# Thread: how to use multimeter...

1. ## how to use multimeter...

I am trying to find out what the current draw that my bookPC is using through the 120VAC.
1) Do i just use a muiltimeter capable of handling 10A?
2)How accurate is the measurement?? for example if it reads 0.7A then it's just 115V x 0.7A = 80.5W.
3)Do I also have to measure the exact voltage on the AC plug with the voltmeter and use that in my calculations also?

i need to know exacly how much power it's drawing so that I can figure out if a 68W ATX DCDC that Jeff is making will work on my system or not. The bookPC I have is 90W max. I probably have to figure out how much the draw is on each output as well( 12V, 3.3V, 5V) and that's gonna be a pain in the *** to do....

2. If you connect your multimeter in series on the power cable of the book pc and let the current run thru the multimeter you can measure how many amps you will be drawing. multiply # of amps it draws at the power source * 115 and you will know how many watts its drawing in AC. What you really need to know is how many amps its using in DC. I'm not really sure of a way to figure out how many amps your drawing in DC without taking readings from the mobo power, hd power, display, floppy, fans, etc etc etc and then adding it all up to know how many amps and then * 12volts to know how many watts your drawing. I think you'd be alright on that power supply without taking any measurements, though.

3. geez take measurements from EACH device...thats crazy...the MOBO ATX connector has a ton of wires... to splice into each one will be one hell of a task. I was thinking about just measuring how much current it uses out of the 115V. I know it's not EXACTLY what the computer is using because efficiency is probably 80% or so...
but still will give me a ballpark of how many watts it consumes. From there I can figure out how many amps its gonna consume off of a 12V. Do i make any sense or do I sound like an electronics newbie

4. lol....prolly Sproggy can help here. I try not to venture too much into this territory

5. Yeah, you sound like an electronics newbie...

lol

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