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Thread: nichrome to lead wire attachment

  1. #1
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    Default nichrome to lead wire attachment

    This is a question, not a how-to- I've had several applications in the past where I wanted to use a heating element made into some special shape, or wound specifically for one application, etc. What I've usually done is mechanically fasten the nichrome wire to a terminal, which then has a copper wire leading away from it to a power supply. In most cases this works, but is not ideal, especially where there's little room and a low profile is required. What would be better is to have a heat-resistant but highly conductive lead-out wire attached to the ends of the heating element wire.

    At first thought, spot welding would seem to be the way, and maybe that is the ultimate answer. How best to do this?

    Most connections I see have the wires crossed, and the spot weld is visible between them. In many cases I would prefer the wires laying side by side, and the spot weld taking up a short length along the sides of each wire. I would also be happy to find that a good connection can be made by butting the ends of the wires together and making the weld.

    The gist of my question is how would one go about making a good butt weld between nichrome wire and a proper lead-out wire? And what should that lead-out wire be made from?

    Then I thought of another option- plating copper on the end couple inches or whatever of the nichrome wire, then plating over that with a protective layer, possibly chrome. I realize that the copper layer would have to be a substantial thickness in order to keep that section of the wire from heating due to the current, and I think it needs to be plated in order to survive. If this kind of thing would work, it would be most elegant. You could just wind or fold the element wire into the shape you need it, making sure that the first and last part of it is where the plating starts. Further to that, if there's some way to protect the copper plating from heat by the heating action itself, you could form the element first, then paint on a protective compound and fire it up. The heat would 'glaze' the paint where it gets hot enough to, and the copper on the rest of the lead-out wire would survive because it doesn't get that hot.

    That's the idea anyway. Comments and ideas welcome.

  2. #2
    Join Date
    May 2011
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    Las Vegas NV.
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    Usually when working with nicrome wire I use the "crimp and solder" method. Using a crimp terminal for a small molex connector I strip down the end of the nicrome, slip it into the connector.

    http://farm3.static.flickr.com/2299/...8802275ec9.jpg

    then add the lead wire to the other end, and solder it all together.

    http://farm4.static.flickr.com/3604/...ae44697e26.jpg
    http://farm3.static.flickr.com/2381/...dc3a14ccf2.jpg

    Then wrap it all in some kapton tape.

    http://farm4.static.flickr.com/3656/...d36d250f1f.jpg

    It is fairly easy to do and I haven't had one melt apart yet. The only downside would really be the cost of the tape. The last time I checked 30 feet of 1/2" wide was like 6 bucks, but it will last a while. Hope this helped some.

  3. #3
    Join Date
    Feb 2012
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    How hot ends of your nichrome wire are getting?

    Incidentally I am making hot air soldering iron used for mounting of SMD chips for a friend (and I will also have a "copy" for myself as it is about as easy and fast to make two at the same time...).

    There is also a connection of nichrome to some better conductor to be made in that design.
    Mechanical connection would be best due to easiness of eventual replacement of damaged heating element but due to constricted space I would rather try to avoid usual setups with tightening screw.

    I am planning to make it from low diameter (3-4 mm) nickel rods with about 10 mm long coaxial hole drilled of diameter allowing for tight push fit in it.
    I will use 1mm diameter nichrome, so the same size of hole will be drilled in nickel rod.
    Thermal expansion coefficient of Nickel is marginally lower than that of nichrome and this situation is very favourable.

    Suitable nickel you will get as Nickel 201, designed to work well in higher temperatures.
    http://www.specialmetals.com/documen...%20&%20201.pdf

    Nickel rods may then be connected to usual copper conductor few cm down the line by brazing.

    Bonus for the hassle is an easy replacement of heating element if it ever got burned.

  4. #4
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    May 2011
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    I'm using the wire in a 3D printer to melt plastic, so probably not as hot as yours will be getting. I am slightly uneasy about any kind of mechanical connection when there will be thermal expansion involved.

    On the topic of what you plan on doing with this, are you going to use it for any SMD rework? If not, may I suggest building a reflow oven. It makes doing an entire board quite simple. The Ben Heck show did an episode on one recently, you may find it helpful.

    http://www.element14.com/community/c...xperts/benheck

  5. #5
    Join Date
    Feb 2012
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    Quote Originally Posted by Tony_Filipiak
    I'm using the wire in a 3D printer to melt plastic, so probably not as hot as yours will be getting. I am slightly uneasy about any kind of mechanical connection when there will be thermal expansion involved.
    But (as measured at 100*C) for Nickel it is reported 13 x 10^-6/*C and for Nichrome it is 13.4 - 14 x 10^-6/*C, so we are close to perfect match.

    On the topic of what you plan on doing with this, are you going to use it for any SMD rework? If not, may I suggest building a reflow oven. It makes doing an entire board quite simple. The Ben Heck show did an episode on one recently, you may find it helpful.
    My friend wants a "pencil", he does some electronic service work and he is not willing to pay $ 800 or so for commercial item.
    I will get my set as a "passenger".
    Setting lathe to fabricate certain parts (mainly a range of gas tight "tips") is where most of time is gone.

    As per reflow oven - well... for making new SMD circuitry it is a very good idea.
    Being a chemist by education I would go for condensation oven which can be assembled out of common lab glassware and selected commercial high boiling fluorocarbon would be used to maintain right temperature with great accuracy but there is one problem here - I don't need it.

  6. #6
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    Jul 2006
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    Dracut, Massachusetts
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    Quote Originally Posted by Martin0001
    My friend wants a "pencil", he does some electronic service work and he is not willing to pay $ 800 or so for commercial item.

    Not to derail your build, but just to toss out a few lower cost ready-made solutions take a look at theses:

    http://www.mpja.com/SMD-Stations/products/479/

    or

    http://www.web-tronics.com/hot-air-rework

    I have one of the units from M.P. Jones at work, it actually is a decent unit and works as designed/advertised. Just FYI.

    I have had a fair number of custom heating elements made up at jobs I worked, pretty much every one I've ever gotten was made up as you first described, either mechanical connections (crimped, terminal block, ceramic wire nuts or bolts) or spot welded. In a few instances when the operating temp was not so high, I have seen them silver soldered.
    Last edited by alanganes; 02-26-2012 at 09:17 AM.

  7. #7
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    Jul 2007
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    Two thoughts.
    Have you considered Monel lead wire, even for a short length? you should be able to get it as fishing leader.
    Have you considered using 1/16" soft copper tube cut in short lengths as connectors. A bit of silver solder in the ends, after mechanical crimping, should limit resistance due to corrosion of the joint.
    Most ideas are al least semi-commercial, and I dont think that you are making electric dryer harness.
    Duffy, Gatineau, Quebec

  8. #8
    Join Date
    Feb 2012
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    @alanganes,

    Thanks for your remarks about lower cost commercial products which I was not even aware of.

    Unfortunately I live in Poland and locally only more expensive stuff is available.

    Of course it could be purchased online but once you add VAT and p&p, these low cost versions are still going to be $200 - 250.
    Anyway that project is close to completion.

    I will get $100 for the hassle and also will end up with second device for myself as a bonus.
    Thermocouple is incorporated close to business end, so my friend skilled in electronics will easily provide for accurate temperature control (I believe, that might be a feature of more expensive units and cheaper ones are regulated by voltage, base on Ohm law principle without any stabilization of temperature of the gas but again, I might be wrong).

    On the top of it I have killed few boring winter days...

    @Duffy,
    Copper tube may well corrode fast at several hundreds *C delivered by hot nichrome wire however one can try to use an adequate diameter of syringe needle as connector for crimping. It is stainless...
    This stuff is also easy for brazing as well.
    Last edited by Martin0001; 02-26-2012 at 10:51 AM.

  9. #9
    Join Date
    Mar 2010
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    I once repaired the nichrome heating coil in a waffle iron with silver solder.

    I just hooked the two ends of the element together mechanically and added a small blob of silver solder to the junction. The solder flowed properly onto the nichrome. Once heated up the blob stayed black, but the nichrome recovered its normal red about 1/8" away from the solder.

    I don't see why you couldn't do the same thing with a nichrome -copper junction. Certainly worth a shot.

    RWO

  10. #10
    Join Date
    Dec 2004
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    a welded joint may lead to failure due to differential expansion/contraction because of the different thermal expansion coefficients for both of your materials.

    for high power connections, a crimped barrel is one of the most reliable and robust interconnect methods for bus bars or conductors that see high thermal gradients. they're also fairly cheap, but have to be done right (read: proper crimp tooling)
    -paul

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