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


q_q_anonymous@xxxxxxxxxxx wrote:
I'd like to see how many amps my devices are pulling on each wire. To
calculate total amps demanded per rail.

It's my understanding that the PSU has a 12V,5V,3.3V rails and they
split into wires. Colour distinguishing the rail to whome it belongs.

I have a multimeter.
I read that Current must be measured in series but I don't want to cut
the PSU wires.

The 4 pin molex connectors on the PSU are male. So if I combine a M-F
F-M adaptor, it'll make a small extension cable . Maybe 1 inch of 3
inches. I can cut that and measure there. Will that wire extension
create too much of a voltage drop though?

is there are better way of measuring the current?

I dont think i'll be able to find a way like that to extend the 4 wire
plug with adaptors. That ATX12V 2x2 plug with the 2 yellow and 2 black
wires. They wouldn't make M-F and F-M adaptors for it.

I would sum the amps to help estimate PSU requirements, and perhaps
make sure that i'm not taxing a 300W PSU too much. And apparently
there's an issue (melting?!) of not wanting > 6A on any 12V rail!
though I suppose i'd know before that happens


thanks

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

.

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