Boat electrics

[Winterbrook]

Apologies if this is a really stupid question. I have only owned my boat (Bayliner 285) for 12 months and electrics are definitely not my strong subject. To date we’ve only used the boat for day trips and it reconnects to shore power on our return. We are shortly taking it on a week long trip, staying on the boat and it won’t always be connected to shore power overnight. How do I preserve the battery overnight?! Presumably ideally fridge etc should be turned off and only the bare minimum? I’m slightly paranoid on waking up and not being able to start the engines! I have bought a book on boat electrics but it’s slow going!

Thanks

 

[sarabande]

It's far from a stupid question: off marina electricals are not a big problem, and the more you understand, the easier it is to manage.

Ok, let's start with a bit more info about the number of batteries on board, the layout and specifications, the control switches (VSR, 121, or other), and what your likely power drains are .

Details and photos please.

 

[markc]

The Bayliner 285 has a dedicated engine start battery and dedicated domestic batteries, so you will be able to start the engine if you drain the house batteries, providing they are not linked. It's a good idea to check the heath of the batteries anyway as that will have a huge impact on power drain. As a fall-back you could buy an emergency jump start power pack, or if you need to support high drain devices you could always buy a small suitcase generator - if so make sure you run it in the open air and the wind isn't blowing the exhaust into the cabin

 

[ChromeDome]

Just FYI: The principle is to automatically isolate the start battery before it gets below the minimum power need to start the engine.

Hence if consumption brings domestic batteries (=battery bank) to its knees, you'll still be able to start the engige and get going, eventually to bring all batteries up to normal charge. It is common that systems prioritize charge of the start battery, then the domestic, treating each bank individually.

For the principle to work, devices and connections must be correct and in good working order. As the battery banks are crucial for storage of power, the type, state and charge regime is are major points to check.

 

[Portofino]

Test Marc’s correct theory by nipping down to the marina and unplug the shore power .Fridge on etc etc
Return 5-7 days later and see if it will fire up the engine (s) .

The fridge on a boat say typically a Waeco brand has a voltage cut off thingy .This means it won’t kill the domestic bank .Works like this say it needs above 11.7 v , when the domestic voltage drops by day 3/4 below 11.7 it switches its self off . So there is no need to second guess when to turn it off , it knows itself .Or should do !

They almost entirely should have separate banks .Left for a week is just like a airport car park scenario , it should fire up

Not what you are asking but kinda good to know if you are new ………
Some boats have a switch on the dash called a cross over or parallel switch .This is to temporarily connect up both banks .
Usually if the starter bank has insufficient power to fire up the motor(s) .Buts it’s robbing the Dom bank .
This should be the only time the two banks are connected …..to get you going .Assuming there’s any juice in the Dom bank .