How to solder battery holder leads?

Discussion in 'General Electronics Chat' started by divisortheory, Sep 4, 2015.

  1. divisortheory

    Thread Starter New Member

    Sep 4, 2015
    I picked up a battery holder with solder lead tabs. Very similar to this


    What is the proper method of soldering connector wires here? I tried to solder the wire to the metal, but even when I made no contact with the plastic casing, enough heat transferred through the tab that it melted the plastic case.

    I had a spare, so I pushed the wire through it and wrapped it back and twisted, and then soldered the wire to itself. But now the wire still hangs loose and flops around. Seems like you're supposed to be able to solder the wire directly to the tabs, but I can't get it hot enough without melting the plastic.
  2. PackratKing

    Well-Known Member

    Jul 13, 2008
    You need at the very least a 20 watt solder "iron" ... I use Oateys' brand of copper-pipe sweat-soldering flux, and 63/37 eutectic solder. You must tin the wire you want soldered to the holder tab... IF your iron produces adequate heat, you should be able to complete the joint in less than 1/4 second, which should not affect the plastic, if you make the connection in that time frame. I have done this literally thousands of times...
    Roderick Young likes this.
  3. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    Attach an improvised heatsink e.g. use a pair of pliers or a crocodile clip to press a small brass nut against the terminal where it passes through the plastic and apply the solder quickly, i.e <1 second, with a very hot iron.
  4. divisortheory

    Thread Starter New Member

    Sep 4, 2015
    I must be doing something wrong because it takes me forever before the solder melts. I'm using this solder and this iron. How am I supposed to know what temperature the dial corresponds to on the station?

    (In case it's not obvious, I've only ever soldered a few times, so I still don't know what I'm doing)
  5. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    My rule of thumb, is that if I touch the solder to the tip, it should melt immediately. Otherwise it's not hot enough to solder.

    Also, the tip must be tinned and cleaned, with no excess solder and a shiny tip. A metal kitchen scrubby is great for keeping the tip clean.

    Secondly, you need to heat the parts before you apply the solder. I mechanically join the parts, hold the solder iron against BOTH parts, count to 3 (not three seconds;count to three) and then place the solder against the joint.

    The solder should cleanly flow between the parts, at which time you gently remove the tip. The solder should not "ball up" on the joint, but "hug" the PCB and component.

    If it doesn't work, remove the soldering iron to let the joint cool down, brush the joint to clean it up (with a wire pencil or a little flux).

    Then repeat.

    Both parts must be heated, so when heating them with the iron, make sure the iron tip is in contact with both parts. Doing this, you can make dozens of joints in a half minute.
  6. divisortheory

    Thread Starter New Member

    Sep 4, 2015
    the solder does melt instantly when I touch the iron directly to it (to tin the tip), and I am heating the material for more than 3 seconds, but when I touch the solder to the heated material it just doesn't melt.

    I will try cleaning the tip, if all else fails perhaps I will make a video of my failed attempt.

    Is there some trick to securing the workpiece? I need one hand to hold the iron and one to hold the solder. It's often hard to secure the workpiece with this arrangement, and in cases like a battery holder which is very light, the force from touching the iron to the material is enough to push it around. I can sit something heavy on it, but surely this is a solved problem.
  7. izon


    Mar 17, 2013
    I think there are at least 3 key things to keep in mind when soldering:

    1. Heat sink the connector part that the battery will contact to pull some of the heat away from the plastic while making a quick
    application of the solder and iron. As mentioned before, you can use an alligator clip or anything metal to clamp to
    that battery connector. Ideally one maybe shouldn't need to do that but unless everything goes perfectly, it will give
    you a better chance of not melting the plastic if you keep the iron on too long.

    2. The solder iron tip must be "clean". Usually they will get covered in a blackish residue. The tip should be silvery from
    the clean area and a light coat of solder. There are cleaning compounds to use but if you don't have that, try gently
    scraping the tip surface cleaner with a knife blade or small wire brush while the iron is hot. Then you should quickly wipe it on the
    damp sponge you have on your solder station. (this should help remove most remaining crud as you rotate the tip on the sponge)

    With everything else being ready (as described below..... very important) you should apply the
    tip to the clean surface you are soldering to along with the solder. You may get the solder to start melting by first touching
    it to the very tip of the iron while on the work surface.... this gets it flowing so it will quickly "take" to the surface.
    Another great help is to first "tin" the "prepared" work surface with a dab of solder. This along with tinning of the wire
    you are attaching will make the two solder covered surfaces quickly take on the additional solder you apply with the iron.

    3. Clean the metal you are soldering to. Even though it may look bright and shiny, it seems that most often the copper or
    brass metal that you are really needing to solder to is plated with a chrome-like metal that will not want to "take" the solder
    at all or only with too much heat. This isn't so easy to do and you don't have to have the entire surface area of the part
    you are soldering to, totally cleaned of the chrome plating. But you should have at least half the circumference showing
    a copper or brass color to have enough surface for the solder and wire to attach to.

    I've used a Dremel or similar tool with a very small grinding stone and worked it around the area I need to solder to or a
    small file which is harder to do. But it will make a world of difference to have that material cleared from at least part of
    the area you need to solder to.
    Along with this goes the "tinning" (putting a light coat of solder on) of the wire you are attaching. That will save the time
    and heat used to get solder onto it. With solder already there, the process goes much more easily when soldering to the
    other surface.

    I've been working in electronics more than 50 years and have soldered thousands of times and may not be perfect at the
    procedure but with the above steps it goes so much better.

    Hope this helps!
  8. izon


    Mar 17, 2013
    Sorry to jump right back but just saw two posts that were entered while I was working on my above reply.
    Very good tips (pointers) from djsfantasi.......well explained.

    Regarding holding the have to use a little imagination often. If you have some small woodworking
    clamp .... clamp the battery holder to your bench or a heavier piece of material..... like a board or metal object that
    won't move very easily. I have a small woodworking "jig" that clamps wood to hold it so you can work with it and that also
    works great for holding objects for soldering, etc.

    You should do a little "practice " soldering of wire ends (tin them) to another copper material or wire to get your technique
    down. Don't need to put excessive solder on the junction... and correct, it should not "ball up" as it has not properly melted
    due to not enough heat or an unclean surface. The finished joint should more or less conform to the material and look like
    one continuous metal surface.

    Best regards.
  9. ian field

    Distinguished Member

    Oct 27, 2012
    Its not easy! - you need to complete the soldering operation as quickly and with the least heat possible.

    An active flux may help, but I usually scrape whatever plating down to the base metal immediately before soldering. Don't expect to make a full rounded textbook solder joint - the bare minimum electrical and mechanical integrity may be as good as it gets.

    Some are made of such nasty plastic that even with careful soldering it loosens its grip on the rivet and the connection becomes intermittent.

    The advice to use a small low powered iron can make matters worse - if it takes a long time to get the tag hot enough to flow solder, that isn't doing the plastic any good. With a decent sized iron that holds its heat, you can flow the solder in not much more than 1 second.

    If you have a soldering iron stand with a wet sponge for cleaning the tip, you can use the wet sponge to quench the tag after soldering.
  10. #12


    Nov 30, 2010
    Just a couple of ideas...I hope I'm not just repeating what everybody else said. I use a diamond fingernail file to damage the coating on the tabs. In this case, a beginner, I would even sink the battery holder in water to protect the plastic at the rivet area. Tin the tab, tin the wire, get in and out quickly!

    You can find the melting point of the solder by fiddling with the dial, but that is not the answer you need. You need hot and fast, just not so hot that the flux seems to explode and splatter all over the place. Lead-free solder is not the most co-operative solder. This might even be unlawful now, but I would do my best to find some old 63-37 PbSn solder. If you can't find that, it is legal to use any flux you can find. I have acid flux and rosin flux in my stores for plumbing. The acid flux will eat anything except the plastic, including your fingerprints. Acid flux is almost never right for electronics. You can get away with it this time, considering that you can sink the battery holder in water for as long as it takes to remove every trace of the acid.

    Practice your methods and materials on the ruined battery holder.
  11. JohnInTX


    Jun 26, 2012
    You might try a bigger tip maybe a 3/16" screwdriver tip - something with more mass. You want to be able to get a lot of heat on the joint fast, solder it and get off. A tip that's too small can't transfer heat fast enough to heat the joint before enough conducts away to melt the plastic.
    RichardO and #12 like this.
  12. ian field

    Distinguished Member

    Oct 27, 2012
    Water can start corrosion between the rivet and tag, this is a consideration with using a soldering iron sponge to quench it as I suggested. The flux I mentioned should also be used sparingly to try and keep that out of the rivet as well.

    AFAIK: Hobby use is one of the valid exemptions from RoHS - attempting to solder battery holders with lead free solder is just asking for trouble!

    It used to be possible to get cadmium based LMP solder - but that is pretty much certainly banned.

    Back in my TV servicing days, I encountered a hybrid CTV with a practically a safety pin thermal cut out in the horizontal output cage. A spring under tension was soldered to a tag in such a way that it would break loose if the solder melted, the spring of course completed the HT circuit to the horizontal output.

    There was a little package tacked to the side of the horizontal cage containing a few turns of solder wire, and a note explaining what it was and how to reset the thermal cut out.
  13. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    I've always struggled using lead-free solder for this kind of thing, fortunately I've still got plenty of the outlawed stuff; it's still available on ebay.
    Sinus23 and #12 like this.
  14. ian field

    Distinguished Member

    Oct 27, 2012
    Its not illegal for hobby use - just don't sell your completed projects within the EU.
    blocco a spirale likes this.