Engine starter/house battery wiring..

[majdrew]

Hey guys!
I'm trying to figure out the wiring on my boat can you help?

I have an engine starter batt. and a deep cycle house batt.
There are 2 isolator switches installed, meaning that I can turn off and on each seperate batt. as I choose, is that right?

so for eg. I can just start the engine with the starter batt. and run the electrics off the house only?

But what if I'm sailing along at night with the house batt. running nav. equipment, and I need to start the engine..

that means I would have to switch the isolator on the starter batt. meaning both batts. would be on, and both batts. would be starting the engine.. is that right?

Because I don't want that.. I want to keep the 2 batts. for their seperate uses..

Am I thinking this through right??

/forums/images/graemlins/confused.gif

 

[ccscott49]

Almost impossible to tell, how the thing is wired up, without a circuit diagram, or looking at the wiring myself, sorry.

 

[NealB]

Why not:

- switch on the engine battery only, and see if it will power up, say, a cabin light. If doesn't, you know it will start the engine only.

- switch on the domestics battery only, and see if the starter will operate. If not, you know it's for domestics only.

If they are separate circuits, you may want to carry a set of jump leads for when the starter battery fails to perform.

 

[Cliveshep]

If it's any help, mine has two alternators charging two battery banks, but only one master switch connecting the negative terminals so the banks stay separate.

 

[Csail]

Get the system looked at....they should be seperate with a X-split charger or similar.

 

[Carduelis]

The Beneteau system, which seemed odd to me at first, seems to work well in practice.

Both batteries have isolators, and separate charging arrangements, but effectively operate in parallel. This means that the start battery (normally switched off while sailing) is saved for engine starting. However, if you really need to, you can start the engine on the domestic. Or you could run the fridge off the Start battery for that matter!

I appreciate that this means that the start load is 'shared' across both, but it seems to work OK in practice. Both batteries are nearly 10 years old and still doing their stuff.

 

[cmedsailor]

Just to add on Beneteau system...
The two batteries are connected with one cable (red) at the two switches. If you add a separate on/off switch on that cable then batteries, as long as the switch is off are not connected in parallel. That means you can leave engine battery on while sailing without any damage to it.

 

[rogerthebodger]

I have a 1 , 2 , both switch in my engine start battery but wired so the battery is connected to the common terminal and the engine is connect to say battery 1 position and the domestic circuit is connected to the No 2 position. I can then connect the start battery to supply the just the engine start or just the domestic circuit or both. I also have a 1 , 2 , both connection my 2 domestic battery banks so I can isolate my domestic circuit from both batteries so I can supply the domestic from the engine start only or I can supply the engine start circuit from either of the domestic battery banks.

If you only have a single domestic battery bank you will only need a simple on/off switch in the domestic supply circuit.

 

[majdrew]

Hmmm.. thanks for the replys!

I don't have batts on board at present so can't test re. nealb. To be honest I do find it a little confusing.. it's only a 'simple' boat but seems to have a load of wires.. 3 isolators [I forgot the other one], smart alt. charger, wind charger..

Luckily I've found an electrician to take a peek..
Thanks for all your help, much appreciated!

 

[William_H]

Re Beneteau wiring if your engine always starts using 2 batteries to share the load then you should be wary. If one battery dies ie is not able to start the engine then the other will do the job. You will not know until the second battery also dies and you will have no reserve start power.
I somehow doubt this is how it works but if it does you should occasionally disconnect one battery to confirm the other will do the job and also test using the other battery alone. olewill