My first Instructable
My day job is a fire alarm installer in Arizona, and on certain (the majority I've worked) available power outlets are few and far between, which can be somewhat of a hassle when your drill and flashlight batteries run dry on a long day. This case is designed for the purpose of removing that hassle.
The most important part of the entire project is the box itself, as it needs to be resilient enough to support the weight of both the batteries and the tools it contains. For this reason, I chose the Ridgid 22" Pro Tool Box, which contains a small upper tray, perfect for the tools I need on site, and a fairly large cavity underneath. The box comes water-resistant, however during the process of making this device, it gains several holes which will need to be patched over to restore the sealing, should you find it necessary to do so for your own.
Inside the box, positioned to either side are a pair of 17.2AH deep-cycle SLA batteries, salvaged from the waste pile at work. I recommend the Shuriken 500W SLA as it has the closest physical profile, and actually a slightly higher capacity than my own batteries. These are affixed to the bottom using double-sided foam tape, positioned with the terminals up, to allow the battery to fit between the wheel mounting bolts without risk of short-circuits.
Centered between the batteries, attached to the bottom with several strips of foam tape is a 19V Dell gaming laptop power supply from XtremPro (which I used because it was available and on sale. Any laptop supply will work just as well), used to supply the battery charger, which is foam taped to the top of the power supply.
Step 1: Wiring the Terminals
The next step is to set up the power distribution through the box. All of the terminal wires are connected via #8-32 1-1/2" bolts with internal-tooth lock washers to keep everything snug.
Crimp the #8 ring terminals onto the end of every exposed wire, and remember, there is no power connected yet. At this point you will want to remove the batteries and leave them somewhere safe, as they are quite heavy and awkward to work around.
The power cord for the laptop power supply will need cut off at approximately 1.5' in length, though this may vary if you use a different case. The orange cable is the tail end of a 25' 16AWG Outdoor extension cord. After connecting the ring terminals, take a 5/16" drill bit and carefully make 3 holes in the side beam, no less than 1" apart, and low enough to clear the tool basket when it is in. When connecting these wires (which will have 110-120VAC running through them) make sure to connect them correctly. Brown to White (Neutral), Blue to Black (HOT), and Green to Green (Ground). Do this before anything gets plugged in. To verify that you connected it correctly, without risking your charger, carefully plug the cord in and test using a high-voltage rated AC voltage tester. Unplug the cord now, and leave it coiled to one side. Verify that all three bolts are torqued down as far as they will go without caving the plastic.
On the opposite side you will be wiring up the DC power. You will need to put the terminal bolts in two separate rails, low enough to clear the tool rack, as there is going to be a large amount of wire coming off of each. At this point, you will need to measure from the terminal side to the battery terminal's final locations. Cut the wire approximately 3" longer than this measurement, running along the sides of the box. At this point, you can decided to use a ring terminal connector, or an FM disconnect terminal and an adapter to make it a quick-disconnect. The two black wires will go to one terminal bolt, while the red wires need to both travel through separate in-line fuses (15A) before being connected to the other bolt. Before inserting the bolts into the two holes drilled in the side rails, connect the ring terminals coming off the battery charger as well. Tighten a lock-washer and nut onto the opposite side of each bolt until it is snug. Now you can connect your accessories.
Step 2: Exterior
To the outsides of the case, I attached a 12V accessory wire (black), 16AWG underground cable, and a 16AWG extension cord (terminated in the last step). Both are run through a 3/8" hole, on the DC and AC sides respectively.
To keep the tangle of cords to a minimum, both cords are wrapped around plastic wire-wraps from Walmart, bolted into the sides of the box at a 45* angle with two #8-32 bolts and lock washers on the inside. The 12V wire is terminated in a waterproof automotive connector, such as would be used on a light-bar. On the inside, the 12V negative wire is attached to a toggle switch, which is screwed into the case directly above the wire access from the inside. The hole for the switch was made by drilling 3 5/16" holes overlapping, which left just enough room for the toggle to move fully. Both cables have zip-ties secured around the base on the inside to provide strain-relief, as well as silicone caulk to reseal the holes from water getting in.
Flip the box upside down, carefully so as to not dislodge the charger, as it is only connected with tape. At this point you will want to position the wheels where you would like them to be and mark the holes for the mounting bolts. Carefully drill all holes with a low-speed 3/8" drill bit and clean off the flash with your finger or a knife. Bolt the wheels with a lock washer on both the inside and outside to ensure that they will not slip. Mine used 1/4-20 1" bolts specifically. This leaves them just short enough to not poke out of the nuts, however I still put protective tape over the bolts before securing the batteries back in place.
As a side note, during the assembly, I determined that the wire-wraps protruded too far out from the case to be easily avoided, so I cut them to a length that sits inside the cross-section of the box.
Step 3: Accessories and Wrap-up
At this point it pays to verify that the tool-basket will fit securely back into the box. You will need to ensure that any chosen accessories will fit with the tray in place.
For my site needs, I determined that I would need an inverter (to provide AC power for battery chargers and small appliances). My needs were under 400 watts, so that was the inverter I chose to use. It is attached to the front wall using 4 #8-32 bolts, trimmed to 1" to keep them from shorting against the terminals on the back and the grounding plugs on the front. The inverter cable is 10AWG, although for a 400W, 12AWG would be reasonable.
I also determined that a USB charger for our cell-phones and radios would be a useful accessory. This one is a 12V automotive charger with 4 2.4A ports. I cut the power wire 3" longer than was necessary to connect ring terminals to the 12V side of the box and fed it between the inverter and the side-wall to keep it out of the way.
Because sometimes 400W and 2 plugs isn't enough for all our on-site power needs, I added an internal 12V socket to the left side. This has a built-in 15A fuse, and can be used for another inverter, or a cigarette lighter, or any other 12V accessory you might need.
The ring terminals for all accessories are now sorted into Power and GND (usually red and black respectively), at which point they can be attached to the DC terminal bolts, and secured with another lock washer and nut. Make sure none of the wires arch up in a way that would prevent the tool basket from fitting properly.
After determining that everything fits, the project is technically finished and the batteries can be connected to their power cords, paying close attention to the polarity. I chose to add one of my previous projects, a remake of https://www.instructables.com/id/Flexible-Camera-... with a lightbar accessory lamp on the end, which tucks nicely underneath the tool tray without touching any of the battery terminals.
If you are worried about it short-circuiting across any of the tools, you can also add shrink-wrap or electrical tape over the exposed bolts and terminals. I chose not to because they are all beneath the tool basket, which will not be removed during work, or on work-sites at all.