Wiring Notes and Related Information
Mar 2018  R. Kwas  Revisions on-going  [Additional Comments]

Some new, some material previously published on the SW-EM site.

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Wire Gauge vs Current
The Lowly .250" Push-On Terminal
Wire Strippers
Crimp terminals, Tools, and making a Proper Crimp
The Lineman's splice
Notes on Making In-Line Connections

Soldering Notes
Lead Poisoning?...Hogwash! 

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Wire Gauge vs Current

Wire gauges: 

Lighting circuits to 10Amps:  18ga.

Charging circuit to 60A:  10ga.

Reference also:  https://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html 

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The Lowly .250" Push-On Terminal is a little marvel of design and function.  It has been engineered to allow a highly reliable, semi-permanent, high current connection to be quickly and effectively made, which still can be disconnected by hand with minimum effort.  It is inexpensive, and simple to be installed onto wires at the factory in a high volume production environment with automated tools, as well as being able to also be installed one at a time with hand-tools (see below!), by Joe-weekend-vintage-Volvo-mechanic....

...the two curved sides of the female contact are effectively a single turn spring (with variations, see below), which keep the two connection areas under constant preload...this accommodates any production dimensional variations, as well as thermal dimensional changes and vibration in-service very well…any variations, are continuously taken up by the constant preload! 


.250" terminal conceptual drawing showing a typical version on the left,
and another version, with even higher contact pressure (because of decreased contact area), on right. 
Spring preloaded electrical contact is made at three places, two at edges on topside, one at retention dimple on bottomside.

...they make a very good mechanical and electrical connection, with the cutting action during connector mating assuring two virginal metal surfaces.  This can be considered a Low-Contact Area/High Force situation.  Add the benefits of long-term protection by ACZP, and we have a semi-permanent electrical connection very well suited for, automotive applications…again, good engineering at work! 

Special versions of 1/4" contacts:  


Fully insulated 1/4" crimp terminals.  Once mated, in an in-line connection,
there are no exposed conductors to make inadvertent contact with anything!

...but beware...there are ways to get it wrong, too...in making harnesses for some of the SwEm Kits, I like the complete coverage of the fully insulated, female crimp-on contacts (...nothin' but the best for my customers!)...shown below is one of these female terminals being pushed on the male terminal of a Brake Light Switch...wrongly!  It is possible to incorrectly insert these onto the mating terminal...this might make a good electrical connection today, but might become intermittent or even work its way apart tomorrow under vibration, because the mechanical connection does not have the retention force of the engaged dimple/pimple.

Insert carefully and correctly when using these terminals!  (Shown clean below for detail, but in service, should have a protective coating of ACZP!)


1/4" female terminal misinsertion...possible because slots on either side of the actual terminal allow this. 
This is an example of poor design!  This should not be possible, as an example of poka-yoke
In kits, this connection is gooped up with ACZP, but that would obscure what we need to see here...

 

Related Excerpt from a Forum THREAD:  http://www.volvoforums.org.uk/showthread.php?p=2040833#post2040833

"Problem solved, was oil/grease buildup on both electrical contacts. No disassembly required."

My response:  "Be aware...if "oil/grease buildup on both electrical contacts" is enough to prevent electrical contact, the spring preload of push-on terminal (which should be present!) must not have been very good, because by design, pushing on terminals should cut through oxidation and surface contamination to allow contact of clean metal surfaces. This means after cleaning terminals of switch, you may want to (at the very least) squeeze (female) terminals to restore some preload, and (at the very most) replace crimps with new! ...and of course: Apply ACZP!" 

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Wire Strippers:  

Many different styles and variation of wire strippers exist.  Below are shown some of the more common styles, presented somewhat in order of cost and effectiveness.  The important thing to note is to use the correct cutting area by gauge, or if adjustable, make a test-stripping or two in order to adjust for the wire gauge being stripped so that only insulation is cut and not the conductor strands...even just nicking the strands is very undesirable as it immediately decreases the conductor cross sectional area (which will increase the I2R losses aka: Make HEAT!  See also:  http://www.sw-em.com/gastight.htm#I2R%20Heating ), and any nicked strands also present a mechanical stress riser where vibration may (will) in the long-term, cause further failure.  In extreme or critical cases such as motorcycle or aircraft duty, or after a long time under vibration, complete breakage will result!  [This is why the author abhors Scotchlok Connectors (and any other connector using Insulation Displacement for that matter!  There are good reasons you would NEVER...EVER find any of them in aircraft!)]

Naturally, the less expensive the stripping tool, the easier it is to get it wrong, but operator care and judgment (and use of ACZP when making and connecting the crimp!) are always called for to get good results over the long-haul...

Very Good Crimpers: 

 
Cutting insulation of various wire gauges, and pulling away the insulation in one operation when squeezing the handles.  Also good for areas with low elbow room!   Modest in price but also with a low chance for nicking a wire.    This is the only style stripper I would use when wiring an aircraft!

Squeezing the handle first cuts insulation (only, due to precision jaws), then pulls it away.  These were the strippers of choice for a high-volume production environment for a long time, and they are still very good, but they have been surpassed by the one shown on the right as those further remove operator error, and possibility of nicking a conductor!  In the stripper on the left, the operator must insert wire into correct blade gauge location...if inserted into a smaller gauge location than the wire to be stripped, damage to the conductor will still result.    Both styles are for single handed operation, and so good for use in areas with low elbow room!

Because of the risk of nicking a wire in all strippers following, I would NOT use any of them for wiring an aircraft! 


A high quality (German) stripper.  Jaw closure must be set for a given wire gauge.  Squeezing the handle only cuts the insulation...which must be pulled away in a separate operation so these require a bit more elbow room to use.  Conductor can be nicked if not adjusted correctly!  ...again operator plays a significant part in getting it right!

The following strippers can be levered against a needle-nosed pliers which is holding the wire to be stripped, so they are well suited to confined areas as the action is gentle and controlled. 

Mid/Low Price: 


Adjustable, in that, operator must insert wire into correct blade gauge location.  These have a "Squeeze Stop" to help prevent over-squeezing.
 

Low Cost (but I'd still rather have them than strip a wire with my pocket knife!): 

 
Least expensive strippers, requiring setting of the "Squeeze Stop" by operator...of course if one is just stripping one lousy wire, one might be tempted to leave the Stop backed way off so that they can also be used as a cutter, and simply use judgment, and "under-squeeze" to cut ONLY insulation...but beware, if the stop is not set, there is a high risk of nicking the conductor which must be managed, because what is a stripper when under-squeezed will quickly become a cutter when over-squeezed!!  Use only with Care and Caution!

How long should the stripping (uninsulated wire length) be?  Answer to this is arrived at after an inspection of the terminal to be crimped...  In general, length should allow stripped wire to fully protrude into crimp barrel to be visible at the other end, but not protruding.

...which all goes to show that;  Many roads lead to Rome, but if and how you get there depends on who is driving the chariot!

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Once a wire is stripped, operator can think about crimping...

Crimp terminals, Tools, and making a Proper Crimp. 

Crimps were developed as a alternative to soldering...sometimes power is just not available for a an electric soldering iron, and soldering with an open flame in a shop where solvents are also in use, is even less desirable.  A crimp is a good alternative to soldering, and properly made, will give reliable service for a the life of the vehicle.  As with wire strippers above, there are many variations in both Crimp Terminals and also the Tools.  So before attempting to make a connection, it is a good idea to inspect both to see what accommodations or special factors or techniques the operator must be aware of. 

Crimp Terminal Styles:  

Best:  Continuous circular barrel in the crimped area.


Ideally, this is what crimps should look like under the insulation...the seam, where the flat stock meets, is brazed together to make a continuous barrel...it might be worth sacrificially cutting some crimps apart to inform oneself of their internal construction!


The better quality nylon insulated type are identifiable by the translucent, color coded insulator (undoubtedly reflected in a higher price!).  A test crimp with Dimple type crimper will show that the insulation will stand up to this and not be pierced.  With inexpensive crimps that use cheapo plastic, the insulation would be pierced by the Dimple of the crimping operation.   

 

Formed flat-stock, so a seam is visible, but only under close inspection at the edge of barrel. 


Inexpensive, crimps made from formed, thin tin-plated copper.  These should be inspected to see it the seam has been connected by brazing (good), making the barrel continuous and strong.  If brazed and continuous, the squeeze type dies may be used, but if unconnected at the seam (even cheaper!) along the barrel, the Dimple type crimper or dies should be used, with Dimple positioned opposite seam to assure a good crimp!  The unjoined seam is not strong enough to stand up to the Squeeze type crimper and would splay open, weakening the crimp and lowering the pull-out force. 


Sold as fully insulated...but one also cannot see much of the metal part, so all the cheapness (thin metal and unbrazed seam) are hidden...! 

...one guess as to which types are commonly available on the popular on-line auction site!

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Crimping Tools: 

Replaceable dies (many other specialized ones are available), fit into the Paladin crimping tool below.  This allows operator to make squeeze as well as Dimple type crimps, as well as other specialty crimps depending on jaws installed.  This tool is high quality, with a ratcheting action due to the segment gear (at Green) and ratcheting pawl in the handle, which does not allow release of the crimp in the tool, until the jaws have been fully closed.  This, along with the precise dimensions of the dies assures that the full excursion and compression has taken place at the terminal, and removes the operator judgment factor...author calls this action "non-crimpus abortus" (you heard it here first maybe!)...but just in case something goes very wrong, there is a release on the ratcheting pawl.

Higher Price-Range (not highest!) Crimping Tool: 

A small extract of the many crimping dies available for crimping everything from electrical terminals, to cable television coaxial connectors, to telephone or fiber optic terminations:  http://www.lashenelectronics.com/p-1370-paladin-die-sets-for-crimpall8000-1300-series.aspx 

Shown here are jaws which will satisfy most if not all of your automotive crimping needs.  The 2035 set is typically used for the insulated terminals used on SW-EM Kit harnesses.  The 2031 set shows the protruding Dimple pin also found on some inexpensive tools, which can be used on non-insulated (or insulated, with judgment, if they are the cheaper barrel with unjoined seam type!), and the 2033 set would be used for replacement (uninsulated) hex-connector pins seen here:  http://www.sw-em.com/voltage_drop_in_headlights_power_in_hex_connector.htm#replacement_terminals

[Paladin tool info was copied from:  http://www.lashenelectronics.com/p-1370-paladin-die-sets-for-crimpall8000-1300-series.aspx  The author owns the Paladin tool plus several different jaw sets, because of the good performance/cost factor.  This is not intended as a specific endorsement of this tool...many manufacturers produce high quality tools for industrial production environment, which will serve a serious home mechanic for a lifetime. ]

Acceptable crimps can also be made with much less expensive tools, but where the Paladin tool takes just about all of the operator judgment away, the simple, inexpensive tools require the operator to know how much force to apply...on which side of the crimp barrel, and when to release the force.  There is nothing wrong with crimps made with these tools (for automotive duty, although one Rod Collins might disagree with you.  See below:  Info from the boating world), as long as they pass the operator inspection which should follow the crimping operation!  The author has several of these inexpensive tools in various tool boxes around the Embassy!

Mid Price-Range Crimping Tool:  


Typical lineman's or electrician's tool.  A beefy cutter at the tip, and or or two different sized crimp jaws...operator judgment is required! 

Inexpensive Crimping Tool:  


Multi-tool with crimping for insulated and non-insulated terminals, plus a few other handy functions available...inexpensive, multi-function, and great to have in an emergency toolbox, but again:  Operator judgment is required!  

Making a Proper Crimp:  Strip for wire gauge to length for the selected crimp terminal, allowing full insertion into the crimp barrel (with insulation stopping at the barrel...point is to crimp onto the conductor, NOT the Insulation!!), not nicking any strands.  After stripping the stranded wire, and inspecting to assure there is no damage to the conductor, apply just a dab of ACZP onto the stripped conductors before inserting into the crimping barrel, and before applying the crimping force.  The ACZP will displace and surround the wire strands-to-crimp barrel interface, protecting the actual connection from oxidation for a long time...if a (soldered) Gas-Tight-Joint is the best at wire terminations, this is the next best thing!...and in a harsh automotive environment (especially under the hood), it will serve well, and long, and trouble-free! 

PLACEHOLDER FOR EXAMPLES OF GOOD AND BAD CRIMPS

Conclusion:  One can see there are a number of places the operator must be aware of in order to get the simple operation of crimping a terminal onto a wire right...it's not rocket science, but carelessness will definitely affect your reliability in the end...and one can be assured that people building rockets and aerospace equipment observe all of the above mentioned factors (and then some!), including inspecting each step by an inspector other than the operator!  Out in the garage, we are both operator and inspector...I wish:  Good Crimping! 

Good reference information:  http://www.pinrepair.com/connect/

More really good Information about Wiring and Crimps from the Boating World:  https://marinehowto.com/marine-wire-termination/  Independent marine specialist Mr. Collins clearly knows his stuff (electrical, as well as boating specific!), and goes into even more detail than shown here, because proper, reliable wiring is even more important in the boating world, where a failure means you might be stuck in the middle of the lake, or even ocean...but he has not yet discovered ACZP (I wrote him and made him aware of it...and if he ever finds the time to write me back, I'll send him a sample of it!  I expect once he uses it, that he will very much appreciate the fact that it will prevent the growth of green copper oxide corrosion on electrical connections in service in a marine environment!).  

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The Lineman's splice (originally developed by Western Union)...when strung between two poles, as far as being able to be put under tension, the end-result is equivalent to a continuous, unmolested wire!  When protected with two layers of heat-shrink tubing under the hood of a vintage Volvo, can be forgotten about because it is as good as an uninterrupted wire.  Can be used on stranded as well as solid conductors (not that any solid conductors should ever be found in an automobile). 

 

1.  Strip Wire, generously, with no nicks in conductor!!  (Add two pieces of Heat-Shrink tubing, for shrinking in Step 5, cut to staggered lengths as shown.)

2.  Join Conductors by twisting, evenly, starting at about the middle of the stripped area! 

3.  Add 3-5 further tight turns (That is taken directly from the WU instructions, but on the low side of that is really OK when these wires are not hanging between two poles and under constant  tension and exposed to buffeting by the weather!)

4.  Trim, and solder (see below!)

5.  Shrink tubing, with staggered overlap. (Using clear HS tubing allows optional future inspection.  HS tubing also mechanically supports the wire which is now more rigid due to the soldering operation.) 

6.  Forget about splice!  (End-product is equivalent to a continuous, unmolested wire!)

 

 


A "tack-soldered" joint where in addition to making the intimate electrical between two wires, the solder is also expected to do the mechanical work of holding them together.  Solder has little mechanical strength(!), so this may be OK on the bench or for quick test purposes , but otherwise BAAAD and unacceptable, and not allowed in critical applications (like the vibration environment of a vehicle), I DON'T CARE if this is mechanically supported by Heat-Shrink tubing!  Use a Lineman's splice instead!

 

Example of a permanent wire repair using the superior Lineman's Splice:  


Splicing and double heat-shrink tubing protection of wiring harness completes a permanent repair.  Color changes apparent are due to variations in production years of harness, and could not be avoided.
Source:  http://www.sw-em.com/740_harness_meltdown.htm    

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Look what I ran across...:  

Nothing new (we used a variation of this product in the avionics industry 30 years ago!), but now available on the open market.  This is not a specific endorsement of this product, but the concept is most certainly sound...I'll have to get some and try them...watch this space for a "Product Review".

 

https://themcdepot.com/products/solder-seal-wire-connectors 

 

Frame capture from their video.

 

My comments to this product:  " This concept is sound, and has been around for 30 years (we used a similar heat-shrink with internal solder ferrule for a one step, wire-to-terminal termination plus insulated protection, in avionics at that time), but when connecting two wires, simply sticking the wires together as shown in the video is not the best practice...the two wires should come together in a "Lineman's Splice" ...then the tubing slid over with solder ferrule over wires, and activated with heat.  This gives the mechanical joint the strength in tension, of an unmolested wire.

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Notes on Making In-Line Connections:

It's always preferable to make connections to wires at an end, but sometimes, this is just not practical or possible...so when making the necessary connections to existing wires in the middle of a run, or in-line, for a reliable connection, crimp connection to the middle of an existing cable.  I recommend using butt crimps to restore the connection, and adding the new wire.   Best practice when crimping a wire is to cut, and strip the wire, apply ACZP to the stripped strands, and crimp them into a proper butt crimp of the correct size-range for the wire gauge (taking into account that the one side will have more strands because of the added wire), using a quality crimping tool...of course, when I want the absolute best and most permanent, reliable crimped connection I can make, I solder it !! (then protect with heat shrink tubing)...because there's just no beating a Gas-Tight-Joint!  See also:  740_harness_meltdown.htm#permanent_wiring_repars

I recommend very much against the Scotchlok clip-on, Insulation Displacement Connectors (IDC) shown below, also known amusingly as "Strom-Diebe" (Current-Thieves) by the Germans (maybe because it reminds them of the way we tapped into the Russian's telephone line running under East Berlin during the Cold War.  See the fascinating story of:  Operation Gold  or Turning a Cold War Scheme into Reality   ...in any case, see below for my explanation of why these are a "Scourge upon the automotive electrical land!", and should never be used.


...because I totally agree with it, I will also show this picture I saw on Bill Pollack's site...: 
http://www.billanddot.com/adding-rivco-led-mirrors.html#crimpers

Excerpt from my entry on Tom Bryant's Blog:  https://thosbryant.wordpress.com/2014/06/28/saturn-fuse-box-repair-1998-1999-redux/
 (yellow highlights are not a part of my original post but added for emphasis):

"I don’t agree with your positive assessment of the “Clip-On” [Schotchlok] connectors you show. They work by cutting and displacing wire insulation. Unfortunately, they also cut into the conductor (they’re actually designed to, with a sharp edge and an undersized slot for the conductor), so they are also damaging the conductor and decreasing its cross-section (BAAAAD) [to say nothing of the potential damage in the form of stress-riser they are without a doubt adding to the conductor...and that in a vibration environment!!  Egad!!]. They are merely OK (short-term) under laboratory conditions only (clean, dry, non-moving), but in a vehicle (and long-term), the connection they make is totally susceptible to moisture, and vibration – at least!  I REFUSE to use them…I throw them out (and I don’t throw ANYTHING out), and I replace them when I run across them. 

Again my rule is: If I want the BEST crimp connection I can get…I SOLDER IT(!), so functionally, I’m OK with your solder/shoegoo technique of adding a connection in the middle of a wire, but for a cleaner final appearance, I would use heat-shrink tubing immediately over [freshly applied] silicon RTV (which had not cured). As the tubing shrinks, it compresses the fluid RTV around the insulation, effectively resealing it completely (just as your goo does)…only a bit neater.
If you must make a permanent connection with very good reliability (only second to the soldered connection) to a wire with no access to its terminations (the preferred place for adding a connection!), and also no ability to solder, cut wire, strip both ends, add new stripped wire, crimp into butt-crimp (suitable for gauge of double wire) after dipping twisted strands into ACZP (see:  http://www.sw-em.com/anti_corrosive_paste.htm ).  Additional protection by heat shrink is optional. " 

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Shown below, from:  http://www.powerboxer.de/elektrik/66-stromklau  ...a BMW motorcycle enthusiast site, a graphic of why NOT to use these little electrical land-mines-in-waiting.  Their function is based on first cutting through the insulation, then into the stranded conductor (YIKES!  Cutting into or simply nicking  the conductor is one of the first BIG NO-NOs anybody having anything to do with electricity learns about...and that in a vibration environment!!  No thank you!).  Graphic is in German, and he calls it Stromklau - a variation on "Electrical Thief", but even non-German speakers will get a lot from the graphics showing how critical dimensions of the wire are for these to work at all... 

Conductors are shown as a solid orange (1) and this is not really correct...this is oversimplified...a solid conductor would not be able to flatten its shape as shown (2, 3) for this connection strategy to work at all.  Conductor should be shown as multi-stranded type (added better and more detailed graphic below!), so that as it is forced into the connection slot, slot splays open a bit under the force, strands also rearrange a bit into the available reduced space, and those conductors contacted by the sharp edges as the conductor is pressed into place are actually cut and weakened.  Add some vibration, and you can guess the inevitable outcome!

Scotchloks are available for different wire gauges, but 4, 5, 6 below show how conductor OD is critical to allow this concept to work at all...at 4, conductor OD is too big to force into the available slot (it would result in some combination of splaying the contact slot open, as well as cutting the conductor...a mechanical mess with unpredictable electrical function!), at 5, conductor is marginally too small resulting in a contact with low cross-sectional area (poor current handling capability!), and possibly intermittency, finally at 6, conductor is much too small resulting in not fully cutting through insulation in the first place.  With that many possible ways to fail, both short and long-term, the reader can see why I hate them...


 Source:  http://www.powerboxer.de/elektrik/66-stromklau   My mark-ups.

Here is a more detailed diagram of what happens when using Insulation Displacement Connectors...you get the cut conductor strands for free immediately, and Lord knows what in the future! 

IDCs are for weenies who don't know how to solder or make a proper crimp connection (see above!)...they should never, ever, ever be used in a vibration environment...you have been warned!!

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Soldering Notes:  Practice helps(!)...the author has been soldering for decades...from Starter Motor Brush wires in a Volvo, to micro-miniature aerospace Surface Mount Devices under a microscope (where the work area for a half day's work was the size of a Pinky nail!), with superheated air or a 25W iron, to Radiator, or Amazon Fuel Tank repairs or Copper Gutters with a 250W iron or even water supply lines with a torch...so it comes rather easy for me...the intent is not to brag, but this experience allows me to state that the rules and techniques for soldering at a micro-small to huge size, are essentially...no precisely, the same!...first, the base metals must be capable of taking solder (not all metals do!), absolutely clean, and during the actual soldering operation, sufficiently heated to allow the solder to wick into between the various elements of the joint.  Some practical soldering notes follow, and it applies to Volvo wires, as well as Gutters(!).

See also:  Preparing for Soldering in Amazon Rear Light Fixture Restoration Tech Article.   

Elements to be soldered should be clean of oxidation and/or contamination.  Abrading them immediately before the soldering operation will absolutely assure this!  Flux (in combination with heat) either applied separately or in the form or "Flux-Core Solder" cleans off small residual amounts of surface contamination, preparing the joint...it also increases the surface tension of molten solder promoting its creepage into crevices and around elements to be soldered.  It is not possible to solder successfully without flux! (...sure, one can try, but the result will inevitably be spherical blobs of solder dropped onto the area...not a "Solder Joint", where solder "wets" the surfaces intimately, and flows between them making a Gas-Tight-Joint (sound familiar?). 

Apply flux (or use a "flux core solder"), then using a clean and tinned soldering iron of the appropriate heat range, heat the joint, first, with as good a thermal contact possible on as many of the separate wires or components possible, then bring in the solder into the iron/joint junction, which results in the solder almost immediately melting (and this helps with transferring even more heat) and hopefully being wicked into the joint.  This wicking is what one should watch for(!) and it will not occur if there is is not yet sufficient heat in the joint, and it is not above solder melting temp [Not Heated Long Enough!], or it is still slightly contaminated...so if solder does not wick in, keep the iron in place and allow further heating...maybe applying a bit more flux and solder to help with heating/cleaning...once the wicking is observed to occur between all elements of the joint, [Heated Long Enough!...the Goldilocks point!] it is not necessary to keep applying heat to the joint after that...all the important action is done!  As a matter of fact, operator can, and should, remove the heat-source at the point it has been recognized that flow has occurred between all elements, tying them together with solder....and at that point, knowing you have a good joint, and because if you have not cooked away the flux, the surface tension of the molten solder will result in an almost pleasant looking concave joint (meniscus) in the corners of the joint.  After removing the soldering iron, it is important not to move any of the elements of the joint while solder returns to its solid state (this can cause loss of the intimate bond of solder to the base metals, and a "Cold Joint", identifiable by a dull surface or visible fractures in the solder). 

Contrast that to continuing to apply heat for too long...it is just not necessary to remain on the joint with the iron for long after you observe the solder being wicked into the joint by capillary action.  If, when you pull away, you pull a small peak of solder (convex) with the iron, it means that you've cooked away all of the flux [Heated Too Long!], and this results in loss of surface tension on the molten solder, which in turn allows the molten solder to stay attached to the iron as it is moved away, pulling a peak.  A solder joint with a peak would be unacceptable in electronics, because the wetting to the elements may also be compromised...correct the condition with a quick dab of flux and "reflowing"...this will quickly bring the preferred concave result. 

Separate flux application and using plain solder wire is fine, but "flux core solder" is also available in various gauges.  This is nice because it applies the flux at the same time as the solder, so there is less time for it to cook away.  Using electronic solder is good because the flux is non-corrosive and doesn't necessarily need to be cleaned off like the more aggressive plumbing fluxes. 

Too much solder?  Sometimes, due to positioning of the junction or positioning attitude of the junction, and continued adding of solder, a blob might make its way to the lowest point, or even drop off...solder which drops off by itself because gravitational forces on the molten droplet overcome capillary forces was never destined to be a part of the final joint, but it surely helped get the joint ready.  Try to minimize the gaps between joint elements when preparing for soldering, to increase capillary holding force.  Any droplets which form but do not fall away, can be encouraged to fall by holding the soldering iron below the drop...this will cause solder drop to wick onto soldering iron and away from the joint, leaving that concave lower surface.

Tinning Soldered Connections:  "Tinning" is a solder-preparation process by which the separate elements of a joint to be soldered are first heated and get a small amount of solder applied. This brings with it a number of advantages...it allows a close inspection of the solder wicking and flowing action as the elements are separate and not in-part covering and obscuring each other (possibly allowing a no-flow, bad joint) condition to go un-noticed, and it also assists and assures heat-transfer and solder flow in the next step.

After all elements (or just the elements which "needed a little help") have been tinned, they are united in the final position and heat is once again added (the tinning improving heat transfer!) to allow solder to "reflow", and a bit more can be added, to fill any remaining voids between elements.

An example of assuring a perfect solder (Gas-Tight!) Joint using tinning is rework of the 122(54412V) Fuseblock.  See also:  http://www.sw-em.com/gastight.htm    After the brass plates are pre-cleaned by media blasting, they are tinned before being reassembled in-place, then reheated as torque is added to the brass fastener (to allow the fastener to compress the stack with only minimal solder in between the plates). Simply soldering without tinning preparation would not assure the gas-tight condition between plates.  The Tinning and reflowing processing results in turning the stack of contacts into a monolithic conductive structure with absolutely the minimum resistance now and pretty much forever more!!  [Not to make too a big deal of this, but this structure is now ideal and the very best it can be electrically speaking...short-term, and long-term!]

Lead Poisoning?...Hogwash!  Finally, the smoke coming off a solder joint as you're soldering is from the flux cooking off, and not from the lead, so relax about any alleged dangers from lead fumes!  The melting point of eutectic (electronic lead-tin alloy) solder is around 390DegF, and while your soldering iron is even heating it up somewhat above that, it is still WAAAAY below the 3180DegF boiling temp of lead, needed to release the (deadly) lead fumes.  Sure, the odd molecule of lead might be released (water releases molecules and evaporates at room, and even frozen, temps too!), but there is a higher danger to the solderer from exposure to cosmic radiation from the Kuiper Belt than from those few lead molecules maybe being liberated!  Safety concerns of lead fumes from soldering are completely overblown by safety nannies who attended Basket-Weaving or Women's Studies classes in school, instead of Physics and Chemistry, where they might possibly have learned about properties of materials in the real world, and how things made of them work!  A little fan to dissipate the (not so deadly) smoke, so you can see what you're doing at the joint, will help!   

PLACEHOLDER FOR LEAD / TIN ALLOY SOLDER VS. (COMMUNIST PLOT) NO-LEAD SOLDER (which sucks!)
Notes:  Non-Corrosive Flux for Lead-Tin solder vs. Corrosive Flux for No-Lead solder.  Formation of Tin Whiskers in non-Lead Solder. 

An excerpt from the article:  Understanding and Mitigating Tin Whiskers by John O’Boyle, Maxim Integrated Products
Reference:  https://www.eetimes.com/document.asp?doc_id=1279227

"  Recall that the expected environmental harm from lead in electronics was the impetus behind the RoHS legislative action. Lead was feared as a contaminant to groundwater. Many well-intentioned people overlook one important fact, however: Elemental lead is not water soluble. Other sources concur: "Lead does not break down in the environment. Once lead falls onto soil, it usually sticks to the soil particles."5 When burned in an open-fire recycling operation, lead was feared to cause a poisonous vapor if inhaled. From NASA6, the facts are:

  1. An open-fire temperature is approximately 1000°C, but lead boils at 1740°C.
  2. Thus, the vapor pressure of lead would be negligible, presenting little possibility of lead-vapor poisoning.
  3. Workers who solder with tin lead (SnPb) solder do not have high lead levels in their blood.
In the end, there is no evidence that lead in electronics presents a health risk or causes environmental harm. Ironically, many of the proposed lead-free solutions do pose environment problems and many are much worse for the environment. "

See also Vid:  Are Soldering Fumes Dangerous?:  https://www.youtube.com/watch?v=EGdlM48eDbA

Good info comparing lead-based to non-lead (communist plot) solder:  https://www.youtube.com/watch?v=reNA5iwcg-w

My comments to that vid:  "You are absolutely right...and give very good objective scientific information indeed!...unfortunately being associated with RC modeling, it might not be taken as seriously as it should...I too was tempted to not watch the vid to the end, but am glad I did! The "environmental issues" you mention, and the reasons for removing lead from solder is the European RoHs and is based on BS substantiations (see Ref!): ...that there is some massive exposure to lead in electronics, when in reality the amount used there is absolutely minuscule compared to the amount used in lead-acid car batteries (which are EXEMPT from these regulations...because its tough to make a lead-acid battery without lead!)...so here we are...
Lead-free solder does absolutely SUCK! ...from a use and effectiveness standpoints (more corrosive fluxes are required, which can corrode electronics if not cleaned off well, much more difficult to use and get a good joint, etc), also from a negative side-effect standpoint (tin whiskers are a serious reliability issue, especially in High-Rel like military and aerospace!)
The fact that ebay suppliers of counterfeit china-crap goods don't know how to tell 1mm from 0.8mm, and lead-tin from no lead, or maybe they do and think the customers are too stupid to notice this...and the fact that those pricks could f**k up a junkyard, is a different issue... You should send that useless crap solder back to the thieves, and let them eat it...its not poisonous!
Reference:  eetimes.com/doc?asp_id=1279227  Cheers  "

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External sources are attributed where possible.  Otherwise this information is Copyright © 2018.  Ronald Kwas.   The term Volvo is used for reference only.  I have no affiliation with this company, other than to try to keep its products working for me, help other enthusiasts do the same, and also present my highly opinionated results of the use of their products here.  The information presented comes from my own experience and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at around the watercooler, or worshipped, at the readers discretion...and lead-less solder really does suck!  As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles!

 

You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the SwEm site as the source.  If you don’t, you’re just a lazy, scum sucking plagiarist, and the Boston Globe wants you!  As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the odd metaphor and probably wise-a** comment. 

 

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