This write up is a trial at using some of the Forum features that I am not well acquainted with and therefore represents an experiment. I am going to try and use the gallery to place pictures inline with the narrative in order to make it more easily followed. If it works out, I will do more future write ups with a similar format to benefit anyone who may wish to tackle similar projects, and also to help my future self figure out what my now self did 
This project is doable, but fairly involved and requires some welding and extensive recabling of the original two battery setup found in U270's of this vintage. Coaches that have three batteries from the factory may be easier to do, or may not even be possible due to the placement of the parallelogram hinges... some precision measurement would be needed. Timing is important, as it is optimal to do it when replacing batteries in order to have the entire bank as close to the same age as possible. Of course, the expense for the batteries is doubled, and the additional cabling and terminations are not cheap either! It wouldn't be that much easier to add a third battery if starting with two than it is to add two more, because most of the work is fabricating the support for the top bank.
You could make it considerably easier if you just added a shelf, instead of a slide, but having had the batteries in and out several times while doing the basement/bulkhead project, I have a strong appreciation of the slide out that came with the coach. At 160 lbs. apiece, it is a lot easier (not saying it is easy!) to load and unload the battery with the slide out extended, particularly without the bus style compartment doors. It figures to be doubly so for the top bank. I have a lift table from Harbor Freight now, that makes the process of removing or installing the batteries much easier than it was the first few times I did it. Having a slide on the upper tier and a Harbor Freight hydraulic lift table makes the job of lading the top bank almost easy.
The project was made a bit more difficult because I want to wire each battery to a set of bus bars rather than paralleling all four, and I want to be able to slide them out without disconnecting the battery terminals, as there won't be much room to reach the back batterie's terminals.
That last part makes this a bit of an engineering challenge. The difficulty is in trying to arrange the upper level to allow the cables room to move with the slide, as well as having room to mount the bus bars. John H. made bus bars for his set up out of ⅜" X 2" wide copper, and while I considered going to ½", the ampacity rating of the ⅜" is more than adequate (copper busbar ⅜" thick X 2" wide has ampacity of over 900 DC Amps) and with space so constrained for cable management, every fraction of an inch matters. By the way, all battery cables are 4/0 Marine tinned copper (normal welding cables would be fine for this application, and quite a bit less costly... but I like the idea of never having to worry about corrosion, and the quality and flexibility of the high grade marine cables is second to none). I make my own cables and have the appropriate crimper to do the job. There are other means of terminating the cables, but a 360º crimp with quality lugs is the best option in my opinion.
The design for the slide that I came up with is different than the ones that Foretravel made for the three battery setups on non-slide coaches of our vintage. They made a support out of angle iron that goes all the way across the compartment and mounted the slide on top of it. This places the slides under the battery tray. In trying to keep the battery tray as low as possible (because of the hinged compartment doors on our U270 that have been acting as DNA collectors since we bought the coach), I elected to mount the slides on each side of the battery tray. To give the cables room to move with the slide, I bolted the left side slide support directly to the partition wall between the batteries and the fuel tank. I used 1" X 2" X â…›" thick walled rectangular tubing to mount the stationary part of the 500lb full extension lock in/lock out slides that I bought on eBay.
I started the process by deciding to extend the partition that separates the fuel tank from the batteries in order to have the upper battery slide supported all the wall to the front.
This was not strictly necessary, but as I plan to add a few 4" wide aluminum shelves in front of the fuel tank for misc. fuel additives etc., I used some rectangular aluminum 1" X 2" X ⅛" thick walled aluminum tubing. I used two pieces on edge to create the 4" extension. I drilled two holes all the way through both prices of tubing and then enlarged the outermost hole on the outside piece to allow a screw head to ft through. I drilled edge of the steel ¾" thick tubing of the partition with ⅜" drill bit and installed ¼"-20 Rivet Nuts and fastened the two sections of aluminum tubing on edge with 3" long stainless screws. I made a trim piece out of ¼" thick X 1" wide aluminum rectangular stock and attached this to the outer rectangular tube with ¼" flat head Allen screws to hide the large holes through which the 3" long screws were inserted.
The next step was to use magnets to mark the framing of the side walls of the battery compartment, though I had already explored the the framing layout with a magnet when deciding how to approach supporting the upper slide.
As I suspected, there was horizontal framing at the exact place needed on both sides of the compartment for supporting a second tier of batteries. Foretravel apparently framed all three models of the Unicoaches with the same basic layout and since the U295's and U320's came with a second layer of batteries, the U270 had the required infrastructure in place. Thank you Foretravel! Next, I welded a piece of 3" X 3/16" flat stock to the 1" X 3" X â…›" rectangular tubing that I used for the 500lb. full extension slide supports, and that 3" flat stock is attached to the wall at the back of the compartment.
Side note: The walls at the back of the battery and propane compartments consist of a ¾" X 1 ½" rectangular steel framed partitions with a ¾" plywood insert with a fiberglass skin bonded to both sides. The space created by these two partitions is a little nook accessible in the center portion of the front wall of the storage bay of our 36' coach. These partitions are extremely important as they provide the vertical longitudinal stiffness to counteract the pull of the rear axle control arms which tugs on the rear bulkhead joint with every bump and application of the retarder.
I used three 1 ½" X ¼" carriage bolts through the middle section of the back support and some ¼"-20 allen button head cap screws threaded into the perimeter steel frame of the back wall. On the right side, where the cables must be free to move over the range of the 20" full extension slides, I welded a support which spans both the horizontal steel frame member and the diagonal frame member on the left side wall in the front of the compartment. I also added 3/16" thick aluminum plates to the side wall which is screwed to the steel framing under neat the fiberglass skin to provide a surface to screw the bus bars to and to provide extra support to the battery slide. I drilled and tapped all mounting supports using ¼"-20 and 5/16"-18 allen head stainless steel fasteners in various locations.
I then proceeded with the fabrication of the battery slide tray, finished welding the frame and did several test fits.
When I was satisfied with the fit, I removed and disassembled the components and painted the frame and slide tray.
I fabricated the busbars after deciding how to minimize the cable connections and provide busbar isolation.
I had it in my head that I would like to be able to monitor the individual batteries so I could catch any problems as early as possible. Since the voltage would read the same for all as long as they were connected as bank, I decided to kill two birds with one stone and use four 500 amp 50 mv Deltic current shunts to provide most of the support for the negative busbar.
The shunts will enable me to add current monitoring at a future dated without modifying the busbar set up. Since one end of each shunt is bolted directly to the negative busbar, that saved me having to make four cables and finding the space to put them (I doubt that it would even be possible to accomplish this in the limited space available). Each shun is screwed to the aluminum plates underneath with two number 10-32 machine screws and the shunts have ⅜" -16 flat head allen screws countersunk into the copper busbars. There is also one additional Blue Sea ⅜" isolated heavy duty terminal normally used for connecting two or more heavy cables used as a isolating mount at the lower end of the negative busbar, mainly to make the installation hole drilling for mounting the shunts easier. In other words, I drilled and tapped the aluminum plate for the two holes of the Blue Sea isolator, bolted the copper busbar to it and then positioned the shunts which were already attached to the busbar at this point to mark the shunt mounting holes for drilling.
Side note: One of the difficulties you run into when trying to position components for mounting is that the drill bit tries to wander just enough to ruin your plan, especially when you are drilling on a vertical surface with awkward access as in the battery compartment. I countered this by making steel templates for drilling the holes outside of the compartment. I then would drill the first hole after center punching the desired location, at which point a drill and tap that hole. I would then screw the template through the appropriate hole, choose one of the holes in the template and mark it. After I drilled and tapped the second hole, I would then have the template attached firmly enough to drill the rest of the holes and have them end up exactly where I wanted them.
I then determined the minimum length of the battery cables to allow full extension of the slides and added about 2" which resulted in 36" long battery cables.
This added to the approximately 42" long inverter cables is about the same as the 72" inverter cable used on the original inverter cables, but minus the interconnects between the two batteries of the factory install since each battery has its own pair of cables connected to the busbar system to which the inverter cables are connected. On the positive bus bar, I used one of the Blue Sea isolated terminal posts and the one end of the 400 amp Class T fuze as bus bar isolation. I then tapped ⅜" -16 holes in the copper to connect the positive cables to the back side of the busbar to keep the profile as low as possible. I tapped a few extra holes to give some different options for cable management. I also decided to add a heavy duty battery disconnect switch to completely remove the house battery bank from the rest of the coach. I am still not entirely happy with the cable management, and will revisit that when I have some more time. I can at least extend and retract the trays without disconnecting any cables, though I have to help guide the cables a little in the process.
Finally, the "beauty" shots of the finished project (well, done for now...)
Project notes;
I got the cables, power lug terminals, battery cable ends, crimper and a few other items for this from Bay Marine Supply in San Diego. The owner of the business, Alan who is a commercial member of our forum, is always helpful and generally has the best prices I can find on the majority of the items I have researched, and sometimes far better than the best internet pricing I could find. Previously, I had installed a Magnum MSH3012M 3000W / 125A Hybrid Pure Sine Wave Inverter/Charger an Magnum MMP MiniPanel, Class "T" fuse, ARC50 advanced remote control, Magnum BMK battery monitor and some other related bits and pieces that I also from Bay Marine Supply. Alan was also great to bounce ideas off as he comes from the marine side of the equation which usually has more stringent standards when it comes to electrical items.
Links;
Wire, cable, and terminals
FTZ Heavy Duty Lug Crimp Tool
1000 lbs. Capacity Hydraulic Table Cart
Electrical: Busbar - DC Copper Busbar Ampacities
Amazon.com : Blue Sea Systems HD-Series Heavy Duty On-Off Battery Switch :...
As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.
Topic: Installing 4 batteries and a busbar setup in a 99’ 36 foot U270 (Read 1350 times)
previous topic - next topic
