[RndTbl] partial PS use?

Wyatt Zacharias wyatt at magitech.ca
Wed Feb 17 16:05:01 CST 2016

I have a whole box full of high wattage resistors (some as big as 25w I
think), if you need some more to play with let me know.

Alternatively, if you decide a cleaner solution is needed, here's an
example of what's available commercially:
http://www.alliedelec.com/mean-well-usa-lrs-75-5/70696528/ 70W 5VDC power
supply for under $20.

Wyatt Zacharias

On Wed, Feb 17, 2016 at 3:51 PM, Trevor Cordes <trevor at tecnopolis.ca> wrote:

> 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.
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