How To Measure DC Amps With A Multimeter
Electricity and electronic components are absolutely nothing without current or Amp.
When you work on an electronic circuit, it may require you to check the Ampere running through it to get a diagnosis of the problem you are experiencing.
There is a lot of confusion when it comes to measuring Amp, and this is owed to the different types of Amperage as well as its similarity with voltage.
In this guide, we cover the whole process of how to measure dc amps with a multimeter.
Let’s get right in.
What Is Amps or Amperage?
DC Amp is only one type of Amperage. You need to know what “Amperage” is before you understand why measuring DC Amp isn’t as straightforward as you’d expect.
“Ampere” is the SI unit for measuring current and “Amperage” is simply the measurement of current running through a circuit.
A lot of people confuse Amperage for voltage and we assure you that there is a difference.
Amperage differs from voltage in the respect that voltage is the measurement of the velocity of current (Amps) running through a circuit.
Take Amperage as water in a pipe and voltage as the amount of pressure pushing this water through or out of the pipe.
The pipe in this instance is the electric circuit.
Now, there are two types of Amperage measurements; DC Amp and AC Amp.
How Does DC Amp Differ From AC Amp?
Direct Current (DC) Amp relates to current that runs in one direction.
Alternating Current (AC) Amp, on the other hand, relates to current that flows in both directions.
DC Amp measurements are usually more common with battery-powered devices, as power is only drawn from the battery and not sent to it.
AC Amp is more common with home appliances or devices that make use of transformers.
AC and DC Amps are the same current. From what has been said, the only difference between the two is that power or current only flows in one direction with DC Amp, while it flows in both directions with AC Amp.
Moving forward, what are the tools you need to accurately measure the DC Amperage of an electronic component or circuit?
Tools Needed To Measure DC Amps
To measure DC Amps, you need
- Multimeter To Take Measurements
- Alligator clips to make connections simpler
- Insulated gloves for protection
You may also use a clamp meter to measure the DC power in a circuit, but this article focuses on how you may use a multimeter to test DC Amp.
How To Measure DC Amps With A Multimeter
Plug in your black probe in the “COM” port, plug in your red probe in the port labeled “A” or “10A”, and set the multimeter to the closest DC Amp range for the device specifications. Place the probes on the appropriate terminals and check the meter screen for the results.
There is more about each of these steps and we will get into them in detail.
- Plug In The Black Multimeter Lead In The “COM” Port
The digital multimeter typically works with two probes; a red positive probe and a black negative probe.
Each of these probes has a large end that plugs into the meter and a pointy metal end that goes to the device you want to diagnose.
Additionally, there are three ports on the multimeter which the probes plug into.
These are the “COM” slot, the “10A” slot, and the “VΩmA” slot. The “COM” and “10A” slots are important when it comes to DC Amp.
Plug in the large end of the black probe into the slot labeled “COM” on the meter. Alternatively, this slot may be labeled “-“, representing “negative”.
- Plug In The Red Multimeter Lead Into The Port Labeled “A” or “10A”
Now, the red probe either goes into the slot labeled “A” or the slot labeled “VΩmA”. “A” or “10A” is used to measure currents below 10 Ampere.
While the “mA” slot represents milli-Amps (low current) of up to 300mA. “V” on the same slot represents voltage and “Ω” represents Ohms or resistance.
For any DC Amp tests you want to carry out, always make use of the “A” or “10A” slots to avoid overloading the meter.
- Set The Multimeter To The Closest DC Current Range
DC Amp is represented by “A-” (with three dots) on the multimeter.
On the side you see this symbol, you also see a range of numbers, with the best digital multimeters coming with five ranges (200μ, 2m, 20m, 200m, and 10A).
These represent the maximum current you expect from the device or wire you want to test.
A “μ” represents micro-Amps, “m” represents milli-Amps, and “A” or “10A” represents the standard measurement for whole Amps.
When you want to set the meter to a DC current range, turn the dial to the closest higher value on the multimeter.
For instance, if you want to measure a device with a specified DC Amperage of 9 Amps, you set the multimeter to the 10 Amp range.
To get the appropriate value, check your device or electrical system specifications for DC voltage output.
Choosing a higher range prevents the multimeter from overloading, so it is very important you get these values and ranges right.
Setting the multimeter to the “10A” range is the best to prevent an overload. You also get results that may be converted to milli-Amp or micro-Amp.
Some multimeters come with an auto-ranging feature that allows you to omit this manual setting.
Nonetheless, knowing this is crucial as most multimeters require these manual settings.
- Place The Multimeter On The Appropriate Terminals
Whether it’s loose wires in your car, connector terminals of various devices, or DC batteries themselves, you place your multimeter leads on the appropriate points to test DC Amp.
These points differ by device and some require that you pay attention to the polarity of terminals.
This means you need to position the multimeter probes between the device and the power supply. So use the multimeter to close the circuit.
In measuring DC current, the multimeter functions as a wire for the current transfer.
For instance, you have to place the red lead on a positive battery post and the black lead on the positive device post.
When testing an electric fence, the probe settings are completely different.
Some electrical components don’t require this, so you want to make a little research before diagnosing with a multimeter.
- Check Multimeter Screen For Results
Just like with the placement of probes, the results you expect from the multimeter differ by the device you wish to diagnose.
For example, a 9V battery is expected to present you with a constant reading of around 0.9 Amps, while testing an O2 sensor presents a result between 0.2 and 1.5 Amps.
Additionally, when looking at results, of course, a value that does not tally with the device’s required specifications means that the DC Amp of a circuit is either insufficient or in excess.
There is a general acceptance for slight deviations in measurement.
Some devices, however, regard a slight deviation as too much, so you also make research to know the exact results for that specific electronic component you are testing.
You can also watch our video on dc amps measurement here:
Using A clamp Meter To Measure DC Amps
A clamp meter is a contactless device that you use to measure the Amperage, voltage, or resistance within a wire. It works just like a multimeter but, instead of making use of probes to touch exposed terminals, you simply place your wire (even when insulated) between the clamps.
Measuring DC Amp with a clamp meter is more straightforward than measuring using a multimeter.
What’s more is that you may measure Amperage that reaches a range of up to 1000A and typically goes to a minimum of 40A (which are large measurements compared to the regular multimeter maximum range of 10A).
This means that the clamp meter is the more feasible option for measuring circuits or wires carrying massive amounts of Amp.
To use it, you simply set it to the appropriate Amp range (40A, 400A, or 1000A) and place the wire between the clamps of the meter.
Your meter displays a value measurement when the wire is properly aligned between the clamps.
Measuring DC Amp majorly requires you to pay attention to the specifications of the device or electrical component to be diagnosed.
Every other procedure is as simple as it gets; plug in the multimeter probes in the right slots, place the leads on the appropriate electrical terminals, and check the multimeter screen for a reading.
Frequently Asked Questions
What Is The Symbol Of Amps On A Multimeter?
Amp is represented by “A-” with three dots on the multimeter. In this section, you also see a range of numbers that includes 200μ, 2m, 20m, 200m, and 10A. The “10A” range is the safest of all.
What Happens If You Measure DC Voltage With AC Multimeter?
If you measure DC voltage on an AC voltage setting using the right polarity, the multimeter presents you with inaccurate results. You get a value of zero (0) when you reverse the polarity.
Alex Klein is an electrical engineer with more than 15 years of expertise. He is the host of the Electro University YouTube channel, which has thousands of subscribers.