Building a transformer
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From: joseph2k on 16 Aug 2006 21:44 John Woodgate wrote: > In message <WuYDg.9847$FN2.3842(a)newssvr14.news.prodigy.com>, dated Mon, > 14 Aug 2006, joseph2k <quiettechblue(a)yahoo.com> writes >>I took a look at the ieeta handbook. Yipee, this is something i want. >>You are right about the heavy physics, not for everybody. Thanks > > There are also a lot of 'mistakes' in it. Schade's curves, for example, > were derived in 1943 for valve/tube rectifier diodes and aren't correct > for semiconductor diodes, which have a much lower 'on-state' resistance. > Some of the waveform diagrams are positively weird, and don't aid > understanding at all. Thanks for the heads up. -- JosephKK Gegen dummheit kampfen die Gotter Selbst, vergebens. --Schiller
From: John Woodgate on 17 Aug 2006 02:59 In message <BRPEg.11891$o27.126(a)newssvr21.news.prodigy.com>, dated Thu, 17 Aug 2006, joseph2k <quiettechblue(a)yahoo.com> writes >John Woodgate wrote: > >> In message <WuYDg.9847$FN2.3842(a)newssvr14.news.prodigy.com>, dated Mon, >> 14 Aug 2006, joseph2k <quiettechblue(a)yahoo.com> writes >>>I took a look at the ieeta handbook. Yipee, this is something i want. >>>You are right about the heavy physics, not for everybody. Thanks >> >> There are also a lot of 'mistakes' in it. Schade's curves, for example, >> were derived in 1943 for valve/tube rectifier diodes and aren't correct >> for semiconductor diodes, which have a much lower 'on-state' resistance. >> Some of the waveform diagrams are positively weird, and don't aid >> understanding at all. > >Thanks for the heads up. > The source I use is 'Single-phase rectifier circuits with CR filters', A Lieders, Electronic Components and Applications, Part 1 Vol.1, no.3 p 153-163 (May 1979), Part 2 Vol.1 no.4 p 216-230 (August 1979) (Philips, Netherlands). A simplified treatment that works well is given in 'DC supplies from AC sources - 3', K L Smith, Electronics and Wireless World, February 1985. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk 2006 is YMMVI- Your mileage may vary immensely. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
From: werty on 4 Sep 2006 15:44 You want 600 va ? But that means 90% effeciency ! That means you must use switch mode . You must choose an ungapped ferrite core with 2000 or more MU , it will need litz wire on output ( simply use smaller wire and mo strands ) . Tiny cores will easy do 600 watts . MJE13005's are the most popular but the Cxxxx ( 2SCxxxx) equivalents are seen more cause all are built in China . You will see all switch mode pow supplies changing to single drive , for they are just as eff as push pull , and cheaper . Thery self oscillate ! Control circuit simply pulls down the Base of bipolar Xisistor to adj output voltage . It is a myth that more power can be sent to output using push pull ! All low end switch mode PS are using single transistor and if you measure the Xformer and other parts , SURPRISE , it is same size and cheaper to build and its also an easier circuit to control ! Simpler parts . You still need a volt ref and Opto and a LM393 to sense current . The myth started when they said the dead time would waste time but as we EE's know the dead time dont exist ! And we dont have to control it as LM494 crowd must do ! Its a simplification made in heaven , no compromises al all . You simply dbl up the Primary winding transistors ! Remember ! Transistors in class D dont worry about balancing ! If standard PCPS has push pull using 2 each C2335/or MJE13005 i simply put them in parallel ! Same power output ! Of course in dumpster diving , you will need to be clever on the 2ndaries to get same voltages Dont be put off , this is so simple it should be used in school to teach . You will be amased at how many parts are tossed out ! BTW Free OpSys for PDA . I'll buy a ARM Eval board ( www.littlechips.com) and create a Forth like integrated OpSys , call it NewForth for now . Wanna learn to do top System software ? Follow me ..... Mark Fortune wrote: > Greetings to the collective. > > For my next project I want to build a bench power supply and do away > with this old switch mode AT computer PSU that i'm currently using. > > The design I have in mind will be pretty beefy, giving a wide range of > fixed and variable output voltages (i'm thinking from -50v up to +50) > and deliver up to 5amps of current. if my estimates are right i'll need > a 600va+ (100v * 5a + overhead) transformer to do the job well. Now i've > had a look at some transformers in this range, and they're a little out > of my price range. so now i'm considering building my own. > > The specifications I need are as follows: > > primary: 0-230v @ 50Hz > Secondary: 60v-0-60v > secondary output current max: 5A > > I have an intermediate understanding of transformers, but have never > actually built one, hence I am seeking advice from those with experience > in this field. > So where do I start? what type of core is best for this application? - I > have a friend who's blasting off that toroids are best, but i'd like a > second opinion, and what kind of wire to use for the primary and > secondaries? what are good safety practices regarding insulation? Is > this even a feasable project to undertake (moreso on the money side than > timewise). Any other advice also greatly appreciated. > > regards, > Mark
From: meow2222 on 4 Sep 2006 21:26 werty wrote: > You want 600 va ? But that means 90% effeciency ! > That means you must use switch mode . > > You must choose an ungapped ferrite core with 2000 or more MU , > > it will need litz wire on output ( simply use smaller wire and mo > strands ) . > Tiny cores will easy do 600 watts . > MJE13005's are the most popular but the Cxxxx ( 2SCxxxx) > equivalents are seen more cause all are built in China . > > You will see all switch mode pow supplies changing to single > drive , for they are just as eff as push pull , and cheaper . > Thery self oscillate ! Control circuit simply pulls down the Base > of bipolar Xisistor to adj output voltage . > It is a myth that more power can be sent to output using push pull ! > All low end switch mode PS are using single transistor and if you > measure > the Xformer and other parts , SURPRISE , it is same size and cheaper > to build and its also an easier circuit to control ! Simpler parts . > You still need a volt ref and Opto and a LM393 to sense current . > > The myth started when they said the dead time would waste time > but as we EE's know the dead time dont exist ! And we dont have to > control it as LM494 crowd must do ! > > Its a simplification made in heaven , no compromises al all . > You simply dbl up the Primary winding transistors ! > Remember ! Transistors in class D dont worry about balancing ! > If standard PCPS has push pull using 2 each C2335/or MJE13005 > i simply put them in parallel ! Same power output ! > Of course in dumpster diving , you will need to be clever on the > 2ndaries to get same voltages > > Dont be put off , this is so simple it should be used in school > to teach . You will be amased at how many parts are tossed out ! 600VA thru litz wire? no dc component on single ended drive? (--> copper losses) cant get more power thru without the dc component? News to me. NT
From: Mark Fortune on 5 Sep 2006 21:03
meow2222(a)care2.com wrote: > werty wrote: > > >>You want 600 va ? But that means 90% effeciency ! >> That means you must use switch mode . >> >>You must choose an ungapped ferrite core with 2000 or more MU , >> >>it will need litz wire on output ( simply use smaller wire and mo >>strands ) . >> Tiny cores will easy do 600 watts . >> MJE13005's are the most popular but the Cxxxx ( 2SCxxxx) >>equivalents are seen more cause all are built in China . >> >>You will see all switch mode pow supplies changing to single >> drive , for they are just as eff as push pull , and cheaper . >> Thery self oscillate ! Control circuit simply pulls down the Base >> of bipolar Xisistor to adj output voltage . >> It is a myth that more power can be sent to output using push pull ! >> All low end switch mode PS are using single transistor and if you >>measure >> the Xformer and other parts , SURPRISE , it is same size and cheaper >>to build and its also an easier circuit to control ! Simpler parts . >> You still need a volt ref and Opto and a LM393 to sense current . >> >> The myth started when they said the dead time would waste time >> but as we EE's know the dead time dont exist ! And we dont have to >> control it as LM494 crowd must do ! >> >> Its a simplification made in heaven , no compromises al all . >> You simply dbl up the Primary winding transistors ! >> Remember ! Transistors in class D dont worry about balancing ! >> If standard PCPS has push pull using 2 each C2335/or MJE13005 >> i simply put them in parallel ! Same power output ! >> Of course in dumpster diving , you will need to be clever on the >> 2ndaries to get same voltages >> >> Dont be put off , this is so simple it should be used in school >> to teach . You will be amased at how many parts are tossed out ! > > > > 600VA thru litz wire? > no dc component on single ended drive? (--> copper losses) > cant get more power thru without the dc component? > News to me. > > > NT > I decided to have a look into switch mode psu's in the end, and furthermore building my own transformers seems far more complicated tham I originally anticipated. So i've looked into the switched mode psu's, and they seem fairly straightforward (famous last words), further to that i'm bugging the local computer store for any and all busted computer power supplies - and i'm not even charging them for 'disposal'. That way I can gather many transformers at no cost to me and experiment away to my hearts content. I figure if I need a lot of power I can run several of these transformers in series or parallel. Mark |