Tomberlin Tech
Edition: January/February 2012
Many times we have discussed batteries but not delved too much into the chargers. As Electric Vehicles (EV’s) become increasingly more accepted and the general public becomes more aware EV’s the topic of fast charging and types of charging have become increasingly more discussed as increasing numbers of charging stations are being installed around the world. Some ways charge batteries that are in the current discussion topics are:
Inductive charging –(not exactly new tech but people do assume it is with the new applications, Nikola Tesla demonstrated it in 1891) Inductive charging does not refer to the charging process of the battery itself. It refers to the design of the charger. Essentially the input side of charger, the part connected to the AC mains power, is constructed from a transformer which is split into two parts. The primary winding of the transformer is housed in a unit connected to the AC mains supply, while the secondary winding of the transformer is housed in the same sealed unit which contains the battery, along with the rest of the conventional charger electronics. This allows the battery to be charged without a physical connection to the mains and without exposing any contacts which could cause an electric shock to the user.
A high power example is a charging system used for EVs. Similar to the toothbrush in concept but on a larger scale, it is also a non-contact system. An induction coil in the electric vehicle picks up current from an induction coil in the floor of the garage and charges the vehicle overnight. To optimize system efficiency, the air gap between the static coil and the pickup coil can be reduced by lowering the pickup coil during charging and the vehicle must be precisely placed over the charging unit.
A similar system has been used for electric buses which pick up current from induction coils embedded beneath each bus stop thus enabling the range of the bus to be extended or conversely, smaller batteries can be specified for the same itinerary. One other advantage of this system is that if the battery charge is constantly topped up, the depth of discharge can be minimized and this leads to a longer cycle life. Battery Life, the cycle life increases exponentially as the depth of discharges are reduced.
One of the greatest advantages of this type is the ease of use. No hard wire connections are required. Just parking the vehicle over the charging station will start the charging process.
Constant-current Constant-voltage controlled
charge system. Used for charging Lithium batteries which are vulnerable to damage if the upper voltage limit is exceeded. Special precautions are needed to ensure the battery is fully charged while at the same time avoiding overcharging. For this reason it is recommended that the charging method switches to constant voltage before the cell voltage reaches its upper limit.
The charge voltage rises rapidly to the cell upper voltage limit and is subsequently maintained at that level. As the charge approaches completion the current decreases to a trickle charge. Cut off occurs when a predetermined minimum current point, which indicates a full charge, has been reached. Used for charging both Lithium and SLA batteries.
V- Taper controlledcharge system Similar to Voltage controlled system. Once a predetermined voltage has been reached the rapid charge current is progressively reduced by reducing the supply voltage then switched to trickle charge. Suitable for SLA batteries it allows higher charge level to be reached safely.
Charging systems will continue to advance as will battery technologies. It will be exciting to see what the future brings and has in store for us all.
