A good, inexpensive PS I''ve found
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The post wasn't really directed specifically toward beginners. If
you're just getting started and know very little about electricity,
I'd recommend buying a commercially available supply. That said, to
answer both questions to be best of my knowledge:
1. Yes, the outputs are completely isolated from the line voltage.
2. The supply is designed so that in the case of short it will
completely shut off. Though this isn't something that has ever
caused me any problems and I have not done so on mine, if you want
to be on the safe side there's no reason you couldn't limit the
current (series resistor, various other methods) to a lower level.
Also, please note that I'm in no way saying that this is a supply
you'd want to use "as-is" w/o at least putting it in some sort of
appropriate box w/ connectors, meter, etc. and I make no claim that
there may not be better supplies out there, but I have found it to
be a very good, simple, reliable, very well regulated, and safe
(relatively speaking) quad. voltage supply for my needs.
I would argue that for beginners this is actually safer than
constructing your own supply because at no time (except for possibly
having to disconnect/reconnect the switch to get it out of the PC's
case) do you ever have to handle a high voltage line (there is no
need to take the metal case off the supply).
--- In basicstamps@yahoogroups.com, "Rodent" <daweasel@s...> wrote:
> Also, are the outputs on the PC supply isolated from the power
line, or is
> their a potential to get zapped if the power supply goes south?
>
> There are lots of "budget" power supply ideas floating around, but
for the
> beginner, why throw in the added potential for disaster?
>
>
Original Message
>
> > Isn't it true that you always need some load on computer power
supplies to
> > work/regulate.
> > Seem to me I read something about this in N&V some time back.
> > Also how would you regulate/limit the current so not to blow
anything or
> in
> > my case blind by the light when (not if) I short something
out. Just
> can't
> > trust us mech types with electricity/
>
> > I've noticed a few questions on here about power supplies and
thought I'd
> > share an inexpensive solution that I've found works well for
me. I built
> a
> > supply for my own use around a PS taken from an old AT (Pentium
or older)
> > computer. The AT supply is a switch-mode supply that easily
provides me
> > with a very well regulated high current +5v (~20A, red), +12v
(~5A,
> yellow),
> > and lower current -5v (white), -12v (blue). Blacks are ground.
Usually
> > there's a sticker on top of the supply with exact current
ratings. You
> can
> > get other voltages between +12 and -12 with the addition of a
simple
> > regulator. I wouldn't recommend it for applications requiring
very large
> > amounts of power, but it works well for electronics work.
> >
> > They retail for about $30 (last I checked) but many times you
can just
> pull
> > one out of an old PC you've got lying around. Just be careful
when
> working
> > with the power switch on an AT supply. Remember that it's
switching both
> > sides of 120 RMS VAC across its DPDT contacts so use caution when
> connecting
> > the four wires! (I've got an AT switch with a black scorch mark
to prove
> > the point). Also, note that even though the supply has a
grounding wire,
> > the chassis still needs to be separately grounded.
you're just getting started and know very little about electricity,
I'd recommend buying a commercially available supply. That said, to
answer both questions to be best of my knowledge:
1. Yes, the outputs are completely isolated from the line voltage.
2. The supply is designed so that in the case of short it will
completely shut off. Though this isn't something that has ever
caused me any problems and I have not done so on mine, if you want
to be on the safe side there's no reason you couldn't limit the
current (series resistor, various other methods) to a lower level.
Also, please note that I'm in no way saying that this is a supply
you'd want to use "as-is" w/o at least putting it in some sort of
appropriate box w/ connectors, meter, etc. and I make no claim that
there may not be better supplies out there, but I have found it to
be a very good, simple, reliable, very well regulated, and safe
(relatively speaking) quad. voltage supply for my needs.
I would argue that for beginners this is actually safer than
constructing your own supply because at no time (except for possibly
having to disconnect/reconnect the switch to get it out of the PC's
case) do you ever have to handle a high voltage line (there is no
need to take the metal case off the supply).
--- In basicstamps@yahoogroups.com, "Rodent" <daweasel@s...> wrote:
> Also, are the outputs on the PC supply isolated from the power
line, or is
> their a potential to get zapped if the power supply goes south?
>
> There are lots of "budget" power supply ideas floating around, but
for the
> beginner, why throw in the added potential for disaster?
>
>
Original Message
>
> > Isn't it true that you always need some load on computer power
supplies to
> > work/regulate.
> > Seem to me I read something about this in N&V some time back.
> > Also how would you regulate/limit the current so not to blow
anything or
> in
> > my case blind by the light when (not if) I short something
out. Just
> can't
> > trust us mech types with electricity/
>
> > I've noticed a few questions on here about power supplies and
thought I'd
> > share an inexpensive solution that I've found works well for
me. I built
> a
> > supply for my own use around a PS taken from an old AT (Pentium
or older)
> > computer. The AT supply is a switch-mode supply that easily
provides me
> > with a very well regulated high current +5v (~20A, red), +12v
(~5A,
> yellow),
> > and lower current -5v (white), -12v (blue). Blacks are ground.
Usually
> > there's a sticker on top of the supply with exact current
ratings. You
> can
> > get other voltages between +12 and -12 with the addition of a
simple
> > regulator. I wouldn't recommend it for applications requiring
very large
> > amounts of power, but it works well for electronics work.
> >
> > They retail for about $30 (last I checked) but many times you
can just
> pull
> > one out of an old PC you've got lying around. Just be careful
when
> working
> > with the power switch on an AT supply. Remember that it's
switching both
> > sides of 120 RMS VAC across its DPDT contacts so use caution when
> connecting
> > the four wires! (I've got an AT switch with a black scorch mark
to prove
> > the point). Also, note that even though the supply has a
grounding wire,
> > the chassis still needs to be separately grounded.