System and method for connecting a first battery in parallel with a second battery by discharging for equalization

Abstract

Disclosed is a battery and load equalization circuit that prevents the in-rush of current when batteries and/or loads are initially connected in parallel. Various techniques are used including charging, discharging and use of DC to DC converters to equalize charges between batteries and between batteries and capacitive loads.

What is claimed is: 
     
         1 . A discharging system for safely connecting a first battery in parallel with a second battery comprising:
 a controller in communication with a first battery to detect a first terminal voltage, the controller in communication with a second battery to detect a second terminal voltage;   a first discharging load for temporary connection to the first battery, the first discharging load activated by the controller;   a second discharging load for temporary connection to the second battery, the second discharging load activated by the controller;   a switch operable to connect the first battery and the second battery in parallel, the switch activated by the controller;   wherein in a first instance the controller activating the first discharging load to discharge the first battery to a first voltage when the first terminal voltage is greater than the second terminal voltage, and in a second instance the controller activating the discharging load to discharge the second battery to a second voltage when the second terminal voltage is greater than the first terminal voltage, the controller activating the switch when the first voltage and the second voltage are sufficiently dose to permit parallel connection of the first battery to the second battery without a damaging current flowing there between.   
     
     
         2 . The discharging system of  claim 1 , wherein the controller activates the switch when the first voltage and the second voltage are essentially equal. 
     
     
         3 . The discharging system of  claim 1 , wherein an initial current between the parallel connected first battery and the second battery is essentially zero. 
     
     
         4 . The discharging system of  claim 1 , wherein the first discharging load and the second discharging load are both activated by the controller to discharge the first battery and the second battery to about an equal third voltage. 
     
     
         5 . The discharging system of  claim 1 , wherein the controller generates a first control signal to activate the first discharging load, generates a second control signal to activate the second discharging load, and a third control signal to activate the switch to connect the first battery and the second battery in parallel. 
     
     
         6 . The discharging system of  claim 1 , wherein a first switch temporarily connects the first discharging load to the first battery and a second switch temporarily connects the second discharging load to the second battery. 
     
     
         7 . The discharging system of  claim 1 , wherein the first discharging load is a first discharging resistor and the second discharging load is a second discharging resistor. 
     
     
         8 . The discharging system of  claim 1 , wherein the second discharging load is the first discharging load. 
     
     
         9 . The discharging system of  claim 1 , wherein the first discharging load and second discharging load are disconnected upon equalization. 
     
     
         10 . A discharging system for safely connecting a first battery in parallel with a second battery comprising:
 a controller that detects a first terminal voltage of terminals of a first battery, and a second terminal voltage of terminals of a second battery;   a first discharging load activated by the controller to discharge the first battery to a first voltage when the first terminal voltage is greater than the second terminal voltage;   a second discharging load activated by the controller to discharge the second battery to a second voltage when the second terminal voltage is greater than the first terminal voltage;   a switch activated by the controller when the first voltage and the second voltage are sufficiently dose to permit parallel connection of the first battery to the second battery without a damaging current flowing there between.   
     
     
         11 . The discharging system of  claim 10 , wherein the controller activates the switch when the first voltage and the second voltage are essentially equal. 
     
     
         12 . The discharging system of  claim 10 , wherein an initial current between the parallel connected first battery and the second battery is essentially zero. 
     
     
         13 . The discharging system of  claim 10 , wherein the first discharging load and the second discharging load are both activated by the controller to discharge the first battery and the second battery to about an equal third voltage. 
     
     
         14 . The discharging system of  claim 10 , wherein the controller generates a first control signal to activate the first discharging load, generates a second control signal to activate the second discharging load, and a third control signal to activate the switch to connect the first battery and the second battery in parallel. 
     
     
         15 . The discharging system of  claim 10 , wherein a first switch temporarily connects the first discharging load to the first battery and a second switch temporarily connects the second discharger to the second battery. 
     
     
         16 . The discharging system of  claim 10 , wherein the first discharging load is a first discharging resistor and the second discharging load is a second discharging resistor. 
     
     
         17 . The discharging system of  claim 10 , wherein the second discharging load is the first discharging load. 
     
     
         18 . The discharging system of  claim 10 , wherein the first discharging load and second discharging load are disconnected upon equalization. 
     
     
         19 . A method for discharging for safely connecting a first battery in parallel with a second battery comprising:
 providing a controller in communication with a first battery to detect a first terminal voltage, the controller in communication with a second battery to detect a second terminal voltage;   providing a first discharging load for temporary connection to the first battery, the first discharging load activated by the controller;   providing a second discharging load for temporary connection to the second battery, the second discharging load activated by the controller;   providing a switch operable to connect the first battery and the second battery in parallel, the switch activated by the controller;   detecting the first terminal voltage and the second terminal voltage, wherein in a first instance the controller activating the first discharging load to discharge the first battery to a first voltage when the first terminal voltage is greater than the second terminal voltage, and in a second instance the controller activating the second discharging load to discharge the second battery to a second voltage when the second terminal voltage is greater than the first terminal voltage, the controller activating the switch when the first voltage and the second voltage are sufficiently close to permit parallel connection of the first battery to the second battery without a damaging current flowing there between.   
     
     
         20 . The method of  claim 19 , wherein the controller activates the switch when the first voltage and the second voltage are essentially equal. 
     
     
         21 . The method of  claim 19 , wherein an initial current between the parallel connected first battery and the second battery is essentially zero. 
     
     
         22 . The method of  claim 19 , wherein the first discharging load and the second discharging load are both activated by the controller to discharge the first battery and the second battery to about an equal third voltage. 
     
     
         23 . The method of  claim 19 , wherein the controller generates a first control signal to activate the first discharging load, generates a second control signal to activate the second discharging load, and a third control signal to activate the switch to connect the first battery and the second battery in parallel. 
     
     
         24 . The method of  claim 19 , wherein a first switch temporarily connects the first discharging load to the first battery and a second switch temporarily connects the second discharging load to the second battery. 
     
     
         25 . The method of  claim 19 , wherein the first discharging load is a first discharging resistor and the second discharging load is a second discharging resistor. 
     
     
         26 . The method of  claim 19 , wherein the second discharging load is the first discharging load. 
     
     
         27 . The method of  claim 19 , wherein the first discharging load and second discharging load are disconnected upon equalization.