A quality battery charger is the foundation for long-lasting and reliable batteries. Chargers are frequently given minimal importance and are seen as an "optional extra" in a price-sensitive market.
Sensible planning on the power supply should be implemented by placing it at the start of the project instead of after the hardware is finished, as is normally the case. Engineers are frequently ignorant of the energy source's complexities, especially while charging under stressful circumstances.
The charging speed of a charger is a popular method for identifying it. When used as recommended, consumer devices are available with a low-cost personal charger that works well.
The industrial charger is frequently manufactured by a 3rd party and offers unique characteristics like charging under extreme temperatures.
While batteries can work at temperatures below freezing, not all types could be charged at this condition, and most Li-ions batteries are among these.
When lead- and nickel-based batteries are cold, they get charged at a slower speed.
Some Li-ion chargers have a "boost" mode that allows recharging after a Li-ion battery has gone to sleep owing to over-discharge.
While keeping the battery in a depleted state, wherein self-discharge takes the voltage to the cut-off threshold, a sleep situation might develop.
A standard charger considers such a battery to be unusable, and the battery pack is frequently destroyed.
To activate the protective circuit, Boost uses a tiny charge current to elevate the voltage to between 2.2V/cell and 2.9V/cell, after which a standard charging procedure begins.
If a Li-ion has been below 1.5V/cell for a week or more, proceed with caution. Dendrites might just have formed, posing a threat to safety.
Constant Current and Constant Voltage Chargers
Chargers constructed for lead and lithium batteries work on a constant current, constant voltage principle (CC/CV). The charge current is continuous, and when the voltage reaches a certain level, it is terminated.
The battery saturates when it reaches the voltage limit; the current reduces until the battery could no longer receive any more charge, and the fast charge is halted. The low-current threshold varies with each battery.
Nickel-based batteries are designed to charge with a constant current and with no restrictions on voltage increase. This is similar to raising a weight with a rubber band in which the hand moves faster than the load. Upon seeing a little voltage decrease following a steady ascent, full charge detection happens.
A peak timer should be included in the charger to protect against abnormalities like as shorted or mismatched cells, ensuring a safe charge termination when no voltage delta is observed.
Temperature sensing, which detects temperature increase over time, should be included. Delta temperature over delta time, or dT/dt, is a strategy that works well with fast and effective charging.
With nickel-based batteries, a temperature increase is usual, particularly when the charge level exceeds 70%. This is caused by a loss in charge efficiency, and the charge current must be reduced to relieve stress.
The charger turns to trickle charge as soon as the battery is "full," and now the battery needs to cool down.
In case the temperature of the battery continues to remain above the atmospheric temperature, the charger may be malfunctioning, and the battery must be disconnected since this may indicate that the charger's trickle charge may be excessive.
NiCd and NiMH batteries must not be left connected with the charger for weeks or months at a time. Maintain the batteries in a cool area until needed, and always charge them before using.
While charging charge, lithium-based batteries should always never be above the ambient temperature. If the temperature increases more than 10oC (18oF) above the ambient value during a typical charging, stop using the battery or the charger.
Using a fixed or constant voltage charger, a fully charged Li ion batteries will be unable to accept over-charge and might stop taking the trickle charge. Thus, it is not important to disconnect the Li-ion from the charger; nevertheless, if the pack was not used for more than a week, it is advisable to store it in a cool area and recharge it before using.
Chargers come in a variety of shapes and sizes.
Slow Chargers: The "overnight charger", often known as a slow charger, is by far the most simplest. This dates back to the days of nickel-cadmium batteries, when a basic charger would apply a constant charge of around 0.1C (one-tenth of the rated capacity) as long as the battery remained attached.
Slow chargers do not indicate when a battery is fully charged; the charge remains active, and a complete charge of a blank battery requires 14–16 hours.
The slow charger maintains NiCd lukewarm to the finger when completely charged. NiMH must not be charged with a slow charger due to its diminished capacity to absorb over-charge.
This charge technique is commonly used in cheap type consumer chargers for AAA, AA, and C batteries, as well as some kids toys. If you find the batteries are heated, disconnect them immediately.
The rapid chargers are utilized in consumer items and are categorized between the slow and fast chargers. A discharged pack takes 3–6 hours to charge. When the charger detect the battery is full, it flips to "ready."
To securely charge a malfunctioning battery, most rapid chargers integrate temperature sensors.
The fast charger has various benefits, the most prominent of which is faster charging times. This necessitates more frequent contact between the charger and the battery.
A discharged NiCd or NiMH battery charges in just over an hour at a charge rate of 1C, which is what most fast chargers utilize. Many nickel-based chargers limit the current as the battery near the maximum charge to compensate for the reduced charge absorption.
The charger is switched to trickle charge, generally known as maintenance charge, after the battery is fully charged. To handle NiMH, many nickel-based chargers now feature a lower trickle charge.
Li-ion has very low charge losses and a coulombic efficiency of more than 99 percent. The battery charges to 70% state-of-charge (SoC) in lower than an hour at 1C; the additional time is used to charge to saturation.
Li-ion batteries need not go through a saturation charge like lead acid batteries need; in contrast, it is preferable not to completely charge Li-ion batteries because they will live longer but have a shorter duration.
Li-ion is the most basic of all chargers. There is no gimmickry that claims to boost power efficiency, as many manufacturers of chargers for lead- and nickel-based batteries advertise. The primitive CCCV approach is the only one that works.
Lead Acid Fast Charge
The phrase "fast-charge" is a misrepresentation because lead acid batteries cannot be charged rapidly. The majority of lead acid chargers charge the battery in 14–16 hours; any longer is a tradeoff.
Lead acid could be charged to 70% in around 8 hours; the leftover time is spent on the crucial saturation charge.
A partial charge is OK as long as the lead acid is completely charged to saturation frequently to avoid sulfation.
Energy Saving Chargers
To save energy, a charger's idle current must be minimal. Mobile phone chargers and other tiny chargers that consume 30mW or even less on standby receive 5-star rating from Energy Star.
Chargers with 30–150mW receive four stars, 150–250mW receive three stars, and chargers with 250–350mW receive two stars.
These devices receive one star since their average usage is 300mW. Portable chargers are frequently left connected in to supply input even while not in use, and Energy Star strives to limit current waste.
At any moment, there could be about one billion similar chargers linked to the grid across the world.
Simple Rules to Follow When Purchasing a Charger
- Whenever a battery's state-of-charge (SoC) is low, charging it is most efficient. Whenever the battery reaches a SoC of 70% or above, charge acceptance diminishes.
- When a fully charged battery becomes unable to convert electric energy into chemical energy, the charge should be reduced to a trickle or the battery should be shut down.
- When a battery is charged past its maximum capacity, the surplus energy is converted to heat and gas. This can lead to a build-up of undesirable chemicals in Li-ion batteries.
- Overcharging for an extended period of time induces irreversible damage.
- Use the appropriate charger for the battery chemistry you're working with. The majority of chargers are dedicated to a single chemistry. Check that the battery voltage matches that of the charger. If the situation is different, do not charge.
- A battery's Ah rating may differ somewhat from what is advertised. Charging a larger battery takes more time than charging a smaller cell, and vice versa.
- If the Ah rating varies too far, don't charge (above 25 percent).
- Although a high-wattage charger reduces charge time, there really are limits to how quickly a battery could be charged.
- Extremely fast charging could be stressful to the battery.
- When a lead acid charger reaches full saturation, this must switch to float charge; when a nickel-based charger reaches full saturation, this should toggle to trickle charge.
- Li-ion batteries are unable to withstand overcharge and therefore do not accept a trickle charge. Battery losses caused due to self-discharge are compensated by trickle and float charges.
- A temperature bypass must be readily accessible on chargers to stop charging a faulty battery.
- Keep an eye on the temperature of the charge.
- Lead acid batteries must be lukewarm to the hand; nickel-based batteries will turn warmer at the completion of the charge and will need to cool down when ready.
- When fully charged, Li-ion batteries must not exceed 10°C (18°F) above ambient temperature.
- When employing a low-cost charger, keep an eye on the battery temperature. If the battery gets hotter, disconnect it.
- Allow for charging at ambient temperature. When it's freezing, charge acceptance lowers. Li-ion batteries cannot be charged below 32°F.