The original version of this device made up to 2008 can be fitted directly to the terminals of most Thunder Sky cells up to 200AH and may also be used with other lithium-ion cells if suitable connecting wires are bolted or soldered to the circuit board. The new version introduced in 2009 can either be mounted on the negative terminal of the cell with a flying lead to the positive terminal, or mounted remotely with wires to both cell terminals. 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 (earlier version) or through two resistors and two potentiometers in series (new version). On the earlier version 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. 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).

On the new version there are two trimmer potentiometers. One of them (controlling the minimum limit) may be adjusted so that the voltage between its wiper and the cell negative terminal will be 1.25V when the cell voltage is at any point between about 2.2V and 3.2V, and the other (controlling the maximum limit) may be adjusted so that the voltage between its wiper and the cell negative terminal will be 1.25V when the cell voltage is at any point between about 3.2V and 4.4V. In this way you can set the maximum and minimum limits to the specific requirements of any rechargeable lithium cell that is on the market at the time of writing of this description (Feb. 2009).

Method of adjustment: overvoltage limit (old and new type devices)

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.

Undervoltage limit (new type only; it is fixed on the old type)

Connect the laboratory power supply and voltmeter as above. Also connect a resistance meter between the Under V+ and Under V- terminals of the device. Adjust the power supply current limit between 50mA and 250mA, and adjust its voltage to the required minimum cell voltage. Turn the undervoltage adjustment trimmer potentiometer on the device until you find the point where the reading on the resistance meter changes between infinity and a low resistance.

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).

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 “IU”. If yours does not, you can get it altered to this by the Zivan agents (in the UK: Electrofit Zapi; 01952 582482).
(Unfortunately they are not willing to make the modification needed for charging the lithium cells.) It should also have a remote start-stop connection. For lithium-cobalt, lithium-manganese and lithium-polymer cells (3.6 to 3.8V nominal) the charger should have a nominal voltage of 24V for each seven lithium-ion cells in series, i.e. 24V for 7 cells, 48V for 14 cells, 72V for 21 cells. Also a 60V charger will charge 18 cells. For lithium-iron-phosphate cells (3.2 or 3.3V nominal) 8 cells may be regarded as equivalent to a 24V lead-acid battery.

It is necessary to identify the charger’s voltage trimmer potentiometer. On the K series (old model with metal case) this is the one identified as “gassif. Voltage” on the information leaflet supplied with the charger. On the NG series (new model with plastic case) it is not accessible or visible from outside; it is on the logic board, which is mounted at right-angles to the main circuit board near the output end of the charger. There are two trimmer potentiometers, marked “I” and “U”. The one marked “U” controls the voltage. It should be adjusted to a voltage of the set maximum cell voltage times the number of cells, or slightly higher. This can be done using a simulated load such as a 60W domestic light bulb in parallel with a large capacitor of suitable voltage rating.

It will probably be necessary to connect a battery in order to start the charger, then carefully disconnect it to make the adjustment. On the NG series this will have to be done with the case open, unless you drill a small hole in the case over the screw. While the charger is plugged in DO NOT TOUCH any metal part except the adjusting screw of the trimmer (which is insulated from the circuit) or the steel backplate (which is earthed). In particular, some of the heat sinks inside the charger are live at well above the mains voltage. After unplugging wait several minutes before doing any work on the charger because it contains capacitors which store high voltages.

The voltage trimmer potentiometer has three terminals, which are soldered to the printed circuit board. It is necessary to solder thin insulated flexible wires to the two of these terminals furthest from the adjusting screw. These are additional connections; the terminals remain connected to the circuit board as well. The wires should be different colours. Write down which goes to the middle terminal and which goes to the one furthest form the adjusting screw. These wires should be connected to a four-way socket, which you fit to the case of the charger. Take care to route them away from the fan and from anything they might chafe on. The other two terminals of the four-way socket should be connected to the remote start-stop connection of the charger, and the corresponding terminals of the plug, which plugs into the socket, should be connected together. (This ensures that the charger will not work if you have forgotten to plug in the charge/discharge controllers). If your vehicle has regenerative braking or other charging devices such as solar panels or a wind-turbine-driven generator, use a six-way socket and plug and leave two of the socket pins unconnected.

Fitting the charge/discharge controllers: first connect up all the cells, replacing the original terminal screws by lengths of studding and nuts if you are going to mount the devices on the cell terminals. The studding should project above the nuts far enough to accommodate the thickness of the circuit board and a second nut. Place the charge/discharge controllers over the studs, or wire each to its cell using a pair of wires TAKING CARE TO GET THE POLARITY CORRECT! (Incorrect polarity on the early type even for a moment will cause failure of the integrated circuit TLC272 and possibly also the two transistors; with a steady hand and a fine-tip soldering iron you could probably fit replacements. The new type has a “crowbar diode” and a “fuse track” on the circuit board adjacent to the terminal that is to be connected to the positive cell terminal; the electronic components should survive the device being connected wrong way round, but you will need to solder a fine strand of copper wire in place of the blown “fuse track”). Secure the devices to the cell terminals with further nuts. The L.E.D.s on the devices may flicker slightly as the devices are placed on the cells, but should not be lit when the nuts are tight. If one is lit it means either that the device’s maximum voltage limit is set lower than the current voltage of the cell or that the TLC272 and/or transistor controlling the over-voltage output has failed; see above warning about polarity.
The terminals “OVER V+” of all the charge/discharge controllers must be connected together. (The terminal blocks can be unplugged from the circuit boards, which makes wiring much easier especially if the battery is in a confined space). Similarly all the “OVER V-” terminals must be connected together, as must all the “UNDER V+” terminals and all the “UNDER V-” terminals.

Connect the OVER V+ and OVER V- terminals to the four or six-way plug, which plugs into the battery charger, ensuring the wires are long enough to reach the battery charger in the place where you normally put it when it is in use. The OVER V- terminals have to be connected to the pin which connects to the middle terminal of the Zivan charger’s voltage trimmer, and the OVER V+ terminals to the voltage trimmer terminal opposite to the adjusting screw.
Connect the terminal at the positive end of the battery and that at the negative end of the battery to the positive and negative terminals of the charger. Before switching the charger on, check the voltages of all the cells. If possible use an analogue voltmeter (one with a needle moving over a scale) whose calibration has been checked. Now switch on the charger, and again measure all the cell voltages. They should have risen slightly. If you use a digital voltmeter, note that some of these are badly affected by AC ripple or electrical noise generated by the charger and may give very inaccurate readings, but in some such cases you can get a sensible reading by taking an average of the readings with the meter connected one way round and the other way round. If there is still a problem, also try connecting a capacitor between the leads of the meter as close to the meter as possible.

During this first charge continue to check the cell voltages at frequent intervals. If possible also check the current using a clip-on Hall-effect meter. When the first cell reaches the maximum voltage that you have set, the L.E.D. on its charge/discharge controller should start to glow and the charging current should start to fall, with no further rise in the voltage of the cell. After some hours all the cells should be at the maximum set voltage and the current less than half an amp, with probably about half the L.E.D.s lit. It is quite likely that the L.E.D. which was first to light will go out as others come on.

If one or more L.E.D.s come on brightly and the voltages of the associated cells continue to rise by more than 0.01V (10 millivolts) without any drop in the charging current, there is a problem with the interconnection between the charger and the charge/discharge controllers; use a voltmeter to check the polarity of voltage present between the “OVER V+” and “OVER V-” terminals on the charge/discharge controllers. If the polarity is found to be incorrect, interchange the wires going to the charger from the “OVER V+” and “OVER V-” terminals. If the polarity is correct, or no voltage is present, stop charging and investigate.

Use with Solar Panels or with a simple Transformer-Rectifier Charger (may also be used with an electronically-controlled charger that has no accessible place to connect the cell controllers, or where the charger is under a guarantee that would be invalidated by connecting internally, or for charging from a DC generator or another battery of slightly higher voltage (“dump charging”)).

The voltage of solar panels used should be such that the maximum-power-point voltage of the panels is just below the fully-charged voltage of the lithium-ion battery, or higher but not much higher. Note that at very high temperatures (sun directly overhead in a tropical country) the voltage of solar panels will be 10 to 15% below the nominal voltage. Allow for this if relevant. We have found that a solar panel with nominal maximum power point at 17V will successfully charge four cells in series to 4.2V each with sun directly overhead and ambient temperature of 40-45 degrees C, but the current drops a bit as full charge is approached.
A transformer should have a nominal output voltage of about 70% of the fully-charged voltage of the battery, if rectification is by a full-wave bridge rectifier. You need also the following components:

• A MOSFET with a voltage rating higher than the fully-charged voltage of the battery and a current rating at least double the output of the power source to be used for charging. It must be mounted on a heat sink which can dissipate a wattage at least equal to the maximum charging current multiplied by about a quarter of the battery voltage. If you are in doubt about the adequacy of the heat sink, attach a thermal switch which closes above about 120 degrees C, and connect its contacts in parallel with “OVER V+” and “OVER V-”. Then if the device overheats the charging will be stopped until it cools.
• A diode, with voltage and current ratings as for the MOSFET.
• A 1-megohm resistor
• A Zener diode, rating approx. 12 Volts

Method of operation: the gate of the MOSFET is charged to 12V (controlled by the Zener diode) via the 1M resistor, keeping it turned on. When any cell of the battery reaches the set maximum voltage the over-voltage opto-isolator of its charge-discharge controller begins to conduct, shorting the gate charge of the MOSFET and hence turning it off (or causing it to introduce resistance into the circuit, reducing the charge current). Therefore no cell can be overcharged, and because the charge-discharge controllers can allow about 200mA to bypass their cells all cells will eventually reach full charge.

Connection to the Motor Controller in a Vehicle, Boat etc.

The charge/discharge controller has a second opto-isolator whose output is connected between the terminals “UNDER V+” and “UNDER V-”. This becomes conducting when the cell voltage falls below the set minimum voltage. (Below about 1.6V it ceases to conduct because the voltage becomes insufficient to work the device, but this situation will not arise in practice unless a cell is defective or an additional load is connected to the battery and not controlled by the charge-discharge controllers. A small additional load such as vehicle lights will not in practice cause problems, but it is very important that any such load should draw current from all cells equally. Lights which are connected to just some of the cells of the battery will overwhelm the charge/discharge controllers’ ability to equalise the cells, unless the charger is left on for an unreasonable length of time).

These under-voltage opto-isolators need to be connected to your vehicle’s controller in such a way that if any of them conduct electricity the effect will be to reduce the current demand. On a controller which has a two-wire 0 to 5k throttle this can be done by connecting them in parallel with the throttle potentiometer, and on some controllers such as the Curtis 1204,1205 and 1221 with 0-5k throttle this is the only way to do it. If you do it this way it is advisable to have also a micro-switch which short-circuits the throttle potentiometer when the throttle is released, otherwise there is a possibility that if the potentiometer fails the vehicle could continue to drive with the throttle released. Check the polarity of the voltage which the controller feeds to the throttle potentiometer, and connect positive to “UNDER V+” and negative to “UNDER V-” of the charge/discharge controllers (all of their outputs in parallel). On a Brusa MD series controller the “UNDER V-” terminals of the charge/discharge controllers can be connected to the “GND” terminal of the plug on the Brusa controller, and the “UNDER V+” terminals to the “RUT” terminal on the Brusa controller.

On a controller with a 3-wire potentiometer, interpose a resistor of 1 K (or more if it does not interfere with controller operation) between the potentiometer wiper and the controller, and connect “UNDER V+” to the wire between this resistor and the controller. Connect “UNDER V-” of all the charge/discharge controllers to the negative end of the potentiometer. In this way if any of the under voltage opto-isolators conducts it over-rides the throttle to reduce power. A controller with 0 to 5 volt or 0 to 10 volt two-wire throttle (using an externally-sourced voltage as the control signal) can also be wired in this way, placing the resistor in the 0-5 or 0-10v wire instead of the potentiometer wiper wire.

If the motor controller provides regenerative braking then it is also necessary to interconnect it with the over-voltage outputs of the charge/discharge controllers. The over-voltage outputs need to be disconnected from the battery charger when they are connected to the motor controller, so the connection will need to be via a plug and socket (or a multi-pole changeover switch if the battery charger is permanently installed in the vehicle). The plug connected to the charge/discharge controllers should have two additional pins connected by a loop of wire (as mentioned earlier in connection with the Zivan battery charger) and the socket connected to the motor controller should have the corresponding terminals connected in series with the key switch input or brakeswitch input, so that the vehicle will not drive if the charge/discharge controllers are not plugged in.

On a Brusa MD-series controller with regeneration via a double-pole changeover contactor, connect the “OVER V –” terminals of the charge/discharge controllers to “GND” on the Brusa controller, and the “OVER V+” terminals to either “POT” or “RUU”.

On a regenerating controller with 3 wire throttle potentiometer (the 4QD controllers for example) you will already have put a resistor in the potentiometer wiper lead in connection with under voltage connection. Connect “OVER V-” of the charge/discharge controllers to the wire between this resistor and the controller. Connect “OVER V+” to the wire to the positive (FULL speed) end of the potentiometer. In this way if any cell reaches maximum voltage the throttle setting will increase, reducing the deceleration and hence the current into the battery. We wish to re-emphasise the importance of ensuring that the motor controller cannot operate during battery charging, otherwise the vehicle might drive away by itself as the battery approaches full charge.

Terms and Conditions

These devices are specially made for Stybrook Ltd, the UK subsidiary of Agni Motors

Stybrook Ltd is not connected with, or endorsed by, any battery manufacturer. 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”.

Stybrook Ltd will repair or replace free of charge a charge/discharge controller which is defective in materials or workmanship. This guarantee is an addition to your statutory rights.

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).

Click here to see a diagram of the lithium cell controller connections