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Old 17-10-2019, 08:46   #1
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One switch - house & engine?

Would it be possible to use one of those main switches that can combine 1+2 and also separate em......but opposite. Instead of combining and separate the batteries....combining and separating the loads....engine and house loads for instance? I'm planning to use one big bank instead of a separate starter.
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Old 17-10-2019, 09:22   #2
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Re: One switch - house & engine?

Of course is is possible... the question is why you would want to?

It is a mystery to me why people spend so much money to add switches and wiring to combine house and starting batteries for the one time in ten years the start battery is flat and needs a boost to start the engine.

My boat came from the factory with a set of jumper cables to start the engine if the starter battery died. A solution that has the benefit of elegance, low cost, and _highly_ unlikely to be accidentally engaged when not appropriate.

Sometime the simple solution is the best.
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Old 17-10-2019, 10:06   #3
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Re: One switch - house & engine?

In fact such switches are in modern designs, **only** used to direct loads, not charge sources.

But just one bank on the boat is dicey, IMO redundancy is critical

Look at the past threads linked to from this recent discussion.

Starter battery VS. Reserve Battery
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Old 17-10-2019, 11:04   #4
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Re: One switch - house & engine?

I have a lithium start booster in case I need more juice to start it....
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Old 17-10-2019, 11:09   #5
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Re: One switch - house & engine?

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Originally Posted by billknny View Post
Of course is is possible... the question is why you would want to?

It is a mystery to me why people spend so much money to add switches and wiring to combine house and starting batteries for the one time in ten years the start battery is flat and needs a boost to start the engine.

My boat came from the factory with a set of jumper cables to start the engine if the starter battery died. A solution that has the benefit of elegance, low cost, and _highly_ unlikely to be accidentally engaged when not appropriate.

Sometime the simple solution is the best.
I think u missunderstood me. I'm not aiming for connecting the battery banks together. I want to be able to have the engine disconnected when not in use...by using same switch as I disconnect the house loads....
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Old 17-10-2019, 15:11   #6
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Re: One switch - house & engine?

I think the Blue Sea Systems series of switches with dual inputs and dual outputs is your best bet. Gorgeous switches that isolate the engine and house systems until you want to connect them all together (as when your engine starting battery is dead).

Lovely, simple solution.

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Old 17-10-2019, 15:21   #7
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Re: One switch - house & engine?

What, precisely, so you mean by: "I want to be able to have the engine disconnected when not in use."?

I don't discern what it is you are trying to achieve, but I take it you have a 1,2,BOTH,OFF switch. From the switch one heavy cable goes from a switch terminal to the positive post of one battery, another heavy cable goes from another terminal on the switch to the positive post of the other battery and a third heavy cable goes from the third terminal on the switch to the terminal on the solenoid mounted on the starter motor.

If, but only if, the wire that takes the output from your alternator is taken from the alternator to the SAME terminal on the solenoid that takes the heavy cable, then the POSITIVE side of both starter and charger circuits are broken when you place the switch in the OFF position, i.e. the batteries are isolated from the engine (or vice versa). The NEGATIVE side of the circuits is NOT broken, but there is no need to do that.

So what precisely is your problem? The house loads are normally fed via a DIFFERENT circuit that leads via a simple ON/OFF ("master") switch to distribution panel with switches and circuit breakers for the various house circuits

The circuit for the windlass/capstan will be a circuit separate from the other house loads because it has to carry an ampage much heavier than the other house loads. It is separate, but it is set up just like the circuit for the other house loads.

Let us know just why you are concerned and we'll sort it out for you

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Old 17-10-2019, 18:03   #8
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Re: One switch - house & engine?

Blue Sea makes a single switch for that. The 90-degree position isolates start and house, 180 degrees combines them.

Some people on this forum think you'll only need this feature once every ten-thousands years. Yes, and that will be when you are being driven on to a rocky lee shore with a weak start battery, at night. One opinion thinks a jumper cable will suffice.
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Old 17-10-2019, 21:04   #9
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Re: One switch - house & engine?

Just feed the 1-2-all backwards.

Battery to common. House to 1. Engine to 2.

Both if you need to power house and engine.

Off kills both.

Label it well. As nobody will know what the f*ck it does.

But personally I would have 2 banks.

A jump pack is not designed to jump a huge bank. It is designed to jump a small battery. There is a big diff.
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Old 18-10-2019, 04:19   #10
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Re: One switch - house & engine?

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Originally Posted by smac999 View Post
Just feed the 1-2-all backwards.

Battery to common. House to 1. Engine to 2.

Both if you need to power house and engine.

Off kills both.

Label it well. As nobody will know what the f*ck it does.

But personally I would have 2 banks.

A jump pack is not designed to jump a huge bank. It is designed to jump a small battery. There is a big diff.
Indeed.
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Old 18-10-2019, 07:35   #11
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Re: One switch - house & engine?

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Indeed.
Yeah this was what I was thinking of doing...just wanted to make sure it would work...

Reason I want to do this?
-Somehow I need a main switch for my engine. And by not adding a separate one I was hoping I could do this by using same switch as house loads. Sure...I can have two normal main switches which still is an idea. One between battery and engine and one between house and battery.

-Trying to save some weight, by not having a separate start battery. Im having 600Ah bank.
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Old 18-10-2019, 07:50   #12
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Re: One switch - house & engine?

The most obvious and simplest arrangement to achieve the OP's goal would be two high current switches. Cheaper and less confusing than a backwards 1/2/both/off switch.

Personally, I wouldn't go with just one battery bank; I'd have a dedicated start battery as well. A house bank can get depleted or killed by overuse or by one or more batteries failing.
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Old 18-10-2019, 08:29   #13
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Re: One switch - house & engine?

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Indeed.
Another vote for this. Only problem I can see would be with addressing imbalaces in the batteries. I, like you, have a single bank (of two batteries). But despite my best efforts the batteries do become imbalanced over time and it's nice to be able to measure this and then address it by charging (or equalising) individually. You can always just disconnect a cable though if you want to do this. No need for another switch.
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Old 18-10-2019, 08:45   #14
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Re: One switch - house & engine?

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Originally Posted by Lake-Effect View Post

Personally, I wouldn't go with just one battery bank; I'd have a dedicated start battery as well. A house bank can get depleted or killed by overuse or by one or more batteries failing.
I've never understood this approach for a liveaboard cruising yacht. I understand that it's perhaps the most common setup and that people like it. Each to his own, but........ why? All that added complexity just to be ready for a 'what if' scenario that just isn't going to happen. If you live on your boat, any problem with the electrical system involving over-discharge of the battery bank (house battery bank if you have more than one) will surely be noticed long before you get to a point where they are dead? Surely?! Add to that the fact that very, very few cruising yachts rely on their engines exclusively for charging - so in the highly unlikely event that you are unable to start it due to low voltage you have an alternative charging source anyway - and the need for a separate, dedicated battery bank 'for redundancy' just vanishes. Doesn't it?
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Old 18-10-2019, 08:55   #15
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Re: One switch - house & engine?

I'm still not clear what you OP are trying to achieve.


"Disconnecting the engine" is not a full explanation. Disconnect what components specifically, and from what power input?

And for what reason? When the engine is shut down, I can't see why any of it needs to be isolated, are there some parasitic loads there from an engine computer or something?

And where is the alternator in this? That needs to be hard-wired to some battery no switch in between. . .

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You definitely need a solid backup for cranking the engine in case the main bank fails.

IMO those little LI jumpstarter powerpacks are only good as belt-and-suspenders, second-level redundancy.

Unless the use case is just short daysails, and **rowing** is an acceptable option.
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