Different types of battery chargers
There are a lot of different types of battery charges for various type of batteries, but I am going to discuss only about “AA / AAA” rechargeable battery chargers for the NiCD and NiMH batteries, these battery chargers are mostly divided into three categories dumb chargers, smart chargers, Battery manager (charger + conditioners + analyzers).
Do note that you should not charge NiMH batteries in a NiCD chargers, but most of the NiMH chargers can charge NiCD rechargeable batteries, also do note that investing in a quality charger is very important as we never give a thought to a battery charger and I have seen a lot of quality batteries being destroyed due to cheap charger and most of the time it’s the charger to blame than the rechargeable batteries.
Dumb Chargers: These are also called overnight / slow chargers and usually charger a battery in around 12-16 hours, these chargers were common with NiCD batteries and these are also bundled with cheap battery packs, do note that these chargers do not know the state of a battery they have a simple timer (12 – 16) hours and once its plugged into a power socket it keep on charging a battery for the specified time, these are the cheapest kind of chargers found in the market and its best to avoid these chargers as they can overcharge a battery and reduce its life considerably.
Smart Chargers: Think of a smart chargers as an intelligent charger, as this charger knows the state of a battery and will stop charging or go to trickle charger mode when a battery is fully charged, as these chargers can determine the state of a battery they have higher charging currents to charge the battery in 2 – 6 hours also most of the smart chargers have a simple computer chip to control the various aspect of charging.
Super Fast Chargers: Its kind of a smart charger which can charge a rechargeable NiMH battery in 15 – 30 minutes, its best to avoid these kinds of chargers as they use a very high current to charge a battery and this in turn heats up your battery a lot which can deteriorate your rechargeable battery quickly, a NiMH rechargeable battery might give only 50 – 75 recharge cycle instead of the normal 500 recharge cycles if used with a fast charger, it’s okay to use a super fast charger once in a while but for regular charging use a normal smart charger.
Battery Managers: A battery manager is a smart charger but can also do additional functions like discharge, condition, analyze the capacity of a battery. A sophisticated battery managers can have LCD displays to show whats happening with your battery in real time, displaying its capacity, voltage etc, if you have a lot of rechargeable batteries it’s a good idea to invest in a battery manager like La Crosee BC 900 / 700 charger or Maha BC9009 charger.
How does a smart charger determine the battery status?
To determine the state of a battery a smart charger employees one or all of these techniques to determine if a battery is charged.
1) Negitive delta voltage detection
2) Monitor the temperature
3) Voltage Monitoring
4) Trickle charging
Negative delta voltage (−ΔV): As a NiMH battery is charged it’s voltage increases constantly but when a NiMH battery is almost fully charged it will show a voltage drop instead of a increase and a charger that uses this method to detect the charger is known as using the negative delta voltage -ΔV, many smart chargers use -ΔV detection to determine the charge of a battery.
Monitoring the temperature : You might have noticed that these rechargeable batteries get hot / warm at the end of the charge this is due to the fact that when rechargeable batteries are fully charged the cannot store the energy and this enegery is then converted to heat and a good smart charger will detect this and most smart chargers will use Negative delta voltage as the primary method to detect a charge and temperature monitoring as a backup methods, many smart chargers can suspend the charging if a battery gets too hots while charging and will wait until the battery cools to recharge them again.
Battery Voltage Monitoring: A NiMH 1.2v battery when being charged can reach over 1.5v and a NiMH battery is fully charged when its voltage reaches around (1.48 – 1.54v) by continuously monitoring the voltage of the batteries as they charge a chargers is able to detect precisely when to cease fast charging and switch to trickle-charge mode this method is known as “Delta V” some charge use Delta V and -ΔV to determine the state of a battery.
Trickle Charging: Most of the modern chargers support trickle charging, after a charger detects a battery is fully charged it will go in a trickle charge mode, which is just 5% charge rate compared to normal charging rate, there is no fixed amount of current for a trickle charge but most chargers supply around 20 – 75 mAh in the trickle charge mode this charge rate is just enough to keep the battery charged at its full capacity.