Building a transformer
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From: Paul E. Schoen on 8 Aug 2006 21:57 "Mark Fortune" <mark(a)fortrex.co.uk> wrote in message news:44d925ee$0$31643$db0fefd9(a)news.zen.co.uk... > peter wrote: >> Do you need both + and - power at the same time? If not, just have 0-50V >> would save you half the power. > > I would need the option of both +v and -v in respect to ground, but only > sometimes at the same time (ie when testing audio circuits, but not when > doing logic circuits) if I switched one of the secondary windings off... > would I still be saving half the power? > >> If you need to use 1V at 5A, your power supply would become pretty >> inefficient (supplying 5W and wasting > 300W). Are you planning to fan >> cool it? If not you need a huge heat sink. > > Wastage is becoming more apparent as I read more and more posts... and am > considering rethinking to a more energy efficient design now. > > I was (originally) thinking big heatsink with some thermal controlled > fans screwed on. > >> >> If you use a switching design, it would be a lot more efficient. >> > > switching psus I know nothing about, but think I will research this. Any > good places to start (apart from the obvious google)? This might be a good candidate for a triac phase fired circuit such as: http://www.st.com/stonline/products/literature/an/3566.pdf These can be noisy, but they are very efficient, and low in cost. If you want to make your own transformer, www.toroid.com has transformer kits. I think a 1.4 kVA core (available in 120 or 120/240) is about $100. I have used that same core (actually 4 of them) to build a transformer rated at 5.6 volts at 1000 amps continuous. I used bus bar for the secondary. You can do the same thing with an old Variac. However, it is a tedious process to wind a high voltage winding. The 1.4 kVA core has 0.7 volts per turn, so you'd need nearly 90 turns for each of your 60 volt outputs. Most importantly, consider exactly what you need the supply for, and build, buy, or modify according to the exact specifications you actually require. You must look at efficiency, weight, size, line and load regulation, max and min voltage adjustment, ripple, noise, overshoot or droop on load change, response time, cost, and time to design, build, and troubleshoot. You can get so much high quality equipment on eBay and at electronic flea markets, that building your own is usually only for very special requirements or as a learning experience. For logic circuits, I would recommend a separate 5 VDC (or 3.3, etc.) designed for that purpose, with a good crowbar overvoltage protection circuit. A wide range adjustable bench supply can too easily generate a spike that will wipe out (or incrementally damage) all the logic circuits. It might be a good idea to put a crowbar on the logic board. Good luck, Paul
From: YD on 8 Aug 2006 22:26 On Tue, 08 Aug 2006 13:52:26 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Tue, 8 Aug 2006 13:44:27 -0700, "RST Engineering \(jw\)" ><jim(a)rstengineering.com> wrote: > >>What primitive semiconductors did you use in the output stage, or was it a >>toob device? Did we have 2N3055s in '75? I don't memember. >> >>Jim >> >[snip] > >I'm trying to remember what semiconductors I used. But, IIRC, >2N3055's *were* available around that time. > > ...Jim Thompson It's in my GE handbook from 1973. ISTR some magazine article from 1971 using it, but I'm not going up in the attic dusting off that pile of old mags. - YD. -- Remove HAT if replying by mail.
From: Bob Eld on 8 Aug 2006 22:17 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in message news:s49id2l8pk4lesllfdcqgctsh63klcm743(a)4ax.com... > On Wed, 09 Aug 2006 00:42:46 +0100, "Dave Plowman (News)" > <dave(a)davenoise.co.uk> wrote: > > >In article <rm7id293e0gk1id8gf4s4fu79aboaf1oae(a)4ax.com>, > > Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: > >> >What pray-tell is an RMS Watt? > >> >" Put out 400W RMS into 4 x 16 ohm speakers in parallel." > >> > > > > >> Sine wave into equivalent of 4 ohm load... 4 each 16 ohm speakers in > >> parallel... I think... it was 30 years ago, might have been 4 each 8 > >> ohm speakers... 2 ohm equivalent load. All I remember is the 400W ;-) > > > >A watt is a watt - a measure of power. So can't be qualified by RMS or > >whatever. Although that doesn't stop the advertising boyos trying... > > I was just trying to distinguish the number from those that the "music > power" types like to bandy around. > > For instance peak instantaneous power would be 800W ;-) > > ...Jim Thompson > -- > | James E.Thompson, P.E. | mens | > | Analog Innovations, Inc. | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | Phoenix, Arizona Voice:(480)460-2350 | | > | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | > | http://www.analog-innovations.com | 1962 | > > I love to cook with wine. Sometimes I even put it in the food. Yea I know. That's very common in the audio industry but we Engineers should know better and use the proper terms. America is stupid enough without us adding to it, don't ya think?
From: Jim Thompson on 8 Aug 2006 22:23 On Tue, 08 Aug 2006 23:26:31 -0300, YD <ydtechHAT(a)techie.com> wrote: >On Tue, 08 Aug 2006 13:52:26 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: > >>On Tue, 8 Aug 2006 13:44:27 -0700, "RST Engineering \(jw\)" >><jim(a)rstengineering.com> wrote: >> >>>What primitive semiconductors did you use in the output stage, or was it a >>>toob device? Did we have 2N3055s in '75? I don't memember. >>> >>>Jim >>> >>[snip] >> >>I'm trying to remember what semiconductors I used. But, IIRC, >>2N3055's *were* available around that time. >> >> ...Jim Thompson > >It's in my GE handbook from 1973. ISTR some magazine article from 1971 >using it, but I'm not going up in the attic dusting off that pile of >old mags. > >- YD. I've run out of library shelf space, so I've been donating out of date books (like "Mother of All Windows" for Win95) to charity book sales ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: James Sweet on 8 Aug 2006 23:11
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 Look for a surplus transformer, you won't save any money trying to build one yourself. That's a BIG supply to be using a linear regulator for, I suggest looking at some of the switcher IC's available now days, National Semiconductor makes a series called Simple Switchers which are FAR easier to work with than designing a switcher from scratch and they have HV versions which are good to 80V or so. |