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I've got a postage scale, on which that the 9V battery connector has fallen off, I bought a new one online for £1 (as below), the new one already has cables coming out of it and the postage scale has cables coming out of it, the cables are quite fine as you can imagine (about 1mm diameter), what's the best way to connect the cables from the postage scale to the cables on the 9V connector?

9v connector

I thought of ripping the cables out of the connector and soldering the scales cables onto the connector, but I thought there could be an easier way.

The other thing I thought of was to use a box connector as the image below, but I think the wires may be too fine.

box connector

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    \$\begingroup\$ Soldering this is pretty easy and compact. Make sure to put some heatshrink tube around the joints. \$\endgroup\$
    – user36129
    Aug 15, 2013 at 13:51
  • \$\begingroup\$ I would stagger the solder joints in the two wires and make sure there is sufficient thickness of insulation (heatshrink) to prevent penetration by spikes of solder in the joint. \$\endgroup\$
    – RedGrittyBrick
    Aug 15, 2013 at 14:02
  • \$\begingroup\$ No pun intended, but if you consider these wires "quite fine", then your safest bet would probably be to use a box connector for now and get some experience with electronics before you damage the scale. Make sure you have a proper small soldering iron and some soldering experience before trying to repair a device that would make you sad when it breaks beyond repair. \$\endgroup\$
    – jippie
    Aug 16, 2013 at 6:41

1 Answer 1

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The best way is to desolder the old cables from the scale's circuit board, and solder on the new ones. That way there are no messy splices. However, to do that easily you may need a solder pump (cost: about $5-$10 USD) to vacuum away the solder from the existing joints. Without a solder pump, you can desolder a through-hole-mounted wire simply by pulling it away while the solder is liquid, but solder may clog the hole. To get around this, you can heat the solder that remains in the hole while inserting the new wire; if you can't get at it with the tip of the iron, then simply add more solder to the area.

The next choice after that is to make rat tail joints (stripped ends of wires twisted together) between the new and existing cable (or else Western Union splice which is neater), and then strengthen these joints with solder and perhaps cover with electrical tape or hot glue. The Western Union is not well-suited for braided wire, but this is only true of the splice alone, not if the splice is flooded with solder.

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    \$\begingroup\$ you DO NOT need a solder pump to desolder a discrete wire \$\endgroup\$
    – Chris Stratton
    Aug 15, 2013 at 16:13
  • \$\begingroup\$ Vacuum pumps sure are expensive in Canada! Here they're about $3. \$\endgroup\$
    – AndrejaKo
    Aug 15, 2013 at 16:22
  • \$\begingroup\$ @AndrejaKo I've seen the type of pump I use go for as little as $7. If you want it cheaper, it would have to be online. The handful of over-the-counter electronics shops in my area know they have the "I need that part/tool today" market cornered. \$\endgroup\$
    – Kaz
    Aug 15, 2013 at 19:21
  • \$\begingroup\$ @Kaz I have the same type of pump. That pattern is called HSP75 here and costs $3.84 to $4.03 in brick and mortar stores. \$\endgroup\$
    – AndrejaKo
    Aug 15, 2013 at 20:03

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