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Measure, In Watts, how much power a PSU gives out?

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Jan 8, 2003
on teh PSU there should be a max output in wattage listed by the +3.3v +5v.

A good spu for todays machines will have atleast 200, or should anyways.


Senior Member
Feb 2, 2003
larrymoencurly said:
0.01 ohm resistor in series with each output rail?

A clamp-on DC ammeter, like this one or this one ?

0.01 Ohm may still be too high under some circumstances.

For the high wattage application and PSU, e.g. 40 A max on the 5V line.

If drawing 40A on te 5V line, voltage drop on 0.01 Ohm (at least 1.6W rated) would be 400 mV (8%), which exceeds the 3-5% line regulation spec of many PSU and componetns. E.g. AMD CPU DC max del is +- 50 mV. For measuring up to 10-20 A, the 0.01 Ohm would probably be OK. But an accurate 0.001 wire wound resistor (small wattage also) may be better (if it can be connected) and it requires accurate voltage measurement across it, down to mV.

Also for practical reason, it is not easy (if not impossible) to insert the resistor into the various current path between ATX connect and the mb, or the molex connectors, ...

It look like the easy way is to get the current measuring instrument such as your link. The sears one does not say how much current it can measure up to.

These instruments measure the steady state DC current, it won't show the transient current surge if one wants to monitor. Transient current can be much higher than steady state DC current.

In order to measure the transient current at various current path, one way is to know the mb circuit or the PSU at various points corresponding the main current path, and use an oscillocope to monitor the waveforms and deduce the current.
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