measuring amps on my computer's power supply with a multimeter

Hi, q_q. Sorry, but you're heading in the wrong direction. If you use a series resistor large enough to get a measurement, you'll cause the power supply to sag, which will affect operation of the PC.

If you want to read DC current with a multimeter, you can either put the meter on DC Amps, break the line and put the meter in series (won't work for the same reason as above), or else use an AC/DC current clamp. This device operates on a hall effect sensor, and outputs a voltage proportional to the current through the wire being clamped.

Fluke and many other manufacturers make AC/DC current clamp accessories for their DMMs, or you can buy a stand-alone unit.

Good luck Chris

I just asked somebody else, they said that it's fine, here was their argument in response to " If you use a series resistor large enough to get a measurement,"

i'm not putting a resistor in there. But, even so,

if I will use a F-M extension cable, so, some short wires, and cut them and put the multimeter in series, measuring the amps. So that will add some resistance.

But the reverse of what you wrote is true, because, the lower the resistance, the better the measurement.

And if I just cut the wire and put the multimeter in series, then it's fine. A multimeter has an extremely low resistance, and in a low voltage low current circuit, the resistance, or the effect, is almost negligible.

In which case, just try it. Worst case, the PC will malfunction due to voltage sag (particularly on the 5V and 3.3V lines).

You have to ask yourself about your ability to measure a small enough resistance to cause a negligible voltage drop. V = I * R, you know. Actual values of resistance may vary significantly from wire tables, you know. Not only that, but an standard multimeter accuracy is very poor at the low end (e.g. a 1 milliohm shunt, 10 amps = 10mV).

Good luck with your project.

Chris

In which case, just try it. Worst case, the PC will malfunction due to voltage sag (particularly on the 5V and 3.3V lines).

You have to ask yourself about your ability to measure a small enough resistance to cause a negligible voltage drop. V = I * R, you know. Actual values of resistance may vary significantly from wire tables, you know. Not only that, but an standard multimeter accuracy is very poor at the low end (e.g. a 1 milliohm shunt, 10 amps = 10mV).

Good luck with your project.

Chris

I wonder how useful a multimeter reading will be. I would imagine the current draw from a computer is anything but constant, and the peak current draw may be in brief spikes that the meter won't read. I'd guess a scope-based reading may be better for this, but then you do get back to the issue of inserting a dropping resistor.

Just a thought...

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