2
\$\begingroup\$

I have a 750 watt ATX power supply that I will be testing with a multimeter to make sure the right voltages are present. How can I make sure that I do this safely? Is there anything that's threatening my safety that I should be aware of before I go prodding away at the leads?

Is the power that the PSU provides through its connectors enough to cause injury?

\$\endgroup\$
  • \$\begingroup\$ Do you have a reason to suspect the power supply is putting out the wrong voltages? If you have a defective PS, it may put out a different voltage with no load (only the meter connected) vs. connected to real loads (motherboard, drives, etc.). A normal ATX power supply should give the correct voltage up to current limits but if there is a problem, who knows. \$\endgroup\$ – DoxyLover Apr 28 '15 at 23:59
  • \$\begingroup\$ I am troubleshooting an issue where the computer gives blue screens when it resumes(occasionally). Everything points to a hardware issue, though I have performed diagnostics on the ram and hard disk. At this point, I'm just moving through the process of elimination. I'm just hoping that a problem will appear when I check the voltages with no load. Otherwise I'll just go ahead and RMA the motherboard and hope that the problem is fixed. Any ideas? \$\endgroup\$ – CanadaIT Apr 29 '15 at 21:32
2
\$\begingroup\$

Many novices seem to want to measure the current output capability of power supplies by setting their meter to read current, then connecting it directly across the power supply terminals. YOU MUST NEVER CONNECT AN AMMETER DIRECTLY ACROSS A POWER SUPPLY Doing so will cause very large currents to flow, and may permanently damage the meter, power supply, or user!

If you keep the meter in voltage mode, and are careful to not short the test leads or power supply wiring, you should be able to measure the supply voltages without any hazard.

Many PC power supplies (and other switch-mode supplies) require a minimum load to operate correctly. Be sure you have a suitable load connected during your tests (or any time the supply is on.)

\$\endgroup\$
0
\$\begingroup\$

Yes, but only if you screw up. The 5V rails in particular have double-digit currents, so be triply sure that your DMM is in voltage mode before measuring each time.

\$\endgroup\$
  • \$\begingroup\$ Can you please explain why this is necessary? I would like to understand what makes this a crucial part of maintaining a proper level of safety. Is it because there is a fuse that will blow and protect me from the high current or something? Can you please provide further explanation or reading material explaining this aspect of electrical safety. A Google search doesn't yield as many results as I'd like. \$\endgroup\$ – CanadaIT Apr 28 '15 at 22:54
  • \$\begingroup\$ The very high input impedance of the DMM in voltage mode will prevent much current from flowing. \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 28 '15 at 23:03
  • \$\begingroup\$ Let's say you try to measure the 5V output and you accidentally have your DVM set for current measurement. The fuse in the meter should blow before much power can be delivered. However, if someone, in the past, bypassed the fuse or you have a super-cheapo meter,you may have the meter blow up in your face. \$\endgroup\$ – DoxyLover Apr 28 '15 at 23:56
  • \$\begingroup\$ Sooo... I should wear safety glasses? \$\endgroup\$ – CanadaIT Apr 29 '15 at 1:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.