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Old 03-23-2018, 09:21 AM   #1
Mini-Skoolie
 
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Adding battery isolator with dual alternators and separated engine batteries.

I am planning for the addition of a house battery bank. I would also like to add a battery isolator between the house and engine batteries. I am uncertain how to wire it in my application, which has 2 alternators and 2 separated engine batteries. One battery is under the hood, the other along the frame. Also, the positive cable from each alternator goes to an individual battery. Alternators are 215 amp and 130 amp. Any ideas on how to add the isolator for the house batteries?
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Old 03-23-2018, 11:16 AM   #2
Skoolie
 
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remove the cable between the positive terminals of the two batteries will
completely separate the two systems,.. (if your rig doesn't need both to start the engine) otherwise wire the isolator in the cable between the two positive terminals
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Old 03-23-2018, 11:25 AM   #3
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or if you are adding a third battery to be house battery I would wire one of the alternators to the house battery and leave the higher amperage one for the 2 engine batteries
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Old 03-23-2018, 11:31 AM   #4
Mini-Skoolie
 
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Yes this needs the 2 engine batteries for the engine (7.3 diesel)and the chassis (marker lights, flood lights). So I will be adding a separate battery pack of (4) 6Volt batteries for the house batteries.

Steve
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Old 03-23-2018, 11:32 AM   #5
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Bear in mind that alternators generally do not have the voltage to fully-charge deep-cycle flooded lead/acid batteries.

The batteries most use for house batteries require 14.8V for the bulk-charge phase. Alternators are usually regulated at 14.2-14.4V. So in addition to the alternator you will need a three-stage DC input battery charger to do this properly.

If you get the second alternator regulated at 14.8V, then you run the risk of over-charging the house batteries on a long journey, so you can't go that way either.
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Old 03-23-2018, 11:38 AM   #6
Mini-Skoolie
 
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Twigg-
Is this how most Coach/motorhomes are setup? Can you post a link to the component(s) needed.

Steve
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Old 03-23-2018, 11:48 AM   #7
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Quote:
Originally Posted by srponies View Post
Twigg-
Is this how most Coach/motorhomes are setup? Can you post a link to the component(s) needed.

Steve
Well a lot of RV manufacturers are still fitting 14.4V converter/chargers with lead/acid house batteries, so looking to them for inspiration can be problematic They fit battery monitors that work from voltage too, so they will show a battery at 100% state-of-charge when it could be as low as 80%. One reason we like the Trimetric monitors is that they show the actual power consumed, and they are expensive because they are more than a simple voltmeter.

There are chargers that will do what you want, and my guess would be that the high-end motorhome builders use them.

This page might have a suitable unit, but hunt around because there are others:

DC powered battery to battery charger
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Old 03-23-2018, 11:56 AM   #8
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I have seen 3 stage regulators that can be retrofit to certain alternators. I believe they were made by Balmar.

I saw them used to charge deep cycle house batteries in marine applications.

May be worth exploring?
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Old 03-23-2018, 03:49 PM   #9
Mini-Skoolie
 
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I was hoping that I would be able to use a simpler isolator. Something like this:
https://www.amazon.com/gp/aw/d/B004QCDE9M/ref=mp_s_a_1_13?ie=UTF8&qid=1521836789&sr=8-13&pi=AC_SX236_SY340_FMwebp_QL65&keywords=rv+batte ry+isolator

Wired between the engine batteries and the house batteries. Alternators charge the engine batteries first, and then excess goes to the house batteries.
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Old 03-23-2018, 11:04 PM   #10
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that would work.
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