Why can't I use a multimeter to test my own battery voltage?

se7ens

Why can't I use a multimeter to test my own battery voltage? [Copy link]

 

RTRT

If anyone knows this question, please enlighten me. Thank you.

maychang

A digital multimeter cannot be used to measure its own battery voltage, but a pointer multimeter can.

Because a digital multimeter needs to use its own battery to power the voltage measurement, the digital meter will not work if its own battery is taken out. A pointer multimeter does not need its own battery to power the voltage measurement, so you can take out its own battery and then measure the voltage at both ends of the battery.

qwqwqw2088

For a digital meter, loosen the screws on the battery cover of the rear shell, do not unplug the battery leads, use a red test lead to touch the positive and negative poles of the battery respectively, and add the absolute values.

Close to the battery voltage

chunyang

The most intuitive way to judge is to find a circuit diagram of a digital multimeter, and then assume that it is used to measure the voltage of its own power supply battery, and then see what the circuit becomes... Are there any workarounds, such as whether what the above person said is feasible, you can also use the circuit analysis method to find out.

As for the pointer multimeter mentioned by Maychang, it can also be analyzed on the specific circuit.

se7ens

maychang posted on 2021-5-26 14:31 Digital multimeters cannot be used to measure their own battery voltage, but pointer multimeters can. Because digital multimeters need to use their own...

It's true that the digital multimeter is not working.

But it's not because of removing the battery.

It can't be tested when the battery is installed.

se7ens

qwqwqw2088 posted on 2021-5-26 14:53 For a digital meter, loosen the screws on the battery cover of the rear shell, do not unplug the battery leads, use a red test lead, put it on the positive and negative poles of the battery respectively, take the absolute value and add them together...

Interesting, what's the principle?

w494143467

I also watched the fun, I have never used a multimeter to measure its own voltage, but what a big guy said makes sense.

maychang

se7ens posted on 2021-5-26 15:55 It is true that the digital multimeter does not work, but it is not because the battery is removed. It cannot be measured when the battery is installed

The two test leads of a digital multimeter are not connected to either end of the battery. Usually, the black test lead of a digital multimeter is the "ground" of the internal amplifier circuit, and the amplifier circuit, including the AD conversion, uses a dual power supply. This dual power supply is powered by batteries, that is, obtained by battery voltage division.

Be sure to measure the voltage of the battery inside the digital meter. You can touch the positive terminal of the battery with the red test lead and read the value, then touch the negative terminal of the battery with the red test lead and read the value. The absolute value of the two measurements is added together to get the voltage of the battery inside the digital meter.

The principle is: the black test lead is the "ground" of the dual power supply. The first measurement is the positive part of the dual power supply, and the second measurement is the negative part of the dual power supply (this measurement result must be negative). The absolute value added is the voltage across the battery.

qwqwqw2088

se7ens posted on 2021-5-26 15:56 Interesting, what is the principle?

See the answer on the 8th floor

maychang

se7ens posted on 2021-5-26 15:55 It is true that the digital multimeter does not work, but it is not because the battery is removed. It cannot be measured when the battery is installed

The reply from chunyang on the 4th floor is worth noting: the most intuitive way to judge is to look at the electrical schematic diagram of the digital meter. The same is true for pointer meters, and the electrical schematic diagram is the clearest.

annysky2012

A digital multimeter cannot be used to measure the voltage of its own battery, but a pointer multimeter can. This is because a digital multimeter needs to use its own battery to measure voltage, and the digital multimeter will not work if its own battery is taken out. A pointer multimeter does not need its own battery to measure voltage, so you can take out its own battery and then measure the voltage across the battery.

Makes sense

se7ens

maychang posted on 2021-5-26 16:08 Neither of the two test leads of a digital multimeter is connected to either end of the battery. Usually the black test lead of a digital multimeter is the &ldqu ...

It is indeed possible to do this to obtain the battery voltage

But if both test leads touch the battery terminals at the same time, the multimeter will shut down.

What caused this shutdown?

I guess this may cause a short circuit in the power supply of the MCU.

You need to turn the switch back on to use the multimeter.

Moreover, the internal logic of the MCU is that if a power failure occurs, it will automatically shut down and need to be manually restarted

maychang

se7ens posted on 2021-5-28 16:51 It is indeed possible to do this to obtain the battery voltage, but if both test leads touch the battery terminals at the same time, the multimeter will shut down. This shutdown is...

"What caused this shutdown?

I guess this may cause a short circuit in the power supply of the MCU.

I guess that the black probe of the digital meter touches the negative terminal or the positive terminal of the battery, causing the negative power supply part or the positive power supply part of the dual power supply to be almost short-circuited.

To find out what is going on, we should analyze it by referring to the electrical schematic diagram of the digital meter.