Tech Projects

Charge! How to Build a Remote Battery Charger Terminal Bracket

(Image/Wayne Scraba)

A few years ago, I had a drag car that needed a place to mount a set of battery charger terminals (lugs). Because of where I wanted to mount the charger terminals, I quickly discovered there was nothing available in the marketplace I could buy or modify to fit.

That meant I had to build one myself.

What I decided to do was to set up the bracket to act as a doubler to cover an existing opening and, at the same time, accept the charger lugs. As it turns out, a little bracket such as this could be used for a lot of things, including a place to mount a battery kill switch, a doubler to reinforce a section of sheet metal, and so on. I used a similar doubler on the trunk floor of a car I built to accept the weight of a heavy (huge-by-large) fuel pump.

Although there are any number of ways to accomplish this, you might find my little “build-it-myself journey” useful.

Selecting the Right Battery Terminal Bracket Material

You can make the piece out of metal or even robust plastic. The most common aluminum you’ll likely find is 3003. And while there are a number of other aluminum alloys available to us, 5052 alloy might be the best choice for this type of job.

That’s because the 5052 alloy has one of (if not the) highest strengths within the range of non-heat treatable aluminum alloys. It provides good fatigue strength properties, plus it is resistant to corrosion. (That’s why it’s often found in certain commercial, marine, and aviation applications too.)

Though corrosion resistance is a good enough reason to use 5052 in a car, perhaps the alloy’s workability is its best attribute. When annealed, 5052 can be formed into some exotic shapes, plus it doesn’t have a tendency to tear as easily as 3003 or 1100 alloys. If necessary, it can be welded with a TIG.

Here’s a bonus as well: 5052 alloy cleans up very nicely. That means the parts you fabricate look good when you’re done.

5052 is available in a number of thicknesses. From my experience, I think you’ll find material thickness around 0.100 inch works out well for most mounting plates, doublers, brackets, and other pieces. For options, 5052 is available in 0.025, 0.032, 0.040, 0.050, 0.063, 0.080, 0.090, 0.125, and 0.1875 inch thicknesses.

In the end, 5052 alloy is relatively easy to source and it doesn’t cost an arm and a leg.

Understand Edge Margins Before Drilling Holes

Edge margins are incredibly important for plenty of fabrication projects. Should a hole be drilled too close to the edge of a given piece of metal, it’s entirely possible for the small amount of metal between the hole and the edge to tear under stress.

The distance between the edge of the material and the drilled hole is called an “edge margin.”

The specified edge margin is the distance from the center of a hole to the nearest edge.

In aircraft practices, the standard edge margin works out to twice the diameter of the hole. For example, if you have a 1/4 inch hole, the center point of that drilled hole should not be closer than 1/2 inch from the edge of the material (1/4 inch drilled hole X 2 = 1/2 inch).

Easy enough, but what if you must drill a series of holes in a component? How close can they get?

In the aviation world, there’s a simple solution: The minimum separation between the respective hole centers equals three times the diameter. This means that if you have a component that needs a bunch of 1/4 inch holes drilled in it for fastening purposes, each hole center must be 3/4 inch apart (1/4 inch drilled hole X 3 = 3/4 inch). Case-in-point is an aluminum plate and it’s mounted to a chassis tab by way of a series of holes. Each hole must maintain the edge margin and in addition, the series of holes must be a precise distance apart.

Some Notes About Drilling Holes in Metal

When it comes to drilling a hole, you’ll invariably discover a burr remains around each hole. Those burrs get in the way when tightening the fastener plus they’re a place for stress risers to start. It’s not uncommon to chatter an oversize drill bit around the hole circumference. Although that eliminates the burr or ridge, it usually destroys the surface surrounding the drilled hole—not to mention enlarging it too.

The recommended aviation practice works like this: A deburring bit or countersink can be used on each side of the hole (using your hands instead an electric or air tool) to remove the burr. Basically, this process bevels the edge and removes the ridge left by the drill bit. If you don’t have a countersink, some careful filing can also deburr the hole. It’s a good idea to use a piece of emery cloth or sandpaper (on a block) over each deburred, drilled hole.

With that out of the way, here’s how the bracket was built.

Visual Walkthrough of the Fabrication Process

You have to start somewhere so you’ll need a pattern. The female charger jacks were placed on a piece of heavy stock paper and then the edge margins were calculated. (Image/Wayne Scraba)
These are the charger jacks used for the project. SummitRacing.com has several different configurations. Search for “Remote Battery Jumper Terminals.” (Image/Wayne Scraba)
When building a bracket for anything, keep in mind you might have to service it. With charger jacks, you’ll be installing and removing the male terminals. This means they must be pushed in and turned simultaneously. You need room for your hands in order to accomplish this. (Image/Wayne Scraba)
Test fit the pattern and tape it to the aluminum sheet. In this photo, the cut is ready to be made, but only after the aluminum sheet is clamped down tightly. A piece of 1″ x 4″ board along with a big clamp does the job. (Image/Wayne Scraba)
A bare-bones basic jigsaw was used to make the cut. For this application, a coarse blade along with a good amount of cutting fluid was added to the mix. (Image/Wayne Scraba)
This is what the finished rough cut looks like. (Image/Wayne Scraba)
Next, the piece was re-clamped with a 2″ x 4″ underneath and a 1″ x 4″on the topside. It’s time to drill holes. Typically the mounting holes are drilled small and then you can work my way up. (Here, the fasteners are -3 AN or 3/16 inch). The clamp will have to be repositioned as you work your way around the pattern. (Image/Wayne Scraba)
Once the mount holes are drilled, two healthy sized holes were required in order to mount the female pieces of the charger jacks. To bore the holes, simply use a good quality bimetal hole saw (a 7/8 inch example here). Cutting fluid also works well here. By the way, Summit Racing offers all sorts of hole saws. (Image/Wayne Scraba)
Here’s the rough cut of the charger jack mount. (Image/Wayne Scraba)
At this point the edges were simply trimmed with a file (after scribing the exact dimensions). A larger half-round file was used to trim the bores for the female charger jacks. (Image/Wayne Scraba)
Occasionally when cleaning up large holes, it’s wise to file the face of the bracket lightly. After filing, you can block sand the mount face along with the edges. Typically, you can start with 120 grit paper and follow up with 320 grit paper using a soft rubber block. (Image/Wayne Scraba)
This is the completed charger jack project. This photo shows the jack without the corners rounded. (Image/Wayne Scraba)
Most folks prefer rounded corners. They’re easy enough to trim. (Image/Wayne Scraba)
As mentioned earlier, the quick release male connectors push in and turn to seat. (Image/Wayne Scraba)
This is a doubler panel used to reinforce the trunk sheet metal in a previous project car. The floor had random holes from a prior install, and as a result, it was starting to look like Swiss Cheese. Underneath the floor panel is a heavy electric fuel pump. The doubler covered up the prior modifications and strengthened the floor. (Image/Wayne Scraba)

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2 Comments

  1. For deburring, another great wat is a deburring tool. Summit has several, but this one looks nice… https://www.summitracing.com/parts/aaf-all11036

  2. Great story Wayne – I learned about edge margins. Good stuff!

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