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I have a horn with spade connectors. They are stamped to the horn body and one is broken. I figured I could just use a stud ring terminal and solder it to the stud.

I cleaned the stud with a copper wire brush, but the solder just wouldn't stick to it?? Any ideas?

Pic: enter image description here

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    Are you sure the post is metal? Have you tried applying 12v to the posts to see if the horn works? – HandyHowie Apr 6 at 8:18
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    A revelation I had when soldering is that you need to get whatever you're soldering hot - not just the solder itself. – Aww_Geez Apr 6 at 18:57
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    @Aww_Geez I remember that revelation. The next revelation was that large pieces of metals are a pain in the behind to heat with a small iron. – Mast Apr 7 at 11:18
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    That doesn't look very clean to me... – vidarlo Apr 8 at 10:51
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    More heat (not longer, you will melt the plastic, but more powerful soldering iron), clean surfaces and flux are your friends. – winny Apr 8 at 10:58

10 Answers 10

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Soldering is a chemical reaction!

Like all chemical reactions, several things need to be correct for soldering to go as intended.

  • You need to be using the right reagents (chemicals.)
  • You need to have removed all impurities/contaminants.
  • You need to get things to the correct temperature.

There are a whole bunch of different types of solder. 60/40, 63/37, lead-free, etc. etc. Further more, there are a whole bunch of different metals with which that solder must get along with. Try soldering Aluminum with 60/40 and you're going to have a rough time. Your solder and metal needs to be compatible.

Creating metal to metal (inter-metallic) bonds require that there be nothing between those metals. Obviously this means things like paint, dirt, rust, and grime; somewhat less obviously is that the things that you can't see also matter, like oxygen, or finger salts/oils. Your solder and metal needs to be clean clean clean.

After everyone is all close, clean, comfortable, compatible, and no one is there to interfere, you can turn up the heat a bit. Do that, and interesting reactions might take place. When atoms get hot and heavy enough for them to rub together, it's pretty natural for them to hook up. ;)

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  • I answered the exact question, as asked, for the benefit of the masses. This does not invalidate the wisdom of a practical answer to OP's specific problem. Connect the wire the correct way, or buy a new horn. – user56927 Apr 7 at 16:26
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To solder this, you need:

  • heat
  • heat
  • and finally: heat

The horn is a massive piece of metal, and will draw away the heat from soldering irons for electrics quite fast. You'll for sure need an iron with 180W or more to get the parts hot enough. A small tourch will also work. BUT... Is that plastics there? That won't like so much heat...

Next, not each metal can be soldered easily. Electric solder and its flux work for copper, copper alloys, tin, zinc, gold, silver and so on. However, the surface must be metallic clean, free of dirt, grease and oxided. (Though, flux is very good in removing that stuff)
For iron, there are special types of solder and flux. It requires higher temperatures, the flux is quite aggressive (yet, the surface must be much cleaner), but still, soldering is not easy.
Aluminum is next to unsolderable. There are products to do so, but that look more like an adventure that a reliable process. Unfortunately, aluminum is a favorite material for rivets etc. May be, this hat-like bolts in the picture are aluminum...

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  • If they're bolts (threaded) then they're likely to be steel, but I can't see a thread, and rivets in a job like that could well be aluminium. – Chris H Apr 7 at 10:44
  • The trick to soldering aluminum is that it must be very clean to start with, then cover it lightly with vegetable oil or light machine oil. You'll want to tin your work first, so start heating the piece with the oil still on it (no torch). Once you think it's near hot enough, start scratching the surface with the soldering iron. The surface aluminum oxide will get removed and the oil prevents it from reforming, allowing the solder to stick. Once you have a solid solder pad, add the ring terminal and solder like normal, removing the oil afterwards. This process takes a while, but works. – computercarguy Apr 7 at 19:43
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I don't think it's wise to solder it back on. A car is subjected to a lot of vibrations, and solder does not make a good mechanical bond (it will break).

I would try instead to break that pressed rivet thing with a Dremel-like tool and then replace the tab and press a new rivet into place using a small washer, small tube and a hammer. Fill the voids with solder.

Another option would be to attempt to weld a new tab on, but considering the small size, you would need high quality welding equipment to avoid just vaporizing what's left of the tab. Also you would need to figure out how to ground the part…

If you want to go the solder way, try to find a way to nudge your wire under what's left of the tab. Clean it thoroughly using abrasives and flux, then pry the tab and rivet, wrap the wire around it and fill any gap you see with solder, to stop the wire from unwrapping itself.

Is all the trouble worth the repair? A horn is a critical safety element and you will know it does not work only when you actually need to use it.

Just to reiterate: putting the ring terminal onto the rivet post thingy and adding solder will not hold it in place. The solder will break. Think of solder not as glue, but as being similar to tying the loose end of a rope just to help prevent the main knot from untying.

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  • A properly soldered joint can be fine for many situations in cars - not to repair a seat frame but I have repaired many things on cars from the printed circuit boards (that were flexible plastic and copper strip an absolute b1tch to repair) to many items such as gauges and tank sender units - all survived the vibrations... – Solar Mike Apr 6 at 18:28
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    "you will know it does not work only when you actually need to use it." - Or worse, as happened to me a few months ago, when it decides to work all the time, even when you're not pressing the horn. (Nothing makes you learn where your fuse box is faster...) – Darrel Hoffman Apr 7 at 19:05
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Could you use the inside of a suitable chocolate block connector?

Remove the plastic case, push the connector over the post, then tighten the screw to secure. Put the wire in the other end of the connector and screw it down.

enter image description here

Image copied from - http://www.lightwiring.co.uk/tag/5-amp-4-terminal-junction-box/

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Look at the nut that the broken tab is on. It's a Hex bolt. Unscrew it, and just slip a new spade connector on (or that ring connector you're showing)

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    I don’t think that is a bolt. Looks more like post to me that has had a ring pressed on. – HandyHowie Apr 5 at 21:56
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    That's correct. It's not threaded, it's a smooth post with a stamped rivet of sorts that holds the spade connector. Otherwise I would have done that! ;) – wild coast Apr 6 at 6:09
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And if you want to solder it, then you need to get both bits clean ie shiny and use a good flux with the solder or a flux-cored solder.

But Pete is right - use the nut...

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  • I used flux-cored solder, but didn't seem to stick. I also tried to rest the soldering iron on the post to make sure it was hot, but no cigar. I wonder if that little post is somehow coated with something.. or it's oxidized more than I thought and I need a ton of actual flux. I red that flux-cored solder only contained 5% flux, which isn't much?... – wild coast Apr 6 at 6:10
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    If it is coated with something then it is not clean. – Solar Mike Apr 6 at 6:19
  • Flux is going to help a lot here - I'd be adding drops of straight liquid flux to the post and heating it with the iron, possibly more than once to clean it. Then I'd tin the post with solder (lead solder if possible) and drop the pre-tinned eyelet on top. Immediately I'd put the iron on top of that to melt the solders together. This will take a lot of heat, so pre-heating the whole horn with a hot air gun/hair dryer would help it be less of a heat sink. If that fails, I'd open the horn body and see what can be done there. – Criggie Apr 6 at 21:59
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You could drill a hole in the stud and tap threads in the hole, then use washers and a machine screw to hold down the spade ring.

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    Cutting a thread on the metal stud is a great idea! Not sure what you mean by 'drill a hole' - couldn't a just run a tap on the stud and be done with it? That stud is pretty small, so not sure it could be drilled out very much, maybe... – wild coast Apr 7 at 6:26
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    @wildcoast - You wouldn't be running a tap down the stud; you use a die to cut an external thread. Of course, a new horn would only be a few bucks at a wrecker and many horns of similar manufacturer have near identical hookups. – user16128 Apr 7 at 7:40
  • This is such an excellent idea. – sleblanc Apr 8 at 5:25
  • @wildcoast i was suggesting a hole with an internal thread. External threads might work too, but it's not clear you have the clearances you need. I was thinking in the mindset of things that could be done immediately, e.g. at night, and wouldn't require another trip to the junkyard. – poleguy May 25 at 14:56
  • @wildcoast I just noticed you still haven't fixed this. I thought this was more of a what-if question. I'd really recommend replacing the part at first opportunity at the junkyard. If this is a car-horn it is a safety item, and shouldn't be treated lightly. – poleguy May 25 at 15:00
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As sweber mentions, not all metals are easy to solder. Cored solder for electronics work contains a non-corrosive rosin flux which is fine for copper and brass but will not work on steels for example. In this case, pouring on more rosin flux will get you nowhere. If the stud is steel, you may be able to solder it using an acid flux such as Hampton paste (sometimes used for plumbing joints), assuming you can get it hot enough with your soldering iron. You'll need to clean the joint well afterwards - this type of flux is generally not recommended for electrical work as any residue you don't clean off can attack the metals and create a bad contact months or years later. If it's aluminium, forget soldering.

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  • that's very helpful. I'm pretty sure that post is steel. Definitely not alu. Will try the other flux. Who knew this was so complicated! Learning lots. Thx! – wild coast Apr 8 at 8:15
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Are you trying to connect both components by holding them together and then adding solder? It doesn't look like there's any solder adhering to the spade connection at all, something I've run into in the past where components have a higher thermal mass than I expected (e.g. the back of a metal potentiometer).

The way I've done similar soldering jobs in the past is by building up a pool of solder on the flat surface (the horn in your case) and then bringing the parts together and heating to melt the solder. This gives a better indication of when the part is hot enough:

http://www.youtube.com/watch?v=EHA4SLN4qeA&t=0m47s

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Take a scrap of brass, saw and drill it as below. You'll make the hole for the post a bit undersize so the sides have to spring open.

Tap the second hole to fit a convenient size of machine screw.

enter image description here

Clean the post with a wire brush or a little strip of emery cloth, and press the brass on. Fix it with a bit of epoxy.

Only tools required, drill press, hacksaw and jeweler's saw.

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    From all the above suggestions sounds like soldering just isn't the right solution. This might be the most durable/reliable option! Will give that a go this weekend. Thx!! – wild coast Apr 9 at 1:03

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