Thread: tank charge advice

I came up with a way to charge my tank battery only when the car is running and the key is on using a 13 v zener diode and some mosfet's

this circuit could also charge the tank battery only when the car is running with out connecting the ing wire to the ing switch the ing wire would need to be connected to the main battery input

the advantage of this design is that even with only 13.2 v being supplied by the altanator the tank battery would alwase be charged to full

voltage regulators and battery charge management circuits require at least
14v or more to fully charge a 12v battery unless the main battery is compleatly dead the altanator will not output more that 13.8v this resualts in the tank battery not charging fully and possably cause it to fail to keep the PC running during engine starting. This is why I have designed this circuit to over come this problem

The only problem I have with this new design is that there is no short circuit protection or current limiting I would be very gratefull if anyone could give me advice on incorperating these features in to my design the link below is a schmatic of my circuit
thanks