12 May
2006
12 May
'06
4:29 p.m.
Roger Merchberger wrote:
I need some help from those who are a lot better than
I in hardware
design...
The problem is I need to use a PC power supply (AT-class with it's own
power switch) as a 12V power source, and the only one I have access to
needs a minimum load of 3Amp on the +5Volt line.
By my rough calculations and allowing for wiggle room, I'd need a
20-watt power resistor of 1.5 ohms to keep the critter happy. "Bare
minimum" is 15W, and I could squeak by with that if I wire the fan to
the 5V line instead of the 12V... but even when I'm expected to
perform a "miracle" I like to have a little wiggle-room. ;-)
Problems I have are: 1) I need this by Monday, and 2) I don't keep
20-watt power resistors in my back pocket. Had I a week, I'd just
order the right tool for the job - I don't have that luxury. ;-)
I was thinking I *might* be able to cobble up enough lower-end power
resistors & figure out how to stuff 'em together to draw 15w+ of
power, but then I thought:
What if I took an older 5V CPU (say... an 80486) and wired 'er up to
just Vcc & Ground - how much power would that use? [[ I've started
some google searches & I will continue, but I was hoping others here
would have better ideas than my lame-azz neurons & google so far ]]
Do you have a AT motherboard to go with the power supply?
If so, you can just plug it in as the load, as long as it leaves
you enough of the 12 Volt current available.
If you don't have one, check out the local thrift stores.
(Unless you really are stuck to using that particular PS).
You may end up with a 386, 486, etc., but it should still have
a 12V line. Why dink around with making a smoke generator
out of a PS when you can bypass the problem for $5.00 or so?
Don't limit yourself to PC cases, these places often have
external disk/CD drives also. These should also have 12V
line, iirc.
Also look in their boxes of wall warts. Sometimes you
will find something with the exact voltage/current
requirements.
I could also wire-wrap all the address/data lines to
Vcc if that would
add a enough extra current draw to make 'er worth my while...
Probably just generate a lot of smoke.
Unless you have the clock running, I don't think it will
use very much power at all. Most of the power in a CPU
is used because of the clock transitions.
For those who are in lust with the "older, but
still plentiful" CPUs
like that, then turn away now, you didn't see this, I was never here."
;-)
Any ideas will be most appreciated!