Measuring the Output of a Power Supply

[claymation]

I'd like some guidance on how to measure the voltage output on a power supply using a Multimeter (Sperry SP-152A).

Dial on the MM is set to 50 (V-....)
Reading on the DCA scale is 7.5

What's the formula for converting the setting/reading into the voltage output?

(please keep in mind I'm a carpenter, so you may have to talk real slow.)

Thanks!

 

[Diver300]

You should be reading on the DCV scale.

That is marked

0    50    100   150   200    250
0    10     20    30    40    50
0  -  2  -  4  -  6  -  8  -  10

You should be reading the voltage on the 0 - 10 - 20 - 30 - 40 - 50 scale, as that was what the multimeter was set to.

As far as I can see, if the needle was at 7.5 on the DCA scale, it would have been about 20 V dc.

A lot of power supplies have an output voltage a lot higher than their rated voltage when there is no load.

 

[Reloadron]

Read the instruction manual, I assume you have it. Connect the Black or Common meter lead to the terminal labeled Com and the Positive or Red meter lead to the terminal labeled V Ω A. Begin reading 5-1) Voltage Measurements on page 6 of the manual.

5-1) Voltage Measurements
1. Follow the Preparation for Use procedure in sec. 4.
2. Read all Safety Precautions in sec. 2.
CAUTION
1000 Vac/dc is the maximum voltage that can be measured
using this meter. Attempting to measure higher voltages may
result in electrical shock, instrument damage and/or damage to
equipment under test.
3. Select an AC or DC voltage range using the selector
switch that is higher than the maximum voltage to be
measured. If the maximum voltage may be higher
than 1000 Vac/dc, do not attempt to take a
measurement.
6
4. Apply the test leads to the two points in the circuit at
which the voltage is to be measured. When
measuring DC voltage the black lead should be
connected to the more negative point of
measurement. When measuring AC voltage the
polarity does not matter.
5. To read DC voltage use the black “DC” arc directly
below the mirrored arc. Use the numbers whose full
scale reading matches the range selected by the
“selector switch”.
6. To read AC voltage use the red “AC” arc. Use the
numbers whose full scale reading matches the range
selected by the “selector switch”.
7. The dB scales can be used to measure the milliwatt
power dissipation in a 600 load by measuring the AC
voltage across a 600 OHM load. An AC voltage of
0.775 Vrms across 600 OHMS is equal to 1mW or “0”
dB. When converting an AC voltage measurement to
dB take the dB readings from the lowest arc on the
scale plate and then add the appropriate dB correction
as listed in the chart printed in the lower right corner of
the instrument scale plate.

Any questions?

Ron