In the Realm of EV Battery Chargers, What is a ‘Smart’ Charger? (III)
Posted on Aug 12, 2014
Trucks, busses and higher performance vehicles benefit from higher capacity and higher voltage battery packs – from 600, 750, and even up to 900VDC. The ability to put two chargers in series to provide charging at increased system voltage is extremely valuable. The smart BC series chargers can also do this, with some simple setup features guided by a GUI provided. A pair of chargers in series gives up to 900VDC at 6kW – and additional pairs of seriesed pairs can be placed in parallel with the first providing 6kW more per pair added. A typical truck 100kW 600VDC battery pack can be charged in eight hours with two such seriesed pairs (four chargers).
Another feature to be aware of in a smart charger is its ability to be used with conventional battery systems, such as flooded lead acid, sealed or gelled electrolyte, or AGM types of batteries. For these applications, stage mode or automatic mode of charging, without the input from a BMS system is needed. Programmable battery stages for bulk, absorption, equalization and float conditions are possible, again using the smart GUI provided. Stage transition trip point parameters such as voltage, current, and time in stage allow programming of a complex battery charge curve suited to the unique needs of each pack.
The real world is full of faults, and electric vehicles are no exception. Operational faults occur due to noise, component variations, operational conditions, AC line dropouts or brownouts. The ability to report and recover from these faults during a charge cycle is an important function of a smart charger. As well as fault handling and reporting, the BC series smart charger also performs a self-recovery function; every so often, in programmable amount of time from the fault (typically from two to 30 minutes), the charger performs a reset and restart function. If the condition that caused the fault has been cleared, the charger resumes charging. This prevents the ‘charging nightmare’ of a minor fault occurring during an overnight charge cycle and the operator returning to a discharged vehicle!
As with all endeavors, improvements in features or functions are noticed as experience grows with a product. After some field experience, it was noted that another integrated smart feature would be desirable so a charge time drive off inhibit signal device was developed.
This device is provided as an easily integrated external module for the 3kW charger family, but will be fully integrated into CurrentWay’s upcoming 6.6kW charger family. The device provides a 12V signal whenever a J1772 charge coupler is connected to the vehicle – if the EVSE is powered AC on or not. This signal allows the vehicle command system to recognize that a tether is attached to the vehicle and the drive inverters can be disabled. No doubt, a number of charging cables will be saved.
By Ken Wing, Director of Engineering, CurrentWays Inc