Custom Lithium ion Battery Pack

How to Calculate Internal Resistance of a Battery-Introduction, Methods and Need

Jan 22, 2021   Pageview:55

Thanks to technology that it has become easier for us to use electronic devices without thinking about their charging. Now you are not required to depend upon the charging stations as now almost every other device runs on a battery. For different purposes and applications, there are a wide number of batteries available in the market. Depending upon your demands, you can purchase the right battery that has a higher capacity for your electronic device.

There are a few aspects that should be taken into consideration before buying any battery so that you can utilize it for a long period of time without any hassle. One such important aspect is the internal resistance of a battery. Further on this page, you will get a broad idea about the internal resistance of a battery. Therefore, let's see some of the important questions related to this down below:

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What does the internal resistance of a battery work for?

Before understanding the need for internal resistance of a battery, it is important for you to know that the capacity of a battery will deliver limited use if it is not able to provide all the stored energy in an effective manner. It is significant for a battery to have low resistance power so that maximum use can be taken out of it.

The internal resistance of the battery is measured in mΩ, i.e., milliohms. It won't be wrong here to mention that internal resistance works as the gatekeeper in the battery. Here is an easy trick to understand about the function of internal resistance in a battery, the lower the internal resistance, there will be less restriction in the pack.

Low internal resistance is important, majorly where the electric devices run on a heavy load; this includes electronics such as powertrains and other power tools. When the internal resistance of the battery becomes high, it impacts on the performance of the battery. Due to high internal resistance, the battery tends to heat up a lot, and the voltage of the battery drops immensely. It can result in an early shutdown or breakdown of the battery and the electric appliance both.

It is vital here to mention that low internal resistance of the battery results in high current delivery when required. On the other hand, if a battery possesses high internal resistance, then it results in heating up of the battery, and the voltage tends to drop. In the latter case, the electric equipment has increased chances of damage, and the overall energy storage gets wasted.

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How do you find the internal resistance of a battery?

Before understanding the ways to find the internal resistance of the battery, you are required to know a fact which is eminent when it comes to the chemical composition of the battery. Generally, lead-acid batteries tend to have a low internal resistance. These batteries have a feature that they respond to the high current bursts in a good manner. Lead-acid batteries have some inherent slowness, and they are not able to perform well with a comparatively high current discharge rate. Therefore the battery needs some time to recover.

There is absolutely no doubt in the fact that apparently, all kinds of batteries have some sluggishness at various degrees. Hence, one thing is confirmed that power delivery of a battery is not only based on the internal resistance, but it also depends on the response factor of the battery's chemistry and temperature.

Grid corrosion and sulfation are the two major reasons that contribute to the internal resistance of the battery. When it comes to nickel-based batteries, crystalline formation is the main cause of the internal resistance. However, the effect of it can be eliminated via deep-cleaning of the battery. Due to prolonged use and aging, the internal resistance in a Lithium ion battery increases, but there are improvements made in the electrolyte additives so that the buildup of unnecessary films can be avoided. Following are a few methods that can be used to measure the internal resistance of a battery:

?DC Load Method:

When it comes to the oldest and yet highly reliable testing methods, it is the ohmic measurement. In this, the battery undergoes a short discharge for a second or so. 1 A or even less is the load current for a small sized battery; on the other hand, 50 A or more is the load current for a starter battery. With the help of a voltmeter, you can measure the resistance as it measures the OCV (i.e., open circuit voltage) with absolutely no load. The reading is followed by a second round along with a load. According to the ohm's law, the resistance of the battery can be calculated by voltage difference divided by the current.

?Electrochemical Impedance Spectroscopy (EIS):

In order to examine the features of a battery, research laboratories use this method. Though the cost of equipment is high, it has slow test times. Also, there is a requirement of a professional in order to decode the data generated.

What tools do you need to calculate your battery's internal resistance?

In order to find the internal resistance of the battery, an equivalent series resistance meter (ESR) is used. AC milliohm-meters are used in order to evaluate the battery's internal resistance. However, in order to perform a quick experiment, you will require a battery it can be a lead acid, nickel cadmium, lithium polymer, or any other kind of battery, a multi-meter, high power resistor (depending upon the battery you are using for the experiment) and a calculator.


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