20
\$\begingroup\$

I need to attach wires to a CR1620 cell battery, in a device I'm repairing with not enough physical space for a plastic "battery holder".

Even the smallest "battery holders" 3D models I saw added a few millimeters which I don't have, so I bought cell batteries with "already attached" connection pins:

enter image description here

How are these pins attached? Glued? Stuck? Soldered?

How could I make such a connection myself on a normal CR1620 that doesn't already have these pins?

Can I solder it (risk because 400°C on a cell battery during soldering) or glue it?

Note: I can see two small "spikes" in the connection legs, how could this help to glue it?

\$\endgroup\$
3
  • \$\begingroup\$ I don't remember how it exactly worked out but I just popped a new CR1620 into the cartridge and it just worked - though not sure if it would've dislodged if dropped hard enough and lost my save \$\endgroup\$
    – htmlcoderexe
    Commented Nov 4 at 23:33
  • 2
    \$\begingroup\$ @htmlcoderexe Which cartridge? I don't really understand your comment :) \$\endgroup\$
    – Basj
    Commented Nov 5 at 3:02
  • \$\begingroup\$ Just to be pedantic it is series restance welding rather than spot welding. Spot welding is done with an electode either side of the join whereas series welding both electodes are on the same side. \$\endgroup\$
    – satyr
    Commented Nov 7 at 10:39

4 Answers 4

Reset to default
37
\$\begingroup\$

They are spot welded.

The two marks you can see are the contact patches where two electrodes were applied.

A short high current burst is applied between the two electrodes, and then because there is a relatively high resistance at these contact points, it causes enough heating to weld the metal strip to the battery. This heating is very localised and for such a short duration it doesn't cause any significant heating of the battery.

A battery welder would allow you to do this yourself. You can purchase them, or for a one off attempting to make one yourself might work. You essentially just need a very large capacitor:

  1. Connect a capacitor to two pins (e.g. sewing needles) via a switch.
  2. Charge up the capacitor fully.
  3. Press the two pins against the metal strip to be welded, making sure to press it hard against the battery.
  4. Flick the switch to short the capacitor out through the battery contact.

If the capacitor is big enough, that should weld the contact in place.

\$\endgroup\$
8
  • 5
    \$\begingroup\$ @Basj You can absolutely do it at home. Battery-based spot welders are available. \$\endgroup\$
    – winny
    Commented Nov 4 at 9:31
  • 1
    \$\begingroup\$ spot welding is not hard, but keep in mind that factory-welded batteries are available \$\endgroup\$
    – fraxinus
    Commented Nov 4 at 18:37
  • 2
    \$\begingroup\$ @Justme: the spot-welding is typically made at the end of the battery manufacturing process. Home-made spot welders often use a discarded microwave oven transformer which secondary is replaced by a few turns of thick copper wire, and the primary energized for a fraction of a second. I've never see one made with capacitors. \$\endgroup\$
    – fgrieu
    Commented Nov 4 at 19:53
  • 2
    \$\begingroup\$ I bought a battery spot-welder from aliexpress for about $50, and while terrifying to use, its a lot nicer than a homebrew solution. \$\endgroup\$
    – Criggie
    Commented Nov 4 at 22:58
  • 1
    \$\begingroup\$ A friend made a uwave oven transformer based spotwelder for 18650 cells - then bought an Aliexpress capacitor based one. He found the uwave based one did not do a good enough job BUT many people report using them successfully. \$\endgroup\$
    – Russell McMahon ♦
    Commented Nov 5 at 10:51
12
\$\begingroup\$

These connections are done through spot welding, you would need to have a battery spot welding machine.

The connections are done in fractions of a second and therefore don't heat the battery as normal soldering would (over-heating a battery is a recipe for disaster).

\$\endgroup\$
7
  • \$\begingroup\$ heating a battery is a reciepe for deasaster yes that's what I was thinking! By the way, when I solder the wires on the connection pins from my photo (the little holes are 5mm far from the battery itself), I'm sure it adds heat to the battery itself... Dangerous? \$\endgroup\$
    – Basj
    Commented Nov 4 at 9:14
  • 3
    \$\begingroup\$ Depends heavily on your solder skills, if solder quick enough, it shouldn't be a problem \$\endgroup\$
    – Hans mitm Flammenwerfer
    Commented Nov 4 at 10:47
  • 2
    \$\begingroup\$ you can hold the battery with a wet tissue while soldering \$\endgroup\$
    – fraxinus
    Commented Nov 4 at 18:36
  • 2
    \$\begingroup\$ Battery casings aren't the right metal for typical solders anyway, which increases the chances of overheating if you were to try that. \$\endgroup\$
    – Chris H
    Commented Nov 6 at 12:05
  • \$\begingroup\$ @Basj Hold the battery, of if possible, the connector itself (between the solder and the battery) with as large a pair of pliers/metal clamps as possible. Soldering kits often come with a spring loaded version, or look for "heat sink pliers" if you want to splash out. \$\endgroup\$
    – MikeB
    Commented Nov 7 at 8:18
0
\$\begingroup\$

I have done this.

First I use a little fine sand paper on both sides of the battery. Heat up your soldering iron so it is pretty hot. Clean the tip, pre-tin the tip, with rosin solder, pre-tin the wire you are going to attach to the battery. Try and pre-tin the battery. Don't get the battery hot. Get the solder on the wire hot, touch it to the battery and you are done.

\$\endgroup\$
4
  • 8
    \$\begingroup\$ For soldering batteries, low temperature solder alloy such as Sn42/Bi57.6/Ag0.4 is useful. But even then, it is almost unavoidable that you'll exceed the battery maximum temperature rating. \$\endgroup\$
    – jpa
    Commented Nov 5 at 9:37
  • 1
    \$\begingroup\$ @jpa A warning that if you use lead-containing solders frequently, bismuth-containing solders are generally incompatible with lead. Mixing tin, lead, and bismuth results in the formation of a phase with a very low (I think less than 100 °C) melting point, and even small amounts of contamination can make the whole solder joint crumble at relatively low temperatures. There are other low-melting solders based on a tin-indium eutectic that are compatible with lead, but their melting point is a little higher and they're more expensive. \$\endgroup\$
    – Hearth
    Commented Nov 7 at 15:23
  • 1
    \$\begingroup\$ @Hearth True, according to this the limit is somewhere around 0.3 %. So far I have managed fine by the usual routine of wiping tip clean, covering with the new solder and wiping clean again - but my prototypes aren't really that critical. You can also sometimes see the lead contamination by lack of shine. \$\endgroup\$
    – jpa
    Commented Nov 7 at 16:57
  • \$\begingroup\$ I wound never even consider soldering directly on a Li/Ion battery. Apart from being likely to damage the battery, it is outright dangerous. Or alternatively if doing as you say here and don't get the battery hot - that's exactly how cold joints are made. As mentioned in other answers, spot welding should be used and ideally by the manufacturer of the battery and not back home in your garage. \$\endgroup\$
    – Lundin
    Commented Dec 6 at 12:35
0
\$\begingroup\$

You should be able to order the exact battery you need. I have an old computer with such a battery for the clock and BIOS settings. Instead of trying to fabricate the uncommon battery, I just do some measuring/research on an electronics parts website with a broad inventory (like Mouser) and buy the correct replacement.

I have soldered wires to batteries before (very hot iron, as quickly as possible, with eye protection), but never that small.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.