Detailed explanation of lifepo4 soc chart and everything about soc

SOC refers to the state of charge of the battery, also known as the remaining capacity. It is used to reflect the remaining capacity of the battery. This article will explain detailed knowledge about lifepo4 soc chart and talk about everything you need to know about lifepo4 soc.

How do you calculate SOC and what factors will affect the soc of the battery

The numerical definition of soc is the ratio of the remaining capacity to the battery capacity. The actual voltage level, temperature, discharge rate, and cell age can all have a significant impact on the SOC of the battery. The most important thing to consider in the selection of LiFePO4 battery is the lifepo4 state of charge. There are also some other methods to calculate the state of charge for the LiFePO4 battery.

Voltage Method：

Using different type of tests, you also can find the state of charge of any battery or it’s left over capacity. The VM uses the chart of parabolic curve between voltage and SOC to find the desired value by knowing the voltage of the battery. Moreover, by finding the values of state of charge current is also used but the impact of voltage is much higher than the impact of current because it has some sought of minor errors.

Kalman Filter Method：
This is the mathematical algorithm in order to find the value of state of charge. Here in this method, we use different types of guesses in order to find the values of unknown parameters such as state of charge. 

This is the most advanced method used with too minimal errors to find the value of state of charge and is now used instead of CCM and VM. However, there are still some types of errors in order to find the values of state of charge of the batteries.

Explanation of the terms about soc-voltage, capacity, rated capacity, DOD and SOH

● Voltage：

Voltage is the potential difference between the positive and negative electrodes. As mentioned earlier, it also affects the battery’s SOC. The SOC, or residual capacity, is determined using the voltage of the battery cell as the starting point.

● Capacity：

Battery capacity is one of the important performance indicators to measure battery performance, which indicates the amount of electricity discharged by the battery under certain conditions. The useful capacity of a cell fluctuates greatly with temperature, charge discharge rates, and cell age, with less of an impact on other parameters like the time between charges, complicating SOC predictions for batteries (due to the self-discharge rate).

● Rated Capacity：

The power bank’s output capacity is referred to as the “rated capacity.” The circuit conversion efficiency has an impact on the rated capacity, which is smaller than the battery capacity.

● DOD：

DOD represents the percentage of battery discharge to rated battery capacity. SOC of a battery indicates how fully charged it is in relation to its potential. The charge state is indicated in percent, with zero to be an empty space and one hundred representing a completely filled region. There is no correlation between SOC and DOD. The batteries with lower DOD can still be charged up to 100% SOC.

● SOH：

A battery’s state-of-health (SOH) compares a battery under investigation to a brand-new battery while taking into account cell ageing. The SOH intends to tell the user how long the battery will take to reach the life terminal. The measurement parameters related to SOH can be the impedance, capacity, voltage, and charge and discharge cycles at the current time point, while the calculation of SOH cycles is completed by the main controller of the battery management system.

What does lifepo4 mean and how do you determine lifepo4 soc

Currently, Lifepo4 (Lithium-Iron-Phosphate) batteries represent the most effective energy storage technology. They provide important benefits including a high energy density and prolonged endurance. We can use lifepo4 soc chart to know better about the charging/discharging performance about Lifepo4. In order to determine the lifepo4 soc we use the formula as under:

State of charge (%) = Remaining Capacity (Ah) / Total Capacity (Ah)

Knowing your LiFePO4 battery’s level of charge is useful since it lets you know how many Amp-hours are still available from the battery.

Lifepo4 soc chart (12v, 24v, 48v)

Keeping the temperature constant (25℃) for 12v, 24v and 48v, we get the results:

Fig1 lifepo4 soc chart between SOC and measured voltage for 12v

Fig2 lifepo4 soc chart between SOC and measured voltage for 24v

Fig3 lifepo4 soc chart between SOC and measured voltage for 48v

SOC chart comparison of different batteries (NiMH, Li-Po, Li-ion and alkaline battery)

Fig4 SOC comparison chart of different batteries vs. voltage

The SOC chart shows the dramatic changes among the different batteries with respect to SOC and voltage.

Is lifepo4 the same as lithium ion and what is lifepo4 battery used for

First of all, they are not the same. Lithium iron phosphate batteries is one of the lithium-ion batteries. According to the different cathode materials, the main customers of lithium-ion batteries are divided into six categories: nickel-cobalt-manganese ternary lithium battery, lithium iron phosphate battery, lithium cobalt oxide battery, lithium manganese oxide battery, lithium titanate battery, and nickel-cobalt-aluminum ternary lithium battery. 

The cathode material of lithium iron phosphate battery is iron phosphate. Moreover, the current application fields of lifepo4 batteries include Marine application, powerwall, golf carts, RVs, UPS solar system and other fields.

How do I know the SOC of a lifepo4 battery

The most natural way to track the level of charge while using a battery is to follow the current by integrating it throughout cell use. We can also use lifepo4 soc chart for determining the SOC. If the battery has a display, or a smart BMS, the simplest way is to directly see how much power the battery still has, which is actually the SOC of the battery.

FAQs about LiFePO4 battery

1.How do you charge LiFePO4 battery according to SOC and at what voltage is a LiFePO4 dead

Lifepo4 batteries do not need to be charged after each use if they are not discharged to only 20% of the charge left. And it will not damage the battery when left in a partial soc. The soc of 20%-80% is helpful for the life span of the battery. So charge the lifepo4 battery when the soc is out of this range.

The lower-voltage cutoff of a lifepo4 battery depends on the battery specification and voltage. It can be seen in lifepo4 soc chart. The low-voltage cutoff of a 12V LiFePO4 battery is below 10 volts. 

2.What voltage should I charge my LiFePO4 battery to and do voltage and capacity vary with SOC

According to the standard values, the charging voltage of a lifepo4 battery cell shall be set at 3.65v, and the nominal voltage shall be 3.2V. Moreover, voltage depends on SOC. As voltage and capacity are directly related, higher the voltage, higher will be the capacity. One important thing to mention is that you must charge lithium battery with a lithium ion battery charger.

3.How long does it take to charge a 100Ah LiFePO4 battery

Due to the low resistance in lithium cells, lithium batteries have a reasonably quick recharge rate when compared to other battery types. A 100ah lithium battery can be fully charged from zero percent to hundred in around five hours using a fifty amp charger.