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20180114 - Soldering Tips

posted Jan 15, 2018, 5:47 PM by Onno Benschop   [ updated Jan 15, 2018, 5:48 PM ]
Denis VK6AKR sends in this information about soldering:

Hello Onno

One thing that time did not permit mentioning this morning relates to power connections.   Mainly DC power connections.   For these, especially those carrying significant current crimping or compression screwing wins every time over soldering.   The reason as you'll doubtless already know is that a soldered joint *may* offer some resistance which will give rise to heating in the presence of significant current flow.

Crimp connectors, correctly sized for the cable and correctly crimped offer gas-tight joints with high quality (low resistance) contact into the connector pin, finger, whatever.   A good alternative is a screw type connector such as an electrical "blue point" connector.   But in this case the individual strands of wire must not be tinned (soldered) together no matter how tempting that may be.   The reasoning is that solder tends to "flow" over time under pressure and this again gives rise to resistance and heating.   With attendant fire risk.   Not a good look.

So important is this latter point (not tinning wire bundles) that back in my apprenticeship days (radio and TV - valve radio, valve black and white TV) we had to obtain our "cords and plugs" electrical workers' licenses.   This enabled us to carry out necessary repairs to electrical appliances of the plug-able variety.   No fixed-wired stoves, hot water system, etc.   Part of the license was a test where we were presented with various flexible cords, plug tops, terminal blocks and so on, screwdrivers and other hand tools, and a soldering iron, flux and solder all in good working condition.   It was an instant fail for anyone tinning wire bundles to be held under screw tension in plugtops, etc for the above reasons.

Above I said that soldered connections *may* offer resistance.  Ideally a soldered joint will use the solder purely as a mechanical bond.   Electrical conductivity a distant second.   So joining wires involves making the tightest possible mechanical bond between the wires prior to applying solder, which will then maintain the bonding.

Not sure if this is selling coals to Newcastle but there you go.

Denis VK6AKR of crappy signal fame!

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