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  #311  
Old 11-08-2014, 01:05 PM
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Keep everything wired as you currently have it. Add the second battery and put the starter and only the starter on it. Your current battery becomes your house battery and the new one becomes your starter battery.

Find out what your current alternator amp rating is. You may need to upgrade that and you might want to upgrade your alternator to battery wire as well.

With the correct amp rated alternator you should not need to replace it as a preventive maintenance measure.
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  #312  
Old 11-08-2014, 01:44 PM
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Originally Posted by CantRepeat View Post
Keep everything wired as you currently have it. Add the second battery and put the starter and only the starter on it. Your current battery becomes your house battery and the new one becomes your starter battery.

Find out what your current alternator amp rating is. You may need to upgrade that and you might want to upgrade your alternator to battery wire as well.

With the correct amp rated alternator you should not need to replace it as a preventive maintenance measure.
Excellent explanation. Thank you
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  #313  
Old 11-08-2014, 04:03 PM
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Question on the isolator, I'm just trying to get the science down. Say I had one of these installed, and someone left the stereo on all night, and the main/house battery completely drains. Theoretically, there wouldn't be any power in the main/house battery to close the isolator and connect the two batteries for charge. So this is the primary reason why we connect the starter to the second battery? Once the engine fires, power draws from the second battery to the main/house battery, closes the isolator, and then the alternator starts charging both batts, correct?
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  #314  
Old 11-08-2014, 04:21 PM
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Originally Posted by paintpollz View Post
OK I need the dual batt setup. I just bought a 197 with 1500w of amps and one battery, trouble waiting to happen. What I've gotten from this thread:

-use the BW isolator. KISS. there will be other people driving this boat, I do not want to have to go thru battery tutorials with them.

-you should use two of the same batteries, although it would be nice to have a deep cycle as the house battery.

-there will be unavoidable strain on the alternator while charging the two batteries when the boat is running. boo hoo.

Question:

-Do I need to rewire the stereo switch to the house batt so that the amps & stereo turn on when flipping the stereo switch, and all pull from the house batt? Otherwise, if I just connect the amps to the house batt, won't the stereo still draw from the starting batt when the key is in the off position?

-When running a dual battery setup in this manner, is it wise to replace the alternator ever so often as preventative maintenance insurance? No one wants to get stranded........

Thanks
Do you define 'house battery', as "the one used for the boat's electronics and engine"? You want a cranking battery for the engine, if the engine's electronics will be sharing the battery used for cranking and if you want to use deep cycle for the audio, that's fine, but you WILL need a heavy duty alternator if you expect your batteries to recharge and be able to supply all of the other electronics with the proper voltage and current. If you were to use a separate battery for cranking and ONLY for cranking, a deep cycle would work, but if you expect to run the battery voltage down below 10VDC, you're not using them according to their design. 'Deep cycle' doesn't mean "deplete them so they're stone dead".

How loudly do you play the stereo, do you crank it while the engine is off, at idle, or at/near WOT and what other accessories would be used at a given time? Those will determine the demands on the batteries and charging system. The charging system must be designed for "worst case" scenarios if it's expected to survive and operate correctly.

Why would you "replace the alternator every so often as preventative maintenance insurance", rather than just design the system correctly in the first place?

If you use a heavy duty alternator, you'll need to use a heavier charging wire, too.

List the stereo equipment by brand and model, too.
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  #315  
Old 11-08-2014, 08:04 PM
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The Official Dual Battery Thread

When you turn the key, both batteries are joined by the isolator relay so which one is drained is not a factor. Essentially they become one battery at that moment so the "good" battery energizes the relay unless I am mistaken.

As for the alternator, I do not know enough about electrical engineering to be an authority. That said, the point of the isolator is to protect the starting battery and therefore it should typically remain at full charge capacity. Assuming the house/accessory battery were completely drained, when joined you'd really only be charging the depleted battery off the alternator (plus a little to top off the starting battery). I have been using the classic dual battery setup as originally described by Diesel in this thread and have never had any kind of issue getting started, charging and operating the stereo/amps/accessories while floating.
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  #316  
Old 11-09-2014, 07:11 AM
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I wouldn't use an isolator. I'd suggest a VSR.

https://www.bluesea.com/products/761...12_24V_DC_120A
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Last edited by CantRepeat; 11-09-2014 at 08:13 AM.
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  #317  
Old 11-09-2014, 08:52 AM
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Quote:
Originally Posted by JimN View Post
Do you define 'house battery', as "the one used for the boat's electronics and engine"? You want a cranking battery for the engine, if the engine's electronics will be sharing the battery used for cranking and if you want to use deep cycle for the audio, that's fine, but you WILL need a heavy duty alternator if you expect your batteries to recharge and be able to supply all of the other electronics with the proper voltage and current. If you were to use a separate battery for cranking and ONLY for cranking, a deep cycle would work, but if you expect to run the battery voltage down below 10VDC, you're not using them according to their design. 'Deep cycle' doesn't mean "deplete them so they're stone dead".
Yes that is my definition of a hous/aux batt. The idea is not to deplete them, I was just throwing out a what if scenario

Quote:
Originally Posted by JimN View Post
How loudly do you play the stereo, do you crank it while the engine is off, at idle, or at/near WOT and what other accessories would be used at a given time? Those will determine the demands on the batteries and charging system. The charging system must be designed for "worst case" scenarios if it's expected to survive and operate correctly.
Correct, I'm aware that I will need a new alternator

Quote:
Originally Posted by JimN View Post
Why would you "replace the alternator every so often as preventative maintenance insurance", rather than just design the system correctly in the first place?

If you use a heavy duty alternator, you'll need to use a heavier charging wire, too.

List the stereo equipment by brand and model, too.
My understanding of charging systems is limited. Now that I know that I can purchase a high output alternator designed for a system like this, I will go that route.
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  #318  
Old 11-09-2014, 09:47 AM
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Quote:
Originally Posted by paintpollz View Post
Yes that is my definition of a hous/aux batt. The idea is not to deplete them, I was just throwing out a what if scenario



Correct, I'm aware that I will need a new alternator



My understanding of charging systems is limited. Now that I know that I can purchase a high output alternator designed for a system like this, I will go that route.
http://www.onallcylinders.com/2012/1...an-alternator/
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  #319  
Old 11-09-2014, 09:59 AM
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Yup, read that article, thanks Tim. Now in the hunt for the product # for an HO alt to fit this motor. I'll likely install the alt and then have an automotive shop around me upgrade the big 3.
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  #320  
Old 11-09-2014, 11:00 AM
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Originally Posted by paintpollz View Post
Yes that is my definition of a hous/aux batt. The idea is not to deplete them, I was just throwing out a what if scenario



Correct, I'm aware that I will need a new alternator

My understanding of charging systems is limited. Now that I know that I can purchase a high output alternator designed for a system like this, I will go that route.
In the '90s and into the early 2000s, people who competed in IASCA and other car stereo "sound off" competitions were running a lot more power than your boat, often in small imported cars. The OEM alternators were often good for 65A, maybe. Your boat's alternator is probably good for 75A and in general operation, there's about 20% of safety margin, so figure that it's using about 50A-60A on a regular basis. What the competitors or installers would do is fabricate a bracket and mount a second alternator, completely isolated from the one that runs the car. This way, the starting batter is never affected by the audio system and vice versa. In this configuration, you shouldn't have any problem charging the audio system's batteries- at 12V (used for system design purposes because it's a real-world number), 95A works out to 1140 Watts. Now, this isn't likely to support that load for long, but it does give a ballpark for estimating what you'll need for recharging the batteries for the audio system. At 14.4 VDC, which is the typically-stated full charging voltage in a car or boat and this is not going to be seen at idle unless an alternator is "under-pulleyed", meaning that the alternator's pulley is smaller than normal, causing it to spin faster than it would if the larger pulley was on it. You would need to find the max RPM for the alternator, in order to avoid damage at/near WOT.

The trick- finding space for a second alternator in a boat. On a V-drive, it should be easier than in a mid-engine model.
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