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Blue Sea Add a Battery


TheHardWay

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In the process of installing my Add a Battery. I am getting to the point where I am going to install the grounds. I was wondering if I can just run the original two cables that are on the boat to the negative post on the house battery, and then run a jumper ground from the negative terminal of the cranking battery to the negative post of the house battery.

The instructions that came with it (page 4 of this link) http://bluesea.com/files/resources/instructions/990310020.pdf

show that the negatives run a common bus bar. Well I have been ALL over town today trying to find a bus bar without luck.

Since both batteries run to this in the diagram with no sort of fuse, I don't see why it would be any different than directly linking the two grounds as I mentioned.

Is has been a long day, so am I thinking clearly?

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Yes, leave the grounds as-is. Main ground to one battery, jumper from that ground to the negative post on the other battery. All you are doing is completing the circuit. The interruption of the circuit (the swtiching) is all happening on the positive side.

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RedRum,

The Blue Sea instructions reference a ground bus bar that they are assuming is already existing at the helm. So whatever is there now is just fine.

Btw, If you get to feeling a little extra ambitious then give me a shout. There is a much better way of wiring that dual circuit switch and ACR combo, especially if you plan on adding a dual bank battery charger.

David

Earmark Marine

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Thanks David. I have already cut my wires to length for the positive terminals/switch and positive/ACR. I have a single bank on board charger now...hadn't thought about putting a dual bank on, but maybe in the future. Perhaps I will give you a call tomorrow to get your input.

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RedRum,

Darn. I wish we would have caught this sooner. Blue Sea actually advocates a single bank charger to service both the house battery and starting battery. However, I don't believe they anticipated the megawatt stereos with the considerable reserves of dedicated stereo batteries. Oftentimes, and especially with the use of an ACR/VSR, we are putting the boat into storage with a stereo battery that is somewhat depleted and in need of more than a maintenance charge. A stereo and starting bank have different capacities, are used very differently, have a different impedance and deserve to be profiled, charged, conditioned and equalizied if applicable on your charger, very differently. Your ultimate battery performance and longevity depend on this. As intended to be serviced by a single bank charger, the Blue Sea scheme serves to circumvent the dual bank isolation when a dual bank charger is used. Also, its hard to find a single bank charger that has the adequate current capacity to chemically excite a deep cycle battery for complete desulphation.

David

Earmark Marine

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Do I need to get a marine grade deep cycle for the 2nd battery to use for accessories and stereo or a regular car battery is just fine? I have a Blue sea charging relay. Thanks.

Patrice

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Do I need to get a marine grade deep cycle for the 2nd battery to use for accessories and stereo or a regular car battery is just fine? I have a Blue sea charging relay. Thanks.

Patrice

You want a marine deep cycle or deep cylcle/starting battery and not an auto battery. An auto battery is a cranking battery and not made for heavy loads (like a stereo) that can deplete the battery. If an auto battery gets depleted even once it can suffer irreversible damage and shorten it's lifespan.

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Don't know if there is any truth to it, but I read that ideally, you want two of the same batteries. Everything is the same when the two batteries are charging back up when the boat is running.

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Don't know if there is any truth to it, but I read that ideally, you want two of the same batteries. Everything is the same when the two batteries are charging back up when the boat is running.

I think that's true where you are running a perko, because the batteries are frequently combined, but not so much where you have them isolated and each bank is serving a distinctly different purpose.

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The way I understood it was that they are isolated when the engine is off and the alternator isn't providing any charge. Then when the engine is running, they are combined and both receiving charge. If you are floating around and jamming the stereo all day and draining the house battery, you will still have a fully charged cranking battery. However, once you start the engine, the batteries combine to recharge. So in an extreme case, you might have one almost dead house battery, and one fully charged cranking battery. When combined, those two batteries are going to equalize each other, and you will have two half charged batteries until both are fully charged again.

Edited by RedRum
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The way I understood it was that they are isolated when the engine is off and the alternator isn't providing any charge. Then when the engine is running, they are combined and both receiving charge. If you are floating around and jamming the stereo all day and draining the house battery, you will still have a fully charged cranking battery. However, once you start the engine, the batteries combine to recharge. So in an extreme case, you might have one almost dead house battery, and one fully charged cranking battery. When combined, those two batteries are going to equalize each other, and you will have two half charged batteries until both are fully charged again.

sortof (and take this with an armchair know-it-all grain of salt).... In the case you outlined, yes the batteries "combine" for charging. but the alternator is going to be putting out more voltage that the charged starting battery or the discharged house bank, so both batteries will be taking a charge from the alternator rather than the starting battery discharging to the house bank. When the alternator current is off, the batteries are again separated (when the voltage sags below 12.75v for more than 30 seconds). So the only time (theoretically) that the batteries are combined is when they are being charged from a source with higher voltage than either battery, and the brief time it takes for the relay to open after the alternator quits pushing current.

I did read on wakeworld that some of the higher end agm batteries will hold a charge state that's high enough to keep the ACR in a combined state (>13v for >2minutes), but I don't think that's a problem for most of us.

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yah man, I am by no means an expert either....that is just the impression I got. I am gonna call David at Earmark either today or early next week with some questions, so I will ask him about this and get the story.

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yah man, I am by no means an expert either....that is just the impression I got. I am gonna call David at Earmark either today or early next week with some questions, so I will ask him about this and get the story.

also keep in mind that if the house bank is FULLY discharged (10.8v or less), it will be locked out from combining....

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Its absolutely true that if you have two paralled batteries on the house/stereo bank that they must be replaced at the same time and be identical in every respect. Otherwise they will ruin one another.

But here is just one of many areas that a boat's charging system is less than perfect. Even with an identical battery on the starting and house/stereo bank, these will be used very differently. So after some use they will no longer be identical or have the same impedance as they are aging differently. I would recommend using two batteries of equal chemistry whether flooded or AGM although many use a deep cycle with a cranking battery and separate banks of a very different amp/hour capacity. Its these differences that you have to have some tolerance for even though they may not be ideal in the strictest sense. If you choose to use identical batteries of identical size (limited to two total) and they're both deep cycle then it would be good to rotate these several times a season. Collectively they should age a little better.

David

Earmark Marine

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Translation: same kind of batteries on same side of switch (I.e. Multi battery house bank). Different batteries ok on different sides of switch so long as you don't mix and match AGM and Traditional batteries.

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