Help: Small guage wire connections plus details

[jxmiller]

I am not an engineer in the sense that I have been educated in or work in that field. Just wanted to get that out of the way.

I am having a problem mostly with types of connectors. I have a design idea (will spare the details for now) that includes the need for replacing a 36 to 38 awg single strand nichrome wire once a month or so. I don't want to have people use solder... I would like it to be more modular. Most of the problem is space limitations. I need something roughly 1mm to 3mm (length width height). My first thought was alligator clips. I have not been able to find any small enough. My second thought was to use eyeglass sized screws which is what I am leaning towards now. Ideally though it would not require tools (like the alligator clip). Also thought of the old speaker wire terminals.

http://www.electronix.com/catalog/images/11-512.jpg

But out of all of these things the screw type terminal is what I end up with. I forgot to mention that the connector or terminal needs to be heat resistant of up to 350-400 C. This means no common speaker wire terminal.


A second idea I had is a little more complex and mildly negates the need to have replacement connections to a degree. The problem I am having here is "engineering" the connection once again. This is a circular type of configuration that would have 2+ nichrome wires instead of one. A knob on the outside of the device could be used to turn the circle on the inside. Turning it I imagine it "clicking" into place just enough to hold and make an electrical connection to the top most section. Making this connection is the current problem. I will try to post a picture or make a video with a model made out of paper clips or something...

I have this feeling that this will be hard to understand and I preemptively apologize for not being able to explain it better nor being able to currently provide any sort of schematic to demonstrate what it is I am talking about.

Perhaps I just need to get the wording right. How about a miniature copper wire connection that will make a connection when turning a knob such that once the connection is made the knob gains resistance (to turning) so that the user knows it has made the connection. turning the knob with a little bit of extra force will disconnect the current connection and rotate the circle so that the next connection can be made.

Thanks for any insight here.

 

[Solveer]

Well, as you point out, I'm not quite sure what you are after. There are a lot of different connectors that you could consider, as you mention, especially the screw terminal type. My favorite place to look for electronic parts is http://www.digikey.com.
One item that I have a problem with though is the 350-400C. You will not find any components that are made from plastic that go that high (for the simple reason that they will melt). If you really need such a high temperature connector (do you?), you will have to go with a ceramic screw terminal. You can find some on www.mcmaster.com but I doubt you'll find a miniature connector.
I am assuming that you are using a NiChrome wire to heat something up and due to the material's resistance you need a high temp connection? how about using a short length of regular copper wire (which will stay cooler unless its exposed to the same environment) and then use a crimp connection (or braze or something like that) between the Cu and the NiCr wires? That would allow you to use more commonly available connectors.
If none of this makes sense, have you considered using a spring (one that is usually used for tension applications). Like that you could pull on it, insert the wires, then let go and it would make a fair connections (not perfect, but your constraints are pretty tough).
Maybe some extra details (and yes schematics/pictures would help) would shed some light on a better way.



<< commercial link removed by berkeman >>

 

[berkeman]

I am not an engineer in the sense that I have been educated in or work in that field. Just wanted to get that out of the way.

I am having a problem mostly with types of connectors. I have a design idea (will spare the details for now) that includes the need for replacing a 36 to 38 awg single strand nichrome wire once a month or so. I don't want to have people use solder... I would like it to be more modular. Most of the problem is space limitations. I need something roughly 1mm to 3mm (length width height). My first thought was alligator clips. I have not been able to find any small enough. My second thought was to use eyeglass sized screws which is what I am leaning towards now. Ideally though it would not require tools (like the alligator clip). Also thought of the old speaker wire terminals.

http://www.electronix.com/catalog/images/11-512.jpg

But out of all of these things the screw type terminal is what I end up with. I forgot to mention that the connector or terminal needs to be heat resistant of up to 350-400 C. This means no common speaker wire terminal.


A second idea I had is a little more complex and mildly negates the need to have replacement connections to a degree. The problem I am having here is "engineering" the connection once again. This is a circular type of configuration that would have 2+ nichrome wires instead of one. A knob on the outside of the device could be used to turn the circle on the inside. Turning it I imagine it "clicking" into place just enough to hold and make an electrical connection to the top most section. Making this connection is the current problem. I will try to post a picture or make a video with a model made out of paper clips or something...

I have this feeling that this will be hard to understand and I preemptively apologize for not being able to explain it better nor being able to currently provide any sort of schematic to demonstrate what it is I am talking about.

Perhaps I just need to get the wording right. How about a miniature copper wire connection that will make a connection when turning a knob such that once the connection is made the knob gains resistance (to turning) so that the user knows it has made the connection. turning the knob with a little bit of extra force will disconnect the current connection and rotate the circle so that the next connection can be made.

Thanks for any insight here.

With that kind of temperature, and the long life that you probably want from the connector, I don't think you will be able to get the screw terminal option to work (you might with the right material...). I'd be tihnking more along the lines of how a stove-top's electrical heating elements connect into the stove -- they use spring-loaded female connectors, with the heating element male end pushing into make electrical and mechanical contact.

Except, with such fine wire, you should look into making the spring mechanism with a zero-insertion-force (ZIF) feature. That is, but pulling on a little lever or something, that opens up the spring-loaded female connector. You put in the wire, and release the lever to let the spring jaws clamp down.

 

[Danger]

A big thing that I notice being missing from the question is what sort of mechanical stress this assemblage might encounter. Something that is subject to vibration or shock loads has to be far more robust than something that just sits on a shelf somewhere.
Spring terminals are excellent under either condition. There are a lot of different kinds of spring terminals, so packaging is still flexible.

 

[jxmiller]

Thanks guys!

I am pretty confident now that the spring is the best choice. This is one I have found that may work although I will have to search a bit more to see if I can find something a little more cost effective. I chose this spring because of the shape. I can imagine, as someone stated, having a key that fits the ends of each spring so that when the coil needs to be replaced the key is put on both springs and lifted. This would release the wire and allow insertion of a new wire. They key thing is just extra really but at this point I am trying make it as easy as possible. Thanks so much for the help here. Here is the link to the spring I found. Like I siad, still looking for a better price.

http://www.mcmaster.com/#9287k122/=4whfqy

 

[Danger]

Your link just brought up a blank page with an order form. In any event, there's no need to buy spring terminals as such. Regular hardware store stuff will work fine. In fact, you can make a couple from one ballpoint pen return spring. The coils at the ends are tight enough to hold a wire securely. Cut one of those in the middle, and you have two good terminals.

 

[Redbelly98]

Your link just brought up a blank page with an order form.

If you copy the part number that appears in the left column (9287K122), then go the main McMaster-Carr page and paste that part number into the search box, a drawing and description of the torsion spring will appear.

 

[jxmiller]

Your link just brought up a blank page with an order form. In any event, there's no need to buy spring terminals as such. Regular hardware store stuff will work fine. In fact, you can make a couple from one ballpoint pen return spring. The coils at the ends are tight enough to hold a wire securely. Cut one of those in the middle, and you have two good terminals.

Awesome, for some reason prior to reading your thread I had thought that but it was unfortunately a fleeting thought. Thanks so much. The part I linked to was stainless steel and while an excellent product was far too costly @ $4.50 each. Ballpoint spring it is! I just hope it conducts well. I will be running 3.7 to 6 volts through it @ about .8 to 1.2 amps via common lithium ion batteries probably the 18650.

I was worried about cost there for a sec, let's hope that random metal can conduct and with stands what I an going to be running through it.

 

[Danger]

You might want to give the springs a quick acid bath, or at least scour them down with a scrubbie or sandpaper to remove any surface contaminants that might impede electrical conductivity.