[sdiy] How to predict a transformer's current capability?

Magnus Danielson cfmd at swipnet.se
Tue Dec 25 02:16:32 CET 2001

From: Jaco Sloof <jacosloof at yahoo.com>
Subject: Re: [sdiy] How to predict a transformer's current capability?
Date: Mon, 24 Dec 2001 12:27:03 -0800 (PST)

> Ok final question then; 
> (sorry 4 al the stupid questions!
> (and then you guys say that there is no such thin as a stupid
> question, just stupiud answers, but i think im not really up to speed
> here... i just took the function of a transformer for granted, but i
> dont even really know how they function, even when i bui8lt my own
> electromotors... whahaha!)

There is however stupid individuals, so don't give me a reason to rank
you in as one ;O) Noooooo.... I wouldn't! ;O)

> final question:
> do the mounting holes affect the effectiveness of the transformer,
> e.a: will maximum performance/stability raise if there were NO holes
> in the laminated core, or if it was'nt laminated, (with alternately
> precautions to prevent magnetic field (mf?) leakage?)

If there is mountingholes through the magnetic core? Sure they would
help to increase the remanence (magnetical equalent of the electrical
resistance) but only sligthly, so it is not much to worry about. If
they are properly placed they have a minimum effect. I wouln't worry
too much unless you are really picky about things and have a good
reason for it. If you are just going to do a powersupply you would
care to have enougth headroom in specs not to worry a femtosecond
about such details. Recall that the powerlines are so far from ideal
all the time that such small details should not be made into a

> Thanx guys for filling me in so far... this list is really
> educational, AND practical too!

Indeed. That's why I stuck on for over 5 years...

> <status on my ASM-1: no progress yet, due to psu-design)
> <ok better then, status on psu-design:
> -PCB made, still gathering components, but its looking good
> -made a spice sim at a friends house, turns out its gonna be 650-700
> mA of current, really stable (10-30 mV ripple), 
> or 1.5 A (30-80 mV ripple) >
> (am i crazy, designing my own voltage regulator out of discrete
> components?)

Well, yes... ;O)

What you *really* like is a stable voltage reference and unless you
are an absolute DIY freak you would not attempt to beat those which
sit there in various regulators. You migth use regulators requiring an
external current-booster transistor, and a handfull of resistors and
such, but the core regulator would anyway be kind of integrated. The
723 is a classic for instance. Contains a fairly good voltage reference.

If you take a look at the SAS-PSU (sorry, Swedish only, but I guess
you can read the schematics at least ;O) there you have a pretty good
design with both foldback and overvoltage protection.


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