Battery Chargers

The recent trend towards use of portable devices has resulted in very power efficient design, allowing the portable devices to run longer off batteries.  Unfortunately much less attention has been devoted to how the batteries are charged.

Statistics indicate that in many cases it takes 6 to 20 times more energy to charge the batteries than the energy that can be retrieved from them, resulting in a system efficiency somewhere around 6 to 20% for AA battery chargers and cell phones. 

Another source of problem occurs when the charger is in standby or idle mode.  Standby mode is when the charger is plugged in but the batteries are not in the charger.  An example would be when a portable phone is left off the base but not being used to make a call. 

Idle mode is when the batteries are fully charged but still on the charger.  In idle or standby mode, a typical battery charger consumes 3 Watts, sometimes 7 Watts or more for less efficient chargers.  This does not sound like a lot of power but consider how many portable devices you have in your home and then multiply by all the homes across the country or world.

The reason for the standby/idle power consumption usually has to do with the AC/DC adapter.  They are designed for maximum efficiency at a specific load.   When the load drops to near zero (batteries fully charged) then the power supply becomes inefficient.

When you buy a portable device you should not necessarily buy the cheapest product.  It will likely be very inefficient at battery charging.  Buy devices with more sophisticated charging capability and if possible find out what power is consumed in standby and idle modes.

Steve Auger