# detecting the type of the voltage source AC/DC.

#### ataro

Joined Aug 13, 2015
6
Hi there,

Is there such device that can detect the type of a given voltage source if it is an AC or DC, assumed that it is not known in advance?
Especially I'm interested if there a way to do that test with a digital multimeter.

Regards,

Ataro.

Joined Feb 20, 2016
3,316
Put a 1uF poly (not electrolytic) capacitor in series with your multimeter on AC volts. If it reads, it is AC. If it just maybe kicks up then zeros, it is DC.
Note: The actual reading may be out of calibration.

But then, if it is DC with ripple, it will read the ripple voltage.

#### AnalogKid

Joined Aug 1, 2013
8,297
All DC voltages have some AC component (noise and/or ripple), although it often is very small. After all, it is an analog world. Using an AC range on the meter usually is enough of a test, because the user usually knows the approximate value of the voltage being measured.

ak

#### Ramussons

Joined May 3, 2013
807
Hi there,

Is there such device that can detect the type of a given voltage source if it is an AC or DC, assumed that it is not known in advance?
Especially I'm interested if there a way to do that test with a digital multimeter.

Regards,

Ataro.
Connect a voltmeter is series with a power diode. Check the voltages with the diode connected both ways. If there is a voltage reading both ways, it's AC. If there's a voltage reading in only 1 direction of the diode, it's DC.

#### ataro

Joined Aug 13, 2015
6
Connect a voltmeter is series with a power diode. Check the voltages with the diode connected both ways. If there is a voltage reading both ways, it's AC. If there's a voltage reading in only 1 direction of the diode, it's DC.
Seems to be interesting solution. but assuming I have a manual range DMM, your solution intended to work if I set the DMM to DC Voltage measurement, am I correct?
In addition, can't it harm the DMM if I measure DC voltage while in AC mode and vice versa?

#### ataro

Joined Aug 13, 2015
6
But then, if it is DC with ripple, it will read the ripple voltage.
Sorry for my poor knowledge but what is "ripple voltage"?

#### AnalogKid

Joined Aug 1, 2013
8,297
You haven't said what kind of AC or DC signal you are measuring, so we are just guessing. One type is the output of a power supply. Any power supply that converts AC powerline to a DC output has an output with both noise and ripple combined with the desired DC voltage. Ripple is an AC signal that is part of either the input power line frequency (50 or 60 Hz) in a linear supply, or the primary switching frequency (usually up in the kHz range) in a switching type supply. These AC components get through to the output because no regulator or filter circuit is perfect. It is very common to connect a meter to the output of a supply and have it read 12.0 V on the DC scale and 0.1 V on the AC scale. This is where the knowledge and experience of the person making the measurement comes in, interpreting the readings to determine what the signal is.

Without knowing more about what you are trying to do, we're just guessing.

ak

Joined Mar 10, 2018
3,881

Ripple voltage, w/o capacitor shows what comes out of rectifiers that
take AC and convert to unfiltered DC. With capacitor ripple much less.

Regards, Dana.

#### Ramussons

Joined May 3, 2013
807
Seems to be interesting solution. but assuming I have a manual range DMM, your solution intended to work if I set the DMM to DC Voltage measurement, am I correct?
In addition, can't it harm the DMM if I measure DC voltage while in AC mode and vice versa?
You put the DMM in DC mode. On Auto Ranging, it might indicate a few millivolts of noise. I'm presuming that the Voltage being tested is more than 1 Volt, and the frequency may be upto a couple of KHz.
A decent DMM will not get damaged by measuring DC voltage while in AC mode and vice versa.