What does constant current charge mean?

You may have plans to buy an EV (Electric vehicle) or is currently an owner. Whatever be it, familiarize with its diverse charging algorithms. It is crucial to ensure making a well-researched purchase and derive value worth your investment. EVs nowadays are adopting the latest technology and has become more sophisticated. They have 234 mile median range. Hence, you need to recharge your EV after driving an average of 200 miles. 

Definition 

It involves charging at constant value while maintaining the current. This popular method is widely adopted around the world. The battery’s initial charge, its running capacity inspection, running traction charging, and the plate’s formation charging uses staged constant current charging or constant current. This method is advantageous as you can determine charging current value depending on your battery’s capacity. Besides this, you can calculate the charging amount directly and determine the duration of its charge completion time.

Charging Algorithms

You should recharge the battery bank after its existing charge gets depleted. Modern electric vehicles use diverse changing algorithms. However, charging algorithms define the way to adopt to recharge the battery bank. Two commonly used charging algorithms are constant voltage and constant current. The latter is more popular among them. 

Know the Advantages

Battery charging method adopted impacts the battery’s life significantly. Simultaneously, the discarding techniques have less impact on the environment. The truth is that most batteries are ‘charged poorly’ and not ‘used poorly’. A quality charger impacts positively the battery’s service life. Numerous EV chargers are sold on the market with varying performances. Few use half-bridge circuit for power conversion, while some have linear transformer for stepping down and later rectify it. Others use single-ended fly-back circuit for power conversion. Basically, they have a relatively simple circuit and offer poor protection function. Charging is not done as per the battery’s charging curve. It can affect the battery’s service life. Hence, choosing a quality charging method helps enhance the battery’s performance and service life. 

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People are immensely benefited with the invention of e-bikes, e-cars, e-buses, and other e-vehicles. They are introduced to replace conventional fuel-based vehicles that cause pollution and deplete existing natural resources. E-vehicles are flexible to use and environmental-friendly. However, lead-acid battery quality installed in e-bikes determine the vehicles’ usage rate. Lead-acid batteries are due to their large capacity, low manufacturing expenses, and price. If used improperly, the battery’s service life is shortened significantly. Several factors affect lead-acid battery’s service life. Correct way of charging the battery prolongs its life.

Being a simple charging battery, constant current has its current level established at 10% of optimum battery rating. It has a lengthy charge time. However, the disadvantage is that an overcharged battery might overheat. It is ideal for Ni-NH batteries. Disconnect the battery or use a timer function after charging. 

Application 

This method charges continuously at constant current a rechargeable battery to avoid over-current charge conditions. Another method is to charge at varying current in different stages or at low constant current to avoid over-voltage charge.

What is the role of constant current charging?

Initially, constant current allows the charger’s current to flow freely into the battery during BULK stage. This is irrespective of the battery’s charge state or temperature until its terminal voltage reaches a certain steady state. At this stage, the battery is >80% of charge state. To prevent unnecessary gassing, constant current charging initial charge current should be set to a particular percentage of capacity. 

Manufacturer Recommendations

Concerning CC charge curve’s BULK Charge phase, different manufacturers publish varying current limits. It includes the following:

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For GELL DEEP Cycle, it is 15% of C20 rating (20%C5).

For flooded Deep Cycle, it is 13% of C20 rating (15%C5).

For Semi-traction industrial GELL Deep Cycle batteries, it is 25% of C20 rating (30% C5)

For semi-traction industrial AGM Deep Cycle batteries, it is 25% of C20 rating (30%C5).

About 30% C20 rating (35%C5) for thin plate and high rate AGM batteries 

Then, charge output switches automatically to ABSORPTION constant voltage phase. Reducing potential difference between battery terminal voltage and charger-output voltage results in tapering down of charging current. Current tapers down continuously until it reaches its low preset limit that is around 1-4 percent of C20 of the capacity or in BULK charging phase with certain percentage of initial charge current. It is maintained by checking voltage stability or for preset period. It is when voltage does not increase over the measured period. 

On the other hand, finishing phases at voltage below gassing voltage of battery could be simple float stage. Highly engineered process might involve Pulsing mode and a special balance. 

Using CC-charge Regime

Sensing battery voltage or using mathe1matical algorithm timer helps determine the point where switch can be determined.

As battery reaches 100% charge from 95%, switch charge current to finishing (tapering) rate from charge current. 

Time calculation to return 108% to about 112% of ampere-hours helps determine smart timer setting. It is developed for Semi-traction GELL or AGM batteries. Avoid this technique unless you adopt smart technology to measure previous discharged capacity consistently and reliably. 

Calculate time needed to reach 125% from 115% of ampere-hours to determine smart timer setting. It is developed for deep-cycle flooded batteries. Avoid using this technique unless previously discharged battery capacity is measured consistently and reliably.

Time calculation to reach 110% from 105% of ampere-hours helps determine smart timer setting. It is developed for general purpose GELL or AGM batteries. Avoid using this technique unless it allows consistent and reliable measurement of previous discharged capacity.

Theoretically, as >95% of previously discharged capacity returns during bulk CC-charge state, absorption of CV continues at reducing rate. It is until >100% of previous discharged capacity gets replaced.

However, the fact is that as it reaches 100% theoretical charge state, it draws small currents. The objective is to compensate for electro-chemical and parasitic/standing losses to ensure achieving required overcharge.

Conclusion

EVs have diverse charging algorithms, like constant voltage and constant current. Few EVs support both the charging algorithms. CC or Constant current, being a charging algorithm uses fixed, constant current.