Translation from article in the FUNKAMATEUR (the German ham radio magazin)
number 7 (1991) page 408
For the occasional use of a mobile telephone in the passenger car the
acquisition of an installation period is not worthwhile itself. It is recommended the
current supply from the socket of the cigarette lighter. In addition there is a suitable
cable with integrated battery charger or voltage regulator to each mobilefone.
In the practical use it turned out that the attached mobilefone reacts sensitively to short voltage drops, i.e. after each starting the engine it switches and requires for it input the pin - number off. Above all, if one " drives " in the back-up is one nerve-ends to thing.
A modification of the battery charger of an unknown manufacturer separated, because no documents were available. Instead the circuit represented in fig. (1) was switched directly before the battery charger. The rfc is to suppress malfunctions from the electric motorcar equipment. The diode prevents a current reversal when breaking down the electrical system and the polarized electrolytic capacitor buffers the voltage for electronics downstream.
The value of the polarized electrolytic capacitor was determined experimentally and is about 10000 µf.
The circuit was built together with the battery charger into a housing, which is larger only around the mass of the polarized electrolytic capacitor; the diode and the rfc fit still piggiback on the printed circuit board. The smallest polarized electrolytic capacitor of this capacity, which was available, had the length of 32 mm (1.25.inch) and a diameter of 22 mm (0.9 inch). In such a way becomes the modified device only imperceptibly more largely than the original. In the indicated sizing it comes to no more failures. The principle of this circuit can be transferred also to other devices, which are to be operated in the vehicle at the on-board voltage.
