Measuring power off a ATX power supply
Measuring power off a ATX power supply
(OP)
Hi! Any suggestions as to how to measure the power given off by a ATX power supply going to a PC Motherboard?
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Measuring power off a ATX power supply
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Measuring power off a ATX power supplyMeasuring power off a ATX power supply(OP)
Hi! Any suggestions as to how to measure the power given off by a ATX power supply going to a PC Motherboard?
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RE: Measuring power off a ATX power supply
RE: Measuring power off a ATX power supply
RE: Measuring power off a ATX power supply
As another suggestion, if the amperage is expected to be less than 10 amps, you can use the ammeter function of a common multimeter. The multimeter ammeter function will have very low resistance and should not cause a voltage drop.
I hope this helps.
RE: Measuring power off a ATX power supply
I, too, agree that a smaller resistor would work, but I would need resistors that can handle that amount of power. My budget is limited... Is there a way to work around this... using the 1ohm resistors(i have 14 1 ohm resistors 50W)?
I currently am using 11 resistors for my current setup.
RE: Measuring power off a ATX power supply
1. A shunt that would produce volt drop for voltmeter with current scale
2. A regular voltmeter
3. Watts= volt x amps
4. The voltage for the motherboard is supposed to be within a certain tolerance and relatively stable. Then, the voltmeter from 1. above could have the scale in Watts.
RE: Measuring power off a ATX power supply
Thank you for your suggestion, but how would I go about using a shunt? Would I place the shunt in series with the multimeter? My multimeter can only handle up to 10A. The max. for the +5V source is 30A. or Do I place the shunt in parallel with the multimeter and measure the voltage across the shunt?
RE: Measuring power off a ATX power supply
RE: Measuring power off a ATX power supply
"Would I place the shunt in series with the multimeter?"
No.
"Do I place the shunt in parallel with the multimeter and measure the voltage across the shunt?"
Yes. "Shunt" is actually another way for parallel.... intended to be connected in parallel with your multimeter (voltage scale) in this case.
Also, normal application of a shunt resistor for current measurement demands that the resistance be much lower than system impedance so that it doesn't affect the circuit current we're trying to measure. Therefore decreasing the resistance should decrease power requirements of the resistor (assumes constant I) and give you a cheaper alternative. But I'm not 100% sure this application is a current-measuring shunt resistor.
RE: Measuring power off a ATX power supply
Connect your Ammeter in series with one 1 Ohm 50W resistor.
Connect these to the 5V, with the PC disconnected.
It will show about 5 A.
Get some iron wire about the thickness of a coat hanger.
Find the lenght which -- when connected parallel to the Ammeter --
reduces the reading exactly to the one forth.
This is your shunt. Connect it parallel to the Ammeter.
Now your max current is 40A-- measure your PC. Your actual current is
4 times of the indicated amount.
<nbucska@pcperipherals.com>
RE: Measuring power off a ATX power supply
nbucska suggested a novel alternate use of a shunt - to divert a fixed portion of the current around the ammeter. That might be a good approach. I would point out that you would be relying on current division among two low-resistance parallel elements (the ammeter and the shunt) and a small change in resistance (as due to temperature variation) might wildly affect the current division.
RE: Measuring power off a ATX power supply
and still usable solution.
<nbucska@pcperipherals.com>
RE: Measuring power off a ATX power supply
Do you think a 12AWG wire will do or should it be thicker?
RE: Measuring power off a ATX power supply
RE: Measuring power off a ATX power supply
RE: Measuring power off a ATX power supply
replace the PC with the 1 Ohm & ammeter. This will give you
about 5 A i.e. less than 10 A which you can read. After you
calibrated it, connect ir parallel to the ammeter and
connect them in series with the PC input, of course you don't need the 1 Ohm any more.
If you knew the resistance of the ammeter and the actual specific resistance of the wire you could calculate the appr.wire lengh.
AWG 12 should be OK. for the accuracy you need.
<nbucska@pcperipherals.com>
RE: Measuring power off a ATX power supply