Cable Terminals - High Current - for Off Grid Solar Batteries

I'm building an off-grid solar power system and wanted a cheap solution to connect my batteries. High powered terminal ends are expensive, so I came up with this!

Because these terminals are so cheap and easy to make, it won't be a long Instructable.

I'm a teacher, so I like to give the 5 second summary upfront for the quicker students...

Summary: Copper tube for plumbing is highly conductive and cheap. Flatten a short section of 17mm copper tube over the end of a cable. Drill a hole for a bolt, and insulate with heatshrink or electric tape. The cross section of the terminal will be around 50 square mm.

Step 1: Tools and Materials

Tools

Angle grinder or pipe cutter

Drill press with an 8mm bit (approx)

Two offcuts of timber to protect the copper when flattened

An axe, mallet or vice

Hot gun (heatshrink)

Pliers

Materials

17mm copper pipe

Electrical tape or heatshrink

Cable (I used 2 gauge)

Step 2: Assembly

1. Cut a section of tube about 70 mm long

2. Flatten half of the tube. Squash it with a mallet or something. Use the wooden blocks to keep it pretty. (I 'axxed mine a question.' It couldn't answer back)

3. Drill a hole for the bolt through the flattened part

4. Strip back the cable about 40 mm

5. Feed the exposed cable into the round half of the tube

6. Squash it flat with your mallet setup. (Axe it another question.)

7. Insulate with a few layers of tape, or heatshrink

8. Repeat as necessary, for the end of each cable

Step 3: Finished Product - in Situ

Here they are, all finished and bolted into my system.

I ran the 2 gauge cable between the positive terminals (24V in parallel).

Do you see those straight links? How did I make them?

I'm so glad you asked...

Step 4: Bonus -- Rigid Battery Links

The cable ends in this Instructable were actually an afterthought. The main deal was the rigid battery links.

I came up with this solution when wandering around my local hardware shop. I saw the copper plumbing tube. Pure copper, I thought to myself. That's meant to conduct water, but it also conducts electricity.

So I bought a straight length for about $17 bucks (Australia) and some heatshrink to make it all look neat.

1. Cut to length, with about 12 mm either end.

2. Drill the holes for terminals all the way through

3. Flatten the ends with the axe and blocks

4. Insulate with tape all over, especially the ends, so they're rounded, not sharp

5. Fit heatshrink tube

6. Cut holes in the heatshrink for the bolts with a sharp blade

7. Done!

Comments

[bougakov]

I'd modify that like this:

5a. Wrap the exposed cable's end in about 5-10cm of solder wire.

5b. Feed it into the round half of the tube

6a. Squash it gently with your mallet

6b. Use butane torch or 100W soldering iron to melt the solder. Make sure you don't burn or melt remaining insulation on the cable. As solder melts, squash copper again to make sure cable is reliably held in place.

This way you ensure that the connection will be reliable and won't heat under heavy load. Solder will prevent copper from corroding and increasing resistance on the joint.

[lrovernut]

My main worry would be that mashing the pipe around the cable would not make a secure enough joint. if the joint is high resistance it will get hot and potentially cause a fire. If the cable slips out it could cause a short circuit, again with the risk of fire.

[jothhughes]

Yeah, I was a bit concerned about that as well, and then I compared this method to how domestic wiring is connected--copper cables are held in place with screws. Still, I think you need to be careful to squeeze the cable evenly along its length. I'll drop a multimeter on it and check the resistance, and post.

[JohnL79]

A multimeter can't accurately measure resistances this low. You really need to pass a large current through it and measure voltage drop (4-wire method). R = V/I. Increase current until you start seeing a noticeable drop but be aware of the power being dissipated and check that it's not heating.

[gm280]

One way to totally solve the worry about the cable getting hot because of a suspect crimp. Before applying the heat shrink, solder the copper cable to the copper pipe after flattening it. Problem solved. Just clean the copper pipe inside and out and use a good flux and heat the pipe much like you were sweat soldering pipes together. Once the solder wicks up inside the pipe, the copper cable is attacked and no worry of a bad connection to cause heat. You could even pretin the cable as well. JMHO

[jothhughes]

Thanks gm280. I only have a small soldering iron, and that wouldn't work. To clarify, do you use a butane torch and a stick of solder, or something else?

[gm280]

A Butane torch would work, but so would a high wattage soldering gun. The flux is the key though. If you pre-tin the copper cable and then pre-tin the inside of the pipe, then put a lot of flux on the cable end and slide it into the pipe. Once you heat the outside of the pipe like you are sweat soldering copper pipes together, the solder will suck into the connection when it is hot enough. You can use regular 60/40, 63/37 rolled solder or copper pipe solder. But that joint will carry tons of current without issue. BTDT

[timothy.robinson.589]

I raise this thought because someone spoke about heat & fire safety ...
Great idea But there is a reason why there are silver mixed into copper cables.
Then there is those
Aluminum Heatsink laying around they are natural coolant to disapate the extra heat buildup....
Remember think Safety First can't reset your life but you can take precautions with thinking correctly also you guys do know they sell liquid electrical tape in 4 colors.....

[Korzer]

could we expect more great ideas like this one? :)
I love that idea

[carlos66ba]

Excellent idea!

[jothhughes]

Thanks! It's my first Instructable.