29 Aug
2001
29 Aug
'01
7:31 p.m.
comments inline:
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk
To: <classiccmp(a)classiccmp.org
Sent: Wednesday, August 29, 2001 4:54 PM
Subject: Re: S-100 Power Supplies: thanks!
"just
> That doesn't make it unreasonable to
wind a transformer, but, I certainly didn't
> > > Winding a transformer is not a way to
save money if you value your time
at
> > > 50-cents per hour. I offered to ship
him a complete S-100 mainframe for
$5
> +
> > > You've made this sort of comment
before, and I still can't understand
it...
>
> Well, take it in context. Go back and read the first post from Jeff
Hellige.
Sure.
What I meant here (and it wasn't Jeff, but I said that already), was that the
original post contained distinct references to both a moderate aversion to
building what he could buy, and to spending too much money. That's what started
me down this road.
It's reasonable for the original poster (whoever it was) to say that he
doesn't want to spend the time winding a transformer and would rather buy
a PSU.
But that's not the same thing as never wanting to spend the time winding
a transformer because you somehow put a financial value on the time spent
on hobbies. It is that last part that I have problems accepting.
No, it's not, and I didn't mean that doing such a thing is not worth the
effort
or investment. I simply meant that I didn't think it met the original poster's
model.
[...]
> > For many of us on this list, classic computers are a hobby. We work with
> > them because we enjoy them. Not because we make money with them (at least
> > not all the time).
> > Classic Computers as a hobby includes a
vast array of things aside from
> hand-building components. If one's hobby is fabricating components, which
may
Of course...
FWIW, I don't particularly enjoy winding transformers. I have done it. If
I can buy a suitable transformer off the shelf, you can bet I'd do that.
But in just about every hobby there are going to be aspects of it that
you don't particularly enjoy, but which you have to do anyway. The
enjoyment you get when the machine finally works, and the enjoyment you
get from using it outweigh the bits you don't enjoy doing.
[...]
> sense "classic." I'd never use a switcher to power S-100 box, simply
because
they
weren't part of that culture, but that's me. OTOH, I've machined
Actually, that wouldn't bother me too much. Well, unless I was restoring
a name-brand S100 system (whatever that really means) when I would want
to keep it original. If I was making a new system now that happened to
use some old S100 cards from the junk box, then I would have no problem
using an SMPSU.
The practical reason for not doing so is that 8V SMPSUs are not at all
easy to find, as we've all heard by now.
One thing I certainly wouldn't do is bypass the regulators on the cards
and supply 5V (and +/-12V) to the bus. The reason is that if those cards
ever ended up in a normal S100 backplane, you'd get a lot of magic smoke
leaking out.
> enclosures, heatsinks, etc from solid blocks of metal, just to have them
so."
As have I on occasions. I've certainly made a lot of
spacers/screwposts/terminal pins, etc from metal rod. Because the exact
part I want is not listed in any catalogue.
> get the impression from Jeff's original post
that he was wanting to do
anything
OK. I was simply suggesting that _a_ way to get a transformer was to wind
it yourself, and that if you use the kits it's not too hard. The primary
windings are pre-wound, so you don't have any HV insulation problems to
worry about.
> like that. It's not an issue of cost, though that's probably a factor, but
I'd
> submit that one who isn't interested in
building his own switcher because of
a
I would not recomend that anyone who can't design and build linear PSUs
attempts to build a switcher from scratch. It's a lot harder.
Exactly!
[...]
> > Hnag on...
> > > Are the S-100 PSU voltages 8V DC and
+/-16V DC, or are they what you get
> > if you rectify 8V AC and 16V AC? I assumed the former, but perhaps I am
> > wrong.
> > They are what they say, so your guess was
correct. The 8-volt raw supply is
> regulated on each of the boards to produce the logic supply and, where
needed,
And IMHO
it is wrong to value time spend on a hobby at anything other
than $0 per hour. You spend that time because you enjoy it. Not to make
money or save money. If you weren't working on classic computers, what
else would you be doing?
It's like fishing ... it won't save money on dinner.
Yes, that's what all the S100 schematics I've seen show...
[...]
I agree. However, sometimes compromises are necessary. The SCHOTTKY rectifier
trip would probably meet the 8V spec if the full load voltage of the transformer
is 10% down from the no-load voltage, however, since the 6.3 * SQRT(2) - 0.5 =
8.3 or so at full load and full load is unlikely to occur. A lot depends on
what the numbers stamped on the transformer really mean.
There are, BTW, some pretty interesting things one could do to a PC PSU to
increase the output on the 5 volt supply. It's risky, of course, because the
capacitors are designed for a 5-volt supply, but, perhaps with an extra turn on
the secondary of the main transformer, and a tweak of the output voltage, one
could squeeze 8 volts out of the thing without running up to the limits. The
consequence would be a proportional increase on the complementary 12Volt
outputs. That's where you might wonder about the capacitor voltages, since it
will be as much as 20 volts. I've got some commercial linear S-100 supplies
that provide 21 volts on what should be +/-16 volts. That suggests it's
survivable at the S-100 end.
were doctored. There's a 3-terminal
replacement for the LM340T-5 that is
actually an encapsulated switcher and it would surprise me to learn that it
wouldn't save considerably on heat if the input voltage were too high as
compared to a linear. That's another option.
Again, if I was making an S100 system, I'd want to be able to use any
S100 cards without modification. Which would mean having the +8V line
high enough that any 3 terminal linear regualtor would work. I'd not want
to have to replace regulators on every card I wanted to try.