The 9V battery in the multimeter reads 9.3V. Why can't I use it?
This will be explained in two aspects. Because 9V laminated batteries are divided into carbon batteries and alkaline batteries!
1. Carbon batteries have large instantaneous current, but they don't last long! The point is cheap! If you don't use it and leave it for a month or two, it will basically consume a lot of power. When you use it up and the battery is low, you replace it with a spare battery, only to find that it runs out of power again not long after use. The specific performance is displayed on the multimeter, and there is no word. Turn it off and on again and it will show up again. Take off the measurement voltage, there is 8V voltage.
2. Alkaline batteries have stable output and long life, and are very suitable for use with multimeters. I used to use carbon batteries, and I used several of them a year. Since I replaced the alkaline battery with a well-known domestic brand, I haven't had any problems like yours. If you think about it, when you are detecting voltage and resistance, the multimeter has insufficient power and a large error occurs. How deceptive? The low discharge characteristics of alkaline batteries enable them to be stored for a long time. The shelf life is 10 years, so you can store it with confidence.
To see whether a battery has power, you don't look at the voltage, but the current. As long as the battery can draw a certain current, the battery can still be used, regardless of the voltage.
Voltage is just a potential difference. It only indicates that there is a potential difference between these two places. The existence of a potential difference does not mean that there will definitely be a current. For example, when a battery is left empty, of course there is a potential difference between the two electrodes, but there is no current because there is no conductor. loop.
What happens if there is a loop? The most extreme case is to directly connect the two ends of the electrode with a wire (such as a copper wire). It is said that there should be a large current at this time. After all, the resistance of the conductor (copper wire) is very small. According to Ohm's law, The current is definitely not small, but the actual situation is not like that. This is because the battery itself, as a power source, has a resistance. This resistance (internal resistance) is very large (relative to the wire). The current that the battery can provide is also affected by this resistance. restrictions.
When the battery is used or left for a period of time, the internal resistance of the battery will increase, and the final result is that it cannot draw much current. Although the voltage can still be measured when there is no load at this time, when you connect it When the load draws current, the voltage will drop rapidly due to the internal resistance, eventually causing the battery to be unable to supply normal power.
In order to solve this problem, some people used to inject salt water into the battery to reduce the internal resistance, which will restore the battery's power supply capability within a certain period of time. However, when the medicine inside the battery or the electrode reaction is consumed, injecting salt into the battery at this time Nothing is of use anymore.
If your 9V battery is used up quickly, it is recommended that you use rechargeable batteries. Even if you use ordinary batteries, it is also recommended that you use the freshest batteries. All batteries have a factory date, but some people will use old batteries or even used batteries to recharge them. Packaging is marked with the date, so the place where you buy the battery is also important.
