Re: compound variable power supplies--possible?



whyzard@xxxxxxxx wrote:
Bennett Price wrote:
Some devices have connectors that put the - voltage on the center pin,
others put + on the center pin. (For center pin, you can substitute big
pin/socket, funny looking pin/socket, yellow pin/socket, etc.)

In your PC, the power supply is generating both +12 and -12 volts -
there's an instance where both voltages are needed - rather than just
swapping the + and - pins.

Distintinguish between ground and minus. Ground in electronic equipment like
radios and PCs can be either positive or negative. If the negative pole of a power supply in a radio is tied to the metal chassis (or the common areas of a PC board, then you can say ground is negative. Alternately, if the supply's positive voltage is connected to the chassis or the common areas of a PC board, you can talk about a positive ground.
In a PC, which uses both positive and negative 12 volts, each is measured in relation to ground (chassis/common) - thus if you connect a voltmeter's black/negative lead to the chassis, you'll measure +12 at certain points and -12 at others. If you clip the voltmeter to the + and - wires, you'll measure 24 volts.

Have you considered a trip to your local public library for an elementary book on electricity?



you can probably just reverse the leads on one of the connections. So a
parallel circuit/device goes minus plus, the other parallel device goes
plus minus. The classic reverse parallel dive. Guess though these would
have to share current. Maybe those professional power supplies devices
are isolating the ground for some reason. Perhaps for less noisy
signals. Is it possible to have a positive ground? Or is that just as
Seussian as DC peaks? Thanks for your replies by the way.

I ordered a book by Witte on electronics instruments. Keeps on getting
canceled and now the shipping is slow cause i am buying one of those
limited distributed (illegal to possess in the west) Hindu pulp mass
copies of copyrighted western textbooks. You can often find them at
bookfinder4u.com.



It doesn't make much sense to talk of DC peak voltages; ideally,
DC voltage is smooth and doesn't have peaks. AC voltage, on the other
hand, can be measured in several ways (Average, RMS, Peak).

Are you sure that both of your scanners need DC? You said one required
15 volts, the other 16. In all likelihood you could use the same power
supply for both. I'd buy 1 power supply (perhaps from the scanner mfr)
and use it for both. Which to buy 15V or 16V? - whichever is cheaper.






i thought about that but decided on the variable 12 v cause its only 20
dollars and a 16v adapter would cost at least that much. Although i
risk burning my house down with bad soldering connections, i also gain
not having to buy all these little wallwarts i have. I think i'm gonna
need a 6v soon too.







whyzard@xxxxxxxx wrote:
You can connect two DC adapters in series (not paralle), plus of one to
negative of the other; then add the two voltages together. In your
example, a 6V and 3V will yield 9V If one is turned off, you will not
warp the universe.
No, but it will damage the smoothing capacitor of the adaptor that is not
powered because reverse voltge will be presented across it. It will be
limited to 1.4-ish volts by the bridge rectifier being forward biased, but
it's still not good news.

Dave



this shouldn't be a problem. The variable would have serviceable parts.
the fixed switcheable universal probably isn't serviceable cause all
the parts are in those plastic cases and they are tightly manufactured,
but these are also quite cheap. I can just replace the switcheable and
fix the variable if needs be.

by the way, looking into power supplies more,
why would someone need negative DC volts. They are below the 0 v line
on a scope right?
What uses negative DC? A 50 dollar elenco variable had a spec of -1 to
-15 dc v

.

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