On the specific energy density of Lithium Polymer (LiPo) batteries are superior to most other types of batteries. Rated output voltage they are also more: 3.7V against 1.2 … 2 others. But if necessary, replace the old 6-volt battery lithium-polymer having some problems. Voltage of one battery is too small, and battery voltage of the two LiPo batteries (with a nominal voltage of 7.4 V) may be too large.
For example, I bought on sale flashlight emitting 2 million candelas. The device gave out a powerful beam of light focused well, but his small lead-acid battery is discharged immediately. I decided to use a flashlight battery of two LiPo batteries for radio controlled model airplanes with a capacity 2800 mAh, which was developed scheme, which I propose for your consideration.
Shown in circuit converts the DC voltage LiPo battery range of 6.4V … 8.4V in the pulse voltage with a nominal rms 6.25 V, which feeds the 18-watt bulb for voltage and current of 6V 3 A. When the battery is coming to an end, and voltage on it decreases to 6.3 V input voltage switching stops and the battery is connected directly to the lamp. At a voltage of 6 V battery, to avoid deep discharge completely disconnected from the load.
The scheme is highly efficient and uses inexpensive, produced over the years component. It is important to note that the scheme is suitable only for power loads can operate on alternating current, such as lamps, relays, motors, and some types of small heaters. The output voltage of the circuit was not filtered or stabilized.
Further explanation: www.rlocman.ru