Economic Battery Sufficiency Tester by BC547

Description: 

Battery level indicators generally detect for the voltage levels of the batteries to give a result. So, tester circuits must not be a heavy load during the measurement process. This tester circuit draws very low current. A short duration of LED bright will show you the battery has still enough voltage level to operate devices. This light brights due to the discharging of C1 on D1 LED, this happens only when the battery provides enough voltage.

When you close the S1 switch, Tr1 transistor makes C1 to discharge through R3 current limiter. Minimum required battery voltage level can be determined by using voltage divider R1/R2. Values of R2 and R3 must be calculated as shown below;

R2 = (0.6 x R1) / (Vbmin - 0.6) Ohm and  R3 = (Vb - 1.4) / 0.2 ohm

For example, for 6.5Vb(min) value (to test a 9V battery) R2 must be 10k and R3 must be 39 ohm. R4 must be between 10k and 1M.

For higher values of R4, circuit becomes more economic but this causes lenghten the test period. When R4 is 100k, battery can be tested after about 10 seconds. 

2-7V / 6-8A Power Supply by 723 and 7812

Description: 

In this 2-7V power supply circuit, for our purpose, we chose IC 723 instead of a three pin voltage regulator for-why we find it protean and more advantageous in technical details.

Notes: 

Heatsinks of Tr2 and Tr3 transistors must be sufficiently large.

To archive R4,R5 and R6 values, we used some suitable resistors in parallel. For R4 and R5 two parallel connected 0.3ohm/5W resistors for each are used. To take 6A output, we connected two 0.22ohm/5W resistors in parallel, and to take 8A output we connected three 0.33ohm/5W resistors in parallel instead of R6 resistor. 

If you change the marked component values properly you can get up to 14V output. For this situation you must disconnect R1,R2,C5,C6,C1,C2,D1,D2  components and connect the positive terminal of D3 directly to the rectified and stabilized supply....