>As the draw increases they put out more power until
>they reach their capacity
Actually, most power supplies work this way. They supply a constant
voltage (over their rated range) and adjust the current to suit the load.
The potential problem is that a short will draw a huge current and melt
something so most power supplies are designed to limit current by letting
the voltage drop if too much power is drawn from the supply.
>which is why if you heat up a power supply and
>take a reading .....your meter will show no power....
Computer power supplies are designed to supply current only if a load is
present. I believe this is to protect against shorts when the cable is
unplugged. Voltage meters are typically high impedance devices (high
resistance) and will look like an open circuit to the power supply so the
meter isn't sufficient load to trigger current flow. With no current flow
you will see no voltage.
>Your mother board ....or other devices you plug into it may make further
>voltage changes but PC motherboards comply with this 12 / 5 DC supply.
It is easy to regulate 5V DC down to 3V DC on a motherboard but it
generates some heat and wastes power (albeit a very very small amount).
The idea behind 3V chips is to generate as little heat as possible inside
the chip and if you put the 3V regulator inside the power supply there is a
small advantage in cost because you don't need to waste motherboard space
on power supply components. However if you have motherboard space to spare
you can put the 3V regulator on the motherboard and buy a cheaper power
supply (Dell seems to have done this here).
>If your Dell is remotely switched to your motherboard how do you turn it
>on.....with a remote signal device ? I find this hard to believe.
I believe all ATX power supplies can be remotely switched on and off with a
momentary contact (normally open) switch that sends a signal up one of the
wires in the motherboard connector. Most ATX compatible motherboard
manufacturers provide a couple of pins that you can plug a switch into to
use this feature instead of flipping the main on/off toggle on the back of
the case. This feature is what allows the computer to turn itself off when
you exit Win 95, or turn itself on when you get a call on the fax/modem
line, or automatically power up at a certain time every day. When you shut
the machine off using the "soft" switch it still provides a very small
amount of power to the circuitry that runs these features so that they can
power the system on if the switch is pushed, or the phone rings, or the
timer says it is time to power up.
>Check to make sure one of the power cords coming from the power supply
does not look
>like a standard black power cord which goes to the front of the case where
>the on off switch is undoubtedly is located.
If you have an ATX power supply there will not be one of these; this is the
older style power supply with a "hard" on off switch only.
>Power supplies usually come with a switch attached....there are three
>different types, push, toggle and the old 286 386 boxes had a large red
>toggle. Just about everything in the last few years has been push button
>which is probably what you have.
There are two types of push button. The "hard" type that acts like a push
button light switch (and probably makes a loud click when activated), and
the "soft" type that activates the ATX power circuitry to power up or down.
>>I removed the power supply, thinking that I'd find someone in town
>>where a new (or used) one could be purchased. The supply looks very
>>much like an ATX type, single 20 pin connector to the mother board
>>and various power cables for peripherals. There is no on/off switch
>>on the unit, but is remotely switched through the mother board. The
>>problem is it only supplies +/- 5 volts and +/- 12 volts. There is a
>>5 volt to 3.3 volt converter on the mother board to supply the cpu
>>and other parts.
If you have an ATX connector then you have an ATX power supply, however it
may not support all the features I mentioned above (they are motherboard
dependant). Any ATX supply should work if it will fit in the case (there
is a standard size but I don't know if Dell followed it with their supply).
>>The question(s), does anyone know the pinout values for this supply
>>and/or know if a standard ATX type of supply (that does provide 3.3
>>volts) will work for this computer.
Usually the supply has a sticker that describes the pinout on the side of
the supply. A full description of the ATX power supply standard in all
it's gory bureaucratic detail can be found at:
http://www.computer-works.com/demo/ATX/ATX_20T.html
>>I've, already, looked through Dell's web site and talked (several
>>times) with Dell service technicians for this information without
>>success. The tech said the connector is standard ATX so any standard
>>ATX supply will work, but in the same breath said they will not be
>>responsible for any adverse reaction the supply should cause any of
>>the components. It took this to mean, it should work, but we don't
>>know for sure and if it doesn't too bad.
I'd say the odds are very small that you will damage anything by plugging
in a different supply as long as the connector fits properly, however it
appears that Dell is not prepared to honor any warranty. Perhaps the power
supply manufacturer might be willing to provide some guarantee but you only
real assurance of recourse is paying Dell to do the work.
HTH,
Max
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