battery 1 or 2 switch

[pvb]

....whereas with a manual system, this doesn't happen until someone decides to switch from '1' to 'B' (if you are still motoring).

And if someone remembers....

 

[pappaecho]

something wrong here. If the chart plotter goes off line when the bow thruster is used, then the engine battery must also be connected to the chart plotter. If you have the engine running when using the thruster, the alternator should keep the voltage up any way. Usually the chart plotters only drop out below 12 volts.
Usually the engine battery is used exclusively for starting the egine with do drain from any other source.
You have a very substantial capacity for the house bank, perhaps the easiest solution is to switch to both banks when using the thruster, making sure the plotter is running on the house bank

 

[Stork_III]

The Bluesea Off-On-Combine switch certainly sounds like an ideal solution for those of us who tend to be forgetful which is the main drawback with the 1-2-B-O switch. BUT it seems to share one disadvantage with it - in the 'both/combine' position, if you use it when the engine battery is flat, you're combining a charged battery with a discharged battery to start the engine. You'll only get a reduced voltage from the combination which may be insufficient to start the engine a re-commence chargine your batteries. If you attempt to start your engine with the 'good' battery alone you'll get the full whack from your 'good' battery which is much more likely to start the engine. I'd prefer to have each battery seperate and an 'emergency start' switch to connect the 'house' battery alone to the starter.
The other advantage of a vsr/combiner is that you always get useful charge into the 'house' battery as soon as the 'start' battery is up to voltage whereas with a manual system, this doesn't happen until someone decides to switch from '1' to 'B' (if you are still motoring).

+1 Exactly as my boat is wired.

 

[halcyon]

something wrong here. If the chart plotter goes off line when the bow thruster is used, then the engine battery must also be connected to the chart plotter. If you have the engine running when using the thruster, the alternator should keep the voltage up any way. Usually the chart plotters only drop out below 12 volts.
Usually the engine battery is used exclusively for starting the egine with do drain from any other source.
You have a very substantial capacity for the house bank, perhaps the easiest solution is to switch to both banks when using the thruster, making sure the plotter is running on the house bank

Depends on thruster, but could be 250 -500 amp loading, far above the standard alternator, so alternator supplies some, batteries supply most, battery on load voltage can fall below 12 volt at those loads. The OP's original question was running thruster with switch set to both, so possible electronic equipment problems.

Brian

 

[prv]

bought a new 1-2-both switch for that too. Simple, versatile and foolproof.

Versatile, yes, absolutely.

Simple - yes, in some senses. In terms of actual use, I suggest "turn on when you board the boat, turn off when you leave" is simpler.

Foolproof - sadly not. It's not even forgetful-proof.

Pete

 

[GrahamM376]

Versatile, yes, absolutely.

Simple - yes, in some senses. In terms of actual use, I suggest "turn on when you board the boat, turn off when you leave" is simpler.

Foolproof - sadly not. It's not even forgetful-proof.

Pete

1,2,both isn't foolproof but, nothing is. However, they're less likely to fail at sea than relays or any electronic charging systems. I have two of them so I can select which domestic bank(s) I want to use or charge and the other switch allows me to start the engine from the dedicated battery or domestics or both.

 

[kalindi]

Thanks for all the comments. I think that for the moment I will switch to both before starting the engine in a situation when I might need the bow thruster and then to 1-2 when the engine is not running. I will use the long winter nights to think through the options before finalising the system in the spring.