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House battery

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northrip

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I have a 1998 searay 270, single engine. Up until now, I have always left the selector switch on "both", as day trips only with very light electrical loads without engine on, other than say a vhf radio, or perhaps a short run bilge pump cycle. And this has worked well, engine always turns fast and starts quickly.

Today planned an overnight, at anchor, no generator or shore power. So I wanted to determine, house, and start. I changed switch to (1), and engine started. I changed to (2), and engine started. I thought this was the purpose of the selector switch, to be able to isolate batteries.

In any case, how can I configure my batteries, selector switch to have one house and one start. Any help much appreciated.
 
Sounds as if you're wired to operate on one battery with the other as back-up. In your light use situation, operate on one and have the other for a back-up, switch up use of '1' or '2'. I consider 'BOTH' to be an emergency situation ... :(
 
Well, I probably needed to provide an explanation. That wiring diagram will give you exactly what you are experiencing. Position 1 connects starter to battery 1. Position 2 connects starter to battery 2. Position "ALL" connects starter to battery 1 & 2 in parallel. There should be a single cable connecting both battery grounds to each other, and a wire from one of the grounds will go to your engine ground. On most outboard engines, the engine positive will be connected to the same post on your starter as the positive wire coming from your battery switch.

Typically, you will have a second cable off coming off the output side of the switch (common) to a bus bar to which all of your "house" equipment is connected. On my boat, I have run # 4 positive and negative cable to a cabin bus bar under the console. Then all my equipment is connected to that bus bar through a fused switch panel - VHF (2) map/gps, fishfinder, spotlight, gauge lights, etc. etc.

So, when you are docked overnight, put your battery switch in the "2" position, which will isolate your #1 battery for starting. Once stared, switch to the "all" position to charge your #2 battery. This assumes you have one of the newer "break before connect" switches so that you do not blow the diodes in your regulator. If in doubt, start from the "all" position. If you plan to use shore power overnight, then that is a whole different setup.

One caution here - your bilge pump should be wired directly to your house battery, not through the battery switch.
 
Thanks Chawk, yr update seems to make sense based on yr notes and addl reading. To review (my understanding):

Switch on both, power from both batteries powering starter and all accesories.

Switch on (1), accesorry power being drawn from battery (1), battery (2) is isolated, but engine will still start because battey 1 goes to common, which is where starter will draw from anyway.

Switch on (2), accesorry power being drawn from battery (2), battery (1) is isolated, but engine will still start because battey 2 goes to common, which is where starter will draw from anyway.

And for simple starting and underway, start as I always have on both, and engine will charge both.

Do you agree? And if so, what would be the simplest way at the dock to confirm this set up.

Thanks again.
 
Sounds correct.

Test 1 - switch to position 1, disconnect battery 1 positive terminal. Engine should not start. No accessories should work. Switch to position 2. Engine should start, and accessories should work. Switch to position 1/2 or "all". Engine should start and accessories should work. Reconnect battery 1 positive terminal.
Test 2 - switch to position 2, disconnect battery 2 positive terminal. Engine should not start. No accessories should work. Switch to position 1. Engine should start, and accessories should work. Switch to position 1/2 or "all". Engine should start and accessories should work. Reconnect battery 2 positive terminal.
 
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