From Cedric's site at
http://agnimotors.com/home/index.php?op ... &Itemid=39
I am sure he won't mind me posting it.
[quote]
Lithium-ion Cell Charge and Discharge Controller
Lithium-ion cell charge and discharge controller to fit Thunder Sky 50 AH, 100 AH and 200 AH cells. (May also be used with other lithium-ion cells if suitable connecting wires are bolted or soldered to the circuit board). One controller is needed for each cell in the battery.
Principle of operation: the device draws a current of about 100 micro-amps from the cell and passes it through a 1.25V precision reference diode. This gives a reference of 1.25 volts against which other voltages can be compared. A very small current is also passed through a resistor and a potentiometer in series. Their values are such that the voltage of the junction between them will be 1.25V in relation to the cell negative terminal when the cell voltage is about 2.95V (plus or minus about 0.15V), which is the lowest voltage at which the cell should be discharged.
The trimmer potentiometer is adjusted so that the voltage between its wiper and the cell’s negative terminal will be 1.25V when the cell voltage is 4.25V, the highest voltage to which it should be charged. (With the aid of an accurate voltmeter and a laboratory D.C. power supply this voltage can be adjusted precisely. Warning: The fact that a voltmeter has a digital display with two digits after the decimal point does not necessarily mean that it is accurate. Some such meters are wrong by 10 per cent. It is the user’s responsibility to ensure the accuracy of equipment used in making any re-adjustment).
There is a dual operational amplifier, which compares the voltage taken from the resistor and trimmer potentiometer with the 1.25V reference. When the cell reaches 4.2V the amplifier starts to turn on a transistor, which passes current through a 15-ohm resistor, thereby loading that cell by up to about 250 milliamps. When the voltage across this resistor reaches about 3V the current starts to flow also through a light-emitting diode and the input of an opto-isolator. The output of this opto-isolator must be connected in parallel with the outputs on the devices on all the other cells, and also to the battery charger or to a device which can control its charging current in such a way that the charging voltage is reduced if any of the opto-isolator outputs are conducting. If the vehicle has regenerative braking, the opto-isolator outputs must also be connected to the motor controller so that if any of them are conducting the brake current will be reduced (to zero if necessary, for example if the vehicle is driven down a hill with fully charged battery). In this way the cell controllers prevent any cell from being overcharged, and they also work towards equalising the state of charge of all the cells during the later part of a charge.
When the voltage of a cell falls to 2.95V, the amplifier turns on another transistor, which passes current through a second opto-isolator. These under-voltage opto-isolators must also have their outputs in parallel, and they must be connected to the motor controller in such a way that if any of them are conducting they reduce the current demand, to zero if necessary (when the battery is flat). This arrangement does not do anything to equalise cell voltages during discharge, but it ensures that during discharge the weakest cell of the battery cannot be taken below about 2.95V. Lithium-ion cells have a high internal resistance at low temperatures, so in cold weather the under-voltage protection is likely to be limiting power even when the battery is nearly fully charged. The performance may improve during discharge as the battery warms up. The battery’s resistance at a given temperature increases as it is discharged, so if it is allowed to cool to freezing temperatures when it is not fully charged its performance will be very poor until it is charged and/or warmed up. Also it will take a long time to charge fully at low temperatures.
The battery should be assembled and installed so that it is likely that all the cells will be at about the same temperature. It is advisable to make provision for thermal insulation, but with ventilation possible in hot weather. Do not install the battery so that some cells are inside a closed compartment and others in a draught or exposed to spray from the wheels! If you do, the performance of the entire battery will be limited to that of the coldest cell. The cell charge/discharge controllers must be completely protected from water, particularly spray (which could have salt in it),otherwise they could be damaged and/or fail to control the voltage correctly. If there is a tendency for condensation to form on them they should be sprayed with water repellent (Duck Oil, WD-40 or similar).
Use with a Zivan Electronic Battery Charger
(K series or NG series).
(The charger has to be modified in a way that will invalidate its guarantee)
The charger must have the charging curve “IUâ€Â
you got yours I presume at a bit of a discount how much would it cost for band new ones ??
