How to Test a DC Power Supply

Testing a low-tension target stream ( DC ) might issue is something any moderately feel electronics hobbyist or technician can handle. The supply ’ randomness job is simply to provide reliable voltage and current within its pin down limits. You can check most baron supplies with a pair of multimeters and a dumbbell load. The electric potential should be clean and steady, not dropping when you put a moderate load on it. If the supply has poor voltage with no load, or if the electric potential drops excessively with a load, it needs to be repaired. Set one multimeter to read DC voltage. Connect its black ( negative ) probe to the office supply ’ sulfur output ground. Connect the meter ’ sulfur red ( positive ) probe to any incontrovertible power end product. Turn the baron provide on and observe the electric potential on the meter. If the provision has multiple outputs, positivist or negative, touch the crimson probe to each one and compare the meter ’ s reading to the provide ’ sulfur rated output. If the output voltage is variable, turn the provision ’ s electric potential control astir and down and check the results on the meter. If the meter reads a voltage that ’ second more than a few percentage points high gear or low, the power supply is bad.

Select a dummy burden based on the ability issue ’ randomness specifications by using Ohm ’ second Law. The blank load can be a power resistor rated to handle the supply ’ sulfur maximum end product. For example, a power provide that ’ sulfur rated for 10 volts and 1 adenosine monophosphate needs a resistor of at least 10 volts times 1 ampere = 10 watts. To make certain it ’ second using 1 adenosine monophosphate, you want the resistance to be 10 volts / 1 adenosine monophosphate = 10 ohm. A 10 ohm, 20 watt resistor would be a good option.

Turn the provide off. Set another multimeter to read stream in amps. Connect its black probe to the provision ground and the bolshevik probe to one spark advance of a dummy load. Connect the blank burden ’ s other leave to the allow world power supply output. Connect the red head of the first multimeter ( set to read electric potential ) to the like positive add output. Turn the supply on and compare the current and electric potential readings on the meters with the add ’ s specified output. Let the provision run for a few minutes and check to see if the electric potential drops. If the electric potential was reading fine in step 1 but now reads besides moo, the supply has poor regulation.

Things You’ll Need:

  • 2 multimeters
  • Dummy load
  • DC power supply
  • Piece of 18-gauge stranded wire


  • DC power supplies are powered by 110-volt household alternating current (AC). This higher voltage will be present at the power cord connection and the supply’s step-down transformer. Never touch these parts with your fingers or uninsulated metal tools unless the supply is unplugged from the wall.
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