The post narrates an SCR based automatic Battery Bank charger circuit with an automatic over charge cut-off feature for operating with an electric car. The idea was requested by Mr. George.
Circuit Objectives and Requirements
- I'm George From Australia trying to convert small car into an electric car.
- The attached PDF show the configuration of lithium battery modules that make the full pack.
- Could be possible for you to suggest what sort of battery charger or configuration can I use too charge the pack.
- I have available 240 Volts or 415 Volts AC.
Battery Wiring Details
The above figure shows the Li-ion battery configuration arranged in series, parallel mode to generate a massive 210V at 80 Amps approximately.
To charge this relatively huge battery set up we need a controller which is able to control current as well as provide the required amount of volts to the pack for charging them efficiently.
The 240V AC source looks more appropriate, so this source could be used as the input for the mentioned purpose.
The next diagram shows the proposed 220V Li-ion Battery Module charger circuit, let's understand its functioning in detail with the following explanation:
The design is quite similar to one of the previous concepts regarding a high voltage battery charger circuit, except the relay section which is replaced with an SCR here, and the inclusion of a high voltage dropping capacitor for an added safety.
The mains high current is suitably dropped by the reactance of the 100uF/400V non-polar capacitor to around 5amps which is applied to the battery bank via the indicated SCR. This current can be increased to higher level by simply increasing the capacitance values of the shown 100uF/400V cap.
The thyristor or the SCR which is used as a switch in this design is held in the switched ON position as long as the associated BC547 at its gate is held switched OFF.
The BC547 base can be seen connected with an opamp output which is configured as a comparator.
As long as the output of the opamp is kept low the BC547 stays switched OFF, keeping the thyristor switched ON.
The above situation continuous to be in the activated state as long as the preset voltage level of the sensing input pin#3 of the IC remains below the reference level of the pin#2 of the IC.
Since pin#3 is hooked up to the battery positive (via a resistive network), it implies that the 10K preset at pin#3 is supposed to be adjusted such that at the full charge level of the battery the potential at pin#3 just surpasses the reference fixed potential at pin#2.
As soon as this happens the opamp output pin#6 instantly reverts its output from the initial logic low to a logic high, which consequently switches ON the BC547 and switches OFF the triac.
The battery charging is immediately stopped at this point.
Function of Hysteresis Resistor
The hysteresis resistor Rx connected across pin#6 and pin#3 of the IC makes sure that the opamp latches ON in this position at least for sometime until the battery voltage has discharged to some predetermined lower threshold level.
At this unsafe lower level the opamp yet again goes through a changeover and initiates the charging process by triggering a logic low at its output pin#6.
The difference between the full charge cut-off voltage and the low charge restoration voltage is proportional to the value of Rx, which could be found with some trial and error. Higher values will result in lower differences and vice versa
The potential divider network made by the indicated 220K and the 15K resistors ensures the required lower proportionately dropped voltage for the opamp pin#3, which should be not above the operating voltage of the opamp.
The operating supply voltage for the opamp at its pin#7 is acquired through a BJT emitter follower configuration connected across one of the end batteries associated wit the negative line of the battery pack.
For further queries regarding this 220V Li-Ion Battery bank charger circuit please feel free to usdethe comment box below.
DANGER: THE DESIGN EXPLAINED ABOVE IS NOT ISOLATED FROM THE AC MAINS LINE, THEREFORE IS EXTREMELY DANGEROUS TO TOUCH IN SWITCHED ON POSITION. PROCEED WITH CAUTION.