Larkinisms
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From: George Jefferson on 21 Jul 2010 13:20 >>If you use wall-warts or they may saturate and not be as effective but by >>paralleling them you'll reduce the current and hence the total flux >>through >>each individual core. >> > > Paralleling the primaries does not reduce flux density. Reducing > excitation voltage, or increasing frequency, does. > > All others things being constant, reducing the load current taken from > a transformer secondary *increases* flux density in the core. > ^^Larkin^^
From: Tim Williams on 21 Jul 2010 13:56 "George Jefferson" <phreon111(a)gmail.com> wrote in message news:i27a9g$sk8$1(a)news.eternal-september.org... >>>If you use wall-warts or they may saturate and not be as effective but by >>>paralleling them you'll reduce the current and hence the total flux >>>through >>>each individual core. >>> >> >> Paralleling the primaries does not reduce flux density. Reducing >> excitation voltage, or increasing frequency, does. >> >> All others things being constant, reducing the load current taken from >> a transformer secondary *increases* flux density in the core. >> > ^^Larkin^^ What, George? Is it supposed to be untrue? Explain how. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: George Jefferson on 21 Jul 2010 14:12 "Tim Williams" <tmoranwms(a)charter.net> wrote in message news:6xG1o.20989$lS1.7902(a)newsfe12.iad... > "George Jefferson" <phreon111(a)gmail.com> wrote in message > news:i27a9g$sk8$1(a)news.eternal-september.org... >>>>If you use wall-warts or they may saturate and not be as effective but >>>>by >>>>paralleling them you'll reduce the current and hence the total flux >>>>through >>>>each individual core. >>>> >>> >>> Paralleling the primaries does not reduce flux density. Reducing >>> excitation voltage, or increasing frequency, does. >>> >>> All others things being constant, reducing the load current taken from >>> a transformer secondary *increases* flux density in the core. >>> >> ^^Larkin^^ > > What, George? Is it supposed to be untrue? Explain how. > > Tim > The magnetic flux density, B, is proportional to i for all inductor/transformer configurations. B = uH, u is approximately constant. H = N*i/(2*pi*r) for a toroid. At 0 current the magnetic flux density is 0. Simple as that.
From: Tim Williams on 21 Jul 2010 15:03 "George Jefferson" <phreon111(a)gmail.com> wrote in message news:i27dat$vr2$1(a)news.eternal-september.org... > The magnetic flux density, B, is proportional to i for all > inductor/transformer configurations. Incorrect. Flux is more fundamental than current, at least for the purposes of transformers. So, how much peak flux is applied by a 120V 60Hz sine wave? What is the resulting flux density in the core? What is the resulting flux when the secondary is heavily loaded? At any rate, even when using H, you somehow forgot to count the amp-turns of primary *and* secondary, which is just silly. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: John Larkin on 21 Jul 2010 15:51 On Wed, 21 Jul 2010 13:12:43 -0500, "George Jefferson" <phreon111(a)gmail.com> wrote: > > >"Tim Williams" <tmoranwms(a)charter.net> wrote in message >news:6xG1o.20989$lS1.7902(a)newsfe12.iad... >> "George Jefferson" <phreon111(a)gmail.com> wrote in message >> news:i27a9g$sk8$1(a)news.eternal-september.org... >>>>>If you use wall-warts or they may saturate and not be as effective but >>>>>by >>>>>paralleling them you'll reduce the current and hence the total flux >>>>>through >>>>>each individual core. >>>>> >>>> >>>> Paralleling the primaries does not reduce flux density. Reducing >>>> excitation voltage, or increasing frequency, does. >>>> >>>> All others things being constant, reducing the load current taken from >>>> a transformer secondary *increases* flux density in the core. >>>> >>> ^^Larkin^^ >> >> What, George? Is it supposed to be untrue? Explain how. >> >> Tim >> > >The magnetic flux density, B, is proportional to i for all >inductor/transformer configurations. > >B = uH, u is approximately constant. > >H = N*i/(2*pi*r) for a toroid. > >At 0 current the magnetic flux density is 0. Simple as that. > > > > > What "I" are you talking about? A transformer has two windings. And each winding has resistance. Take a typical power transformer. Connect the primary to the AC line and leave the secondary open. Measure or compute the core flux density. Now short the secondary. At least before it catches fire, shorted-secondary flux density will be about half of the unloaded value. Loading the secondary of a transformer reduces flux density... just look at the directions of the primary and secondary winding currents. It's surprising how many people get this wrong, and think that a transformer "saturates" if you short its output. John
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