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Old 01-05-2013, 08:55 AM   #15
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I also have two strings of 6 volt batteries for a 440 AH supply. The only issue that I have had was with the alternator working very hard to fill them up after a long day on the batteries. I do have a solar panel as well, but it does not keep up with the load. If the batteries are down, I will start up the generator and allow the converter to fill up the batteries for a while so the alternator does not have to take the whole load. I melted down a 100 A alternator one time.


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Old 01-05-2013, 10:37 AM   #16
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Originally Posted by Damon92 View Post
The microwave to me is not worth upgrading the inverter. I just don't use it that much. I would like to stay with the setup I have because even if my chassis battery dies I have an override switch for the isolator that allows me to draw from the coach side of things. (Cummins doesn't like the cold) Im looking at adding 1 more deep cycle 12 v to my coach bank. My question is if I have 2 coach batteries....which one should I hook my inverter to and does it even matter?

Thank y'all!
Not a problem, If you have connected them positive to positive and negative to negative then you have doubled the amp hour capacity (if you have used the same batteries). You should have used as large connector cables within the bank as possible (you might want to consider welding cable). Then make sure the set of cables going to the inverter are a little larger than spec'd by the inverter maker.

It does not matter, If you oversize the cables now as you load the system in the furture you will be able to grow a little without re-cabling. My coach came with 2 12 volt batteries if no inverter was installed and the factory increased this to 3 batteries if it was equiped with a inverter. I have added one more to the coach battery bank for a total of 4.

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Old 01-05-2013, 11:23 AM   #17
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Adding one battery usually is not a problem that this post is responding to. But if one more if OK then 2 will be better. As we look at the battery bank that is true.

But there is more to this than the number of batteries. The cables connecting the batteries together must be able to handle the entire current draw on the entire bank.

The cables going to a load must be able to handle the maximum current of that load. Most of the time the inverter is one load on the bank and the coach 12 volt circuits collectively are another load. This means that the cables to the fuse block must be able to handle the entire fuse bank load.

If you add additional loads then you must keep these rules in mind and change cables as needed.

Everything comming off the battery bank needs a fuse to protect it. This means all cables EXCEPT THE GROUND are fused before they leave the area of the battery bank. Even though there is only 12 vdc available the current draw can be massive. This represents a higher fire hazzard than the 120 vac circuits. Pay attention FIRE hazzard.

Having covered the basics of cable and load safety, you must keep these batteries charged. Most modern converters are self limiting in the current output they will produce. They are rated at this maximum current. If you choose to load your converter to the maximum then you can consider the life of the converter will be short as comapred to the other guy who only loads his converter at 75% of maximum rating.

If you allow the battery bank to drop to the low limit each morning when you fire up the converter (genset or shore power) then you will load your converter to the maximum. Your battery bank should be big enough that the voltage is within reason when it comes time to charge it. Your converter rating should be large enough to take care of the entire coach load except the inverter that is used for short times. If the converter is being used to supply a domestic refer then its load is also part of the constant load on the converter. Then you should have converter capacity to charge the batteries in addition of the constant load of the coach. The short story here is as you add load you also need to keep in mind that you should someday add converter capacity.

Some coaches but not all have a battery isolator. This is designed to charge through but to block discharging through the battery isolator. Now with this bi-directional device we can charge both banks from either the converter (read the preceding) or the engine alternator.

An important note here is with one of these devices you now have added additional batteries to the load side but isolated them from the discharge side. You need to add the charging load of the second battery bank as load.

The alternator is a self limiting current device. Technically you can not overload it. A 30 amp alternator should do just fine charging a huge bank. The only condition is that it will take much longer than a 200 amp alternator.

In the real world that is not the case. The internal regulator which handles the current output is set to load the windings to what some would consider a overload. This causes heat build up in a alternator which is running in a hot enviroment anyway. This will cause a alternator failure. Larger alternators will help but they come with regulators that load their windings just like the smaller ones. Generally the best thing to do here is to get your hands on a alternator as large as you can mount or afford. When and if it fails you might want to contact a alternator shop and ask about getting windings that are rated for more amps. This will not increase the output but because you will use the original regulator it will get you a built-in margin for the alternator running at maximum output.

Used to burn out the alternator in my Goldwing now that I have used windings rated at 40 amps it does just fine. It still gets loaded at 30 amps which limited its life as that was its maximum rating with the faqctory windings. When overloade to charge dead batteries it generates less heat in feeding that load.
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Old 01-05-2013, 11:47 AM   #18
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Q1. Should I hook up a 2nd house battery parallel? Since there is an isolator between the 2 batteries on it now, I should still be safe from draining starter battery?

There is nothing you can do to be 100% safe but, the more batteries you have on the house, the longer it will take before you have a problem.. NOTE: You need more battery.

Q2. Will I be hurting or helping my alternator by adding a 2nd house battery?

You will not be helping it,, As for hurting... Well, likely no but I won't guarantee.

q3. Current House battery is 6 months old. Is that too old to mate with new battery?

There are some who shudder at connecting batteries that are not twins, I mean consecutive serial numbers if possible. (Ok perhaps not that far) but you are well within the safe range in my opinion.

Now, You said you want the inverter to run a fridge.. Most residential refrigerators are in teh 100-200 watt range.. RV absorption types 300-400 watts. (That's running of course)

100 watts is about 10 amps (10 amp hours per hour running time) on the 12 volt system via the inverter (It's not exact, but it's very close and it really makes the math simple)

A common group 27 battery has about 95-100 amp horus at the 20 hour rate, A group 31 perhaps 130. If they are DEEP CYCLE you can safely use 1/2 the capacity or 100 amp hours, if they are Marine/deep cycle, about half that

A pair of golf car batteries in series are deep cycle, and 230 amp hours (115 usable) AGM's (Some brands like Lifeline) may be able to give up more of their capacity before serious damage sets in but they are EXPENSIVE!!!. I'm also not convinced they can in fact give up more.

Now if you are running an Absorption type Fridge (RV type) on PROPANE.. the 12 volt demand drops to a single digit,, and a small one at that (Less than half the light bulb if door closed)

And there are high efficiency compressor units that draw 30-40 watts (Right in the range of some of your light bulbs)

I know this is confusing, but if you post more specifics.

What fridge,
What else the inverter will power
and what size group the batteries are, plus battery type. We can get more specific.
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Old 01-05-2013, 05:02 PM   #19
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Like my earlier post, interested in fridge and tv while traveling down road. I appreciate the input and I'm gonna hook up 2nd battery.
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Old 01-05-2013, 05:10 PM   #20
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Originally Posted by Gorlininc View Post
Hi Mr D

You would gain 50 percent more usage. The real question is how often do you dry camp. I thought about the same thing. But I realized I don't dry camp that much or for very long. Either way you have a generator you can turn on to charge the batteries you have. My conclusion was it was not worth it to me. Unless one other reason. If you have a residential refrigerator. Then it may be worth it, if you plan on dry camping.
That's one mans opinion.
Don't dry camp often, usually just in Wal*Marts on the war to a destination and then usually only for one or two days so the battery capacity is OK unless we go to a residential refer. I've replaced the cooling unit with an Amish unit, then the heating element burned out and I've found the door gaskets are splitting and no parts available from Dometic although other places have them but the cost is high, almost $300 for the two gaskets! At that rate I might as well replace the whole thing next.
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Old 01-06-2013, 03:33 PM   #21
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I'm doing the opposite next time. Going to only 1 12V Deep Cycle battery instead of 2 6v golf cart batteries. This will save me about $100 and 75lbs weight.
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Old 01-06-2013, 05:40 PM   #22
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Originally Posted by RV Wizard View Post
If the house battery you now have checks good on a battery tester you should have no problem adding a 2nd (like) battery to the equation. I would also recommend you do add a battery, connected in parallel to the house battery already in the coach. It will not harm the alternator as long as it and the others do not short out internally. Good luck and keep us posted.
Times two.
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Old 01-06-2013, 05:51 PM   #23
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Every Rig should have 4-6volt house batteries.

I have added two more 6 volt batteries to my allready two. I may not dry camp very often but when I do if my batteries get too low I just turn on the Gen set for a while it brings them back up.
Just a thought

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