Starting with house vs start battery

[mainesail]

What is the problem with using the house batteries for starting and general usage, and keeping the remaining battery just as a backup if needed?

If you have a 1/2/B switch there is nothing wrong with that and it will lead to less human induced errors... if you are trying to avoid brown outs, that is more complex, can happen regardless of which bank of a 1/2/B switch you start off and may have numerous causes. To keep it simple start the motor then boot instruments. If you want a more complex solution those exist too.

[mark_53]

What is the problem with using the house batteries for starting and general usage, and keeping the remaining battery just as a backup if needed?

To keep it simple start the motor then boot instruments. If you want a more complex solution those exist too.

So when your under sail using instruments and you need to restart the engine, you lose your instruments?  Not an optimal solution. Tell him about start isolation.

[mainesail]

There is only start isolation if you have a dedicated start battery on its own circuit.  SI does not apply to a 1/2/B which, by his description, he seems to have..

[SPembleton]

Mark, that is NOT the situation.  I start the engine, instruments work fine. After i am out to the big lske, i shut off the engine, instruments still work.  I try to remember to switch from start to house.  Instruments still work.  After a few hours sailing, voltage drops to 10.8v and the gWind bluetooth sensor stops working.  I usually continuing sailing.  After a while i return to port, i try to remember to switch back to my stsrt battery, start my engines and the gWind starts working again.

I have replcaced all 3 batteries.  I am now going to test to see if the voltage drop has anything to do with which battery i use to start the engine.

[mark_53]

There is only start isolation if you have a dedicated start battery on its own circuit.  SI does not apply to a 1/2/B which he has...

I believe that's what he says he has, "2 house batteries and 1 start battery".  and his instruments are crapping out when using the house bank to start.

[mainesail]

Mark, that is NOT the situation.  I start the engine, instruments work fine. After i am out to the big lske, i shut off the engine, instruments still work.  I try to remember to switch from start to house.  Instruments still work.  After a few hours sailing, voltage drops to 10.8v and the gWind bluetooth sensor stops working.  I usually continuing sailing.  After a while i return to port, i try to remember to switch back to my stsrt battery, start my engines and the gWind starts working again.

I have replcaced all 3 batteries.  I am now going to test to see if the voltage drop has anything to do with which battery i use to start the engine.

Your house bank is toast or you have a bad or loose connection or grossly undersized wire.Your batteries should only briefly drop below 12.1V under short duration high current loads otherwise you should never see them drop below 12.1V and especially not under just sailing instruments after a few hour sail... you need to measure the actual battery voltage at the terminals when you are seeing 10.8V.

[mark_53]

Mark, that is NOT the situation.  I start the engine, instruments work fine. After i am out to the big lske, i shut off the engine, instruments still work.  I try to remember to switch from start to house.  Instruments still work.  After a few hours sailing, voltage drops to 10.8v and the gWind bluetooth sensor stops working.  I usually continuing sailing.  After a while i return to port, i try to remember to switch back to my stsrt battery, start my engines and the gWind starts working again.

I have replcaced all 3 batteries.  I am now going to test to see if the voltage drop has anything to do with which battery i use to start the engine.

Okay, I see.  The house cable run to start is probably longer than the start battery's. I don't understand why your switching from start to house all the time. 
You may be wired differently then me but my start battery starts the engine regardless of where the 1-2-B switch is set.

[mainesail]

my start battery starts the engine regardless of where the 1-2-B switch is set.

If that is your only battery switch it should not behave like that...

[mark_53]

my start battery starts the engine regardless of where the 1-2-B switch is set.

If that is your only battery switch it should not behave like that...

There is a separate battery switch.

[Jon W]

For what it's worth -- I have a 4 x T105 house and 1 650 CCA as a "reserve". The house is on position 1 and the "reserve" is on position 2 of the 1-2-B selector switch. I can start on position 1, 2 or B and the instruments, chart plotter, radar, and network continue to function as intended. The only time I had an issue after starting is when I switched from position 2 to position 1 by going through the "OFF" position. Operator error not system error.

Energy consumption-- After a full day sailing with instruments and chart plotter on, fridge, plus starting the engine twice, my Smartgauge reads ~98% charge for the house bank.

[KWKloeber]

Jon

Are you saying you blew the diodes going through "off"?

[J_Sail]

I'm pretty sure he was saying that by inadvertently going thru OFF he briefly lost power to his instruments, etc (as expected).

I have previously looked at his wiring diagram and his alternator goes directly to his house bank, so going thru OFF wouldn't impact his alternator.

[Jon W]

Jeremy has it correct. The AO connects to the house bank. The 1-2-B switch only chooses which bank is being used. By accidentally rotating the switch through "OFF" I shut the power off. Duh. I should have rotated through "B".

[KWKloeber]

Gotcha! DUH! Thanks for the  clarification Jon and Jeremy,

Of course that episode speaks to what RC says with a set up like Steve has. (Paraphrased) "Just leave your selector on the house bank and avoid the well intended (insert brother-in-law, guest, etc. as appropriate) human intervention that can blow your alternator diodes."

Jeremy has it correct. The AO connects to the house bank. The 1-2-B switch only chooses which bank is being used. By accidentally rotating the switch through "OFF" I shut the power off. Duh. I should have rotated through "B".