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Old 11-30-2014, 12:02 PM   #1
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rv vs 12v charging from alternator

Okay, I did some searching but didn't find an answer. It's time for new batteries, SO:
1. Do I stay with 12v or make the switch to 6v?

2. If I make the switch to 6v, how do I wire them so I can charge them while running the vehicle? I understand how to wire something in series, but then where do I connect the 12v line from the separator/starting battery?

The goal here is to gain Amp Hours. I have a furnace, fridge, stereo, lights (LED), 12v outlets, etc. Not a huge demand, but with 212ah I'm waking up in the morning with my charge controller blinking red telling me low batteries.

Any help would be great.
Thanks!
C
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Old 11-30-2014, 01:08 PM   #2
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Re: rv vs 12v charging from alternator

Only way to gain amp-hours is by adding more batteries or providing input (eg solar or generator) from alternate source.

For AGM/flooded: 212 aH sounds like a single 4D 12volt. That gives usable 106 aH. You first should look at what your electrical usages are for a 24 hr to 48 hr period, then size your battery bank from here. Re: 6 or 12 v? Not sure it matters as to achieve for example 220 aH total, you can have four 6v golf cart style at 110 aH each or two 12 v group 31's at 110 each or one 12v 4D at 220. To achieve 440H, you would double all those quantities. I personally would stay with 12v rated batteries for simplicity and go w/ AGM. We just have to be very careful to monitor drawdown and charging to get good life out of lead acid based batteries. Good monitoring systems are pretty much essential in our set ups.

Now, if you go Lithium (if your van.bankacct can tolerate the $$ withdrawal) things change quite a bit. You can draw down a Lithium battery by 90%, so the usable capacity of a 125 aH Li batttery is about equal to a 212 aH AGM or flooded battery. It also weighs about 75% less than an AGM. Some reported downsides are poor charging charteristics in cold weather, which would be an issue where you are. Upsides are something like ten year life.

Some else cna answer the connection question if you decide to go 6 volts.

Ray
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Old 11-30-2014, 01:20 PM   #3
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Re: rv vs 12v charging from alternator

Thanks Ray!
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Old 12-01-2014, 08:27 PM   #4
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Re: rv vs 12v charging from alternator


Results = 12v @ 220ah not 440ah

Some factors to think about:
What is the quality of the lead used.
How many cycles does each type have.
How deep can you discharge the battery.
How well does each stand up to off road use.
How fast does the battery charge up.
How many connections that can fail.
How difficult are they to maintain.
What effects does cold weather have on each type.
Self discharge rates.
How long will they last.
Price.

For me it was a no brainer... 12v 220ah AGM. But YMMV.
This is from the FAQ in this section and there are a few posts you can look at too.
http://www.solar-electric.com/deep-cycl ... y-faq.html
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Old 12-01-2014, 08:32 PM   #5
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Re: rv vs 12v charging from alternator

Quote:
Originally Posted by 1der

Now, if you go Lithium (if your van.bankacct can tolerate the $$ withdrawal) things change quite a bit. You can draw down a Lithium battery by 90%, so the usable capacity of a 125 aH Li batttery is about equal to a 212 aH AGM or flooded battery. It also weighs about 75% less than an AGM. Some reported downsides are poor charging charteristics in cold weather, which would be an issue where you are. Upsides are something like ten year life.

Some else cna answer the connection question if you decide to go 6 volts.

Ray
I agree Ray and I can't wait until the price of those go down.
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Old 12-02-2014, 12:25 AM   #6
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Re: rv vs 12v charging from alternator

A 117lb battery or two doesn't make that much difference in a 10,000lb vehicle.

Also if I switched to 6v say, that would at least four in my house bank and I have enough trouble with the two I've already got.

If I was building from scratch and only needed two 6v I'd probably give it a go, but just swapping I'll stick with the big AGM.
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Old 12-03-2014, 02:34 PM   #7
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Re: rv vs 12v charging from alternator

2 6V 200Ah batts = 12V/200Ah (with roughly 100Ah +/- usable) Series wired

2 12V 100Ah batts= 12V/200Ah (with roughly 100Ah +/- usable) Parallel wired

The above batteries should be roughly the same size (volume) since it's mostly about energy density, so TINSTAAFL.........

Obviously, if you only have room for one battery, the 6V solution won't work.

One disadvantage of 6V wired in series is if you have one go bad, you are left with no power. With 12V there is the possibility of limping by on one.
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Old 12-03-2014, 04:42 PM   #8
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Re: rv vs 12v charging from alternator

The single 4-D 210ah battery I had was a bit too small for me so I added a second. I barely had enough room to add another battery box. One of the best upgrades I've done but not cheap by any means. If I wouldn't have had the room I would have looked into going with an 8-D but two 4-D's are way more amp hours (420) than a single 8-D (255). The bad thing about multiple batteries in a bank is if one fails, it takes any others in the loop down with it. The other battery or batteries might not be destroyed but in many cases it will weaken them and it's not a good idea to add a new battery with old ones. Multiple battery systems can be very costly if you don't frequently monitor their charge status and keep them all up to par.
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Old 12-03-2014, 07:33 PM   #9
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Re: rv vs 12v charging from alternator

200ah Lithium $2,399

http://www.lithiumion-batteries.com/...m-ion-battery/

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Old 12-03-2014, 09:31 PM   #10
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Re: rv vs 12v charging from alternator

Quote:
Originally Posted by Tapatio
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