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Post Info TOPIC: Battery Bank Location


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Battery Bank Location


Hello, folks. I am in the process of fixing up an old Class C.   I put in a new house battery, in the engine compartment, and have not hooked it up yet because I am going to add two more batteries to the bank.  (I don't think my 200W solar panels will fit on the roof, but I'll figure that out...) The new batteries will be in the rear of the rig, about 20ft away from the existing battery (40ft of cable) .  Any thoughts on how the grossly-different cable lengths between batteries will affect my bank life? 

TIA, Stew



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What gauge wire do you plan on using?

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Winnebago TT 2101DS & Tahoe LTZ, 300 watts WindyNation solar-parallel w/MPPT, 2 Trojan T-125s. TALL flag pole. Prefer USFS, COE, BLM, USF&WS, NPS, TVA, state/county campgrounds. 14 year Army vet-11B40 then 11A - old MOS 1542 & 1560.



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They have 6AWG ruining from the house battery, located under the hood, to the fuse panel in the very rear of the coach (26ft +). That sounds okay for a few lights and charging, but not for a heavy load such as an inverter. So let me rephrase my question ;

On a bank with one remote battery, and given the losses in the longer run, will the remote battery discharge at the same rate as the other two, which are only1ft apart?

If so, I think I can tie them together and charge them with one controller (alternator, shore power or solar). But if the long cable run will damage the bank I could leave the house battery on its own and set up the two other batts for only the inverter. (not my favorite option). I guess my third option is to tie them together, monitor the remote battery and see what happens...

FWIW,  a voltage regulator is NOT my preferred method of charging.  I will need to find a smart charger to put between the alternator and the battery bank.



-- Edited by s2man on Sunday 9th of September 2018 06:32:18 PM



-- Edited by s2man on Sunday 9th of September 2018 06:34:16 PM

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I think 6 awg will let you have a draw of 780 watts. Not a lot of power. I'm thinking that maybe 1 awg may be a better bet which will give you 1500 watts of draw capacity. This chart may be of some help. cerrowire.com/ampacity-charts. You don't say what your draw will be but you seem concerned about the inverter. The inverter itself won't draw much power until you hook up something that is actually going to do some work (draw power). This is what you need to concern yourself with. The device you are attaching to the inverter divided by the efficiency of the inverter will give you the draw on your battery bank. For instance, if you have a appliance that will draw 100 watts of power and your inverter is 80% efficient you will be drawing 125 watts from your batteries (100/.8=125). This may be one of those situations where 12v appliances etc. may be your best bet. You also might want to check out this video. www.youtube.com/watch After looking at all of this I think you may want to relocate your battery that is under the hood. Just my two cents.

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Arca, the mfr's house battery location will have to stay under the hood. It is attached to the alternator, the house 12V distribution panel, the 110V charger and a solenoid to make it a backup starting battery.  Hence my concern about the differing cable lengths between batteries :-/  

If my inverter asks for 600W, that is only 200W/battery.  That doesn't sound bad.  To clarify my question ; How will differing cable lengths between batteries affect the life of the bank?   Will the remote battery discharge faster or slower than the rest of the bank?   Will they equalize when the load is stopped?   Will it cause one or more batteries to die prematurely?



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Sorry, answers to your questions are above my paygrade. I will be interested in the answers however.

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Winnebago TT 2101DS & Tahoe LTZ, 300 watts WindyNation solar-parallel w/MPPT, 2 Trojan T-125s. TALL flag pole. Prefer USFS, COE, BLM, USF&WS, NPS, TVA, state/county campgrounds. 14 year Army vet-11B40 then 11A - old MOS 1542 & 1560.



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I think this may be above my pay grade too but I'm going to give it a shot. Being that the batteries in your bank (3) should all discharge at the same rate they should all be identical. Once that's accomplished you have the issue of voltage drop between the front battery and the back two batteries. This voltage drop must be kept to a minimum, preferably less than 1%, thus my suggestion for the large cables above. The computation of the voltage drop is a math problem. I believe that the formula is

VD = I × (2 × L × R / 1000)
Where ;
VD = Voltage Drop in Volts.
I = Wire Current in Amperes.
R = Wire Resistance in Ohms (Ω) [Ω/kft].
L = wire distance in feet.

Which I found here:www.electricaltechnology.org/2014/12/advance-voltage-drop-calculator-voltage-drop-formula.html

You might want to check my computations but from what saw on the site you would need a AWG of 6/0 which is pretty sizable wire, and that's at 90 deg. F. If the temp goes up, the wire size goes up. Even if my computation is off, and it may well be as I don't know what a -6 size wire is, this is still going to be pretty big wire due to the 125 amps to get 1500 watts at 12 volts. Obviously, if the watts go down the amperage goes down. You can get the information for the formula above at one of many sites on the web. I believe that the second video above has the required information and the appropriate search criteria. My brain is mush now so I'll leave the rest to you.

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But Larry, i have security clearance on a need-to-know basis. You can tell me. ;-D

Thanks, folks. I'll let you know when/if I get a definitive answer. It seems to spell premature bank failure to me, but you fit things where you can in an RV.

In the meantime, I guess I'll tie them all together properly. Three identical batteries ;When one dies I'll replace the entire bank.

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s2man, while a had a security clearance I never got to the pay grade to give one to others or determine who needed to know. lol I do remember the "secret" classrooms at Ft. Benning and the joke was always "the Russians already know."

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Winnebago TT 2101DS & Tahoe LTZ, 300 watts WindyNation solar-parallel w/MPPT, 2 Trojan T-125s. TALL flag pole. Prefer USFS, COE, BLM, USF&WS, NPS, TVA, state/county campgrounds. 14 year Army vet-11B40 then 11A - old MOS 1542 & 1560.

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