Soldering Boat Wiring
Soldering boat wiring is a subject fraught with misinformation. What is it about soldering wires on boats? The various “experts” and much uninformed comment contend that this increases the integrity of an electrical wiring joint, improves electrical continuity and provides low resistance as well as in many cases postulating that it is all about the mechanical joint with electrical properties secondary. I am mystified as this is quite a false and inaccurate narrative. To play the devil’s advocate answer this question. “Why is soldering not done in all commercial marine electrical installations?” This ranges from container ships to naval frigates and submarines, to offshore oil rigs and fishing trawlers.
It isn’t mandated in ship classification rules and certainly it was not part of any professional marine electrical training in my extensive marine electrical and electronics career. We always had a soldering station on our various workshop benches BUT that was for doing soldering on an electronic printed circuit board (PCB). Crimping is the preferred method over soldering for all boat wiring. Why is crimping also the preferred method of wire connection in aviation, industrial plants, bio medical and so on. It mystifies me as to why these "experts" seem to argue that small boats are somehow different.
Reasons to Avoid Soldering Boat Wiring
I do not advocate using soldered joints on any boat wire, and dissent most strongly with the many “experts and gurus” who continue to advocate and include soldering training in the various training courses. I guess that statement will ruffle a few feathers however I am frequently having to address failures resulting from this with way too many who followed this faulty advice. Improper and low-quality soldering is a major cause of boat wiring faults as are wiring termination failures. It is easy to argue that the solder joints should have been done properly however most are not. The various soldering faults include cold joints, excess solder issues, dry solder joints, insufficient solder and solder bridging when done on Printed Circuit Boards. The main factor behind these issues are poor soldering techniques, defective or improperly selected soldering iron tips and improper preparation. A common mistake is to argue that soldering is designed to provide a good mechanical joint and this only partially correct. All connections should have separate mechanical support and strength. Solder is intended to make a good "electrical" connection. Read this opinion on soldering boat wiring versus crimping for wire connections. Read more about your boat electrical systems in the latest 4th Edition of the Marine Electrical and Electronics Bible.
What is a soldering flux?
A bit more about soldering boat wiring. Electronics solders contain a rosin core flux. The rosin flux is designed to flow over the job and prevent contact with the atmosphere. Metals, particularly copper when heated tend to "oxidize" and prevent the alloying or a good electrical bond forming between the copper and the solder. Good solder containing the rosin will have rosin flowing over the leads and prevent this oxidization process and as the solder flows the rosin is displaced allowing the solder to form an "atomic" bonding with the items being soldered together. A good rosin also assists in keeping the surfaces clean. As a note rosin is distilled from pine tree resin. Most solders in use are 1.o mm 60/40 resin cored. That is 60% tin and 40% lead.
About Cold Solder Joints
If you are adamant that soldering boat wiring is the way to go then best understand a few key points. Sometimes referred to as false joints because they look good but, in most cases, they are caused by the use of insufficient heat during the soldering. This leads to only partial solder melt and a poor quality electrical and mechanical bonded joint. As they look good, they may work for a long period but the hardened solder joint is actually weak and brittle with a tendency to crack after prolonged exposure to vibration. Cold joints have an inconsistent electrical conductivity and varying resistance values. Resistance means heat and affects circuit performance. If the soldering iron tip is too cold and not heated to maximum value, or the heat is unevenly distributed, or the soldering iron tip is dirty or the wires being soldered are contaminated or the solder iron is removed before the bond is complete a cold joint will occur. Cold joint prevention means making sure the soldering iron tip is at the right temperature. Most soldering irons don’t have settable temperatures however soldering stations do and the temperature should be set to just above the solder melting point. When soldering make sure you allow enough time for the solder to melt and flow over the wires being joined. Finally, preparation is key and make sure wires are clean without surface contamination that would prevent the solder from adhering properly. Most solders are flux resin cored which helps this process. If you do suspect you have made a cold joint, then reheat the solder until it flows and settles. Excess solder should be removed using one of those desoldering vacuum pumps.
About Excess of
Solder
A common problem whether soldering boat wiring or PCB’s is using too much solder. This is down to low competence levels and practice makes perfect. Excess solder is characterized by a big round ball of solder. They need to be corrected or they will cause issues later. When created on a PCB they can assist in short circuit and bridging problems. Often these balls of solder do adhere properly and there is actually a cold or dry joint underneath. This leads to high resistance in the connection. To avoid this always set the soldering iron to the correct temperature, avoid the application of too much solder at the soldering iron tip or applying solder before the joint has properly heated. Another common cause is the application of too much pressure on the joint with the soldering iron tip. The general rule is less solder is better. You only need enough solder to make a good joint; more solder does not equal a better joint as seems to be a common misconception. You need a light touch when soldering. Again, use a desoldering vacuum pump to remove excess solder. If you are one of those talented people who do work on your printed circuit boards then you will be aware that excess soldering can create solder bridges between component pins creating short circuits, or heat and damage along with damage to the board traces. Small components require the right iron tips.
About Not Enough
Solder
Insufficient solder or solder starvation creates an unreliable joint, and failure is inevitable. Failure modes are linked to physical stress through vibration and current levels as a high resistance joint is often created due to poor electrical conductivity. Technique is critical, the soldering iron must be heated to the correct temperature. The correct amount of solder should be applied. You have to allow enough time for the solder to start flowing and keep the soldering tip on long enough to achieve this. As a note lead free solders require a higher temperature than lead types.
About Dry and
Disturbed Joints
This is also referred to as insufficient wetting and is where the solder does not melt completely and results in a poor bond. This is similar to insufficient solder with same outcomes. The difference is that the solder does not properly adhere to the wires or components. The physical appearance is similar to not enough solder, being rough and lumpy and you may observe gaps where solder has not flowed. A disturbed joint is a common event when joining wires. This happens when the joint is subjected to movement (shaky hand syndrome), or vibration just as the solder was solidifying. The outer appearance of the solder has a crystallized or frosty appearance or a rough surface. These faults are also referred to as heat faults as the dry joint starts causing problems when it reaches a certain temperature. This is often during a peak load condition or after a certain operational time period. The quick fix is to reheat the joint and allow it cool down again without disturbing it. To prevent this always immobilize the joint and holding the work in a small vice will help. If you have a shaky hand then do not apply too much pressure with the soldering iron tip to the joint. Always make sure the soldering iron tip is up to temperature.
About Overheated
Joints
Soldering boat wiring myths include the proposition this will give a better joint. An overheated joint occurs when solder has not flowed properly and you end up with burnt flux residues which make correction difficult. To remedy this, you will need to scape off the burnt flux residues to clean it and also the use of isopropyl alcohol with an ear bud or a toothbrush will aid in flux removal. The usual result of such joints are unreliable connections, electrical conductivity and high resistance issues which lead to overheating. All this makes the joint unreliable and weak. Overheating also has the effect of altering the solder characteristics, which will reduce electrical conductivity. If you are doing PCB work this overheating can damage components and board pads. Wire joints suffer from conducted heat to the insulation and damage, and when attempting very fine wire soldering the wires themselves may be damaged and conductivity and resistance affected. It is best to use irons with a rating of less than 30 watts when doing fine work. Again, it is a fine balance but allow proper solder flow and enough to do the work so as to not burn the solder, flux and components. Keep the soldering iron tip clean to avoid uneven heat.
Soldering Summary
Soldering is a skill, not something properly learnt in an hour on some quick course. If you must solder best practice on some old bits of wire first before you attempt the real job. Soldering defects are very common and many will not show up until later when you are out on the water. Industry professionals have training for soldering but that is electronics circuit board related and it is a skill that takes time to master. Soldering boat wiring is more complicated than most boat owners understand.