Building a transformer

I've run out of library shelf space, so I've been donating out of date books (like "Mother of All Windows" for Win95) to charity book sales ;-)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

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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I love to cook with wine.      Sometimes I even put it in the food.

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.

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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.

Wasn't that around the time the Dynaco ST-400 came out? I rebuilt one of those once, seems like it used a bunch of big Motorola power transistors, I forget the numbers but they weren't 3055's. Seems like there were 4 of each polarity per channel, or maybe it was 2, I do remember the heatsinks were HUGE.

In message , dated Wed, 9 Aug 2006, James Sweet writes

Many manufacturers used 'custom' devices which were allegedly tested to custom specifications by the device manufacturer. The Vcc max might be higher than for the normal device, and/or beta range might be less.

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John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

I admire your desire to have a go at such a large project, although I have to ask if you are really all that keen to learn transformer design.

An old (now deceased) engineer friend of mine was gun at designing transformers and even he required about 3 iterations to get the design right for maximum efficiency. And he wasn't designing anything quite as big as you are after. A 350VA transformer isn't all that small especially if you are using other than a toroidal core, and those are a bugger to wind by hand.

Quite frankly, I don't think the exercise is all that worthwhile unless you plan to use the expertise gained in the future. Transformer design and building is somewhat a "black art" and you can easily get bogged down. If you really only want to design and build a bench PSU then this exercise in itself would be an achievemnt to be proud of. But you don't want to spend 6 months building transformers before you get to the rest of the design.

I have to agree with the sentiment 100%. Surplus transformers are always going to be cheaper than custom-built :-). Most oddball transformers on E-bay sell for pennies on the dollar (actually most don't sell at all!)

And construction and mounting-wise, a lot of small transformers are way easier to deal with than one mammoth one. Above a very small number of VA you start building the case and mounting reinforcements around the transformer anyway :-).

Tim.

Look for a blown-out 200-400 watt audio amplifier (or receiver) at a garage sale. The transformer you'll find in it will be pretty close to what you want. The amp will also include a lot of other very useful items such as big heat sinks, and so on.

Isaac

2N3055s ...and AD149s ... all Si too ...

u know ...if u really wish to "learn" ...why dont you design yourself a

50A, 0-50V continuously variable SMPS ....capable of operating in both CV and CC modes.

(i know what some ppl are going to say ....he wants to learn ...not repent)

I have a HP 6268B here with a bad transformer. I didn't even think of rebuilding the transformer. Well it did do 0-40 volts at 0-30 amps. I just recently got the idea to buy another used transformer at some reduce specs to install in the beast. Hmmmm.

greg

Given the replies i've had on this, it seems the more sensible way of going about it. Whilst i'm sure I will enjoy with experimenting with transformers in the future, building a power transformer - specifically the beast i'm after does seem to be costly and time consuming going by the responses i've had on this thread, and is unlikely to work (first time around anyway), where in contrast I could just pick up old/broken equipment at the local car boot sale for under a fiver. I've had a little read on (very basic concepts of) switching mode power supplies, and this does seem to way to go in terms of efficiency and size.

So yes, forgive me for my sins, I repent! ;)

Thanks to all those that offered their advice however, it's been insightful to me, and I certainly wont give up the opportunity to build my own transformers in future... just not on such a power crazed level where there are better solutions.

Regards, Mark

Also realize 50A at 50V is 2500 watts at 100% efficiency. If you are in the USA, you will need a 220V power connection to do this.

David

Yes, you need about 50% more wire on the primary to get the idle current down from 3 amps. I think microwave transformers go into saturation with no load. Another problem is the iron laminations are all welded together on the base plate, so the iron gets hot from the huge eddy currents. Probably better to use some other kind of transformer. I have one from an old pin ball machine that idles at 10mA with no load.

-Bill

--------------8 So yes, forgive me for my sins, I repent! ;)

Wow, pretty sure i'm not going to need 50A at any voltage... not sure where that came from as originally I only wanted 10A. Incidently though, im in the UK so we have 230V by default.

All Pro-Electron numbered devices beginning with "A" are Germanium!

Not to mention the heatsinks it'll take when you want to deliver, say,

12 volts at anywhere near that 50 Amps. Hint: Plan on a fan and wheels.

Isaac

I'd also query the need for such a large bench top supply - unless you're regularly repairing or building things like power amps.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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aha, you've discovered one of my planned future hobbies :) any money in it though?