Scotchmo
Member
If you put a resistor in series with the charge current as you have done, you reduce the available charge current all the time. That circuit might be correct if your are building a general purpose 7.2v power supply with an ample input source (such as an AC supplied transformer). When powered by the white wire, your circuit will charge the battery some, but I guarantee that the circuit posted in the first post of this thread will charge much faster. Using a 7.2v zener is OK. Anything between 6.8v and 7.2v will work well enough. If you use a 5w 7.2v zener, you could probably eliminate the resistor altogether. If you use the 6.8v zener, put the resistor in the circuit, but in series with the zener regulator, not the charge current. In either case, the resistor will prevent overheating of the zener if you blow your fuse.Btw
I've modified your circuit a bit - this is what I believe it should be...
The zener diode should be wired across the battery terminals, to limit the voltage at the battery to the zener voltage*. If the resistor is included in the portion that's wired across the battery, you're trying to drop the entire voltage out from the white wire (minus the .6 volt forward diode drop) across the battery terminals...
*I also believe that, in order to provide adequate charging voltage, you should increase the zener to 7.2 volts. (Nominal charging voltage for a 12V system is 14.4 volts... and a 6 volt system should charge at half that)
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