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Lots of scattered info that was very helpful to me. Here are a few details of mine. I'm sure there are many other ideas that work for different wants and needs that can be posted here.

I wanted my batteries close behind the driver seat. I wanted them in a protective box and secured to the floor with bolts and underneath steel reinforcing. My wiring feeds up the driver B pillar.

I tapped the positive cable on an unused post. Had to trim some plastic near the post to direct the cable under the driver seat. Ground attached to same bolt as van battery.

Chose Decka GS25 6v 488 minute reserve at 25A draw.Thats the only metric I have. Weigh 68 ea. Didn't notice appropriate name of battery till I had them home. Small local long-time battery shop carries them, they make my cables for cheap and are fun to work with. Put batteries in a QuickBox dual end to end battery box. Placing along longitudinal axis or using side-by-side box may be better for some. Fused on both ends of her pos cable.

Boxed beams in floor prevented placing them as close to the seat as I wanted. Built a frame of 1.5" angle x 1/8". Bolted through floor and 3/16" bar strap reinforces from under floor. Removed foil muffler guard brackets to reach some bolts. You have to plan the bolt locations carefully. Welded pre-formed attachment loops I found at a welding supply to frame. Bolted to floor with 5/16" galvanized bolts with lock washers and primed. Then placed 4 ratchet straps across the box to secure everything to the floor and frame. Each one has a 1320 pound breaking load. You can get beefier ones but the ratchet is bigger and they don't attach right. I'll build a cabinet over this array that will house other power distribution components. The top is removable to provide access the the battery box for maintenance.
 

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Not suggesting right or wrong, but you realize there is no fuse protecting the red wire? I've seen fuses later down the line, or at the battery box. I'm assuming the red wire is going to an isolater....

Install looks nice and solid!

Ed
 

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Great install, overkill, I like it. I have to think of other cars I have that have the battery in the car body like my wife's Miata or all the VW bugs (old school). They had a wimpy metal hold down with a 1/4 inch bolt holding them. If that was safe yours is Fort Knox. For mine I positioned them against a platform that is butted up to the ledge of the cab floor and used a 5/16" eyebolt through the D ring and a top brace to keep them down. Underkill I know but they can't go forward in a crash, can't drop on me in a rollover, can't go to the left due to the ridge there and can't go right unless they rip the factory hold down out. Somewhere in between us is probably simple and enough but you didn't scrimp on material or effort, great job.
 
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Re the red wire at the battery: It was mentioned above about a fuse. Looking at the picture there are three wires with individual fuses and the one on the right is a red fuse. On my PM that position/wire was used for only one thing; that is, the wire ran to the optional up-fitter connection in the pillar behind the passenger seat. Since most of us want the connection/house battery behind the driver's seat I simply disconnected that wire and used that fuse position for my added wire to lead behind the passenger seat. I had considered re-routing the existing wire but it was easier to simply add a new one. I also changed the fuse from 50 amp to 80 amp. The 50 amp fuse would not hold the initial surge lasting just a few seconds when the combining relay closed. Since I could not find a 50 amp delayed action fuse (slo-blow) I went with the 80 amp. It is important to protect the wire run by having a fuse at the battery end especially as any added wire might be undersized or not well protected from chafe.

I also used a simple battery hold down system -- ROPE! Rope of all sizes is now available in super high strength, high tech materials. West Marine stores sell small diameter line that is stronger than equal size steel and is used to replace wire rigging on some sail boats. Line less than 1/4 inch diameter is rated at over 2000 pounds!
 

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Seapro,

I mentioned the fuse because I noticed that the wire used in the pictured install is connected before the fuse, essentially direct to the battery + post.

I'm doing the same thing you did. I'm going to connect the feed to the aux battery on the fuse going to the upfit connector.

I set up a temporary 30A fuse and wire a few months ago and it hasn't popped yet. I haven't run the aux battery down very much so I'm guessing the 30A fuse worked because the aux battery was not calling for a big current load to refill the charge in it. I have a single 100AH AGM battery. Maybe I can try the 50A and up it to a 70 or 80 if it pops under load!

Good info!

Ed
 

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Discussion Starter #6
I mentioned that both ends of positive were fused but pics didn't show that. Coming off the coach batt the cable goes under floor mat for only 1.5" then comes out under the seat where the fuse is. It's 11" from terminal under the tray that is too much trouble to remove to take a better pic. I wanted it closer to terminal but space is tight. Fuse on other end is between aux batt and isolator; 4" from terminal; a very short run. That's how isolator install suggested and in line with what many of you have posted. These pics should show it a bit better.
 

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Rodlee -- Good that you fused near the battery. Be very careful that you do not have any way the wire could chafe between the battery and fuse. In the marine (yacht) business standards call for the fuse to be within 7 inches of the battery unless the wire is in a conduit.

Proeddie -- When I connected to the fuse location at the battery I had one problem and this is perhaps why Rodlee and others do not use that existing fuse location. Those 3 fuses are recessed on a plastic assembly that has ridges between the fuses for extra safety. American terminal lugs, at least those that I could find, have a different form factor. To get a lug of proper size for the wire resulted in a more rounded lug that would not fit down between the plastic separators. What I did was to file the side edges off of the lug to reduce its width so it would fit. Doing this it is most important is to have the hole just big enough for the screw so there is ample contact area.

Re fuse size. I have a 230 amp hour AGM battery. Yes, if the battery is well up there is little surge. If the battery is well down the surge is bigger especially in the case when you start up and drive off and the relay closes 30 seconds later with the alternator able to put out max amps. Also the surge is big if the alternator has to accommodate a load while charging the battery. This happens if you have an inverter drawing big to run some AC load. To be safe (unless I know the battery is well up) even with the 80 amp fuse I do the following: I start the engine and wait 30 seconds while at idle until the relay closes. At idle the alternator puts out minimum current and the surge is mostly just one battery to the other. After another 30 seconds or less the house battery is well up over 13 volts (you do have a meter I assume) and its internal resistance is such that it cannot accept high current and the fuse will hold.
 

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Seapro

I' m losing something in the translation... You start Van, wait a minute, then __________ (turn on the isolator?)

The rest of the info makes sense to me. I tried to fit a 80a breaker in the van battery box, couldn't find a spot.

Ed
 

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Proeddie -- The "isolator" is a relay always on. Between the two battery systems I have a Blue Sea ACR relay. This is a voltage controlled relay and these are available from various manufactures; Blue Sea is the most accepted in the marine industry. You can go to the Blue Sea website for operating details. It is all automatic. When the engine battery has reached a certain voltage (I think 12.8 to 13, reached within seconds of engine start) and held that for a full 30 seconds the relay closes and connects the two battery systems. Surge occurs at relay closure but is limited if the alternator is only at idle speed as its output is low and surge is mostly battery to battery. After just a few seconds the surge will diminish and the alternator at idle will bring the voltage of both batteries up to higher voltages around 13.3 or higher usually within 30 seconds or less. Once the voltage of the connected batteries has reached that level their internal resistance is such that they can only accept current at amperages below 80 amps. As you drive off the alternator will put out more amperage, voltage of the batteries will rise very quickly to the van regulated voltage of 14 plus and everything will charge quickly.

Although I have manual switches between each battery and the relay I leave them closed all the time and they could be omitted. There are only three wires to the relay: A big fat wire from each battery and a tiny wire to ground so the relay can sense the voltage at each battery.

When the engine is shut off the engine battery drops below the threshold and the relay opens separating the two systems. The system also will work in reverse. If you play the radio or leave lights on that depletes the engine battery and if you have a shore power charger you can plug in and raise the house battery and the engine battery will be recharged.

I have a house battery voltmeter at my electrical panel behind the drivers seat. I generally stand there and reach over to the key switch and start the engine. Within seconds there is a faint click of some relay closing behind the dashboard. Within 30 seconds there is a clearly audible click of the ACR voltage controlled relay closing. Within another few seconds the voltage of the combined batteries has climbed to over about 13.3 and I get in the seat and drive off. When camping this is only necessary for me at first start up of the day. After a half hour there is enough charge in the house battery that there will be no surge so I can just get in, start, and drive off. For my 230 amp hour battery about half down (12.2 volts) it seems to fully recharge in little over 90 minutes of driving.
 
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