Crimping two wires together on the same crimp-connector it's criminal?

Kermit2

Joined Feb 5, 2010
4,162
You should carefully remove 1/2 inch of the wire insulation about 1 inch back from the stripped end of your wire. Wrap the stripped end of the wire you want to add around the 1/2 inch of bare copper on the other wire and solder then add shrink tubing over the soldered joint. Crimp and seal the the bare end of your original wire as usual.
This is how we added jumpers inside connectors. One wire per crimp and other wire added by surgical cuts and soldering on the original wires, but placed away from the crimp. Not a quick job, but a reliable one.
 

GopherT

Joined Nov 23, 2012
8,012
To return at my question: would you crimp two (smaller) wires together onto a connector designed just for one (greater) wire? If not, why?
At least four members have given you a thumbs up on the two wires into one connector, are you looking for more? A majority?

Also, for soldering a crimped connection comes down to strain relief. When you bend a stranded wire against a connector, the stress is on only ONE layer of strands (tension on the outer radius, compression on the inner radius - assuming vibration and no additional tension/compression on the wire). A good connector will have some extension to the body of the connector to prevent strain right at the crimp. If you solder the crimped connection, the same compression/tension happens where the solder front ends on the copper wire. All is fine and dandy with doing bothe solder and crimp until solder flows up (wicks up) the cable insulation. At that point, you have no control of where the solder ends and where strain relief is needed. It is easy to say, "I can control that", but, since there is no way to control what flows through a crimp or how an individual solders any crimp, it is safest for the connector manufacturer to say, don't solder. Also, the polyolefin body used on many connectors is not high temp and will deform.

Finally, I using spring connectors or press-fit connectors, the soldering process can change the temper of the alloy and, therefore change the spring tension or make the alloy brittle and create a high resistance connection. Also, solder wicking onto the spring or press fit connector can prevent the full range of movement on the connector and, again, change the current rating (resistance) of the connection.
 

nsaspook

Joined Aug 27, 2009
8,648
For example, when you join two wires with solder you get a bullet-proof solid joint. You can try to pull out the wires with all of your strength and... the wire will break but the joint will stay there! The same happens with crimped joints?
Electrical solder is not a mechanical fastener and even properly soldered connections usually fail under stress before a properly crimped connection. I've seen many a 'solid' soldered connection in a high power circuit recrystallize over the years into a cold solder joint and fail from increasingly resistance to the point the insulation starts to melt and burn as the metal/solder/metal connection becomes loose. A properly 'cold-welded' crimp is a mechanical and electrical fastener.
 

Thread Starter

gimpo

Joined Jan 27, 2016
124
At least four members have given you a thumbs up on the two wires into one connector, are you looking for more? A majority?
I thought that you have a different opinion about that too. I'm learning a lot from this discussion and other ideas are welcome. That's all.

All is fine and dandy with doing bothe solder and crimp until solder flows up (wicks up) the cable insulation. At that point, you have no control of where the solder ends and where strain relief is needed. It is easy to say, "I can control that", but, since there is no way to control what flows through a crimp or how an individual solders any crimp, it is safest for the connector manufacturer to say, don't solder.
Interesting point. But, again, we could use the magic word "properly". We have properly crimped connectors and properly soldered connectors. :D
 

GopherT

Joined Nov 23, 2012
8,012
I thought that you have a different opinion.
I do have a different opinion but I don't care if you use it or not. There are already 64 comments with arguments and experiences pointing in both directions. Therefore, any reasonable person would realize that the risk of being wrong is minimal. None of the 64 comments described a motorcycle bursting into flames or any personal injury, instead, just a munch of comments of regarding time, effort, training, difficulty and possible long-term durability issues (for both sides of the arguments). You seem to believe you are highly skilled in the art of soldering and crimping so those are not even discussed and I hope they do not need to be debated here.

After 64 posts, I would like to ask if you have a medical condition that prevents you from making a decision with symptoms of endless need for reassurance or if you are simply a forums troll - dragging this topic out for the joy of getting some response from other people. Or, is there another reason you do not make a decision?
 

SLK001

Joined Nov 29, 2011
1,548
I love the way some people can sum the whole thing up in one sentence. Crimping is more reliable without solder. It has better pull-out strength without solder, resists corrosion creeping in between the strands better without solder, the conductivity of the joint is made worse by adding solder, and adding solder will make the connection fail sooner in the presence of vibration.

Unfortunately, I disagree.:(
Well, you certainly have the right to your opinion. However, you don't have the right to your own "facts". The research (by many millitaries and the aerospace companies) has been done and the facts are in. A properly done crimp is superior to a soldered joint (and let me modify my original statement to "a proper crimp is a more reliable joint than soldering").

A joint under "pull-out" conditions has issues unrelated to the joining conditions. Under pressure, solder will flow (it takes time, so don't try this for only 5 minutes).

A proper crimp is oxygen free, so there will be no corrosion.

If you are using solder to increase the conductivity of the joint, you are wasteing your time. Solder is a poor conductor.

A soldered joint will fail sooner in the presence of vibration.
 

MrSoftware

Joined Oct 29, 2013
2,015
My real life experience; for my side job I sell wire harnesses made form 20awg braided copper. The harness includes joints where 2 wires are crimped into a single disconnect connector. The first several hundred I manufactured myself, soldering the wires together first and then crimping on the disconnects. A small handful came back with intermittent conductivity. The solder was too rigid and no mater how tight I crimped, the crimp would work loose. I changed to crimp-only and the problem was solved. Now I'm having them commercially manufactured in China as crimp-only and with sales in the thousands I haven't had a single one come back.

It is my understanding that the most reliable connections in high vibration environments are pressure fit connections. This tends to make me think that crimping without soldering afterword would also be more reliable. FF to 3:00 in this video for the explanation:

 

MrSoftware

Joined Oct 29, 2013
2,015
I need to "steal" +12 Volt from a motorcycle power connector in order to power my custom circuit. The smarter solution seems to be crimping my two wires (+12V and GND) together with the pre-existing ones and plug them into the same housing receptacle.
I've read that two wires should be never crimped together; on the other hand I saw many people doing that. Anybody has experience about it?

(Before you ask: yes, I would love to make a more reliable soldered-joint, but then I don't know how to make an "Y-joint" insulated and waterproof - i.e. there are not Y-shaped heat shrinks.)
Another option; Check out http://cycleterminal.com/ and/or http://easternbeaver.com/Main/Elec__Products/Connectors/connectors.html, etc.. and see if you can find the connectors nearest where you want to steal power, and make yourself a plug-in pigtail.
 

Marcus2012

Joined Feb 22, 2015
403
If your connector/crimp is in a high vibration environment the designers usually favour cable strain relief over the mechanical properties of any crimp termination. This is because a crimp is not and never has been a structural element as far as I know.

A proper crimp is oxygen free, so there will be no corrosion.

If you are using solder to increase the conductivity of the joint, you are wasteing your time. Solder is a poor conductor.

A soldered joint will fail sooner in the presence of vibration.

How do they make it completely oxygen free? I get that the interface is under pressure in that area but I would assume there is always some conductor that is in contact with the atmosphere unless it is potted or really good shrink.

Solder isn't the best conductor you're right but I can't help but think the intrinsic resistance of a soldered joint would be less than the contact resistance of a crimp. Maybe this is a misconception on my part I'm not sure.
 

SLK001

Joined Nov 29, 2011
1,548
How do they make it completely oxygen free?
The contact point (the only point that counts) is metal-to-metal.

Solder isn't the best conductor you're right but I can't help but think the intrinsic resistance of a soldered joint would be less than the contact resistance of a crimp. Maybe this is a misconception on my part I'm not sure.
OFHC copper has a resistivity of approximately 1.724E-08 ohm-m. Solder has a resistivity approximately 10% of that. Soldering a crimped joint is like putting five 1,000 Ω resistors across five 1 Ω resistors (units are ohm-m, not simply ohm). The benefits of the additional resistors is negligible and is only measureable with sensitive instrumentation.
 

Thread Starter

gimpo

Joined Jan 27, 2016
124
@MrSoftware :
big thanks for that links, I have bookmarked them. A variegated collection of connectors of any type that can help me to have some new ideas.

A question about your first version of crimped wire harnesses wires: it could be possible that by soldering and then crimping you was damaging the pre-existing solder joint 'cause of the crimping pressure?
 

MrSoftware

Joined Oct 29, 2013
2,015
No, I got the harnesses back from the customers so I could inspect them, and in every case the solder joint was fine, but it was loose within the crimp. You could not pull it out, but with enough fiddling you could get it to move slightly. My take on it was the solder joint didn't have any elasticity when crushed, so the crimp didn't maintain pressure. I said before I thought the solder was too rigid, but the more I think about it, the solder just wasn't elastic at all. In any event, the bare wire crimps all stay tight and maintain good connection.
 

mcgyvr

Joined Oct 15, 2009
5,394
The "key" word is "properly"..
A "properly" crimped connection does NOT require soldering at all..
And yes as stated above soldering a "properly" crimped connection offers NO real benefits and some proven negatives.
But some people do it thinking it "can't hurt"..

"properly" here basically means that the crimp connection/number of wires,etc.. are exactly how the manufacturer of the crimp had the terminals tested and used a "listed" crimping system as specified by the manufacturer..
Some terminals are also "listed" by the testing lab (UL, Intertek,etc..) to allow multiple conductors in the same crimp barrel.. Many do not..

A crimp tool from the local hardware store does NOT make a "proper" connection and is not allowed on "professional" products.. Only through using the crimping system specified by the manufacturer can it be done "properly" (or as tested/approved by the testing laboratory).

Can you use multiple conductors? Yes if the terminal manufacture has had that tested/approved..
For "personal use" how could one know that using multiple wires would be "ok"? #1 through contacting and following the manufacturers recommendations/listed tooling,etc.., #2 by performing a pull test on the wire, #3 crap shoot

Oh and one more thing.. Almost all "professional/listed" hand tooling is "controlled cycle" in that it must fully close before its allowed to open again.. This guarantees that the crimp is fully "crimped".. Hardware store hand tools don't have that and hence are prone to allow a "user" to under crimp a connection..
 

Thread Starter

gimpo

Joined Jan 27, 2016
124
A joint under "pull-out" conditions has issues unrelated to the joining conditions. Under pressure, solder will flow (it takes time, so don't try this for only 5 minutes).
What about crimping and then soldering? I think that #12 was talking about this option.
I mean, after the crimp operation is done (properly) then filling the gaps with solder can only bring additional benefits, or not? :confused:
 

Thread Starter

gimpo

Joined Jan 27, 2016
124
You should carefully remove 1/2 inch of the wire insulation about 1 inch back from the stripped end of your wire. Wrap the stripped end of the wire you want to add around the 1/2 inch of bare copper on the other wire and solder then add shrink tubing over the soldered joint. Crimp and seal the the bare end of your original wire as usual.
Thanks for the suggestion Kermit2. My only doubt is how to properly seal an Y-shaped joint with "cylindrical" shrink tubes.

Anyway, usually the main problem is the minimum space available inside the connector housing. When it's not possible to plug two wires in the same "slot" (I don't know if the term is right) then your solution became interesting.
 

SLK001

Joined Nov 29, 2011
1,548
What about crimping and then soldering? I think that #12 was talking about this option.
I mean, after the crimp operation is done (properly) then filling the gaps with solder can only bring additional benefits, or not? :confused:
If the joint is static (like soldering the joint for a door bell), then soldering doesn't hurt (it doesn't help, but it doesn' hurt either). If the joint is under vibration, the joint will fail due to the brittleness of the solder in the wire.

Solder flows under pressure. This means that it provides no long term mechanical strength to a joint. Where I used to work, we would perform a "red dye" test to soldered BGA ICs (re: remove the device without heating the solder) by epoxying a string on the top of the BGA, then hanging a 1 pound weight in tension on the string. In about two hours, the device would pull off the PCB, usually without damage to either part. The red dye was used to indicate unsoldered pads under the BGA. This indicates just how weak a soldered joint really is.
 

Thread Starter

gimpo

Joined Jan 27, 2016
124
If the joint is static (like soldering the joint for a door bell), then soldering doesn't hurt (it doesn't help, but it doesn' hurt either). If the joint is under vibration, the joint will fail due to the brittleness of the solder in the wire.
Ok, I've got the point SLK001 ;)
By adding solder the stranded wires became "prisoners" of a solid block of material. No more flexibility or movements are allowed, so you can have micro-fractures or cracks into the material (and/or wires) in an environment rich of vibrations.
thanks!
 
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