I need to evaluate the build quality of 3rd party 120V AC -> DC 5v 1a wall wart type switch mode power supply/adapter. The supply is supposed to have over current and short circuit protections as well.

My question is how do I safely test all the specs are working as advertised?

I'm self taught w.r.t electrical engineering so I guess I'm looking for a sanity check on my approach.

  • My first test will be to hook the supply up to an adjustable current load so that I may check the voltage ripple (if any) with my oscilloscope. Nerve level on this test: 0 out of 10

  • Second, I will up the current load and see what happens approaching and above 1a. I will monitor the temperature of the supply while I do this. Nerve level on this test: 3 out of 10

  • Third, I want to test the short circuit protection, but just shorting the supply output to ground sets off warning flags in my brain. Nerve level 10 out of 10

Is there a safe way to test short circuit protection without damaging my equipment? Or, should I just plan for it to either a) work or b) fail catastrophically?


  • \$\begingroup\$ Just grab a few values of 10 W resistors, \$\ge 4.7\:\Omega\$. Start with the highest value and scope the voltage across it. Record the results: average voltage, peak voltage, sensible temperature of the power supply itself, and any oddities about the waveform shape. Work your way down to the lowest resistance of \$4.7\:\Omega\$. Post your results and then ask about your third test. It will be easier to address then. \$\endgroup\$ – jonk Apr 8 '18 at 6:43
  • \$\begingroup\$ Do you want to test someone elses specifications, or the specifications that you make for your intended application? \$\endgroup\$ – Whit3rd Apr 8 '18 at 6:50
  • \$\begingroup\$ You probably also want to check temperature (and basic survival!) at full load for several hours. \$\endgroup\$ – Brian Drummond Apr 8 '18 at 10:16

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