Inverter and Power Supply Installation…
The first step was to install the ½” watertight non-metallic conduit from the generator bay to the inverter and power supply bay. It carries what amounts to a heavy duty 3 wire extension cord that brings 120V AC from the generator to the DC Power Supply / Battery Charger and only to the DC Power Supply / Battery Charger (PS). The battery charger is rated at 90A DC so it only requires about 11A AC, and the extension cord is only about 14’ long, but I still used 12AWG wire. I mounted a plastic box on the back of the inverter and PS bay and used standard home electrical stuff including a 3 prong outlet, front plate, etc. I did put a gasket between the electrical box and the back wall of the inverter and power supply bay, just to keep it water tight. Since all this is exposed on the underside of the truck I don’t want tire splash or dust getting into the electrical bays. I also took some advice from Geofkaye and attached a Velcro strap to the center screw on the face plate to tie the plug into the socket.
I thought long and hard about how to provide adequate cooling to the inverter and battery charger. They both have built in fans and will generate a fair bit of heat over time, especially if they are both working at maximum capacity like on a hot day with the AC running, microwave, etc. I could have just mounted them inside the underbed bay, which is essentially a steel box about 2’ cube. There might be enough exposed surface area on the outside of the box to transfer the heat out, but I didn’t want to take the chance. I decided that I wanted to manage the air flow so the inverter and PS would get cool filtered outside inlet air and then exhaust cleanly out of the bay with a minimum of backpressure. That implies large air inlets and exits with louvers, screens, filters, and other provisions to prevent tire sling and dust from getting into the electronics.
I also wanted to make some provisions to shock mount the electronics and hopefully reduce some of the beating it would take over time. On top of everything else, I wanted to give due consideration to access and maintainability. Filters have to be accessible and washable without tearing the whole thing apart. All of the equipment has to be easy to mount and dismount with a minimum of order of operations dependencies, etc. For example, the rear mounting tabs for the inverter and PS are slotted so they just slide in under the screw heads while the front screws lock them into place.
I ended up with a simple 3 shelf design, but the devil is in the details. An opening was cut in the back wall of the bay with 4 each 10-32 studs mounted sticking out the back (towards the underside of the truck). The filter box was made using a off the shelf louver 5” x 15” with the openings to the rear to shed water while driving. The filter is general purpose washable random strand plastic filaments about ¾” thick, with an additional layer of aluminum screen of the sort you would use in a screen door. If that doesn’t block the fine dust sufficiently then I have enough area to add a single layer paper filter as well. Access to replace and clean the filter is from under the truck but I figured that was easier than ripping out all the electronics to get access from the inside of the electronics bay.
The air inlet filter boxes are made from a couple of standard 12” by 4” plastic floor registers cut down to ¾” thick, with most of the outer rim removed. The inner portion that slides to adjust the airflow was removed as well. These were filled with the same random strand plastic filter material and backed with a layer of screen. They screw into the side of the bay with 4 each 10-32 screws.
The frame for the shelves is 1” by 1/8” hot rolled steel, welded into the metal bay. The bottom shelf is 2” above the bottom of the box to keep it well clear of any water that should somehow get in, either from the small drain holes, or via condensation. I used some recycled 7/16” FRP (Fiberglass Reinforced Plywood) for the shelves. The mounting plates for the Inverter and PS are made from .06” aluminum recycled from the original side doors. They are glued to a 1” thick layer of EPP (Expanded Poly-Propylene open cell foam, commonly used as packing foam in high end applications.) The EPP is glued to the aluminum mounting plate and the FRP shelf using Goop (AKA Eastman 6000). I cut some holes in the EPP to reduce its stiffness and give my electronics a bit of a softer ride. There are also some small nylon straps that loop loosely over the electronics to keep them from bouncing and ripping their base plates up off the foam.
The inverter and PS are both oriented on their respective shelves so they draw air in the front and push it out the back. In order to insure that the exhaust air doesn’t just recirculate back to the input I needed to seal the inner cabinet with lots of high density weather stripping. I also need easy access to all the various wires and cables going in and out so I made the entire side wall removable. When it is closed everything is nicely protected and the remainder of the bay is available for storage. Since the bay door already has a rubber seal all around it wasn’t necessary to duct the air from the inlet filters. I will need to make sure that door is reasonably well sealed though. It’s not high pressure or anything, but I don’t want to be drawing in dust around my inlet filters.
Here’s quick run down on all the wiring. I already discussed the 120V AC path into the bay. I dropped 4 pieces of ½” non metallic conduit into the inverter and PS bay from the inside of the right side outer wall. That should be plenty of wire path for two 120V AC circuits, 12V DC, 24V DC and some low voltage low current control wiring. I ran two short runs of non-metallic water tight 3/4” conduit from the inverter bay to the battery bay which is the next bay over, about 4” away. They will carry the very heavy wires (about 200A maximum) from the batteries to the inverter. Note that the batteries are in their own heavy duty steel box that is separate from the electronics. There shouldn’t be any acid fumes or hydrogen out gassing from sealed AGM (absorbent glass matt) batteries, but they are isolated just to be safe. That just leaves the heavy duty (90A) wires from the battery charger to the inverter (and then via the heavier wires to the batteries of course). They only run about 10” as the PS is on the shelf above the inverter.
The top shelf is mostly just a space to keep the wires organized but it also provides a place for the small 12V DC power supply that sits electrically on top of the 12V from the batteries to provide 24V. It is not very large or heavy, so it is just attached to the shelf with some sticky back Velcro. There is a small sheet metal front panel to close this top opening except that it has two apposing layers of high density weather strip which act as an airtight seal and a strain relief for the 12V, 24V, and control wires that need to exit the sealed inner cabinet.
I should note that I am not intending to use the truck chassis or any part of the box to carry DC ground return current. I will just run 12V power and ground return wires everywhere they need to go, much as you would for hot neutral and ground wires for AC power. The inverter chassis will be grounded to the truck chassis, which implies that the generator will be grounded to the truck chassis through the AC cord between them, but mostly the truck chassis just floats relative to earth ground. If I provide shore power to the Battery Charger / Power Supply instead of from the on board generator, then the PS will effectively isolate the entire truck from shore power, so I don’t think it will matter if the shore power has hot and neutral reversed or not. There is no direct path from any AC input to the chassis, and therefore no way to generate a potential between the chassis and mother earth. After it’s all wired I will have to test that assumption, but for now, that’s the plan.
It doesn’t sound like much but this all took me about 5 very full days to design and build. Now that I have a clear understanding of where the AC and DC wiring enter the living space I can finalize all the wiring inside the walls.
As always pictures are available under keyword “Stealth”.
To be continued…
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