Thread: How much power does this thing use?

ummm.. well power and current are two different things.

power is current multiplyed voltage

your multimeter should measure current (in Amps), most do, but only to some extent (more then 10A toasts 'em)

Current will probably the more useful measurement, it is the amount of drain on the battery/energy used by your player.

I've heard figures of around 2-5 amps for the amount of current most DC-DC players draw.

Originally posted by Machs_FueL
Current will probably the more useful measurement, it is the amount of drain on the battery/energy used by your player.

I've heard figures of around 2-5 amps for the amount of current most DC-DC players draw.

Yup, that's what I want to measure!
Every setup is different... If a $10 off the shelf device will let me measure current, then I'll probably get one. If it's a pricey specialty item, then I'll perform the good old test of leaving the computer on for a few days and carry a spare battery in the trunk!

I have also got the $10 Radio Shack Multimeter... I use it for everything, except testing current draw.

Why?

Because it only measures mA (Mili-amps)... so I pop the fuse on it every time I try. If your multimeter only does Miliamps, forget about it, but take a close look and make sure that it can handle fill amps before trying this:

To test the current draw of any line, place the multimeter (set to the Amp-Meter) in series of the line that you're testing. like this:

+V Source --------<Red probe>----<Multimeter>----<Black Probe>---> Power Supply.

Now I maybe wrong about which probe comes first, but it shouldn't be too hard to figure out.

Good Luck,
-Miles

Originally posted by PatO
Please don't laugh, I knew I should've taken that circuit design course in college...
My cheap radio shack multimeter measures voltage and resistance, right? So what do I use to find out how much power (current?) a device is using?

The best way to do it is to use a resistor.

Try this:

1-10 amps use a 0.01 Ohm resistor
0-1 amps use a .1 Ohm resistor

That is what your current meter does anyway...............

Think of the resistor as a valve. You measure the voltage across it to get the current. V=I*R V/I=R V/R=I

Example:

You hook a .01 resistor (3 watt) up to your car mp3 player using the MPBS1 Power Supply inline with the +12 volt wire.

You hook your DMM up across the resistor.

It measures .035 V That is 3.5 Amps. At 12 volts thats 42 watts. And you didn't blow any fuses.

Have fun.

Jeff