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Old 03-18-2016, 03:40 PM   #221
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Actually, that is not really true. The two 6 volt batteries are in series, you cannot charge or discharge one without the same current flowing from/to the other. When you charge them, the same voltage will be applied (and dropped by each battery.)
Scott,

How will placing a higher resistance than needed between the cells not effect the overall performance of the stack?

As the batteries discharge, won't the internal resistance load have a real impact on performance? These schematics show a 12 volt battery with an internal resistance under various states of discharge. Picture if you will a similar example but just put that resistor (unnecessary wire resistance) "in the middle" of the battery stack pictured.

I can be taught!
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Old 03-18-2016, 05:08 PM   #222
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Scott...
Sure, any resistance will drop voltage and it really doesn't matter where it is as long as it is in the circuit. Resistance is resistance.

Now, hopefully I didn't make a math mistake here, but the numbers feel right. Let's say that your load (power panel, hydraulic jacks, inverter) is 6 feet from the batteries. If you use #4 cable, that will be 12 feet of #4 at 0.0002530 ohms per foot. (Actually these cables have such low resistance it is quoted in ohms per 1000 feet! At 100 amps, that will drop the voltage (let's say it is 12.7 volts unloaded) 303 millivolts or about 2.39%. Decent drop, but most people calculate less than 3% for critical loads and practically speaking, a hydraulic pump is not a critical load. But no matter! If you add 12 inches of #4 between two 6 volt batteries, rather than using a single 12 volt battery, that cable will simply add its own 25 millivolts of voltage drop at 100 amps...which is an additional .14%, for a total drop of 2.53%. It's really like moving the load another 6 inches away from the batteries.

Now, it you go absolutely crazy and use a #0000 cable between the two batteries rather than the #4, it will add its own 5 millivolts of drop, saving you about 20 millivolts (.04%) when compared to the #4 cable, and .1% in voltage drop. Not a number to go crazy about and remember, 100 amps is not exactly a light load!

These are all for stranded conductors.

Your example diagrams have very significant resistances in them, 1 foot of #0000 cable has a resistance of 0.00005 ohms, while 1 foot of #4 has a resistance of 0.000253 ohms, both of which are really small numbers. Sure #0000 has a resistance of around 20% of #4, but it still is negligible when compared to the rest of the wiring, connectors, switches, solenoids, etc.

Bottom line is that it doesn't matter where the resistance is...as long as it is somewhere in the circuit between the battery and the load (or even between two batteries and the load.

I am still mad af Forest River for putting my converter in the rear power bay and running 22 feet of #6 to the batteries up front. That is 44 feet of #6 and costs me a significant amount of voltage drop with a 70 amp converter. At the very least they could have grounded the converter negative to the chassis and cut the effective amount of #6 to maybe 22 feet since the chassis acts like a pretty big conductor, virtually eliminating half of the run and voltage drop!
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Old 03-18-2016, 05:45 PM   #223
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Yes, chassis = Buss Bar we talked about.

I believe the graphics were from an article on deep cycle lead acid battery internal resistance at various states of charge. I seem to recall the discussion revolved around the internal resistance going up as the capacity to deliver electrons went down (battery discharged). The higher the internal resistance got, the lower the delivered voltage or some such.

Car batteries, which are made different (very thin waffled plates) have much lower internal resistance numbers than deep cycle batteries (thick flat plates). DP (marine) have thicker plates than car batteries and also have grids on the faces and fall in the middle.

Thank you. Like I said; I can be taught.
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Old 03-18-2016, 06:32 PM   #224
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Originally Posted by Herk7769 View Post
Yes, chassis = Buss Bar we talked about.

I believe the graphics were from an article on deep cycle lead acid battery internal resistance at various states of charge. I seem to recall the discussion revolved around the internal resistance going up as the capacity to deliver electrons went down (battery discharged). The higher the internal resistance got, the lower the delivered voltage or some such.

Thank you. Like I said; I can be taught.
You are absolutely correct about internal resistance increasing as a lead acid battery is discharging, it is almost linear. This results in it being less efficient (the more it is discharged) when there is a high amperage draw.
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Old 03-18-2016, 07:00 PM   #225
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Here is a terrific article on battery banks.
It also recommends 0 wire "inter-battery" ...

https://www.windynation.com/jzv/inf/...ight-wire-size
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Old 03-18-2016, 07:11 PM   #226
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Here is a terrific article on battery banks.
It also recommends 0 wire "inter-battery" ...

https://www.windynation.com/jzv/inf/...ight-wire-size
Well, I agree with it, but that means that every wire on the 12 v load side, including the inverter feed and converter feed should be #0 or whatever. My response was that the wires that go from the batteries to the loads are far more important than the inter battery leads, since they are way, way longer and carry the same current. Replace your longest feed wire with something big and the benefits will be greater than just doing the interbattery leads. If you are going to wire your panel and inverter with #0, by all means do it for all of the battery leads.
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Old 03-18-2016, 07:44 PM   #227
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Too Tall by the time this tread finally wears it's self out you will have had the most researched, analyzed, detailed, taked about, 12 volt to 6 Volt system on a TT know to MAN. You can put a sign on the tung "Approved by Forest River Forum" I will stick with 12V but know where to go if I decide to change.
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Old 03-18-2016, 08:09 PM   #228
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I have really not search info for batteries, and have learned a great deal and never probably never really done this much reading unless it was here, great info, and I too have learned from your posts, thanks
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Old 03-18-2016, 08:39 PM   #229
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Too Tall by the time this tread finally wears it's self out you will have had the most researched, analyzed, detailed, taked about, 12 volt to 6 Volt system on a TT know to MAN. You can put a sign on the tung "Approved by Forest River Forum" I will stick with 12V but know where to go if I decide to change.
As the starter of this thread I will admit that there is a lot of good info here. Not that the average new RV user could understand most of it. My main question was if 2- 6 volt batteries would last longer than 2- 12 volts and if it was worth spending the money for the upgrade. I think I got out of this thread the answer is yes Today I took the plunge and ordered a Duel golf cart battery box like Too Talls. Once it arrives I will probably be purchasing 2 Energizer 6 volt GC2 batteries from Sam's club. Will I still be able to use a regular 12 volt charger? (And how about some simple answers)
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Old 03-18-2016, 08:50 PM   #230
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Yes.


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