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I bought a current sensor (link). I would like to connect it to my project, and I was planning to do so by just soldering on copper wires.

enter image description here

enter image description here

There is a resistor on each side, with blobs of tin on each side to keep it in place. These blobs reach out to the place where cables are supposed to be soldered on.

I haven't tried yet, but I imagine, that if I try to solder on the wires this, the tin blob will melt enough that the position and connection of the resistor will change. Thus the resistance will change and the current sensor is no longer useful.

How should I go about this?

In general I wonder about the construction of this board. If the blob on one example reaches just a tenth of a milimeter further towards the other side of the "resistor bridge", then the resistance will be lower.

On the picture from the website (shown below) the blob is smaller, and it would be easier to solder witout changing the connection to the resistors. However it does not look like the resistance is the same from board to board, with this type of "human" soldering. It looks very imprecise.

enter image description here

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I don't really see you'll have a problem, for the resistor to move the solder on both ends would have to be molten. For that to happen a lot of heat would have to conduct through the resistor and at that stage it'd be getting it so hot that damaging the PCB and/or resistor would be likely.

I'd just start by soldering one side as per usual and then give it a minute or two until it's cooled entirely before starting on the other side.

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  • \$\begingroup\$ Good point, but wouldn't the one blob "move a bit" maybe towards the other side (lowering the resistance), or maybe away from the other side (raising the resistance). \$\endgroup\$ – Mads Skjern Oct 11 '14 at 8:29
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    \$\begingroup\$ The resistance will mainly depend on the resistor itself. Unless it ends up with quite a bad connection or shorted them being mounted dead-center isn't critical. But that resistor is quite large as far as SMT parts go I wouldn't expect it to move at all. \$\endgroup\$ – PeterJ Oct 11 '14 at 8:33
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    \$\begingroup\$ I think you misunderstand exactly how the resistor works. It's the internals that make it the resistance it is. The solderable pads on the ends are effectively 0 resistance, so it doesn't matter where you make a connection to them or, within reason, how much of a connection you make. \$\endgroup\$ – brhans Oct 11 '14 at 21:37

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