How Do Battery Chargers Know When To Stop?

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The durability and general performance of a battery are highly dependent on the type of battery charger used in recharging the battery.

A good battery charger will maintain the battery life span and will not get the battery overcharged- one of the leading causes of a shortened battery life amongst other side effects.

So, how do battery chargers know when to stop? Different battery types have different mechanisms through which they stop the battery from getting overcharged.

Here in this article, we shall consider the popular battery types and their mechanism of stopping the battery from getting overcharged.

Contrary to what is obtainable with most persons, battery chargers should receive a considerable amount of prioritization and should not be given the “afterthought “status as they do matter.

They determine a lot about the battery, especially its performance and longevity by not allowing the battery to get overcharged at any point.

When buying a battery, ensure to get with it its specified battery charger as battery chargers are crafted for particular types of battery and not for all types of batteries.

Cross using a battery charger with a battery it is not specified for is the commonest reason for a battery getting overcharged.

Rather than prioritizing qualities of a charger such as its charging speed or cost, how safely the charger charges the battery should also be on the priority list and should be carefully considered.

While it may not be necessary to remove certain types of batteries from their chargers immediately they are full as they are designed not to get overcharged, leaving a battery on the charger for a prolonged time duration such as weeks or months is generally not advisable.

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Different types of battery chargers and how they stop overcharge

There are several types of battery chargers based on their working mechanism as well as based on the speed of charging.

Some are designed with sophisticated methods of detecting full charge and terminating further charge while others are not. Here are some of the common types of chargers including how they stop overcharging of batteries.

  • Slow chargers

Slow battery chargers are otherwise known as overnight chargers. These are amongst the earliest types of chargers developed. Their design is therefore limited by the available technology of their time. what is the working mechanism of these chargers? They are designed to send in a fixed amount of charge into the connected battery. 

These chargers will continue to send in this fixed amount of charge into the connected battery irrespective of the charge status of the battery and will not stop until the battery is disconnected. They are more like the primitive design of battery chargers.

They are designed to send about one-tenth of the battery’s rated capacity. Even when the said battery is fully charged, slow or overnight chargers are incapable of detecting the battery status and therefore do not recognize when the battery is fully charged.

Certain battery types are unaffected by this type of battery and can therefore be charged with it. The nickel-cadmium type of battery is designed not to get overcharged and can withstand this form of continuous charging. The battery simply gets warm after 14 to 16 hours of charging after which it attains a fully charged status.

However, batteries such as the NiMH type of battery should never be connected to this form of chargers as they, unlike nicd batteries, are not designed to withstand overcharge.

Where else are slow or overnight chargers useful? Well, these chargers irrespective of their primitive design are still very much useful to this present day.

They are used in charging the AAA, AA, as well as C types of cells and are also used in charging things like children’s toys that make use of rechargeable batteries.

The temperature of the battery can be used to estimate the charge status. When full, most batteries become warm as a result of pushing out the excess charge.

Therefore, by checking the battery temperature and disconnecting it when it gets abnormally warm, one can protect the battery from getting overcharged.

Batteries such as nicd batteries will not be affected adversely even when left connected to the charger after attaining a full charge. No battery should however be left connected for a prolonged period such as weeks or months.

  • Rapid chargers

In terms of charging speed, rapid chargers can be said to fall in between the slow or overnight chargers and the fast chargers.

Rapid chargers have a place in charging modern electrical devices as they are being used in so many consumer products.

Unlike the slow or overnight chargers which take about 14 to 16 hours to get the battery charged, the rapid chargers are faster than that and will only take about 3 to 6 hours to get the job done.

Rapid chargers also differ from slow or overnight chargers in terms of detection of full charge status. The chargers are designed to know when the batteries are fully stopped to stop sending in further charge which could be detrimental to the battery.

Once the battery is full, there is a system in place that causes the charger to be switched from charging mode to a “ready” mode, during which it no longer charges the battery.

So, whenever the peak voltage for the battery is reached, the rapid charger safely stops charging the battery further.

Additionally, rapid chargers are also designed with a temperature sensing apparatus that allows them to detect a change in the battery’s temperature indicating a fully charged status to safely charge defective batteries.

  • Fast chargers 

fast chargers have numerous advantages over other types of battery chargers. In terms of charging speed, fast battery chargers are capable of charging the battery in the shortest time possible. Users of rechargeable batteries who like to charge their batteries speedily, therefore, go for such battery chargers.

The ultra-fast speed of fast battery chargers in charging the battery demand that the charger maintains a very close relationship with the battery at all times and can detect at a fast speed the charge status of the battery.

Unlike the slow or overnight chargers which are designed to send in about 0.1C, that is, about one-tenth of the capacity the battery is rated for, fast chargers can send in as high as a 1C charge, therefore, st chargers have no problem charging the battery speedily.

They can charge nicd or NiMH types of battery at an unprecedented speed of an hour and some minutes. Once the battery is fully charged, how do the fast chargers deal with the situation to prevent battery overcharge? 

Whenever the battery connected to becomes fully charged, the charger is switched from a charging mode to a trickle charge or maintenance charge mode.

In this state, it no longer sends in more charge and is unlikely to get the battery overcharged. It is therefore saved for batteries such as NiMH type of battery which are sensitive to overcharge.

  • Smart chargers

These are technologically advanced battery chargers that can monitor the battery’s voltage while charging.

This way, the battery automatically stops charging immediately the battery gets full. When looking for chargers that protect your battery from overcharging, maintain battery durability and longevity, smart chargers are top of the list.

  • Trickle charger

they are designed to send in a low amount of charge ( a trickle) over a prolonged period which differs according to the battery capacity. When charging with trickle chargers, the excess charge leaks away naturally to prevent overcharging.

The working mechanism of battery chargers

A battery works by using up its electrolyte which is converted to electrical energy. Recharging the Battery means restoring the used-up electrolyte.

This is achieved by the battery charger which supplies the battery with a direct current that restores its lost electrolyte. Once a charge can restore all of the used-up electrolyte, it automatically stops charging the battery.

How to buy the right charger for your battery?

Several things should be put into consideration before buying a battery charger to ensure the charger is right for that given battery. These include:

  • The size of the battery
  • The peak charging current
  • The voltage rating
  • The battery amperage
  • The type of battery.
  • And the price of the charger.

How to make the most of your battery charger?

  • The battery should be charged preferably when the ” state of charge” of the battery is low. This is the most effective period to charge the battery.
  • Avoid charging the battery beyond the “full state of charge”. Overcharging a battery leads to overheating which can cause permanent damage to the battery.
  • Chargers are specified for given battery chemistry, ensure to use the appropriate charger for the battery type. 
  • High wattage chargers, charging at ultra-fast speed can place a lot of stress on the charger.
  • Charging should be done at room temperature and the battery temperature should be carefully monitored.

How Do Battery Chargers Know When To Stop – Conclusion 

Many battery chargers are designed to prevent the battery from getting overcharged. Some are less sophisticated in this regard than others and may lead to overcharging of the battery especially when left plugged in for a prolonged period.

The smart battery charger is top of the list of battery chargers that protect the battery from getting overcharged.

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