Adding 120V AC Power To a Truck Bed (Part 3)

The Installation (Continued)

Once The Box Is On The Truck

Highway Products (the manufacturer of the tool box) recommends that the tool box be spaced 1/8" away from the forward wall of the truck bed to avoid vibration. While this sounds like good advice in general, I decided that the Rhino bed liner and the weight of the components would prevent vibration, and I wanted to minimize the amount of rain getting into the bed, so I mounted the box flush with the forward wall.

This picture is the underside of the tool box in the bed and shows the conduit entering from below. Note the nice fittings that made securing the conduit a breeze. The fitting has a sleeve that clicks into place to prevent the conduit from moving around, yet comes apart with a slight prying from a screwdriver. I’m really impressed with the industrial design of this conduit and its fasteners.

Here’s a view of the charging cables coming through the bottom of the box. To the left of the cables is a corner of a battery tray. Notice that I left about an inch between the side of the tool box and the battery tray; this allowed me to run the cables behind the batteries to the far end of the tool box. It was also a little easier to get to the mounting hardware since I didn’t situate the components up against a wall of the tool box.

Now it was time to put the batteries in. When I did my test fit (with the tool box turned upside down) I discovered that the battery trays were exactly 1" wider than the Optima Batteries I was using. This probably wasn’t going to matter, but I wanted the batteries to be as secure as possible, so I made a trip to the hardware store and got some 1" aluminum box stock and some end caps. I cut the stock into lengths slightly shorter than the battery trays, tapped on the end caps and slid them into the back of the battery trays to provide a tighter fit for the batteries. Now when the batteries are strapped down, they don’t budge.

Here’s a view of the battery bank, installed and connected. As I mentioned above, this installation is rather a tight fit, as I would imagine most others to be as well. It’s helpful to cut your power cables to be just long enough to comfortably reach, without a lot of extra length to make the cables bow and get in the way.

Safety Note: once the batteries are in the tool box, you are working in a "live" environment. The cramped quarters, moreover, make it really easy to accidentally touch a wrench to both poles of a battery simultaneously. If you happen to do this, the battery will voice its displeasure with a bang, a big spark or two, and a bit of melted metal where the unfortunate wrench happened to contact the terminals. I did this more times than I care to admit to…please learn from my mistakes and try to avoid doing this.

Against the wall of the box you can see one of two fuse blocks used in the installation. This fuse is between the batteries and the battery isolator in the engine compartment, and is intended to protect the isolator in case the batteries malfunction and release a huge rush of current. You can also see the whitish battery venting tube, to be explained below:

During the course of this project, I had a conversation with a battery engineer at Johnson Controls, Inc. (the parent company of Optima Batteries). He told me that, while these batteries were very unlikely to emit any gases, and would only do so if greatly overcharged, it would still be wise to ventilate the batteries to the outside of the box. Failure to do so could conceivably allow explosive gases to build up inside the box.

So, another trip to the hardware store equipped me with some 3/8" ID tubing and barbed fittings. The tubing fit snugly over the oval vents on the tops of the batteries. The tubes from each battery were joined by some T-connectors, then routed to the outside of the box through the tube you can see in the picture above. This precaution turns a small-probability hazard into a non-issue.

Here’s a closer look at one of the batteries (the rightmost in the bank). It’s easy to see that there’s a lot going on in this box; which underscores the importance of good planning of component placement. The wire from the fuse block will run to the inverter, which will be mounted just in front of this battery.

The ventilation tube can be seen in the upper left of the photo.

The thin gray wire coming from the right terminal also goes to a battery temperature sensor in the inverter…if the batteries get too hot from extreme usage, the inverter senses it and shuts down. Cool, huh?

After the batteries were installed and connected, it was finally time to install the power inverter. This view is looking into the tool box from the passenger side of the truck. I mounted the inverter close enough to the side of the tool box to be easy to reach, but still a few inches back to make it easy to access the power receptacles.

The inverter is held in with four small carriage bolts that enter the box from the underside. The rubbery spray-in lining on the floor of the box also helps to securely grip the inverter.

Here’s a view of the completed installation from the other side of the tool box. Notice the large cooling fins on the back of the inverter; these will help keep the inverter running cool even when working at its capacity of 1600 watts.

Also note the extra space in the tool box. This can be used for storage, or for the installation of other goodies (keep an eye out for a future article from me on this!).

Beside the power cables running from the inverter, it’s a good idea to connect a safety ground. This is similar in principle to the ground wire on the AC appliances and receptacles in your home. The idea is that if the hot wire in the device (in this case, the inverter) slips off its connection and touches the frame of the device, this safety ground gives the electricity somewhere to go instead of through your body (if you happen to be touching the appliance).

One end of the safety ground, of course, connects to the inverter. I connected the other end to one of the four hold-down screws for the tool box. My multimeter indicated a mere 2.4 ohms of resistance between the inverter’s ground lug and one of my door post screws. The inverter manufacturer had told me that anything under 200 ohms was indicative of a good ground, so this felt pretty safe.

It’s time to see if all the hard work has paid off. To verify voltage, I inserted the probes from my multimeter into one of the AC receptacles. As the multimeter’s display reads, I have 121.2 VAC available at the inverter’s receptacles. Success!

Verifying voltage is nice, but it’s also useful to know that the inverter can generate the wattage it claims. Fortunately, I had handy a 1500 watt space heater, representing more than a 90% load to the interter. I plugged it in, and turned it on high. The inverter performed without a hiccup. Success again!

A possible third test would be to capacity-test the battery bank. This could be accomplished by using that heater again, running it on high, and timing how long it takes before the inverter shuts down because of depleted batteries. I’d do this if I ever need to know exactly how long I can run a particular appliance, but at present, this isn’t too important to me.

Here’s the box in the truck, fully configured and connected. Isn’t it beautiful?

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