# detect whether current is ac or dc

#### johnboyman

Joined Jun 1, 2019
39
Hello I have some circuit board that I am trying to repair for one of my appliances but I can't figure out if some parts are ac current or DC and don't want to break my multimeter. Are their ways to tap a circuit and find out weather it has ac or dc current running through it. Thanks.

#### MrChips

Joined Oct 2, 2009
23,519
Use an oscilloscope to show the waveform in question.

#### dl324

Joined Mar 30, 2015
12,871
Are their ways to tap a circuit and find out weather it has ac or dc current running through it.
You can determine that from the schematic.

How can you break your meter? DVM's should be able to measure positive or negative DC current. With alternating current on the DC current scale, you should measure 0.

#### johnboyman

Joined Jun 1, 2019
39
Ok good to know thanks

#### dl324

Joined Mar 30, 2015
12,871
Ok good to know thanks
Just make sure you set the range high enough for the maximum anticipated current. Most meters should be protected by fuses, but you don't want to have to replace them because you made a mistake.

#### Glenn Holland

Joined Dec 26, 2014
705
Hello I have some circuit board that I am trying to repair for one of my appliances but I can't figure out if some parts are ac current or DC and don't want to break my multimeter. Are their ways to tap a circuit and find out weather it has ac or dc current running through it. Thanks.
If you're trying to find out "weather" it's AC or DC, current, you need to use an outside thermometer the measures the current temperature.

#### rsjsouza

Joined Apr 21, 2014
311
@johnboyman, are you trying to measure current or voltage?

At any rate, the safest way to find out if a specific point in your circuit has AC or DC or a combination of the two is to use the Volts ranges of your multimeter. Differently than the Amps (current) ranges, the Volts ranges has a very high impedance and therefore much harder to make mistakes.

In addition to the suggestions above, even if you measure a point as AC or DC, keep in mind it may not be "pure" but maybe a sum of the two. To be absolutely sure, make two independent measurements at each point (DC and then AC). Always take @dl324 suggestion as well: start with the highest range.

#### AnalogKid

Joined Aug 1, 2013
9,249
Start with the meter on an AC range, and see if there is a significant reading. If not (after the initial transient), then move to a DC range.

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