Ni-Cd battery deep discharge protection circuit

I have a LED lamp in my workshop which I supply from a recycled 12V 3Ah Ni-Cd battery. To protect the battery from a deep-discharge I built a simple circuit from what I found around. The circuit is built into the lamp and starts to beep when the supply voltage drops to 10V. The beep means that the battery has to be replaced.

The potentiometer PR has to be adjusted: Just set the desired voltage at which the circuit has to beep and then find a position of the PR at which the circuit starts to beep. The TL431 is a shunt voltage regulator and will pull down the pin 1 of the CD4093 when the voltage on its pin 1 is higher than 2.5V. One gate of the CD4093 forms an oscillator running at audible frequency. 3 unused gates have their inputs tied to GND. Piezzo is a of a passive type, it doesn't have built in generator.

The circuit has been built a piece of prototype PCB.

How much can DRL lights improve fuel consumption?

Lets say that DRL lights power consumption is about

P_DRL = 10[W].

Alternatively you can drive with “normal” lights on, that is: a front low beam + rear position lamps and registration plate lamps (in my case H7, R5W, W5W respectively)

P_NORM=2*55+2*5+2*5[W] = 130 [W],

we have omitted dashboard back-light but it shouldn't introduce too much error.

Volume of fuel V with energy density E_d needed to supply power P in time t is given by

where η_total is total efficiency.

Distance S is:

S = vt

where v is speed. We can also write:

lets insert t in the first fraction and we get:

Efficiency η_total is product of a engine efficiency η_engine, and a belt and alternator efficiency η_balt

If we want to calculate the volume fuel difference we should insert power difference into formula so:

Lets assume that belt and alternator efficiency is

η_balt = 50%.

In case of diesel engine

Ed = 37.3[MJ/ltr]

let also assume peek diesel engine efficiency

η_engine = 40%

The table shows fuel consumption at different speeds calculated according to presented assumptions calculated with formula (*)

In case of petroleum engine

Ed = 34.0[MJ/ltr]

and peek engine efficiency about

η_engine = 30%.

In real life we can expect much lower engine efficiency, depending on various conditions you can expect larger numbers, it is larger fuel savings.