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A few questions about powering projects from mains

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aju11:
In addition to fuse you may consider using series Lamp protection.

Place a tungstan lamp in series with your mains supply.
Select tungsten lamp's wattage as per the current demand by your circuit. (Higher watt lamp for higher current circuit)

This will avoid fireworks-like situation if you have serious fault in your circuit.

ejeffrey:
In the UK plugs are fused so it is ok to use thinner gauge cord wires as long as the fuse is rated appropriately.

Note that you still should be using mains rated wiring in terms of insulation.  Standard hookup wire or low voltage cables are not appropriate for a power cord regardless of wire gauge.

JoeP:
Many thanks for the pointers. Since posting the question I did realize that the mains devices you get commercially have some circuitry before the transformer, which explains why the one I'd need would be so much heavier.
Is a home made SMPS out of the question?
Also, is there any possibility of avoiding a transformer all together - such as a capacitor divider circuit? Or would that use too high currents?

mariush:
The transformer has a super important role: ISOLATION .... it protects you from high voltages , mains... it's SAFETY.
Those capacitor dropper based tiny power supplies only work for small currents and they're meant to be used where someone has no way of touching wires .. like let'say something wrapped in plastic and/or glass (led lamp).
It would not be safe otherwise ... and again shouldn't be used for more than 2-3 watts.

ejeffrey:
I don't think a home made offline SMPS is a good project, certainly not for someone with your apparent experience.  It is a relatively complicated project both in terms of performance, safety, and usually requires custom high frequency transformers which you would probably have to wind yourself while maintaining isolation safety.  If you want to build a switcher, a much better option is to get an off the shelf fixed AC-DC power supply then use that to power a DC-DC converter.

For a basic lab supply to test out home built projects, a transformer + linear regulator is really the way to go.  It is a simple starter project and relatively easy to get the safety side right because the transformer itself is designed to provide isolation.  If you use an IEC mains entry jack with a fuse and a switch, it can really be as simple as two wires.  The weight is an advantage: it keeps the device planted on the bench when you are plugging connectors into it.

Capacitive droppers are not suitable for a lab power supply.  They can only provide relatively small currents and they do not provide isolation, so they are used for devices that are themselves isolated: plastic enclosure, no exposed metal or connectors, or maybe devices that primarily exist to handle or switch mains power such as mains power meters or light timers.

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