Flutterby™! : Things to do with 5 volts 2003-01-25 00:38:32+00

Things to do with 5 volts

2003-01-25 00:38:32+00 by Dan Lyke 11 comments

So it looks like a standard PC switching power supply is the cheapest way to power this project I'm working on, replacing the power strip worth of wall warts I've been using for prototyping. The 12v side will run the regulators for the various controller cards, and we can use the 5v side to run the stepper motors. But we don't want to apply holding torque to the steppers when we aren't actively using them because the user should be able to rotate the system by hand. So we need a minimum current draw to keep the switching power supply from eating itself. Anyone got any imaginative ideas for wasting 2 amps at 5 volts?

Run it through some resistors and generate waste heat in your mannequins; claim in your product literature that this improves the drape of clothing, and results in a more life-like modeling.

(It's possible that 3+ days of extreme suit exposure at LWE has had a bad influence on me...)

I'm just amazed that I understood the jargon of Dan's comment; ah, home electrical repair has changed my life in so many ways ....

My usual empty load is a light source of some kind that doesn't burn out very often. That way I have a built-in circuit continuity check.

By the by, I didn't know that a standard PC power supply output power at two voltages. One for the power for rack devices (i.e. hard disks) and another for the boards?

The quick-and-dirty way is Ohm's Law, E = I * R, so a 2.5 ohm resistor would draw 2 amps at 5 volts, dissipating 10 watts in the process. Use a 20 watt resistor to be safe. There are fancier ways that would only draw current if needed, but they involve transistors and a little circuit design.

Old ones have +5, -5, +12 and -12. P4 and Athlon power supplies add +3.5. The 12v is used for fans, hard drives and that sort of thing. The weird bit is the minimum power draw, those of us who grew up on transformers and diodes with a couple of capacitors to even things out don't get that.

Blinkenlights and extra fans was exactly the direction I was thinking of, although I don't want to do it with LEDs 'cause you've gotta line up a boatload of 'em to suck down 2 amps. I like the mannequin warming idea, might have to follow up on that.

That's only ten watts, you ought to be able to burn that easily using resistors, or you ought to be able to find a 6V-rated light bulb that'd do the trick.

Now, wasting it creatively, that's a good question... Maybe you should mount one of those old governors to the top of the thing and spin it; that'd look interesting...

Unlike REAL power supplies, a switching supply uses the intended load as part of the circuit. Makes for a cheap to make power supply.

Oh yeah -- you wanted to make your PC double as an OGG player, didn't you? I think a small stereo audio amplifier is in order.