We will teach you how to properly crimp battery cables by utilizing a hydraulic lug crimper in order to create a strong, low-resistance connection that will not only last for years, but also will reduce the risk of fire or property damage due to an incorrectly terminated cable. In our example shown in the pictures, we are replacing an existing piece of Aluminum wire, with our newly made properly crimped copper cable!
Tools & Materials Required:
- Tape Measure & Marker
- Knife/Razor Blade for Cutting Insulation
- Heat Shrink Tubing
- Battery Cables & Corresponding Lugs
- Hydraulic Crimping Tool
- Wire Cutters
- Heat Gun
Step 1: Determine Cable Length
First, you will want to determine how much cable you need.
To determine cable length we need, plan the run from A to B, but don’t forget to factor in how much length is taken by the lug. We find it is easiest to mount the lug on the final terminal connection to hold the lugs in place while determining length.
From there you can hold the cable next to the lug at the starting point and lay out the run to the second lug.
Alternately, a measuring tape may be used if this proves to be too difficult, but be very cautious using a metal tape measure near batteries of any type!
Step 2: Cut to Length
We used our newly updated Klein Journeyman cutters, which are great for this use. Klein changed the design of their cutting edge, and now it works even easier than our Klein 16-inch / 350MCM Cable Cutter.
Even though this cable is outside of their typical cutting range, they were still able to cut through with ease. This is the exact tool that our team uses to fabricate our pre-made battery cables.
Step 3: Mark Insulation Strip Length
The easiest way to determine how far back the wire will need to be stripped is to hold the wire next to the lug. Locate the end of the wire at the point of the lug where it starts to taper down to the flattened area.
Make a mark at the open end of the lug, compensating that some of the insulation will press against the lug
Make sure not to strip your wire too long – exposed copper is not desirable. Too short of a strip length will not allow enough wire to enter the lug for proper crimping.
Step 4: Strip Insulation
This is not a job for conventional wire strippers, side-cutters or cable cutters.
Use a sharp knife to cut approximately 3/4 of the way through the rubber insulation. Make sure to avoid cutting all the way through and touching the copper; it is extremely soft and the fine strands are easy to nick with a knife.
Nicking the copper can turn into a weak spot in the connection, leading to failure in the future. This is especially true for smaller gauge cables that utilize finer strands.
Step 5: Remove Insulation
Since we are already most of the way though, you can now bend the wire at the score line and the insulation should snap and separate at the slice.
If it doesn’t break free, you can lightly touch the knife against the rubber that is still connected and it should snap right off.
Once fully separated, simply pull on the section of insulation to be removed until it is clear of the wire.
Step 6: Insert Wire & Ensure Fitment
With a lug that corresponds to the wire size, inspect for any defects or oxidation. If it is oxidized on the inside for any reason, you should consider using a different lug; if one is not available, you can scuff with either a wire brush or some fine-grit sandpaper. Any oxidation will increase the conductivity of the termination and lead to heating and catastrophic failure.
Slide the lug over the stripped end of the wire and make sure that the proper amount of insulation is stripped back (no copper exposed.)
Step 7: Prepare Crimper
Our hydraulic crimper comes with a variety of die sizes, but unfortunately the die sizes for our demo crimper are wrong, they are meant for mm² wire sizes, not AWG sizes.
We highly recommend buying the Temco Crimper because it has the proper dies for AWG sizes and will provide a more robust connection, in addition to stamping the die size used into the lug during crimping.
After installing the proper dies, you must check to ensure the release valve is closed.
Step 8: First Crimp
Place the lug into the dies and pump the handle a few times so that the dies snugly grip the lug. Make sure the lug is oriented as shown in the picture. Some lugs are large enough to require crimping in two places, in which case, make sure the dies aligned as close to the open end of the lug as possible.
Once the lug is held by the dies, fully insert the wire, ensuring there is no copper sticking out past the end of the lug.
As you are crimping, make sure the wire remains fully inserted into the lug.
Be careful as you are crimping!
Make sure the wire is properly inserted into the lug when you crimp your battery cables. Maintain pressure on the wire during crimping. If the wire is not fully inserted, a proper crimp will not be established.
Step 9: Finish Crimping
Continue actuating the handle of the crimping tool until the dies touch together. At this point you are ready to release the pressure and continue with the second crimp.
If you utilized correct tool and die configuration, the wire should be firm in the lug and will not fall out if you tug on it.
However, if the wire does start to come out, confirm your die selection and reduce size as needed. If the sides of the crimp where the dies meet look smooshed out, then use a bigger die.
Step 10: Second Crimp
Place the lug back into the crimper, this time on the remaining area that was not crimped during the first operation.
Continue to crimp the battery cable just like before. Once completed, pull on the wire to make sure it does not come out of the lug.
Step 11: Success!
If your cable looks like ours, then you have successfully crimped your first lug! You can now proceed to the other end of your cable.
Pay extra attention when crimping the lug on the other end of the cable; with thicker cables, you will not be able to twist the cable to compensate for an improperly oriented lug. If needed, make a mark on the wire and lug to note where to line things up during crimping.
Step 12: Second Lug
With our orientation established, we can align our marks and crimp the second lug on the cable. Just like before, ensure the wire is fully inserted before crimping.
Step 13: Test Fit
Now that the crimping has successfully been completed, test fit your cable to make sure proper length and rotation have been achieved. If everything checks out, we are ready to move to the next step.
Step 14: Heat Shrink
For our 4/0 cable, we are using a heat shrink tubing that is a 3:1 shrink ratio. When the tubing is flat, it measures at 1 1/2″ wide, and we cut a 3 inch long piece for each end. Smaller diameter cables can have shorter lengths of tubing. The goal here is two fold; reduce the stress from cable flexing from fatiguing the crimp, as well as preventing moisture from entering the crimp and causing oxidation.
Step 15: Heat Shrink Continued
Begin heating the shrink tubing with a heat gun. We have a wide tip that spreads the heat out across the entire width of the shrink tubing. Continue to turn the cable to apply heat consistently around the whole circumference of the tubing.
Should I solder my lugs after crimping?
In marine applications solder joints are forbidden and in most jurisdictions residential and industrial power circuits, soldered joints and lugs are not code. The reasoning is that if the conductor is overloaded, the solder would begin to flow and the juncture would overheat catastrophically. For parts subject to flexure and vibration, solder can wick into the strands past the crimp and the wire will eventually work harden and break just past the lug. In marine environments the dissimilar metals of the solder lead/tin/zinc to the copper just adds more issues. Best is a quality lug, quality fine strand tined wire, quality crimp, with adhesive lined heat shrink tube. Studies have shown that a proper mechanical crimp using a hydraulic tool can “cold weld” copper to the terminal, creating a superior connection compared to soldering.
Do I need heat shrink tubing that has glue on the inside?
Shrink tubing that has glue inside will provide a superior seal. We highly recommend this type of seal for marine applications or environments that have high humidity. It ultimately comes down to personal preference and evaluation of the installation environment, as well as how long you desire the connection to last. Terminations that utilize top-quality components will last the longest.