Photography 101
A Beginner’s Guide to
Flash Photography
Power Management of Your Flash
(Part 42)–
One of the top priorities of an event photographer going for an appointment is to ensure that he has enough charged battery for his camera and flash – sufficient enough to last throughout the whole affair he is covering. This task is observed by professional photographers like a commandment. And to be sure and confident, it has become a habit for many photographers to leave the battery being charged until the last minute they’re packing their bag to leave for an appointment. Indeed this practice is among the commendable habits of a reliable photographer.
Benjamin Rivera
However, this practice could also be the cause of many cases of overcharged and/or undercharged batteries. Charging overnight is not a guarantee to fully charge a battery (see our sample illustration, Picture Perfect, January 5, 2010 issue).
As we have already defined the battery charging key words such as Battery Capacity, Ampere/hour, Charge rate, Trickle charge, and Overcharged battery in previous issue, we will now continue our discussion on Battery Charging.
What is the correct procedure of charging NiMH batteries?
There are three known ways to charge Metal Hydride batteries. Each method has its own advantage and inherent disadvantage.
1) Overnight Charging - This is the cheapest way to charge a nickel metal hydride (NiMH) battery because the charger for this method is generally cheaper. Its method of charging is to apply small amount of charge current into the battery. It ranges around not more than one tenth of the mAH capacity of the battery. So, a 1000 mAH battery would be fully charged in 12 hours with an overnight charger of a charge current of 100 mA at 20 percent efficiency loss.
Matters of Concern in Overnight Charging:
The first thing to note when buying an overnight battery charger is the current capacity. Charging hours depend on the charging current rating and the battery capacity in mAH. Here is a guide for starters:
For 400 mA charger at 20 percent efficiency loss
(See table in our December 22, 2009 issue)
The charging hours of other battery capacity can be calculated manually based on the table above or log on to: http://www.csgnetwork.com/batterychgcalc.html for automatic charging hour calculation.
2) Fast Charging – In this method, charger delivers a very high current to the battery. The typical charge current is 100 percent of the battery capacity. This means that fast charging a single cell (of the type: 2400mA-hr AA) requires a current of about 2.4 amperes. Many of this type of chargers are called “intelligent chargers.” It can detect full-charge condition like the increased terminal voltage or the rise of temperature of the cell when fully charged. With this type of charger, you don’t have to worry about overcharging because it is mostly automatic. It stops the charging once full-charge condition is detected in the battery. There are a number of fast chargers in the market. These chargers, however, are expensive.
(See table in our December 22, 2009 issue)
The charging hours of other battery capacity can be calculated manually based on the table above or log on to: http://www.csgnetwork.com/batterychgcalc.html for automatic charging hour calculation.
2) Fast Charging – In this method, charger delivers a very high current to the battery. The typical charge current is 100 percent of the battery capacity. This means that fast charging a single cell (of the type: 2400mA-hr AA) requires a current of about 2.4 amperes. Many of this type of chargers are called “intelligent chargers.” It can detect full-charge condition like the increased terminal voltage or the rise of temperature of the cell when fully charged. With this type of charger, you don’t have to worry about overcharging because it is mostly automatic. It stops the charging once full-charge condition is detected in the battery. There are a number of fast chargers in the market. These chargers, however, are expensive.
(See table in our December 22, 2009 issue)
The charging hours of other battery capacity can be calculated manually based on the table above or log on to: http://www.csgnetwork.com/batterychgcalc.html for automatic charging hour calculation.
2) Fast Charging – In this method, charger delivers a very high current to the battery. The typical charge current is 100 percent of the battery capacity. This means that fast charging a single cell (of the type: 2400mA-hr AA) requires a current of about 2.4 amperes. Many of this type of chargers are called “intelligent chargers.” It can detect full-charge condition like the increased terminal voltage or the rise of temperature of the cell when fully charged. With this type of charger, you don’t have to worry about overcharging because it is mostly automatic. It stops the charging once full-charge condition is detected in the battery. There are a number of fast chargers in the market. These chargers, however, are expensive.
Matters of Concern in Fast Charging:
Pseudo-Fast Chargers (or Rapid Chargers) are also abound in the market. They call themselves Auto Fast Chargers because they can also charge in automatic shut-off fashion, like the fast chargers I mentioned above. But they are sold substantially cheaper than their real counterpart. However, as economics dictates, there is always something hidden from the buyers. These chargers indicate certain battery capacity to be charged.
Say for example, a 2000 mAH cell can be fully charged in 4 1/2 hours. In reality, this charger is a 400 mA unit equipped with timer that shuts down at pre-determined time. Many of these chargers are sold in pair with a set of AA batteries whose capacity is matched with the charger. The likely problems of these chargers are:
• If you do not notice that this charger is specified for 2000 mAH cell only and you happen to charge a 2500 mAH cell in it, you end up undercharged because this charger is timed to stop at 4.5 hours.
• If you charge a battery that still has, say 70 percent of its capacity when the timer starts, you would have a sure chance of overcharging the battery. This is somewhat risky. Overheating batteries emits noxious gasses and is a major fire hazard.
• To avoid this to happen is to have the battery fully discharged before charging. A battery that is discharged to 1 volt per cell has the advantage of eliminating any chance of battery memory.
3) Trickle Charging is a method used to recharge a battery for losses from self-discharge as well as to restore the energy discharged during intermittent use of the battery. The charging rate applied to the battery is almost equal to the rate of its self-discharging, thus maintaining the full capacity of battery.
As we have learned, rechargeable batteries, particularly nickel cadmium and metal hydride batteries gradually lose their charge even if they are not used. Trickle chargers work to keep the battery fully charged. A stored fully-charged battery is ideal for trickle-charging once a month or so for a day or two to keep its 100 percent power.
