I bought some marine‐grade cable, heavy duty lugs, adhesive lined heat‐shrink tubing, silver solder and flux, some sort of torch (butane, MAAP or propane) and battery terminals. Everything is tinned (dipped in a molten solder) to prevent any chance of corrosion. I purchased most of it from www.mcmaster.com
Wiring Sizes: Wiring sizes from largest to smallest: 4/0, 3/0, 2/0, 1/0, 1, 2, 4, 6 and 8 gauge
I used 2/0 gauge wire for the following reasons. I have a Optima Blue‐Top Marine battery, Warn Electric Winch, 200 amp alternator, dual electric cooling fans that consume 50‐125 amps and a ton of other electrical modifications. For me it was easy to justify the heavier cable. I believe the factory uses 4 gauge wire or at the least it is 6 gauge. If you are going through the hassle of making your own I would encourage you to go 2 gauge or larger.
Types of cable: There's automotive battery cable that has a SAE designation (Society of Automotive Engineers) which is characterized as extremely coarse strands (least efficient electrically) and makes for an extremely stiff cable and is the least desirable cable (as an example of its coarseness it may contain 100 strands in a 1 gauge wire). Then you have welding cable, which has finer strands of wire and makes for a better cable in terms of flexibility and its ability to conduct current as finer strands will flow current more efficiently than coarse strands (as an example of its coarseness it may contain 500 strands in a 1 gauge wire). Last is marine‐grade wiring which usually has a USCG designation somewhere on it (United States Coast Guard) and is fine stranded like welding wire (I never did look into the strand differences between the two) and has the advantage of being dipped in solder (tinning) to prevent electrolysis of the copper strands. Obviously in marine applications this is very important. In my Jeep that sees salt in the Chicago winters and mud water when off‐road I value this as a worthy additional expense. Which one is best for you will vary on your own environment and budget.
Heavy Duty Lugs: Not much difference in lugs from one to the next with the only possible exception being some are tinned from the manufacturers while others are bare copper. Once again the tinned pieces are preferred but not necessarily essential. Otherwise just match the lug to the size of the wire purchased.
Adhesive Lined Heat Shrink Tubing: McMaster.com uses 3M as their supplier of HST. The adhesive is on the inside of the tubing and is used to seal the elements out from corroding the wire. HST comes in different compounds, thicknesses and shrink‐ability. I purchase Polyolefin Thick Wall‐Adhesive Lined and it is a very tough HST that won’t be worn through without a fight.
Solder and Flux: Instead of crimping the lugs on I prefer to soft solder. Soldering happens when a joint is heated and the solder becomes a molten alloy that flows into the joint and bonds it together. There is different alloys of solder, but for the ultimate in strength you want a solder that includes Silver. In the old days solder was an alloy of Lead and Tin. Lead and Tin solder has a fairly low melting point is real easy to work with but is not the strongest. An alloy of Silver, Lead and Tin or just Silver and Tin (Lead is frowned upon now days) will give a stronger electrical joint. The last item you need is flux. There’s different types of flux and you want flux that is meant for electrical soldering (non‐acid core).
Torch: I have used a small but powerful Butane torch. Also a MAAP torch is more than up to the job. Lastly a simple propane torch is a little cumbersome but will bring the heat extremely quickly. Any one of the three will get the job done.
Battery Terminals: There are a few different styles out there from Mil‐Spec and on. Mine came from a marine vendor and have a post with a thumb‐screw to tighten the cables down.
This is somewhat of a labor of love. If you shop around you could save some money but it won’t be dramatic unless you skimp on the components. There’s always a debate between crimping and soldering. If you have a fancy hydraulic crimper then you can get a durable, mechanically sound connection. If not then I would be seriously concerned about the lug gradually working loose over time. Soldering creates a permanent bond between the lug and wire. The only downside with soldering is the risk of creating a cold solder joint. Basically this is analogous to doing a poor job crimping a lug on a wire as either one won’t last long. With just a little practice though you can avoid creating cold joints. My own personal preference would be to use both whenever possible, although I never do with larger gauge wires like these.
Here’s my approach. I take a lug and with the end that the cable goes in pointing straight up I clamp it tightly into a vise. Then I take some flux and a small paint brush and brush it along the interior of the lug. Then I take the silver solder and my electrician’s scissors and cut short ¼” pieces and drop them into the lug until the lug is roughly half full. Then I carefully strip the insulation around the cable deep enough to fill the lug plus another ¼”. Then I take my flux paintbrush and liberally apply it to the end of the cable. Now is a good time to test fit the cable to the lug and make sure it will go in without a fight.
Now it is time to apply a lot of heat. You might want to consider eye protection, and a shop apron to prevent any molten solder from getting to your skin. Unfortunately the vise being clamped to the lug is going to act as a heat sink and draw the heat you’re adding to the lug. Fortunately the torch will overpower it eventually. Heat the lug until the solder inside becomes molten. Once it does insert the cable into the lug in the appropriate angle. I then continue to heat the lug and add more solder around the exterior of the lug until it won’t accept anymore. The flux acts as a medium for the solder to follow. The flux will liquefy and wick into the strands. The solder then becomes molten and using the same capillary action goes inside the strands of the wires as well. You end up with a lug that is one solid piece of alloy metals. Once done with the solder, HOLD THE CABLE VERY STILL FOR A GOOD 15‐30 SECONDS. Silver solder is slow to change from a molten state back to a solid. Moving the cable while this transition occurs will create an unwanted cold solder joint. So be patient and wait for it to cool. Once it has cooled for the 15‐30 seconds you can remove it from the vise. When you do use a set of rawhide gloves as the lug is still going to be extremely hot! Resist the urge to dunk the lug into water as you run the risk of it becoming a cold solder joint once again.
The last step is to seal this joint from the elements. I usually take a strip a silicone tape and wrap it around any exposed cables. Then I cut an appropriate length of HST and slip over the lug. Take the torch and run at its lowest heat setting. While spinning the cable around lick the flames on the HST. In short order you should see the heat‐shrink do its thing and shrink on down. You are finally done with one end.
Now it is time to do the other end. Make sure you measure multiple times how long you want the cable to be. Once ready use a large cable cutter or a hack saw if none is available to cut the cable to length. The next thing is to get the orientation of the lug on the end of the cable correctly. Do you want it on exactly the same way? Maybe turned 45 degrees or perhaps 90 or 180… Once you figure it out mark the cable with a marker so you know the center of the cable for when you slide it into the lug with the molten solder. Beyond this aspect the procedure is identical to what was already described above.
When doing this I haven’t had a failure. I changed my wiring after 5 years to accommodate some changes. I decided to test the strength of one of the existing wires. I clamped it on a vise on one end and wire a 10 pound weight on the other side and repeatedly dropped the weight. Despite this continuous shock the soldered joint didn’t come loose. Consider me satisfied.
Some horror stories (not my own but from other Internet web searches) regarding crimped connections and pre‐fabbed cables:
“I used to make battery cables for electric forklifts, and the old timer that trained me would not crimp...only solder. The proper terminals had reliefs on the inside diameter that "keyed" the joint to prevent pull out. He would put the terminal in a vice with the thimble facing up. He used a butane torch to heat the terminal and completely fill the thimble with molten solder, then insert the prepared cable into the thimble, pushing out the excess solder and then remove the heat, holding the cable until the solder cooled. Then heat‐shrink. I'm not saying this method is correct, but I never saw one made this way that failed. Also, careful with welding cable. The insulation (as I remember) was not resistant to sulfuric acid. I'm pretty sure welding cable is not to NEC code for this application…”
“A few months ago I discovered my first problem. One of the parallel battery cables slipped out of its terminal end when I checked it, essentially meaning that there was a failure in the crimp that holds the end on the cable. I immediately replaced the cable with new one and figured it was just a one‐time failure of the crimp caused by heating and cooling as current flowed through the cable. Boy was I wrong.
This was where I found my second problem that may have contributed to the premature failure of one cell. As I was removing the series cabling I found to my horror that when I removed the bolts holding the cables in place and picked up the cables, the ends promptly fell off. These were cables that I had purchased from a well‐known national catalog company, made up by them in their office, when I had purchased the original batteries.
When they made them they used shrink tubing to seal the ends, shrink tubing that hid the extremely poor job of crimping they had done connecting the cable ends to the cable. Three of the series cables had the ends fall completely off and others were extremely loose. After 7 years even the shrink tubing couldn't hold them together. This meant that there was a high probability that there was a more resistance in those cables than there should have been, which meant more work for the batteries and charging system and less efficient energy availability to the inverter. They hadn't even been crimped enough to deform the ends of the cables (see the picture at left), on most of the cables not enough insulation had been stripped back to put the correct amount of wire into the cable end.”