How to Test and Calibrate Power Supply Voltage/Current Readings

Have you noticed that the readings on your power supply for voltage or current, don't seem to match with your usage?

To test the power supply output voltage:

Grab your digital multimeter or whatever standard you can use to objectify your results, and check to see if intuition is indeed correct. Set your multimeter to VDC, and connect your probes to the supply in parallel.

To test your current reading:

Set your digital multimeter to its amperage setting capable of tolerating >= 5 amps with your meter probes in series with the supply. To ensure you're getting a valid reading, use an electronic load or resistor capable of dissipating the heat. Remember P=I^2*R. See the pictures below for an example of what the voltage test would look like.

If you find that your display doesn't match what your meter reads, then the display does need to be calibrated. See below.

Caution: handle the unit with care after remove the enclosure as electrocution may be possible. We recommend this to be done by a train technician.

You'll need to remove the back panel on whatever supply you have and locate the potentiometers on the back of the display, as seen below.

In this supply, the potentiometers are marked A for amperage, and U for voltage. Since we're using the multimeter as the objective marker, that means the supply is too high, and needs to be adjusted to a lower value. Turn the knob until the values match, as seen below. This is of course assuming that your DMM is the device closest to the real value, something incredibly complicated to derive. Read more

If your voltage was out of spec, then repeat the same procedure, but adjusting the voltage pot instead. Once you've completed both, you're done, and you can now trust your display readings again.