some of that stuff in it. It says: > > L = N^2*mu*A/10^8*l > > (L equals N squared mu A over ten to the eighth l) > > where L is in henries, > > and N = number of turns > > mu = permeability of core (in English units) > > A = area of core in square inches > > l = mean length of core in inches > > The mean length would be {twice the length of the center leg (with the I > > part on there) plus twice half the width of the core} plus [the perimeter of > > one window} / 2. > > Trying to draw pictures with words is not my strong point. If you want, I > > can scan the pages and email them to you. > > > > later > > deano Hi James.... if you plan to use a transformer for ballasting, there are a few things to consider looking for. The EI core should be of a healthy size , the center leg should be approximately a minimun of 9-10 square inches of area. the primary winding should be made of a #8 wire ( #10 will work for short term runs (( 20 secs on 2 min off). the secondary wire size is determinded by the winding ratio. ( if the transformer is a welding type transformer, the secondary has very thick wire, very few turns. if it is a voltage increasing (( NST MOT OBIT)) transformer, then you will find small gage wire on it with many turns usually thousands of turns) if the transformer you plan to use is too small for the current you plan to pump thru your Tcoil transformer, the primary in the ballasting transformer will meltdown. ( example - Tcoil to run at 40 amps, ballasting trannie rated for 20 A, ooops ... hot ballasting trannie. in this case the maximun Amps to be allowed into Tcoil trannie is 20 A) the problem with using transformers to ballast Tcoil trannies is that the ballasting transformer is subject to saturation problems, and that results in a runaway condition that allows the amperage to shoot sky hi. if you have an amp meter ( which can handle 100A + ) you can do a quick test to see just how much the ballasting trannie is rated for ... connect the primary to your supply voltage ( check secondary voltage to determine the possible amperage delivery (( also the size of the secondary wire thickness is a hint as to how much amperage is to be delivered by the secondary the thicker the wire the higher the delivered amperage)) example - 120V in 12V out, primary wire about a #16, secondary wire about a # 6, expect about 50 amps on the secondary side, 5 amps on the primary side. once you have connected the primary to the supply voltage and checked the secondary voltage you have your winding ratio available. next step ... disconnect primary voltage , connect the secondary leads to each other ( short the secondary side) and reconnect the primary to the supply voltage ... 2 things will happen where , either the fuse will blow or it wont, if it doesnt then check the amperage drawn by the primary. this amp reading will be the nominal rating of the transformer, and that is about what you will be limited to as a ballasting current to your Tcoil. Scot D

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