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Introduction

Soldering heavy-gauge wires may seem highly specialized.  Actually, there are many situations that call for this skill.  

Sometimes you need to make a new battery cable, or fix the connectors on an old one.   It could be somewhere that's far away from a store, where you need to fix the cable right now. 

There are many articles on how to make your own battery cables.  This one details my own experience, with some tips you might not find elsewhere.

DIY battery cables are not for everyone.  Many will find it easier to order ready-made ones and be done with it.  This link, this one, and this one will take you to some ready-made cables. 

Whichever you do (store-bought or DIY), never underestimate the importance of good battery connections.   

Now let's see how to make some heavy-gauge cable connections.





Important Caution

You assume all responsibility for anything bad that may occur if you try soldering, crimping, or whatever. 

Cables that carry a lot of amperes would be dangerous if a connection were to fail suddenly.  A couple of stray wires, and things suddenly get interesting.

None of this information pretends to be up to electrical code regulations.  Proceed at your own risk.



A Quick Note

Articles like this one are possible only with the support of readers like you, when you use the links on here to purchase your gear. 

The small commissions from sales are what allow me to keep this site going.   Thank you in advance for your help.



In This Article

Cable Splicing & Appliance Cords

Wire Sizes & Amp Ratings

The Workspace

Gonna Git Me Some Metal Glue

Battery Clamps

More Soldering Tips

Silver Braze

Prep the Cables

Crimp-Only Method

Summary



Cable Splicing & Appliance Cords


Most of this applies to battery cables.   If you want to start putting new cables on appliances, there's a little bit of question.  Most times, the smartest thing is to replace the whole power cord, tying it in at the junction block inside the appliance.   

I wouldn't recommend using a power cable splice inside your residence, unless you have the experience to know what to do and what not to do.  

Then again, a solder joint is not really a "splice".  It is a metal bond that is usually stronger than the wires themselves. 

Unless you're using wire that's too thin for the amount of current, there is no reason why it should ever get hot enough to re-melt the solder.  We'll look at this in more detail shortly.

Sooner or later you will find the deal of a lifetime on some piece of equipment that has to be modded.  It's got a plug that looks like something out of a Soviet-era power plant in the Ukraine.  And wouldn't you know it... there's no terminal block inside the appliance;  just a hard-wired connection.

Use common sense before you tackle a problem like that.  Know your equations like V=IR, P=VI, and P=I2R.  Check the electrical codes and other regulations.  No guarantees there;  I'm just tellin' ya the technical aspects. 



Wire Sizes & Amp Ratings


Know your wire gauges.  50-amp power cables are going to need 6-gauge wires at least.  It's often a good idea to use thicker wires than you need.  

Use copper, not aluminum.  I would avoid any copper-bonded aluminum, although I'm sure plenty of people use it without issues.  For high-current stuff I would use real copper, if possible.

The diameters are available in a much more comprehensive chart through this link


Wire Gauge
Current Rating
Bare Conductor Diameter
Standard Copper Tube Size
Ready-Made Lugs
8 AWG
50 amps
0.13 inches
so-called 3/16" refrigerator tubing (0.128" I.D.)
buy here
6 AWG
65 amps
0.16 inches
so-called 1/4 inch refrigerator tubing (0.19" I.D.)
buy here
4 AWG
70 amps
0.20 inches
1/4 inch (usually about 0.30" I.D.)
buy here
2 AWG
110 amps
0.26 inches
1/4 inch (usually about 0.30" I.D.) buy here
1 AWG
110 amps
0.29 inches
1/4 inch (usually about 0.30" I.D.)
1/0 AWG
125 amps
0.32 inches
3/8 inch (usually about 0.40" I.D.)
buy here
2/0 AWG
145 amps
0.36 inches
3/8 inch (usually about 0.40" I.D.) buy here

Current ratings vary depending on the intended purpose, the insulation type, etc.  I'm going by the ratings for THHN stranded wire.   Look around enough, and you'll find different ratings.  Err on the low side.  Even if you find a table that rates 6-gauge wire at 100 amps, I wouldn't try that.

Copper tubing sizes are also confusing;  some standards name it by the inside diameter.  Refrigeration tubing is called by the outside diameter.    I listed the sizes that should work as terminal lugs or sleeve connectors.  You can also buy ready-made lugs for the particular gauge of wire. 





The Workspace


This is really important.  Don't do any of this on a rickety platform or in a poorly-lit space.  A couple of pallets tossed down on gravel is not a good workspace for soldering cables.  (I might know a thing or two about this...)

A concrete floor, or a solid work table, would be better. 

It really helps to have something to hold the wires while you solder.  You can pick up a couple of these mini bench vises for cheap.  Clamp 'em to the edge of your work table.  Use one to hold each cable.   This is not really optional.  If you don't hold the wires in place, you'll waste enormous amounts of solder and probably have to snip the wire ends and start over again a bunch of times.

Never underestimate the importance of good workspace preparation.  Work a few times on gravel... or muddy ground... and you will really appreciate a good workspace.

Don't forget ventilation.

Get a respirator right now.  Don't even hesitate here;  you need one of these.  If you go back and forth between different work sites, get a couple respirators. Even if you solder outdoors, you need a respirator!  Rosin fumes will destroy your lungs. 

A lot of people soldered for many years without wearing respirators.  Later on, they wondered what happened and why they couldn't breathe anymore. 
Can't fix that one.

I would also use a fan to carry the fumes away from your immediate area.




Gonna Git Me Some Metal Glue

Heavy cables use stranded wire.  Solid wire would be really tough to bend at these diameters.

Solder makes stranded wires into solid, which means there is no flexibility.  Just keep this in mind.  It won't be such a big deal if the solder joints are at the ends, where you'll have battery lugs anyway.

It's widely said that solder is not supposed to be a structural glue.  One reason is that someone might try to solder dirty or greasy wires, or use the wrong flux, or employ bad technique. This would make a solder joint that's not very strong.  A good solder joint can have a few thousand psi of breaking strength.  The copper wire will usually give way before the solder does.  Still, don't use it for mountain climbing rigs or something. 

You shouldn't be using electrical wires to support heavy weights anyway.   For making a welding cable or a battery cable, solder joints should be OK. 

Couple of soldering tips here:  use the right flux... and be sure to heat the metal where you want the solder to go, not where the solder is.



How Not To Make Battery Cables

Solder should not look dull or frosted when it cools.  This solder joint could give way at some point.  Here I used the wrong flux at the beginning, and the wrong blend of solder.  If I'd started out with rosin-core, this would be an OK solder job.



Also, the battery clamp is a little too flimsy for the gauge of wires being soldered to it.  (Incidentally, notice that I used two pieces of 6-gauge wire to make a heavier cable.  Kind of redneck.)

That brings us to.....



Battery Clamps


I used spring-type battery clips.  The smarter thing would have been to solder copper lugs onto the cable ends.  Make sure the lugs are made for the size wire you're using.

Then, use wing nuts to clamp 'em down to a pair of these battery terminals

Marine batteries have threaded posts already built-in.  If you have to use your car battery to power something, you probably don't have marine posts, though.



One thing to remember with marine battery posts:  sometimes the posts are two different sizes.  The positive could be 3/8" and the negative would be 5/16". 

Another alternative is to attach jumper-cable clamps on the ends of your cables.  Many of these clamps are actually steel, with copper or nickel plating.  Solid copper conducts the best, but it also bends rather easily.  Nickel plating is OK, but cheap plating can flake off or corrode.

Manufacturers like to inflate the current ratings of their battery clamps.   I would get ones from a brand-name manufacturer.  Forney makes welding gear;  since they put their name on these, they are probably at least halfway decent.  (I haven't tried 'em though.)  





More Soldering Tips


Want to know how not to solder the cables?   Try solid-core solder with zinc chloride flux, a.k.a. acid flux.  Put the flux on after you start heating the metal.  This is how not to do it.  The metal won't wet the strands.  It just rolls off. 

If you're anything like me, you will waste about $19.37 worth of solder before you realize it isn't going to work.  Acid flux, which would have worked on a copper pipe, is no good for stranded wire.  Even if you could get it to wet all the strands, it will cause corrosion later.

If you want to solder it right, there are two ways.

1.)  Use rosin flux.  You can use liquid rosin or paste rosin.  Put the flux on the wire before you even start heating it.   Every time I solder, it seems I start heating first and then add the flux.  (A habit developed from brazing with flux-coated wire.)  The flux should be on the wire first, to prevent oxide formation.  Then the solder will wet the metal. 

2.)  Use rosin-core solder!  This doesn't put the rosin on the metal early enough to stop the oxide formation.  How does it work, then?  Rosin gets corrosive when it's hot, so it lifts away some oxide.  Added activators make it even more effective.

There are three types of rosin-core solder:  R, RMA, and RA. 

R-core is pure rosin-core with no activator.  It's best to have clean metal.  Torch soldering is probably not that good with R-core solder, because the copper tarnishes so quickly.  I don't have R-core solder to test, but there's a reason why companies started putting activators in the rosin core. 

Next up is RMA-core ("Rosin, Mildly Activated").  This has a little bit of activator to help remove oxidation from the wires. 

Then there's RA-core ("Rosin, Activated"), the most highly activated rosin core.  If you're going to solder heavy copper cables, use RA. 

Kester 44 solders have RA-core.  For really heavy-gauge cable, get this one.  Their 44 series is widely acknowledged to be the best rosin-core solder you can get, or one of them.  Yep, the brand and type of solder makes a difference.   





Silver Braze


Solder melts fairly easily.  Some of them melt at 600 to 700 Fahrenheit.   Several lead-tin solders, including 50/50 and 63/37, melt below 400 F.  Oatey Safe Flow, a lead-free solder, melts at about 450.

If the wires carry an extreme overload of current, they'll re-melt the solder.  The wires could then fly apart.  Live wires hitting random stuff would be bad.

Silver braze has a much higher melting point (around 1300 to 1400 Fahrenheit).   If your wires carry so much current that they're getting to 1300 Fahrenheit, you probably made a design error somewhere.  Point is, silver braze will not melt when you don't want it to.

Don't try to silver-braze circuit boards;  it's too much heat.  For big copper cables, though, I would definitely try silver braze.

You'll need something that puts out enough heat for silver brazing.  You can silver braze with ordinary propane (a.k.a. "LPG") and one of these torches by Bernzomatic.   This can even work for bronze-brazing, as long as the workpieces are small.


              


Or you could use air-acetylene, which uses one of these torch kits hooked up to a "B" tank of acetylene.   Better yet, get this torch kit.  Super-hot swirl flame.

Finally, you could even use oxy-acetylene.  That's sort of overkill for silver brazing, but actually the very intense heat can allow you to get in there, braze the workpiece, and remove the heat.  Cooler torches take longer, which means the heat has more time to spread out and heat other stuff.   Oxy-acetylene also lets you do welding without the need for electricity.  And with oxyacet, you can do regular bronze brazing, applying it very thick like a weld.

If you're going to braze cables, best bet is to use a copper or brass sleeve that fits over the wires.  Get some pieces of 1/4 and 3/8 copper tubing and cut them to the desired length.

There shouldn't be much space around the wires, if any.  The braze will wick into the narrow space between the bare cable and the copper sleeve.  This forms a structurally strong bond.  A good braze joint is about as strong as a weld (60,000 to 70,000 psi).  Silver braze should be good to at least 40,000 psi, if I remember correctly.

Silver wire can get expensive, but it's possible to buy the stuff fairly cheap if you just buy a small coil of 20-gauge wire.  Get the "medium silver solder wire", which is not solder at all;  it's a type of brazing wire.  Get a tub of Handy Flux.  You will need this for silver brazing.  This combination seems to work great for copper-to-copper, copper-to-brass, brass-to-steel, and probably other stuff.

Another alternative is this kit from Harris. 




Prep the Cables


You'll want to have a good workspace and the right kind of solder or braze.   And the right kind of torch. 

Now, the wire prep.

I already mentioned using a pair of cheap bench vises.  These will hold the wire or wires in place while you solder.

You'll need to remove enough insulation from the wires to make the bond.  Problem is, if the bare copper is too short, the insulation will be too close to the heat.  It will melt and burn.  There will be black smoke and a nasty mess. 

The typical lead-tin solder doesn't have to get that hot before it melts.  You should be able to get the copper hot enough without burning off all the insulation.   The main thing is to make sure the bare copper is clean before you put the flux on it.  (If you're using activated rosin-core solder, it's OK to have a little bit of tarnish.)

Wire Prep Checklist:

- Insulation removed far enough

- Copper is clean

- Cables held in place with mini bench vises or something.

- Flux the cable ends with rosin before you apply heat;  or, use RA-core solder.


Then, solder.



Crimp-Only Method

Some people recommend crimping without soldering.  Using a special tool, you crimp a short piece of tubing onto the cable (or cables).  If you do this right, they probably won't pull apart.

If you have a way to keep the workpiece from slipping, you could even use a hammer and a steel punch to make the crimps. 

Crimp connections are kind of sketchy for narrow-gauge wire.  When they're outdoors much, they can start to go intermittent on you.   To make matters worse, a lot of these connectors aren't even made of copper.  

For heavy-gauge copper wire, crimp connections might be OK.  I still think they're sketchy if they don't have solder.  Nothing beats a soldered or brazed joint for electrical conductivity.  Crimped connections are mechanical, and mechanical connections can develop oxidation.  You might think the metal has no space, but there is a gap.  It could be a thousandth of an inch, but corrosion can form in there. 





Summary

Most cable connections can be soldered or even brazed.  For making battery cables or welding cables, solder is better than crimp connections.  The most important things are: 

1. Have a good workspace with some way to hold the wires while you solder them.

2. Use the correct diameter of copper tubing to make your own lug connectors.  Or, just buy the right size ones ready-made.  For example, you can get 1/0 gauge terminal lugs here

3.  Use the right kind of flux.  For anything electrical, use rosin flux, or just get rosin-core solder.

4.  Don't forget the respirator.  Rosin fumes will wreck your lungs, for real.  

If you found this page useful, informative, or entertaining, please help me out by purchasing your stuff through these links.   Your support is greatly appreciated and is the only way I can keep this website on-line and adding helpful articles to it.

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