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Battery Charging States: What You Need to Know

Batteries are in a constant state of change. Even if you’re not using them, they’re slowly discharging. When you do use them, they discharge even faster.

However, charging them back up and maintaining their charge is crucial to keeping them healthy and long-lasting.

There are four stages to battery charging, and each one is important to know. They are:

  1. Bulk Charge Stage,
  2. Absorption (Regulation) Stage,
  3. Float Charge,
  4. Equalization Charge.

Each state has a specific purpose and thus its own voltage, current, and temperature limits. Knowing these limits and how to properly charge your batteries will help you get the most out of them.

Here’s a quick rundown of each state.

Bulk Charge

The bulk charge is the initial charging state where the maximum current is delivered to the battery until it reaches a certain voltage. The primary purpose of the bulk charge is to bring the battery up to an acceptable voltage level.

During the bulk charging state, the current is applied to the batteries at the highest safe pace they will tolerate until the voltage reaches near (80-90%) full charge.

The battery voltage increases as the charging current supplied by the battery charger replenish the battery’s internal charge capacity. The charger current stays constant (flat), while the battery voltage increases during this stage.

After the battery voltage reaches its peak (full charge), the charger switches to the absorption mode.

Absorption (Regulation) Stage

The absorption charge is the second charging state where the voltage is increased to its maximum, while the current decreases. The purpose of this stage is to ensure that the battery is fully charged.

The absorption stage is where the battery charger applies a constant voltage to the batteries, while the current decreases as the batteries become closer to full charge. The battery voltage will remain constant during this stage, while the current decreases until it reaches a very low level (trickle charge).

At this point, the batteries are considered to be fully charged and the charger will switch to the float mode.

Float Charge

The float charge is the third and final charging state where the voltage is reduced to a level that maintains the battery in a fully charged state. The purpose of this stage is to keep the battery at full charge without overcharging it.

The float stage is where the charger applies a constant voltage to the batteries, while the current decreases to a very low level (trickle charge). The battery voltage will remain constant during this stage, while the current decreases until it reaches a very low level.

Equalization Charge

The equalization charge is an optional fourth stage that is sometimes used to bring all the cells in a battery pack to the same voltage. This is done by applying a higher voltage to the batteries for a period of time.

The equalization stage is where the charger applies a higher voltage to the batteries for a period of time. This helps to bring all the cells in a battery pack to the same voltage.

Is it possible to charge a battery with a constant voltage?

Yes, it is possible to charge batteries with a constant voltage. Constant voltage charging charges batteries at a maximum voltage, often 13.8V to 15V, and a maximum current, depending on the charger specification.

When a “flat” battery has been charged for a period of time and the maximum voltage is approached, the charge current will decrease in proportion to the battery’s internal resistance. The time taken to decrease from the maximum voltage to the “trickle charge” current is known as the “top-off time.”

Is it possible to charge a battery with a constant current?

Yes, it is possible, but the process requires a specially designed charger that keeps a constant current until a certain voltage is reached.

These types of chargers aren’t very common. Because they can overcharge and overheat batteries if they are not carefully monitored and the battery temperature is not maintained.

What is the effect of temperature during charging?

The temperature has a significant effect on charging. Higher temperatures increase the rate of chemical reactions inside the battery, which can lead to faster charging and higher capacity.

However, if the temperature gets too high, it can damage the battery. That’s why it’s important to use a charger that has temperature correction so that it can adjust the charging rate according to the battery temperature.

For example, at 20°C, a 12V battery should be float charged at 13.5V. If the temperature is increased to 30°C, the float voltage should be brought to 13.3V in order to compensate for the higher temperature.

What size of battery charger should you have?

The size of the battery charger you need depends on the type and size of the battery you are using. However, as a general guideline, you should have a charger that can produce at least 10% of the battery capacity, i.e. a 15A charger for a 120Ah battery.

Please note, that this is just a guideline, and you should always check the manufacturer’s recommendations for the specific battery you are using.

Conclusion

Now that you know the different charging states of batteries, you can be sure that your batteries are properly charged. By using a charger with temperature compensation, you can ensure that your batteries are charged safely and efficiently.

And by using a charger that is the right size for your battery, you can be sure that your batteries will be properly charged without overcharging them.