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Old 09-19-2011, 12:32 PM   #1
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2nd battery - advice requested

First time posting here, thanks for any advice. It seems like somebody might have already asked these questions, but I looked through the existing threads and didnít find the exact answers to my questions. If this has already been addressed and I missed it, please direct me in the right direction.

I just bought a Ford E250 and am in the process of converting it into a poor manís RV. Despite a ton of web research, Iím still a bit perplexed. My power needs are pretty basic, I just need to run some lights, an ipod dock, a roof vent fan, and maybe plug in a portable inverter to recharge a laptop. To rig up a house battery, can I do the following?
1- run a thick gauge wire from the positive terminal of my starting battery to an isolator. What gauge wire is needed for this?
2- Run wire from isolator to auxiliary battery.
3- Negative terminal of aux battery goes to ground. Positive terminal goes to 12V fuse box
4- Fuse box goes to lights and 12v outlets.
5- When I need to charge the laptop, plug a portable inverter into an outlet.

This system doesnít involve the use of a converter. Is that OK?

Battery thoughts Ė Iíd rather keep it simple and purchase an AGM battery and mount it under the driverís seat. The ones that Iíve seen feature fairly low amp/hours. Any suggestions on a make/model? Lots of options out there, Iím having a hard time picking one. Not totally sure what my capacity needs are (how many amps the above mentioned devices will pull), so I need to figure that out too.

Many thanks,
Chris
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Old 09-19-2011, 01:20 PM   #2
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Re: 2nd battery - advice requested

I would put a separator in instead of an isolator.

The isolators I'm familiar with should have 3 pins, one from the alternator and one to the starter a third to the house.

Separator has two pins, wired like you said. There may be some isolators like that according to Google images.

#3 "Ground" being the frame

Convertor puts 120v charge into a battery, so you'll only be charging from the alternator without it.

Go with all LED bulbs and a Group 27 should be enough. Deka is what I chose based on recommendations, but as long as it's sealed AGM I'd go based on price.

You can add a convertor, solar or another battery if your needs are greater. Also make a habit of charging the laptop when driving.
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Old 09-19-2011, 01:28 PM   #3
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Re: 2nd battery - advice requested

Am I at risk of overcharging the battery, reducing it's life, if it's wired like what I wrote above?
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Old 09-19-2011, 06:33 PM   #4
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Re: 2nd battery - advice requested

Quote:
Originally Posted by SLCChris
Am I at risk of overcharging the battery, reducing it's life, if it's wired like what I wrote above?
An alternator will generally not fully top off a AGM battery so unless the regulator fails for some reason, it shouldn't overcharge, rather it will always be slightly undercharged. Having a good 3 stage charger or solar to top it off will help a bit with longevity. The rule of thumb is never let the battery go below 50% (or about 12.2v) before recharging and top it off or charge it back with a smart charger.
Some people run a inverter off the alternator that powers a 3 stage smart charger so when driving down the road the house battery is brought back up with a good clean charge. The inverter must be connected to the ignition so when the engine is shut down the inverter turns off or you'd end up with a dead starting battery. If I did something like that, I'd want a A/B switch so I could cut in the alternator if needed.
The bad thing about many of the converter/chargers out there are they usually have poor battery chargers in them so a good 3 stage charger is a better choice. [edit] There might be quality converters available and many high end inverters also have multi stage chargers built in them but they can be expensive.

You can google 3 stage chargers and read how they work. Stay away from standard garage chargers if you want to get the most life out of your battery.

Quality in batteries is usually in the lead that is used. Lifeline/concorde are some of the best but Deka, odyssey, and a few other make high end batteries.
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Old 09-20-2011, 12:42 AM   #5
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Re: 2nd battery - advice requested

All the name brand deep cycle AGM batteries have about the same capacity for a particular size. The different sizes seem have random dimensions, so you have to check the width, length, and height of the space you're putting it in then select the biggest battery or batteries that will fit. The terminal location isn't always the same either, also the type of terminals. Probably best to actually inspect the battery before purchase.
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Old 09-26-2011, 08:41 AM   #6
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Re: 2nd battery - advice requested

Thanks so much for all of the help. I've ordered a bunch of parts, they should arrive this week. Can't wait to start putting it all together! I'm sort of obsessing...
Two things:
1-Does anyone have a recommendation on the size of the wire that should come from the starting battery to the separator? Should the wire coming from the separator to the aux battery be just as beefy? 4 gauge? Should this be routed through an existing port in the firewall, or straight down from the battery to the frame and then up through the floor? The separator and AGM battery will both be behind the driver's seat (inside the van)
2-I've decided to add a 3-way refrigerator. As long as I'm super diligent to turn the DC power off (and the propane on) as soon as I stop driving, can I still operate this system on a single battery? Canít see a reason why this wouldnít work, but thought I'd ask the experts...

Thanks a ton,
Chris
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Old 09-27-2011, 12:03 AM   #7
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Re: 2nd battery - advice requested

There are a lot of different requirements depending what loads you are planning to feed. Generally, the wire coming from the alternator to the separator doesn't have to be near as large as the wire running from the house battery to the separator. I have 4/0 stranded copper (hot and neutral)running from the house batteries to my separator with rated lugs. Then I have 4/0 running to the 2000w inverter as that's the big load item in the van. There are smaller runs of various wire sizes branching out of the fuse block to other 12vDC items such as outlets and what not. I think I have 1/0 feeding the fuse block and a 2 str ground. Sorry it's difficult to pin down what you need without knowing what you plan to power. 4 str runs between the starting battery and the separator but I wish it was no smaller than 2 str.

In the battery FAQ's there are all kinds of load charts, and amperage draw stats of RV items.
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