Re: radar battery drain
OK, easy enough, first your direct answer and then come comments. If you have a 40W draw and a normal system voltage of 12.4 volts the draw is 3.2 amps per hour, obviously on standby its half that. Standby in the case of Radar means that it is simply turned on but the antenna is neither turning or sending out signals, although the 'magnatron' is turned on and heated up.<br /><br />The information you gave on the batterys has no meaning, but we'll go ahead and assume they are some sort of standard sized starting batterys, most of which have a capactiy of about 80 amp hours total. Just about any battery can be considered to be stone dead by the time it has been discharged by half of its capacity, so you have at a maximum 40 amps to work with. That makes is simple, 40 amps divided by 3.2 amps draw gives you 12.5 hours until one of your battery is stone cold dead. Actually what would happen is that somewhere around the 12 hour mark your radar would probably shut itself off for lack of voltage.<br /><br />This assumes that you have good, new, fully charged battery to start with, which is rarely the case.<br /><br />Now some comments. First off if you haven't bought that radar yet, don't. There are better radars around for the money. The second thing is that there are few times when you would be running a radar full time while the boat wasn't running. Its nice to know when something enters your 'guard zone' but in truth radar is primarily a tool of collison avoidance and if you aren't moving you are already doing your part towards avoiding collisions. Maritime law makes a point of holding everyone responsible in the event of a collision but in fact if you are not under way and making way its sort of hard to pin a bangup on you. The next thing that sort of jumped out at me is that you apparently have twin engines and two batterys. Let me suggest to you that you might want to go to a 3 or 4 battery system, and of course to use the largest battery you can fit in your storage area.<br /><br />Thom
