Charging batteries, from laptops to electric vehicles, requires the right rate based on battery chemistry. Around 50% of our clients prefer the faster charging solution for batteries, but only 1% understand the potential dangers of charging too quickly. In this blog post, we will explore fast charging and its safety considerations.
Which Battery Chemistry Enable Fast Charging?
Not all batteries can be charged quickly. Understanding battery chemistry, power use, and charge rates will help you get the right charging method.
Lead Acid Battery Charging
Lead-acid batteries are typically slow-charged using a constant current/constant voltage approach. The charger maintains a preset current and voltage, moderating the current until the preset voltage is reached, then reducing it until the battery is fully charged.
For lead-acid batteries, the constant charge continues until 70% voltage is reached. Then, the charger steps down the current for the final 30% of voltage, called a topping charge. Unlike other batteries, lead-acid batteries can undergo a float charge to prevent self-discharge if the charger supports that option.
Nickel-Based Battery Charging
Nickel-based batteries, such as NiMH and NiCad, can be charged using rapid, quick, or ultra-fast methods. New NiCad batteries require a 16-24 hour initial charge before use.
Both NiMH and NiCad use constant current/constant voltage charging. Once fully charged, the voltage drops to a trickle charge to offset self-discharge.
NiMH chargers employ a step differential method. They fast-charge the battery until reaching a threshold, then reduce the charging rate. The battery and charger undergo a cool-down period at each threshold before resuming charging.
Lithium Battery Charging
There are six lithium battery types; LFP and NMC are the most widely used.
Traditionally, LFP batteries suit slow charging, while NMC batteries are designed for fast charging. However, continuous development in battery technology has improved the fast-charging performance of lithium iron phosphate batteries.
Both LFP and NMC batteries utilize a battery management system (BMS) that monitors charge, temperature, and other factors to moderate temperature and prevent undercharging or overcharging. Despite this, damage to the battery or BMS can still result in overcharging issues.
Lithium-ion batteries should never be overcharged. The current must be removed before the battery reaches maximum capacity, as trickle charging can cause plating of metallic lithium, leading to safety issues.
Things To Understand About Fast Charging
Battery chargers use current and voltage to power batteries.
Current is the amount of electricity flowing from the charger to the battery, while voltage is the electrical current’s strength. Wattage is calculated by multiplying voltage and current.
For fast charging, battery pack manufacturer can adjust voltage or current rate. Increasing current strength allows more power to enter the battery. Decreasing voltage based on battery level is also common.
However, charging circuits have limits on the power they can manage. Exceeding these limits can lead to overcharging, high temperatures, and other issues. The device, charger, and cable must be able to handle fast charging.
When fast charging, always do so at moderate or room temperatures. The charger should also switch to a regular charge as the battery nears full capacity to limit stresses.
Types Of Fast Chargers
There are three types of fast chargers as follows:
Rapid Chargers
Rapid chargers charge at 0.3-0.5C (C is short for C rate). They stop current when temperature, current, or voltage hits the limits. The safe operating temperature range of these chargers is 50-115°F. It takes 3-5 hours to reach full charge.
Quick Chargers
With 1C charging, quick chargers can charge the battery to full around 1 hour. The charging temperature is recommended at 50-115°F like rapid chargers. It will terminate the current when reach the limits as well.
Ultra-Fast Chargers
Ultra-fast chargers support specialty batteries that allow for charge rates from 1C to 10C, enabling a full charge in 10 to 30 minutes. However, they only charge the battery to 70% state of charge. Charging temperatures should also remain between 50°F and 115°F.
Conclusion
Moderate charge/discharge rates are best for battery performance. Fast charging can shorten battery life due to the added stress.
If fast charging is required, larger and heavier batteries are ideal. Always consult the battery manufacturer to determine if fast charging is safe and viable for your specific needs before implementing a solution.
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