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Figure 1 shows the minimum way of getting power to your rig. Hey, you don't even need the switch. Just rip the battery out of your car, hook it up to your radio, and Go!  | ||||
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Figure 2 is probably the most efficient and economically feasible. You could use either a smart charger combined with a lead/acid deep cycle battery or gel cell's. You could substitute the smart charger with a solar cell and a similar smart charging device. In either case, an automated emergency power back-up circuit is an easy project to implement. This type of circuit offers the most effective means of power transfer.  | |||||
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Figure 3 is less efficient, but is still economically feasible. As, above, you could use either a smart charger combined with a lead/acid deep cycle battery or gel cell's. You can also substitute the smart charger with a solar cell and a similar smart charging device. This type of circuit has some drawbacks. You should only use Shottky (low PN junction voltage) diodes. A normal diode has a 0.6 volt drop across itself when forward conducted. At high amperage, the voltage drop across the diode multiplied by the current can result in some outrageous heat values (I*E=P, watts, that is...). Let's explore a simple example, You buy some heavy-duty 40 Ampere Shottky diodes at a hamfest. They have a voltage drop rating of 0.28 volts. Sounds good? Let's draw 20 Amps across it. Figure the wattage across the device (0.28 volts X 20 Amps) and you find that the diode itself is a heater that will dissipate 5.6 instantaneous watts of power. That power will have to be dissipated through a heat sink (and possibly a fan), just to keep the device from destroying itself. How do you size the heat sink? What about the fan? Please send your comments and queries to: KB8WOW  |