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Old 11-15-2019, 06:17 PM   #1
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Adding 2 more house batteries and removing chassis batteries?

I have 4 6volt AGM batteries for my coach (2008 Newmar Ventana 3933) that are just about a year old. I have 2 Group 31 starting batteries for the engine.

It's time to replace the engine batteries. Has anyone here removed just added 2 more house batteries to their rig and tied the engine into it? I know the main down side is that if they get low I would have to jump start the engine. But, as it stands right now, I have to press my battery boost button to start the engine.

The (obvious) reason for wanting to do is is to add 50% more capacity, which I greatly need. My battery compartment will ONLY hold 6 so just adding more is not an option.

I'd love to hear thoughts from people that have actually done this as opposed to just ideas as to why it's not a good thing to do (cus I can list them).
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Old 11-15-2019, 06:48 PM   #2
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One thought is that the alternator is going to take a beating, recharging 600+AH of 50% discharged house batteries.

Right now, the BIRD will not let that happen. It will open the isolation relay if alternator can't keep up and the chassis batteries voltage drop, while connected to the house bank.

You can work around that by running the generator for the first hour of your days travel, if the batteries are deeply depleted.

I had a 800 AH bank on my boat and a 250 amp alternator. I did what your proposing and had to keep the RPMs down for the first hour, otherwise the alternator would overheat. Thats easy in a boat that went 7 mph anyway.
I had a external regulator that I could cut back the output when it overheated, but your alternator doesn't have that.
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Old 11-15-2019, 07:25 PM   #3
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Originally Posted by midwest22 View Post
But, as it stands right now, I have to press my battery boost button to start the engine.
That tells me that your alternator is struggling. It must not be keeping your battery charged as it should. Or maybe your battery is has a bad cell so it simply isn't holding the charge it's getting. Either way, I'd recommend fixing the problem before trying to bandaid it.


Quote:
Originally Posted by midwest22 View Post
The (obvious) reason for wanting to do is is to add 50% more capacity, which I greatly need. My battery compartment will ONLY hold 6 so just adding more is not an option.
This tells me that you're already taxing the house batteries pretty hard. If you connect the house batteries to the chassis battery, you'll be depleting the chassis battery pretty hard too. With a bunch of mostly dead batteries, you'll never get that engine to turn over, and you'll be hurting the batteries. If you do manage to get it started, you'll stress the snot out of that alternator trying to recharge them all.


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Originally Posted by midwest22 View Post
I'd love to hear thoughts from people that have actually done this as opposed to just ideas as to why it's not a good thing to do (cus I can list them).
Full disclosure: I haven't done what you're suggesting. I just really don't think you're going to help yourself by doing what you're thinking about. You'd do better fixing the actual issue with starting first.
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Old 11-16-2019, 08:45 AM   #4
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I am not sure how your batteries are laid out, but I would not just delete the chassis batteries like you are suggesting. I would look for a place to move your Chassis batteries to.
On my Coach I have considered moving my chassis batteries closer to the engine probably under the bed area and putting more house batteries in the slide out tray. I do have room between the frame and engine to add a new tray, but!, and a big one that would make accessing the engine more difficult. I also have a built in area at the foot of the bed that is in front of the engine that could easily hold several batteries, but I am not sure I want the batteries that close to the living area, and they would need to be the type that would not off gas.
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Old 11-16-2019, 08:59 AM   #5
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You can certainly do it, but there are practical reasons the two systems are kept isolated, e.g. some of those reasons already mentioned above. Perhaps the most important reason is that you can easily run down the combined battery bank to the point where the engine cannot be started, leaving you stranded.


There is nothing that prohibits you from using the power in the engine batteries when the house batteries get too low. All you need is a jumper cable from the engine battery positive post to a house battery positive post (the negatives are already connected. The Aux Start "boost" switch on the dash accomplishes the same thing, but somebody has to hold the switch on. Using a jumper cable makes a continuous connection that is easily removed when no longer needed. I used to carry a short piece of 6 gauge wire (50A rated) with alligator clips on each end just for that purpose.
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Old 11-16-2019, 09:02 AM   #6
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Your starting batteries are isolated from the house so you cant run them down, leaving you stranded somewhere because the engine wont start. Have you taken a voltage reading on the starter batteries? Are you sure they are charging? Dead engine batteries can be caused by several problems. I wouldn't just assume the batteries are toast without taking some voltage readings, or having them load tested. Starting (cranking) batteries, and deep cycle batteries are two different animals, and don't work well in the wrong roles.
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Old 11-16-2019, 10:16 AM   #7
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Another way to skin the cat.

First replace your isolation solenoid with a latching type. They stay connected without power drawing down the batteries ( Blue Sea markets one )

Now you can install deep cycle batteries in place of the failing start batteries and change the push button boost switch with a on/off switch. A jumper cable is not always easy to get to, connect or convenient.

Deep cycle batteries can start engines.

Starting batteries will fail quickly if deep cycled often.

The Blus Sea latching relay will sense alternator overload and drop the house batteries for a while, giving the alternator time to cool down, just like the BIRD.

While dry camping, switch it on and now you have 6 house batteries. Switch it off when on the road and let it charge your batteries.

As a backup, a booster pack strong enough to start the generator, or a portable generator to run your charger will get you going in a bind.

I always had a Honda eu2000 as my backup, incase I ran the only battery bank down to deep. It never happened and I was starting a 6 cylinder diesel engine.
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Old 11-16-2019, 10:30 AM   #8
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I posted about my Blue Sea ML-ACR here.


Replace Big Boy with Blue Sea ML-ACR
https://www.irv2.com/forums/showthread.php?t=468617

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Old 11-16-2019, 11:25 AM   #9
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I wouldn't do it! Having a set of dead batteries with a big diesel engine that won't start is not my idea of fun!
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Old 11-16-2019, 10:56 PM   #10
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Agm batteries are not starter batteries. They don't have the plate surface area to discharge at a high rate of amperage like a starter battery. Not sure how detrimental to them it would be but all things considered I wouldn't do it.
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Old 11-17-2019, 01:44 AM   #11
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Agm batteries are not starter batteries. They don't have the plate surface area to discharge at a high rate of amperage like a starter battery. Not sure how detrimental to them it would be but all things considered I wouldn't do it.


My group 31 AGM starting batteries are rated to have 1000 amps of cranking power at 0 degrees.
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Old 11-17-2019, 03:57 AM   #12
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Deep cycle batteries don't have as high a CCA as a standard starter battery, flooded or AGM, but now he will be starting the engine with 6 of them.
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Old 11-17-2019, 06:41 AM   #13
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Maybe adding some solar panels to assist the four house batteries would be an option. I personally don't like modifying things from the way they were engineered. This can sometimes have unforeseen consequences.
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Old 11-17-2019, 07:27 AM   #14
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You can certainly do it, but there are practical reasons the two systems are kept isolated, e.g. some of those reasons already mentioned above. Perhaps the most important reason is that you can easily run down the combined battery bank to the point where the engine cannot be started, leaving you stranded.


There is nothing that prohibits you from using the power in the engine batteries when the house batteries get too low. All you need is a jumper cable from the engine battery positive post to a house battery positive post (the negatives are already connected. The Aux Start "boost" switch on the dash accomplishes the same thing, but somebody has to hold the switch on. Using a jumper cable makes a continuous connection that is easily removed when no longer needed. I used to carry a short piece of 6 gauge wire (50A rated) with alligator clips on each end just for that purpose.
On my 05 Journey. I do as you since access is easy And my model does not have an. Amp L Start or the like That keeps the house battery’s charged while I drive
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