Motorcycle batteries are normally a lot smaller with their sizes and ratings compared to the vehicle and the usage. The main use of the battery present in mo-bikes is for enabling electronic start through a press of the given start button.
However this small sized battery also has to undergo further stresses while operating excess loads such as the horn, the indicator lights, the tail light and the brake light.
Even though the above loads mostly tend to depend on the motorcycles battery power, these do not affect the battery charge level significantly.
The one that truly affects the battery is the motorcycle headlamp, which when switched ON starts drawing huge current via the alternator and the battery in a shared manner. This the reason why we normally see the headlight intensity vary with varying mo-bike speeds.
At higher speeds the alternator shares the load to fair extents, but in cases when the vehicle is not moving or is idling in the neutral mode, the lamp starts consuming substantial amount of battery power, depleting it's charge to dangerous lower levels, and this may happen within minutes if not switched OFF.
The proposed circuit of motorcycle headlamp battery discharge protector circuit is intended exactly to tackle this issue automatically.
It's nothing complicated, it's a simple low battery cut-off circuit set to switch of the link between the battery and the headlamp whenever the battery level falls below some set predetermined level.
The circuit may be understood as follows:
The opamp 741 IC is configured as a comparator here.
It's pin#3 is referenced at a fix voltage determined by the connected zener voltage. Pin#2 of the IC executes the function of the sensing input and keeps the output of the opamp pin#6 low as long as its potential stays above the reference value of pin#3.
The above condition is held in position as long as the battery voltage is above the set safe threshold level, which in turn keeps the output pin#6 at a low logic level.
The low at pin#6 ensures that the p-mosfet is allowed to conduct and illuminate the attached headlamp.
Therefore the headlamp is allowed to receive the required power through the mosfet as long as battery voltage continues to be above the safe threshold.
Now suppose the battery level begins falling beow the set level, this would mean pin#2 potential going down below the reference level at pin#3, or in other words pin#3 reference getting higher than pin#2 potential.
The above situation instantly prompts the output of the opamp pin#6 to pull at the supply level or at a high logic.
A high at pin#6 means the mosfet is now inhibited from conduction, switching off the headlamp.
The above situation continues in a flip flop manner until the battery voltage is no longer able to rise above the safe threshold when the lamp is permanently switched Off.