Build your own torch     circuits



The torch (unproven)




The charger (unproven)



The transformer, bridge rectifier and capacitor are part of the original mains adaptor. The original regulator IC and any support components should be removed
The regulator LM317 UF27E, and the resistors are available from Maplins


Charging Current:

R1 should be selected according to the required charging current:

   For 9Ah cells, ideal charge = 0.9A, ideal R1 = 1.25/0.9 = 1.4ohms, available = 2.2 // 3.9 = 1.4, actual charging current = 0.9A

   For 7Ah cells, ideal charge = 0.7A, ideal R1 = 1.25/0.7 = 1.8ohms, available = 3.3 // 3.9 = 1.8, actual charging current = 0.7A

   For 4Ah cells, ideal charge = 0.4A, ideal R1 = 1.25/0.4 = 3.1ohms, available = 10  // 4.7 = 3.2, actual charging current = 0.39A

   etc.


Charging Times:

The required charging time can be estimated as follows:

   Using a fully charged 12V, 9Ah battery to run a 50W lamp for 30 minutes and then recharging at 0.9A as calculated above

   50W / 12V = 4.2A, for 30 mins = 2.1Ah discharged from battery

   2.1Ah / 0.9 = 2.3 hours, at an approx. charging efficiency of 66% = 2.3 / 0.66 = 3.5 hours, round up to 4 hours charging time to ensure a full charge

   For this specific system: Re-Charging Time = approximately 8 x use time