Battery switches

[wgkenney]

You wouldn't turn one OFF before turning the other one ON, as it may blow a diode in the alt. You wouldn't do it if one battery was severly drained, but if they are close in charge state, not a problem and you can have both on to charge both. I usually start the engine in the slip with the start battery to make sure it works, then by the time i get to the sailing grounds it has replaced the used amps. After raising sails and shutting off the engine i turn on the house then off the start batt so the house charges when returning. This way i know all batts function as they should.

Got it. I misunderstood.

 

[Mal]

Great discussion. Ron, I like your technique but need a simpler way of doing it.

I have just started sailing a 39.3 and have been having a devil of a time getting my head around the electrical system. When I got to the boat, one of the 4D house batteries was dry and the start battery was dry. The other house battery was wet but dead. I was able to rejuvenate one house and sail with it and a hot shot box. I only sail this combo if I am comfortable with the winds being suitable for sailing to the slip.

I am gradually coming to like the three switches (4 with the inverter) in the system. The only real problem I see so far is human error. If the batteries are paralleled for charging, one bad battery can take out the whole system. Further if they are paralleled accidentally and battery condition is not monitored properly an automotive battery would be stressed and the engine might not start. I'm developing check lists but want operators to be able to use the boat day sailing and weekends without touching the battery switches except in an emergency.

I'm thinking a simple echo charger bridging the start battery on off switch would do it. The boat would be operated with house on and start off. As long as the house were not discharged beyond where it would start the engine, the engine battery would be full and charged and the house would do it all.

The no start checklist would read:

1 Reduce electrical loads, radar, refer, nav, etc.
2 Select house battery OFF
3 Select start battery ON
4 Start engine
5 Select house battery ON
then and only then
6 Select start battery OFF

I think we'll sail this way until we get an echo (suggestions?) as most will be day sailing where the shore power charges both directly anyway.

I'm hoping for critical comments. I'd really like a battery monitor but can't justify it's cost. I also think an ammeter is needed, perhaps in the common ground. I still can't figure out how the stock volt meter is wired.