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Old 09-26-2009, 09:21 PM   #1
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Expanded Battery Bank?

Not quite sure where to post this question...

I am considering expanding my battery bank on the trailer from 2 to 3 AGM group 27 marine batteries (weight/balance issues permitting). But in addition to that, I want to know if anyone has expanded their battery bank to include an in-bed bank in their tow vehicle. I would make sure that the weight/balance was within parameters for the TV and towing the trailer. My intent would be to connect the two via a marine grade umbilical.

Has anyone done this? Am I crazy?

I like to boondock, but periodically stay at full hookups along the way. I could charge up the combined bank at the point and have more "staying power" once I am in the "wilds".

Any input/encouragement would be appreciate.

The wife is giving me that funny look...
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Old 09-26-2009, 09:40 PM   #2
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Quote:
Originally Posted by BeBop View Post
Not quite sure where to post this question...

I am considering expanding my battery bank on the trailer from 2 to 3 AGM group 27 marine batteries (weight/balance issues permitting). But in addition to that, I want to know if anyone has expanded their battery bank to include an in-bed bank in their tow vehicle. I would make sure that the weight/balance was within parameters for the TV and towing the trailer. My intent would be to connect the two via a marine grade umbilical.

Has anyone done this? Am I crazy?

I like to boondock, but periodically stay at full hookups along the way. I could charge up the combined bank at the point and have more "staying power" once I am in the "wilds".

Any input/encouragement would be appreciate.

The wife is giving me that funny look...
I am going to upgrade from two to three batteries when mine go flat. They are headed that way after several years of heavy use. I currently have two sealed G27s. I will be adding a third on under the couch (in front) after I clean up the mess the factory calls wiring. I am adding extra solar panels next weekend.

Adding batteries in the TV bed would work but you would need a way to charge them and heavy guage wire to connect back to the trailer.
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Old 09-26-2009, 09:53 PM   #3
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you might want to contact this member:
http://www.airforums.com/forums/memb...ter-10325.html

he has done a lot with solar and added batteries in his sprinter van. i'm sure he can can steer you in the right direction.
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Old 09-26-2009, 10:11 PM   #4
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You're thinking just as I am thinking: a few more batteries will give you quite a bit more boondocking time between recharges; and Lewster is indeed the expert.

I also have considered adding a battery or two or three in the pickup bed (up front) - weight not a problem there, and then using welding cables (#4 or so) to connect them to the main coach battery bank. Welding supply shops sell high-currrent d.c. cable connector plugs for easily and quickly connecting / disconnecting such a battery bank.

Lewster will tell you to go with 4/0 cables to reduce voltage drop, and in an ideal world, he's no doubt right, but I think you might go lighter if you don't plan on large current draws. There are charts on the Internet which will give you voltage drop formulae, etc. so you can do your own calculations. In my case, current draw would be minimal ... just for a few lights, occasionally the pump, and perhaps the stereo, though in cold weather, I tend to use the furnace, and its fan is a pretty significant amp hog.

When boondocking, charging would be with generator for a few hours every few days or so, or if I can swing it, via some solar panels on the roof of the 'stream. My truck's got a 190 amp alternator and a "camper wiring harness" in addition to the trailer wiring harness, so I might be able to run that camper harness into the bed and tap it for a few amps of charging capacity while towing, thus at least arriving in the middle of nowhere whith fully charged batteries.

Good luck. Let us know what you do.
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Old 09-26-2009, 10:13 PM   #5
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Quote:
Originally Posted by BeBop View Post
...in addition to that, I want to know if anyone has expanded their battery bank to include an in-bed bank in their tow vehicle. I would make sure that the weight/balance was within parameters for the TV and towing the trailer. My intent would be to connect the two via a marine grade umbilical...
hi 'bop

i'm planning to do the 2 to 3 battery dance too.

THAT is one of the reasons to stick with 12 volt cells.

4 or 6 i'd consider 6 volt cells but there are DOZENS of thread they argue this issue, without end...

connecting is pretty straight forward, but i'm no electrican...

-the batteries need to be the same type and capacity and age...

-the wiring to each battery needs to be the SAME LENGTH, so that they charge/discharge evenly.

-in extreme temps (hot or cold) the batteries need to be ~ the same temps.

-the charger/converter needs to have adequate CAPACITY for the battery banks...

for example the 40-45 amp units many trailers have isn't ideal for charging more than 2 batteries at faster speeds.

i've upgraded to an 80 amp charger/converter that will operate better with 3 or 4 grp 27s

artstream has 3-4 batteries in the truck along with 2 at the nose of the stream...

his solar panels are on the truck too and the pv controller is also truck side.

not sure how he handled the wiring issue, but one could account for the distance by using LARGER gauge wire, i think.

there are formulae for the wire length/gauge voltage loss issue.

here are 2 threads where he briefly mentions his set up...

http://www.airforums.com/forums/f448...ice-39392.html

http://www.airforums.com/forums/f448...wer-42328.html

and a single post on his usage...

http://www.airforums.com/forums/622744-post30.html

the wiring segments can be purchased PRE made to length/gauge with end fasteners..

OR one can buy wire and ends and roll your own, how the end/connectors are fastened is important for GOOD juicy flow.

my intention is too mount the 3rd battery under the sofa between the others and vented into the existing boxes...

whatever you do TAKE pictures and electrify us with the images!

cheers
2air'
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Old 09-27-2009, 01:47 AM   #6
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Another option for the the 'third' battery....
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Old 09-27-2009, 04:58 AM   #7
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I've a total of 4 AGM batteries now. 440ah.
One in the tongue box, three positioned under the front couch.
Weight is about 280#. Or, ~ 180# more than the the two 24 series that were originally there.
Goal is to watch limitless big-screen TV, and, still be able to run lights, fans, etc.
I'll charge them each day. I guess in a pinch, we could become conservers and make those batteries last 2-3 days.

Tom W
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Old 09-27-2009, 08:42 AM   #8
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Quote:
Originally Posted by 2airishuman View Post

-the wiring to each battery needs to be the SAME LENGTH, so that they charge/discharge evenly.
I checked with a guy that is a licensed electrician and solar guy he thinks the lengths makes no difference.

It is more important to have the correct guage
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Old 09-27-2009, 09:29 AM   #9
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If you mount additional batts in the truck bed (to connect to TT with long cables), be sure and mount a fuse/curcuit breaker, as close to batts as is practicable, to protect the wiring. A disconnect switch also should be used in the installation.
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Old 09-27-2009, 11:56 AM   #10
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I checked with a guy that is a licensed electrician and solar guy he thinks the lengths makes no difference.

It is more important to have the correct guage
hi bob

your info might be right, i haven't a clue.

but ALL of the links i've found suggest voltage loss is a function of...

LENGTH, GAUGE, and internal resistance (type of wire) with varied importance for each.

perhaps a few inches or feet is no biggie but the voltage loss calculators ALL include length, maybe just to confuse us

it appears this all depends on how much system loss is tolerable (1% or 50%), voltage (12v or 240v) ac/dc and sensitivity of the gadgets involved.

search "voltage loss wire length" and a plethora of links light up.

Stealth 316 - Wire Resistance and Voltage Drop Calculator

for a good starting point on all things 12v here is a link to a guy that writes for the escapees.

The 12volt Side of Life (Part 1)

there are many ways to make/extract juice, an equal number of needs for power, but only a few correct wiring schemes...

keep in mind parallel wiring means 2 sections of wire for each battery, connected to the charger and grid...

cheers
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Old 09-27-2009, 12:26 PM   #11
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He went on to say that if you had say a ground 2' long and a positive 6' you figure the loss at 8'

Another battery could have 6' & 6' =12

Both going to the same converter or charger

You take the combined lengths of all the cables, but they need not be equal.

In this case 20'
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Old 09-27-2009, 08:02 PM   #12
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I am going to upgrade from two to three batteries when mine go flat. They are headed that way after several years of heavy use. I currently have two sealed G27s. I will be adding a third on under the couch (in front) after I clean up the mess the factory calls wiring. I am adding extra solar panels next weekend.

Adding batteries in the TV bed would work but you would need a way to charge them and heavy guage wire to connect back to the trailer.
I have been looking at Blue Sea Systems Catalog of and on all day. I had to study for a math test tomorrow. I am going to install three battery switches so I can isolate one if it goes bad. Fuses of course. I am also going to install a real distribution panel with real circuit breakers. One will have the solar on it. An Amp Meter for each battery, so I can see the draw. Yeah I know I can get a tri-metric. A volt meter for each battery isolated and compensated by a diode.
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Old 12-18-2009, 02:03 PM   #13
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The lengths do matter but maybe not much. It depends. Here's the math.

In general, there's not much benefit in lowering the difference in voltage drop between battery strings to less than 0.1 volts, because differences in battery and terminal performance, and battery temperature, will predominate at that point.

The voltage drop in a piece of wire is given by Ohm's law:

E = I * R

I is the maximum current per battery. In RV applications, the charging current will almost always be greater than the maximum discharge current that sustained for any length of time unless you have an inverter. If you have a 50 amp converter, and 3 batteries, I would be 13.33 amps (50 divided by 4). R is the wire resistance, and E is the voltage drop.

There's a table of wire resistance here:

American Wire Gauge, AWG Cable Size Description for Copper Wire Cable

4 gauge wire has a resistance of .2533 ohms per thousand feet, or .0002533 ohms per foot.

So E = I*R, with, say, 30 feet of difference between wire lengths between the closest and farthest batteries in a three battery setup, and the 50 amp converter, would give us E = .007599 * 13.33, or about 0.1 volt.

As others have noted, it's the total wire length that matters, adding together the difference in the negative cable length and the difference in the positive cable length.

With most 12V battery installations most of the voltage drop is at the terminals, not in the wire. Having larger size cable helps a little, but it's really about getting the highest quality ends and crimping or soldering them in place properly. I've seen lots of battery cables overheat at the terminals in regular use. The only ones I've seen overheat in the middle are the ones that have suffered an unfused short, which is a subject for a different thread.
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Old 02-14-2010, 03:35 PM   #14
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My 01 Excella has 2 and I will be going to three in the next month. I plan on using the “tool-box” on the tongue for the additional group 27, the other two in the normal place. All Lifeline AGM’s. Lots to consider…fuses, wire size, wire length, charging capacity of the TV and converter….the list goes on. I have also upgraded the TV with an additional 105A alternator dedicated to the RV. Will be running 2/0 back to the RV with a separate 10-gauge battery sensor wire…Anderson plug and a 4pin for that stuff. Should be able to get realistic charging from the TV to the 300A bank. The added tongue weight should not be an issue given its location…may need to beef up the box, just in case. There is probably more, just haven't thought about it yet.
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