Author Topic: "No-crimp" connector idea  (Read 5294 times)

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Online Zero999

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Re: "No-crimp" connector idea
« Reply #25 on: September 15, 2019, 07:32:26 pm »
It's about the voltage level and safety regulations on mains plugs. Plenty of connectors are rated for high voltages and disconnect everything at once.
But it's not safe to use one of those for the earth, as well as live conductors. Look at any properly mains electrical plug/socket and you'll find the earth connection is always designed to make first and break last.
 

Offline Nominal Animal

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Re: "No-crimp" connector idea
« Reply #26 on: September 15, 2019, 07:46:40 pm »
Where I live, outside temperatures can easily vary by about 60°C during the year.  This means that screw terminals can fail due to thermal expansion, whereas spring-loaded terminals will keep contacts (due to spring action) regardless of temperature changes.  Even indoors you can have 20°C temperature swings, especially if you leave your house at maintenance temperatures (around 10°C) for a winter month, due to a well-earned holiday somewhere warmer.

Because of this, I trust (locally sourced from reputable sources) Wago-style connectors way more than screw terminals.  So do all the local electrichickens I've talked to.
 
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Online ebastler

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Re: "No-crimp" connector idea
« Reply #27 on: September 15, 2019, 07:59:55 pm »
Instead omega shaped contacts are used. Where wire is inserted in to an "eyelet" and affixed in place by the spring action of the contact. Thus special tools are not needed.

How much spring travel do you expect those "omega contacts" to have? Your renderings look like the inner diameter of the eyelet which receives the wire is pretty much fixed. How would these contacts clamp wires of slightly varying diameter? (Or worse, multi-stranded wire twisted in slightly different ways, and with some room for the strands to move relative to each other?)
 
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Offline Simon

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Re: "No-crimp" connector idea
« Reply #28 on: September 15, 2019, 08:28:23 pm »
It's about the voltage level and safety regulations on mains plugs. Plenty of connectors are rated for high voltages and disconnect everything at once.
But it's not safe to use one of those for the earth, as well as live conductors. Look at any properly mains electrical plug/socket and you'll find the earth connection is always designed to make first and break last.

They are not meant for such a use. They are equipment interconnection connectors that will only be mated or unmated when the equipment is powered off.
 

Offline tooki

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Re: "No-crimp" connector idea
« Reply #29 on: September 16, 2019, 03:40:12 am »
There's a simple trick for fine stranded cables and insertion into crimp lugs, ferrules and the like.

Pull off ~6"or more of insulation tape and spin it loosely into a soft round rope shape and bind the strands not too firmly together starting from the insulation sheath nearly to the tip of the strands and then back towards the insulation a couple of turns. Keep finished end taught.
Insert exposed strand tip into lug and press not too firmly home.
The tape rope slides down the strands and will bunch up at the end of the sheath between it and the lug.
Unwrap tape rope then press cable fully home..... done !
Done properly you'll never miss inserting even a single strand.

This tape rope can be used again and again.

Thanks to my sparky mate Wayne for that one.  :)
Could you maybe make a video of this? I'm having trouble visualizing what you mean, but it sounds useful!
 
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Offline tautech

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Re: "No-crimp" connector idea
« Reply #30 on: September 16, 2019, 04:13:18 am »
There's a simple trick for fine stranded cables and insertion into crimp lugs, ferrules and the like.

Pull off ~6"or more of insulation tape and spin/twist it loosely into a soft round rope shape and bind the strands not too firmly together starting from the insulation sheath nearly to the tip of the strands and then back towards the insulation a couple of turns. Keep finished end taught.
Insert exposed strand tip into lug and press not too firmly home.
The tape rope slides down the strands and will bunch up at the end of the sheath between it and the lug.
Unwrap tape rope then press cable fully home..... done !
Done properly you'll never miss inserting even a single strand.

This tape rope can be used again and again.

Thanks to my sparky mate Wayne for that one.  :)
Could you maybe make a video of this? I'm having trouble visualizing what you mean, but it sounds useful!
Working with Wayne here tomorrow I think so I'll try to grab it with my phone.

Added the word twist for hopefully more clarity. ^^^
While it took a few minutes to write to get good meaning it takes but seconds to accomplish.  :)
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Offline ElectronicSupersonicTopic starter

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Re: "No-crimp" connector idea
« Reply #31 on: September 16, 2019, 05:49:02 am »
Maybe I'm just not getting it, but I don't understand what stops individual strands from squeezing out into the open side of the 'omega' when compressed?  That would spoil the 'perfect fit'. Wire diameters will be subtly different between types too.
Most multi-stranded wires are twisted, thus form sort of single core (especially when twisted some more, at least what's what I do before applying solder to the wire ends). Anyway in IDC connectors (say AVX Series 9176 http://datasheets.avx.com/StandardIDC_00-9176.pdf ) the slot for wire strands is open from one side (top) and strands going loose through that opening doesn't seem to be an issue. More other since the opening is omega shaped, the open part of it is somewhat narrower, thus to a degree should prevent strands from squeezing out. Another feature that could be done to enhance retention is an waist-like indentation perpendicular to the axis of a wire made in the middle of the contact "barrel".

836673-0

As to wire diameter, connectors are usually rated to a specific AWG range. It can be designed to tight fit the particular range.

What voltage is this connector going to be working at?
These would be (in theory) used for logic levels and/or 12V DC. Again these is basically just an idea - not something that is to be implemented in the form exactly as shown.

How much spring travel do you expect those "omega contacts" to have? Your renderings look like the inner diameter of the eyelet which receives the wire is pretty much fixed. How would these contacts clamp wires of slightly varying diameter? (Or worse, multi-stranded wire twisted in slightly different ways, and with some room for the strands to move relative to each other?)
Again, wire diameter somehow it's not an issue in IDC connectors. Say the above mentioned AVX Series 9176 are rated for a range of different AWGs (18-24 in this case). Also a dedicated groove to surround the eyelet can be made in the plastic shell, that would apply an additional pressure enhancing retention.
« Last Edit: September 16, 2019, 06:53:45 am by ElectronicSupersonic »
 

Offline Simon

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Re: "No-crimp" connector idea
« Reply #32 on: September 16, 2019, 06:38:37 am »
You are missing the point. You can't accommodate precisely one wire size. The same gauge in different strands is different diameter. I use Raychem 44 wire a lot and it's always seems smaller than equivalent commercial wire (and is 30% more resistive but is not pure copper). So that won't fit.
 

Offline T3sl4co1l

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Re: "No-crimp" connector idea
« Reply #33 on: September 16, 2019, 07:22:20 am »
A slitted/opened figure-eight shape is probably practical, being an extrusion of the IDC connector spring-and-knife structure.  Or put another way, take what you've drawn but open the metal (opposite the open side) into another loop, to grant more spring (compliance range).  Vary material thickness to get required clamping force.  Possibly it could be used on two or three different wire gauges, rather than exactly one size (stranded or solid only).

It'll still need a tool to force the spring apart or punch the wire in.

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Offline Simon

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Re: "No-crimp" connector idea
« Reply #34 on: September 16, 2019, 08:33:37 am »
The simple fact is that any connector contact/terminal has the wire forced onto it to reduce the resistance of the junction. Simply holding a wire in a sprung part is not enough. I use D38999 connectors, they are not cheap, but the exceed the power handling capability of a mains plug in the same space. But they are not cheap because the design is much more well refined.

Horses for courses, but this design is a rather poor horse. If you are interested in connector design there is the wurth book on the very subject: https://simonselectronics.co.uk/product/trilogy-of-connectors/
 

Offline ElectronicSupersonicTopic starter

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Re: "No-crimp" connector idea
« Reply #35 on: September 16, 2019, 08:59:55 am »
A slitted/opened figure-eight shape is probably practical, being an extrusion of the IDC connector spring-and-knife structure.  Or put another way, take what you've drawn but open the metal (opposite the open side) into another loop, to grant more spring (compliance range).  Vary material thickness to get required clamping force.  Possibly it could be used on two or three different wire gauges, rather than exactly one size (stranded or solid only).
That's a very good idea! Thanks!

Yet another approach would be to make the omega shape more 0 like. Plus add some inward pointed leafs to provide better contact and prevent strands from being pulled out (wire should be oriented accordingly). Like so...
836760-0

836766-1
 

Offline Simon

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Re: "No-crimp" connector idea
« Reply #36 on: September 16, 2019, 09:01:33 am »
But this is still all relying on moderate friction?
 

Online ebastler

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Re: "No-crimp" connector idea
« Reply #37 on: September 16, 2019, 10:33:04 am »
Yet another approach would be to make the omega shape more 0 like. Plus add some inward pointed leafs to provide better contact and prevent strands from being pulled out (wire should be oriented accordingly). Like so...

The inward-pointed leaf is moving this closer to an IDC connector -- it provides a small clamping area with high local pressure (force per area) for good contact, ideally gas-tight. Now you will need a tool to squeeze the wire in (or worse, multiple wires in one go).

But then, why do you need the narrower opening of the Omega shape? If that is needed to stop the wire from slipping out of the eyelet, then you are obviously not holding it tight enough for good contact. So omit the narrow opening, and shape your contact as an steep "groove" with two parallel side walls. That will also accommodate stranded wire bundles of slightly varying thickness, which will fill the groove to varying height, while always being squeezed tightly in the lateral direction.

Oh, now you have reinvented the IDC contact geometry.  ;)
 
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Offline Simon

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Re: "No-crimp" connector idea
« Reply #38 on: September 16, 2019, 10:39:29 am »
Of course contacts need to be manufactured and that will not be cheap. With the cheap connectors you will find a plastic housing is £0.05 but the pins are £0.30 each! It's the metal parts that cost the money.
 

Offline ElectronicSupersonicTopic starter

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Re: "No-crimp" connector idea
« Reply #39 on: September 16, 2019, 06:32:42 pm »
But this is still all relying on moderate friction?
To a degree. It's more "the bite" that would provide retention in this instance.

Of course contacts need to be manufactured and that will not be cheap. With the cheap connectors you will find a plastic housing is £0.05 but the pins are £0.30 each! It's the metal parts that cost the money.
True. The price would depend on quantities (i.e. how mass of a production it would be) and many over factors.

But then, why do you need the narrower opening of the Omega shape? If that is needed to stop the wire from slipping out of the eyelet, then you are obviously not holding it tight enough for good contact. So omit the narrow opening, and shape your contact as an steep "groove" with two parallel side walls. That will also accommodate stranded wire bundles of slightly varying thickness, which will fill the groove to varying height, while always being squeezed tightly in the lateral direction.
The "bottle neck" is there for several reasons. One is to assist assembly — while inserting the conductor in to the contact, it spreads the thing apart (slightly) thus guiding it through.

Another function would be to affix it in the housing with dedicated protrusions. Plus it can serve as a spring to provide more pressure (provided the right shape of the contact and the housing).

Oh, now you have reinvented the IDC contact geometry.  ;)
To an extent. IDC (as I understand it) solves two issues at once 1) No need to stripe the wire — thus no special tools required 2) No crimping needed (just a press-fit action) — thus again no special tools required. In IDC it's accomplished via blade like geometry that both cuts through the insulation and "bites in" in to the core.

With the contacts in question only the second one is true since a wire does need to be striped. Plus there is a larger area that comes in contact with the core (albeit a secondary contact).
« Last Edit: September 16, 2019, 06:36:07 pm by ElectronicSupersonic »
 

Offline tooki

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Re: "No-crimp" connector idea
« Reply #40 on: September 17, 2019, 08:38:29 pm »
Maybe I'm just not getting it, but I don't understand what stops individual strands from squeezing out into the open side of the 'omega' when compressed?  That would spoil the 'perfect fit'. Wire diameters will be subtly different between types too.
Most multi-stranded wires are twisted, thus form sort of single core (especially when twisted some more, at least what's what I do before applying solder to the wire ends). Anyway in IDC connectors (say AVX Series 9176 http://datasheets.avx.com/StandardIDC_00-9176.pdf ) the slot for wire strands is open from one side (top) and strands going loose through that opening doesn't seem to be an issue. More other since the opening is omega shaped, the open part of it is somewhat narrower, thus to a degree should prevent strands from squeezing out. Another feature that could be done to enhance retention is an waist-like indentation perpendicular to the axis of a wire made in the middle of the contact "barrel".
No, only the plastic housing is wider. The contact blades remain parallel.

I don't think you really understand the forces at work, namely, that you need REALLY significant forces on a wire to make a reliable connector without solder, which is why crimping is hard to do without the right tool. A proper crimp creates a cold weld; it's not just wires casually hanging out with the contact. That you are even thinking about strands "squeezing out" indicates that you don't understand how wire attachment works. If the wire is loose enough for strands to be able to work loose, then you are orders of magnitude away from the grip forces needed for a reliable connection.


But this is still all relying on moderate friction?
To a degree. It's more "the bite" that would provide retention in this instance.
Yyyeah, no.


But then, why do you need the narrower opening of the Omega shape? If that is needed to stop the wire from slipping out of the eyelet, then you are obviously not holding it tight enough for good contact. So omit the narrow opening, and shape your contact as an steep "groove" with two parallel side walls. That will also accommodate stranded wire bundles of slightly varying thickness, which will fill the groove to varying height, while always being squeezed tightly in the lateral direction.
The "bottle neck" is there for several reasons. One is to assist assembly — while inserting the conductor in to the contact, it spreads the thing apart (slightly) thus guiding it through.
Huh? How does narrowing it "guide" anything? That makes no sense. There's a reason why the openings to so many things are funnel-shaped.

Another function would be to affix it in the housing with dedicated protrusions. Plus it can serve as a spring to provide more pressure (provided the right shape of the contact and the housing).
The force of a bit of springy metal is simply not enough to hold tightly.

Oh, now you have reinvented the IDC contact geometry.  ;)
To an extent. IDC (as I understand it) solves two issues at once 1) No need to stripe the wire — thus no special tools required 2) No crimping needed (just a press-fit action) — thus again no special tools required. In IDC it's accomplished via blade like geometry that both cuts through the insulation and "bites in" in to the core.
While IDC tooling is simple, it still needs special tools to do reliably. That's why there are IDC crimpers and presses for typical IDC ribbon connectors, and punchdown tools for the punchdown terminals which are omnipresent in telecom, which are also IDC just under a different name.

With the contacts in question only the second one is true since a wire does need to be striped. Plus there is a larger area that comes in contact with the core (albeit a secondary contact).
Except it's probably not as large a contact area as you think. With the insignificant pressures involved, there will be substantial air gaps (meaning not only air in there, but also formation of oxides over time). A proper crimp connection has a much larger contact area, since it squeezes out the air and actually cold welds the metals together!


Also, think about this: while the mating surfaces of connector contacts have continued to evolve continuously since, well, forever, the kinds of wire attachment to connector contacts have barely changed at all: we still use soldered, screw terminal, crimped, or IDC, for the most part. The fundamental geometry of each type of wire attachment side haven't changed much, either. (Nor do they vary much in principle between manufacturers, other than minor size changes to force you to buy expensive proprietary tooling.) So why haven't they changed? Could it be because we fairly quickly figured out what does and doesn't work?

I don't want to squash your enthusiasm, but this omega idea just doesn't make any sense to me. On the one hand, it's trying to solve a nonexistent problem. And on the other hand, the design seems to almost deliberately avoid firm pressure on the wire, insofar as it actually widens exactly where the wire needs to be squeezed the hardest. Again, I think there's some kind of fundamental misunderstanding about what the forces are that you need to design for.
 
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Offline ElectronicSupersonicTopic starter

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Re: "No-crimp" connector idea
« Reply #41 on: September 18, 2019, 03:26:51 am »
...I don't want to squash your enthusiasm, but this omega idea just doesn't make any sense to me. On the one hand, it's trying to solve a nonexistent problem. And on the other hand, the design seems to almost deliberately avoid firm pressure on the wire, insofar as it actually widens exactly where the wire needs to be squeezed the hardest. Again, I think there's some kind of fundamental misunderstanding about what the forces are that you need to design for.
It's quite possible that this design idea is a complete and utter BS since I'm not an engineer (I have a degree in design — not engineering). My intention was merely to share the idea. Whatever comes out of it (if anything) is OK with me.  :)
 
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Online ebastler

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Re: "No-crimp" connector idea
« Reply #42 on: September 18, 2019, 06:03:02 am »
Whatever comes out of it (if anything) is OK with me.  :)

I'm afraid that would be the wire, coming out of the contact clamp.  ;)
 
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