OK a noob question about wattage and PS

When someone actually defines themselve as a "newbie" then basically the question belongs in sci.electronics.basics

Michael

Did you do science at school ? Ever heard of the law of conservation of energy ? ( not perhaps what it might sound like btw )

Aaaaarrrrrrrrggggggghhhhhhhhhhh!

Yes it's Google Groups and Gmail-man again !

Graham

No, but it may not operate at all. PC power supplies are designed for a very specific range of load currents and often refuse to run at all if connected to a load that draws much less current.

I would suggest getting a wall transformer ("wall wart") that outputs something from 9 to 12 V.

You might have considerable heat being dissipated in the potentiometer. Rigging a variable voltage regulator (such as an LM317 or 7805 regulator) would be better.

The law of conservation of energy does not tell him the answer to his question. A shunt-regulated Zener circuit, for example, *would* still draw maximum power even when lightly loaded. Fortunately that is not what we power PCs with.

A rheostat configuration is more practical in this instance than a potentiometer too.

Graham

Conservation of energy means energy in = energy out. Ergo 4W out is not 100W in. SMPSs aren't shunt regulated !

Graham

You should follow the potentiometer with an emmitterfollower, because the fan needs a lot of turnon current. The pot can be anything between 500 and 2000 ohm. Without the follower,the fan will not start when it ages a bit.

How many 100 Watt Zeners have you seen? By your example he would be using 4 Watts to run the fan, and dissipating 96 Watts as heat in the Zener Diode.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

potentiometer

No, because the fan's starting current is a lot higher than the running current, and the speed will not be well regulated. You either need a regulated voltage, or hook the fan between the +12 volt rail and the +5 volt rail to give you a fixed & regulated 7 volts for the motor.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

I know that and you know that, but HE wasn't born knowing that!

Why does everyone object to answering this poor fellow's questions? Is this a forum only for people who already know everything?

Lucas, AKA Prince of Darkness on my Triumph Bonneville, their shunt regulator was pile of shit. Apart from that, nowt.

The Lucas regulator was built better than the bike, but the Ducati

750S had even worse lectrics, designed for Italy, used in the UK, ughh, 0-50 in first, when you gave it a handfull, so the battery never ever got charged unless you went on a "Sunday Run"

Certainly beat the hell outta SED

martin

Must admit that the FAQ for SED has not been seen in many megacycles, but using AltaVista , et al, may provide some info before posting a message here.

Always thort that entering an uknown noosgroup was bit like entering a singles bar after a year in a Tibetan monestry

martin

My MGs know the God of Darkness and Warm Beer from personal experiences.

He is All Powerless.

Don

[snip] [snip]

ROTFLMAO!

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Actually, a regulated current would work better than a regulated voltage, assuming it's a PM or universal DC motor. If it's one o' them newfangled "brushless" with the PWM control and all, then you'd have to hack its controller.

Good Luck! Rich

If they need their hand held, they belong in news:sci.electronics.basics which is for beginners. This group is for people that have a good idea what they are doing. Like the old saying, "If you can't run with the big dogs, stay under the porch". news:sci.electronics.basics was created to give the extra guidance needed for beginners.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Is that why you left England? ;-)

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

nope, windsurfing is better here.

martin

draw

You don't like windsurfing in fog? ;-)

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida