There are so many types of battery chargers available. How do I select a suitable one?
To put it simply, there are basically two types of chargers in the market that uses the popular constant current charging technique. The time based charger and the more sophisticated smart/intelligent charger. You may be able to find a few temperature based chargers but these chargers are generally not effective as temperature is environment dependent, thus severely affecting the performance of the charger. There is also a high risk of overcharging associated with such chargers.
Time-Based Chargers
For most budget chargers, a time based scheme is usually used. For a time based charger, you can find commonly used descriptions like 3hr fast charger, 5hr charger, switches off automatically after X hours, etc. The charging current used is relatively low, in the region of 125mA. Some models are equipped with a fast charge mode, boosting charging current to 250mA for a certain duration, thereafter automatically switching back to the standard charging current for another predetermined duration.
!Remember!
Before proceeding further, a basic formula to keep in mind when computing charging time/capacity of battery supported:
Estimated Charging Time (in minutes) = [(Battery Capacity / Charge Current) / 0.8] * 60
Suppose you have an 8-hour charger with a specified output charge current of 125mA, using the above formula, it will be able to fully charge a battery with a capacity of up to 1000mAh in 8 hours. What happens if a battery of a different capacity is used? Since the charging current and the charging time is fixed, a time based charger will not be able to correctly charge a battery with a different capacity. A battery with a rated capacity below 1000mAh will be overcharged while a battery with a rated capacity above 1000mAh will not be fully charged! Overcharging a battery can severely shorten its life span. Prolong overcharging will damage the battery permanently!
As
the risk
of
overcharging
is very
high for
time based
chargers,
a
relatively
low
charging
current is
used to
reduce the
risk.
Using a
low charge
current
means that
it will
take a
much
longer
time to
fully
recharge
the
batteries.
Smart/Intelligent
Charger
A smart/intelligent charger is equipped with a microprocessor to monitor and control the charging process. It uses a technique called delta voltage control. Just prior to being fully charged, the battery voltage rises sharply and then falls. The microprocessor is programmed to detect this characteristic which indicates that the battery is fully charged. This technique is by far, the best and most accurate for charging batteries. There is little risk of overcharging batteries. With higher accuracy, a larger charging current can be used to reduce the time required to fully charge batteries. The drawback will be higher costs associated with the microprocessor and a more complex circuitry.
In summing up, use a time-based charger for applications which do not require a high capacity battery. In addition, using the above formula, ensure that the charger is capable of properly charging the required battery. Bear in mind though, it has no means of determining the state of the battery before charging, possibly leading to an overcharge condition. For high drain applications, a good quality smart/intelligent charge would be the ideal solution. It may cost more initially but in time, you will be rewarded with higher efficiency, longer lifespan for your batteries and greater savings.
