[RndTbl] partial PS use?

[Trevor Cordes]

On 2016-02-17 Wyatt Zacharias wrote:
> Do the resistors have their power rating on them? 1.6A at 12V is 19.2
> watts total. You'll need some hefty resistors to sink that much power
> into.

10W resistors, 2 of them should take 19.2W.  These are the biggest
resistors I've ever personally seen.

> Out of curiosity, how much power do you actually need from the 5V
> rail? Single voltage switch mode power supplies can be had for under
> $50 with decent amperage ratings.

I need 10A 5V.  I don't want to use a wall-wart as they don't usually
put out very clean power compared to a "real" power supply.  As for
buying one, the idea here is try the "free" stuff first, buy something
second.

On 2016-02-17 Gilles Detillieux wrote:
> half the heat of a 40 W incandescent bulb. Any load you use will put
> out that much heat for the same amount of current.

I thought maybe I'll try putting in a .5A fan to take up a chunk of the
12V output, and have it blow on whatever hot resistors I need for the
rest :-)

> It seems to me a decent switching power supply should be able to 
> regulate voltage with much less draw than that, though. I'd try a
> single 15 Ohm resistor and see how well it holds the +12 & +5 V, and
> if it's good, try even higher resistor values than that. You might be
> able to get the current draw down below 100 mA (1.2 W) without any
> loss of stability.

That's voodoo territory for me.  I'm not sure what the characteristics
of the PS are with different loads on the unused lines.  I'm not
certain I could a) reliably measure stability in a short amount of time
and b) project those results out over the (offsite) usage lifetime of
the PS.

What I could easily do is check if I have some other PS's with a lower
min 12V rating on their label.  Maybe I just picked the wrong one with
the initial grab.