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Old 06-01-2014, 01:17 AM   #1
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Four battery, split parallel rig

Today I put the finishing touch on my split parallel battery setup. I don't boondock a lot, but when I do, I do. One, maybe two weeks in the woods going to town every now and then so I can get cell signal. Only way to live.

On my TT I had a steel battery box that held three batteries. Well with the 5er front bin so big I had to go with four, nice evenly split system.

This is two batteries in parallel, positive to one side of a switch, two more on the other side of the bin positive on the other side of the switch. Four gauge cable, copper lugs soldered on the ends of the cables and heat shrinked.

Tomorrow is the test, I've got a 1200W inverter that I used to run a TV for the ex, now it will power my CPAP machine. The CPAP is supposedly about 140W which will be a roughly 12A drain. I'm going to setup and measure the actual draw on the system, by the numbers I'll have more than enough capacity for two batteries overnight, but will need to sort out a charger I think. I'm going to experiment some tomorrow and see.

Anyhow, here's a few pics. Hope you like what I did with the place!



The cables between the batteries are equal length on both pairs to make them behave more like one battery, note the posts are opposite each other, makes equal length leads easy.



Here's how I grounded it. I thought I had more star washers, for now it's good with one.



Here's the layout, two on one side, two on the other. The cables and the vent hoses are run across the top and tied in with the factory harness. The blue wires are for an overhead light and will be rerouted now that I'm happy with this and the positive cable will be tied down with cable mounts.



My switch. It has batt one, batt two, both and off. It's a starter amperage rated piece from an ambulance, I've had it 12 years now and it works awesome.



My vent hose solution. I teed the two boxes together, using 1 1/4" plumbing tees from Lowes. I put a zip tie on to seal it off then ran a screw through to hold the hose in place. These two are tied together, then the hose is run across the top of the bin tied to the harness, then forward and teed into the factory hose just behind the wall vent. Both sides are set up the same. The battery cable will be tied to the wall now that I'm happy with the results.

That's it. I'm actually quite pleased with the results, rock solid, should give years of trouble free service and is quite simple to access.

I've got one more thing I'd like to do with this project. Add some jump start lugs like race cars use so that way I can independently charge one pair while the house runs on another pair. I'm thinking of Making a bracket and adding them in next to the switch. One ground, two positives on a bit of metal. I'll sort that out later!
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Old 06-01-2014, 06:52 AM   #2
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Where did you find the battery boxes? I could not find them. Very nice set up. You could not have done it any cleaner IMHO
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Old 06-01-2014, 07:19 AM   #3
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One suggestion:

Move the ground wire to the last battery.

By attaching the ground and positive wires from the camper to the same battery, you create an "out of balance" resistance bridge between the four identical batteries. The resistance of the connecting wires is added to the internal resistance of the paralleled batteries as you move down the stack.

While we are talking about a small difference in battery resistance, it will make your effort to build your bank with identical batteries (so they will work together evenly), wasted effort.

The "leading" battery will have lower charge/discharge resistance than the succeeding ones and will therefore charge and discharge faster than the "back" batteries. Over time the out of balance setup will get worse until the battery bank spends most of its effort trying to equalize with the leading one and not contribute as much to your available capacity as you expect.

Interconnecting cables in a stack must always be as identical as possible in length and gauge.

With 4, you must have the ground on the very last battery and the positive on the very first battery. This "snip" is from the attached article on the electrics of battery interconnections.

Herk
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File Type: pdf How to correctly interconnect multiple batteries to form one larger bank.pdf (106.1 KB, 43 views)
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Old 06-01-2014, 12:10 PM   #4
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Thanks! The boxes are factory Forest River units, get your dealer to check into them. They were $16 each compared to the $25+ ones. The three boxes and hose cost me $60 which I consider a steal.

Thanks Herk, I've read it both ways actually, I think I have leeway to move the positive cable to configure it like your diagram. The other side I didn't open up for pics is actually wired like that. I was going to take some measurements one day to confirm then go with the better balanced setup but your article makes good sense.
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Old 06-01-2014, 12:25 PM   #5
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A few more specs, the cables are Standard CS4RV for the positive, CS4V on the negative, those numbers are for 25' spools. It took a full 25 feet of positive along with enough to reach the inverter in the bedroom, I grounded it to the slide frame so I only had to run the positive through the floor.

I went through nearly 20 copper lugs and four feet of heat shrink.

The cabling parts were around $150.
The boxes were $60, $16 each for the boxes and eight feet of hose at $2 a foot.
The batteries are about $100 each so $300 there. That's where you'll see the biggest variation in price, I went with group 27 Interstates.

So all told it was about $510 in parts. It took me about seven hours to do this (about four had I not taken my time and plenty of breaks) so if you need to pay someone to do this then it's going to run probably $300 in labor. Worth it? I think so, I'll know soon enough!
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Old 06-01-2014, 02:39 PM   #6
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What effect will this have on your converter to charge 4 batteries? Does the convertor need to be upgraded also? If I don't have a genny, would my 7 pin to the TV recharge the batteries? I don't or haven't yet, dry camped because I haven't the frame for it yet (full timers)?
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Old 06-01-2014, 02:53 PM   #7
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Quote:
Originally Posted by donanddona View Post
What effect will this have on your converter to charge 4 batteries? Does the convertor need to be upgraded also? If I don't have a genny, would my 7 pin to the TV recharge the batteries? I don't or haven't yet, dry camped because I haven't the frame for it yet (full timers)?
If your TT is plugged into shore power your converter will do just fine maybe take a little longer to get full charges back up, depending on how low you pull the batteries. If you are not on shore power you need either a generator or solar to charge the batteries. You don't want to use the TV to charge the TT batteries the TV alternator is not designed for that, it will send a small charge through the 7 prong plug but will take way to long to bring the TT batteries up because the TV alternator sees the charge status of your TV battery as near full and cuts way back on output.
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Old 06-01-2014, 03:49 PM   #8
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I've got a 65 amp converter so I'm not going to upgrade it, it won't care while the batteries are topped up but likely wouldn't be too happy with four dead batteries. That's where the switch comes to play, two batteries wouldn't be an issue to charge up. Plus once I add the charging lugs I can switch from the discharged batteries and charge the isolated batteries with my generator and a dedicated charger.

As for your truck, it will charge them normally but if they're down any amount I'd switch to the battery pair that's in the best shape to pull it home. To recharge without a genset there's a 12v lead through the 7 pin, you'll need to confirm that your tv is equipped to feed it. It would take a long time to top them up though especially idling. It would do it, but a 2,000 watt genset with a dedicated charger would work much better and be far more efficient.

I'm giving to boondock in the driveway for a few days and see how well it works and what my best recharge options are
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Old 06-01-2014, 04:09 PM   #9
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Here is an EXCELLENT article on why using the TV's alternator to maintain a fully charged battery (or bank) is fine, but trying to charge a depleted SINGLE battery is a bad idea; lord knows what 4 of them would do to your truck.

Also remember you are talking about hundreds of amp hours to replace. If your car alternator is pulling it's heart out you are most likely getting 10 - 12 amps of charging. You would need to run the TV for many hours to fully recharge a single deep discharged battery.

Even a 100 AH battery getting 10 amps will take 10 hours to recharge at 10 amps; BUT, as the voltage on the battery recovers, the charge rate drops to a maintenance rate (about 2 amps).

Even multi stage chargers only bulk charge to 50%; then step down so the battery can absorb the deep charge.

If you plan on operating solely off the batteries, invest in a cheap 1000 watt generator (wear ear plugs) and buy a GOOD 4 stage dedicated battery charger. Plug the battery charger into the generator and connect it to your battery bank. (Use your disconnect if you want - I do - but I have been told it is not required as the converter can handle an additional charging source - like a solar charger).
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Old 06-01-2014, 04:44 PM   #10
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Would the 1000 watt gen be good enough to run the picture tube for 4-5hrs and charge the battery bank also?
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