Building a transformer
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From: Lostgallifreyan on 8 Aug 2006 15:50 Mark Fortune <mark(a)fortrex.co.uk> wrote in news:44d8d62e$0$26602$da0feed9(a)news.zen.co.uk: > 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 By a lot of cheap toroidals on eBay, 5A at some low voltage that doesn't sell well. Outputs in series, inputs in parallel. Switch-select to get coarse adjust, variable regulate over one output's voltage range to get any voltage over a large range with little loss.
From: John Woodgate on 8 Aug 2006 15:47 In message <44d8d62e$0$26602$da0feed9(a)news.zen.co.uk>, dated Tue, 8 Aug 2006, Mark Fortune <mark(a)fortrex.co.uk> writes >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. You need more than 5 A AC to get 5 A DC. The rough rule is that a bridge rectifier needs a factor of 1.6 times, but with modern huge filter caps, think of at least 1.8 times. That's a BIG transformer, with THICK secondary wire. Not a project to learn on, I would say. It's not even easy to buy parts for transformers now. Maplin used to do kits - bobbins, laminations etc. , but not now. To learn about transformer design, you need a textbook and one of the best is a classic - Radio Designer's Handbook, by F Langford Smith, which was reprinted by Newnes (Butterworth-Heinemann/Reed) a few years ago. ISBN0 7506 3635 1. Modern core material (silicon-iron) is better than the materials mentioned in the book. You may be able to get the information on current materials (maximum recommended induction, core loss power/kg, magnetizing VA/kg) from the web. -- 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: Eeyore on 8 Aug 2006 15:52 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, Toroids are relatively lightweight and more efficient that most E-I designs. They also have relatively low stray flux which is nice if that's important to you. > 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. For an uncomplicated requirement like that, simply buy one off the shelf. You have no chance of competing on price, never mind your transformer's unlikely to meet safety regs if you don't know what you're doing ( which clearly you don't since you're asking basic questions ). Graham
From: John Woodgate on 8 Aug 2006 15:51 In message <qI-dnR0veMUYQkXZnZ2dnUVZ_radnZ2d(a)insightbb.com>, dated Tue, 8 Aug 2006, t.hoehler <t.hoehler(a)insightbb.com> writes >Not really worth the effort, IMHO. However, take a look at All >Electronics, Hosfelt Electronics, MCM Electronics. A bit difficult for a person based in UK, perhaps. And 60-0-60 V at around 9 A is a BIG receiver or amplifier. Around 300 W/channel. -- 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: zekor on 8 Aug 2006 16:21
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. I would recommend reading up from every source. I have built torroids using the winding which was orginally a variac. These were 110 volt units. You automatically have a primary so all you need to do is wind the secondaries on top. I have also done the other type of transformer, schelacing.the iron plates. I would also recomend what others have, buy surplus on the market. Combine transformers if you can't find them. greg |