Lithium-ion Cell Controller

Lithium-ion Cell Controller

Lithium-ion Cell Charge, Discharge & Balancing Controller

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18,98 € tax incl.

Model 1b


65 items in stock

This single unit BMS device can be fitted directly to the terminals of most Thunder Sky & Kokam cells up to 200AH and may also be used with other lithium-ion cells. One controller is needed for each battery cell. Over-& Under Voltage levels are set by a trim potentiometer.


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. The values of the resistor and potentiometer 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 2.8V (plus or minus about 0.15V), which is the lowest voltage at which the original Thunder Sky cells 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 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.


Method of adjustment: overvoltage limit

Set the voltage of the laboratory power supply to about 5 volts, and the current limit very low. Connect the laboratory power supply and also an accurate voltmeter to the terminals of the cell controller that are to be connected to the positive and negative terminals of the lithium cell. Turn up the power supply current limit to 250mA (no higher), or until the LED on the device comes on (not very brightly). Turn the overvoltage adjustment trimmer potentiometer on the device until the voltage shown on the voltmeter is the required maximum cell voltage.


How the device works:

There is a dual operational amplifier, which compares the two voltages taken from the resistor and trimmer potentiometer series with the 1.25V reference. When the cell reaches the set maximum voltage 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 the set minimum voltage, 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 the set minimum voltage. Some older 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. Most current cells have very low internal resistance except in extreme cold.

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).


Terms and Conditions

The charge/discharge controllers have been individually tested and will, when correctly installed, keep the cells of a battery within the voltage limits to which the devices have been adjusted. It is the responsibility of the customer to ensure correct installation (and adjustment of the devices to voltage limits that are suitable for the customer’s cells) and also to check for correct operation of the system (warning: some voltmeters, even ones with digital displays having two or three digits after the decimal point, are very inaccurate and some others are inaccurate in the presence of electrical noise such as may be caused by high-frequency battery charger).

The charge/discharge controllers are not C.E. marked for electromagnetic compatibility because they are components, rather than a complete system in themselves. They do not do anything likely to generate radio interference. Current production devices conform to the “Restriction of Hazardous Substances Regulations”.


We will not be liable for consequential losses (customers should check that their systems are working correctly) or for devices which have been damaged by the customer (for example by incorrect connection) or by a defect in the cell to which the device was fitted. (A cell which becomes open circuit may cause failure of its charge/discharge controller by causing a reversed voltage to be applied to it when an attempt is made to take current from the battery).

These charge/discharge controllers are not suitable for use with a motor controller which has a two-wire throttle input on which the resistance has to be decreased to obtain increased speed, or which requires a voltage input other than one which can be obtained directly from another terminal on the controller in order to give zero output. (Some unsuitable controllers can be modified or reprogrammed so that they become suitable; contact the makers of the controller).



Over V+;  optocoupler output signal for over voltage, positive

Over V-;   optocoupler output signal for over voltage, negative


Under V+; optocoupler output signal for under voltage, positive

Under V-;  optocoupler output signal for under voltage, negative


Only 2 wires (black & red) are connected to the positive & negative terminal of the battery.

All Over & Under Voltage signals are daisy chained through a 4-wire flat cable. For each cell controller there's a connector on the flat cable.




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