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Old 03-16-2016, 12:21 PM   #1
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Combo Battery Wiring Question

Greetings all,
I have a 1998 National Sea Breeze Gasser. While making some modifications the other night, I had to disconnect the shore power for a short period of time like 30 minutes maybe. Since it was dark outside, i had several lights on insie but no furnace, refrigerator, water heater, etc. My batter level dropped so low that I got a waring beep from the LP leak detector due to low power and the lights were dim. I noticed that when I switched off the vanity lights (the detector in mounted in the base of the vanity cabinet) that the lights would not go totaly off, just real dim, I am assuming a safety feature due to the detector warning beep. After getting all of my 110v wiring modifications complete, I reconneted the shore power and all was back to normal. The following day in the daylight I investigated the battery problem. Upon inspection I noticed that instead of having the expected (2) 6 volt batteries wired in series, I had (2) 12 volt wirede in parallel. One of these is the chassis battery for cranking and the second one is a deep cycle for the coach. I did some meter checks and did verify that they both get charged by shore power (converter) as well as by the eging alternator. It appears that they both get charged by the generator but not as high of voltage as the other 2 methods. I have the start boost switch on the dash as well. With the background given, here is my question:

The 12volt cranking battery that is required for thr chassis is in the same compartment under the steps as the coach battery. What I am thinking would be the best way to go is to get (2) 250+ AH batteries wired in series for the coach/house batteries to get longer lasting power. Then, wire this assembled pair in parallel to the chassis battery so that I get the start boost as well as charging the coach batteries while driving. Has anyone out there done this and are there any pitfalls to watch out for. I will try to get some pics posted to show the setup as it is now with the many wires coming into and attaching to the chassis battery. Thanks in advance.
Marty
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Old 03-16-2016, 12:30 PM   #2
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Do NOT wire two 12 volt batteries in series ! ! ! You will fry multiple 12 volt powered items in your vehicle.

There is a reason that chassis (engine) battery and coach battery are separate, so you can still start your vehicle when you run down your coach battery. There may already be a device that allows your converter/charger to feed power to the chassis battery when its voltage drops below a certain point, there is on newer RVs but don't know if you'll have it on your '98
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Old 03-16-2016, 02:29 PM   #3
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I would venture to guess that the 2, 250AH batteries you are talking about are 6 volt. Yes they can be wired in a series set.

You don't want to parallel them to a start battery. The ability to temporary parallel is what the boost switch does.

Your batteries are only charged by two sources, the engine alternator and the converter.

When the alt is charging the start batt, there is probably a parallel relay in the circuit to connect the house batt. Some sense voltage some just engage with the key.

On the converter side, it charges your house batt. It runs off the shore cord or generator. The output will be the same.

You may have an automatic device to parallel it to the start batt, when charging but many do not.

Have a good start battery and a seperate house bank. ( as many as you like ). Join them when charging is available. Seperate them when it is not.
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Old 03-17-2016, 08:40 AM   #4
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Originally Posted by powercat_ras View Post
Do NOT wire two 12 volt batteries in series ! ! ! You will fry multiple 12 volt powered items in your vehicle.

There is a reason that chassis (engine) battery and coach battery are separate, so you can still start your vehicle when you run down your coach battery. There may already be a device that allows your converter/charger to feed power to the chassis battery when its voltage drops below a certain point, there is on newer RVs but don't know if you'll have it on your '98
I guess I left some detail out. I was not considering wiring 2 12volt batteries in series as this would produce 24volts. Yes the batteries I mentioned wiring in series are 6volt. I was thinking of once these 2 are paired in series wiring the pair as 1 12volt in parallel to the chassis battery. I have to get under and behind the coach and trace all of the wires coming into the battery compartment as there are a few pairs coming in there. Thanks for all of the advice guys.
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Old 03-17-2016, 09:00 AM   #5
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Originally Posted by m.elliott63 View Post
. . . Yes the batteries I mentioned wiring in series are 6volt. I was thinking of once these 2 are paired in series wiring the pair as 1 12volt in parallel to the chassis battery.
I wouldn't do that. You don't want to run your chassis battery down to 50% on a regular basis and you need to be able to start the engine if you do run the house batteries down. You've got a boost switch, that will let you connect the two sets if needed. You should probably figure out what the manufacturer designed, then determine what got changed and finally decide for yourself what is really needed.
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Old 03-17-2016, 09:37 AM   #6
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Quote:
Originally Posted by m.elliott63 View Post
The 12volt cranking battery that is required for thr chassis is in the same compartment under the steps as the coach battery. What I am thinking would be the best way to go is to get (2) 250+ AH batteries wired in series for the coach/house batteries to get longer lasting power. Then, wire this assembled pair in parallel to the chassis battery so that I get the start boost as well as charging the coach batteries while driving. Has anyone out there done this and are there any pitfalls to watch out for. I will try to get some pics posted to show the setup as it is now with the many wires coming into and attaching to the chassis battery. Thanks in advance.
Marty
m.elliott63
Are you aware that the chassis battery and the house batteries in a motor home are never permanently wired together?
They are wired separately to provide the necessary battery power to 2 similar, (but completely different 12V systems).

However the house and chassis batteries in most motor homes can be temporarily connected together, (with the "battery boost switch"), if/when you allow one or the other to discharge to a voltage so low that it can't do it's job.

Mel
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Old 03-17-2016, 10:24 AM   #7
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Good Advice

Quote:
Originally Posted by mel s View Post
m.elliott63
Are you aware that the chassis battery and the house batteries in a motor home are never permanently wired together?
They are wired separately to provide the necessary battery power to 2 similar, (but completely different 12V systems).

However the house and chassis batteries in most motor homes can be temporarily connected together, (with the "battery boost switch"), if/when you allow one or the other to discharge to a voltage so low that it can't do it's job.

Mel
'96 Safari
Mel,
I was not aware that they are not permanently wired together. That is why I posed the question and I thank you for clearing that up for me.

mriderleon,
That is a good point I did not consider of running down a non-deep cycle battery on a regular basis...makes sense. To your point, I am trying to figure out what the manufacturer designed and determine what got changed so I can correct what I inherited when I bought this coach in November. She is at the shop today getting all new shocks, steering dampner and all new fluids. I will post some pictures when I get her back home and spend some quality time tracing all of the cables down. Thanks for all the good advice guys.
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Old 03-17-2016, 11:17 AM   #8
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Mel,
I was not aware that they are not permanently wired together. That is why I posed the question and I thank you for clearing that up for me.
m.elliott63
I found all 7 of the short videos, (part 1-7), here helpful when trying to understand how the different electrical systems work in my coach.
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