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Safety tips for using mains power

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shadewind:
I'm working on a project to install some lighting in guitar amplifier head (that might sound weird because it will look neat ;) and I don't want have an extra power plug just for the lighting. I thought about using the power supply from the amplifier but I don't want to mess with that and possibly (probably) introduce noise and interference to the amplifier output. So I was thinking I could add my own power supply to this and learn something in the process.

So my thinking was using a transformer from 230V to 12V AC, rectify, filter and then use a switching regulator to give me a stable 5V output. Maybe not the best solution, I don't know, but that's not the point really. I believe in learning by experimenting so we'll see.

But since I'll be experimenting with mains power, safety is very important and something I take very seriously. Do you have any tips on working with mains powered projects and power supplies? Safety precautions, tips, tricks?

mikeselectricstuff:
Why don't you just buy an off-the-shelf PSU? Will be easier and cheaper than building something.

shadewind:
Simply because then I will have learned nothing. But sure, I might end up doing that in the end.

Psi:
- Use a RCD
- Keep one hand in your pocket when live 230v parts are exposed
- Its a good idea to have another person nearby who can see/hear you and give CPR if its necessary.
- Don't think of it just as a 'circuit' when it's live, think of it as a loaded gun pointing at you.

That being said, while 230VAC can definitely kill, most people on here will have had multiple shocks from mains voltage and are still here.


This next tip can be used to protect a circuit from faults while you design and test it.
- You can put an ordinary 40-200W mains voltage lightbulb in series with the 230v to your circuit, that way you form a current limit. Normally the current will still be enough to kill but it will stop the components from exploding instantly if you get something wrong, instead the lightbulb will illuminate. It will protect your components from damage and could save you from an eye injury. You need to pick the right wattage lightbulb so it doesnt illuminate with normal operating current.

This trick doesn't work so well for some switchmode power supplies, as they want to draw a huge current at the start and common wattage lightbulbs don't allow enough current for the switchmode to start up. A really high wattage lightbulb that would alllow enough current for the switchmode to start wouldnt protect it much when the current is much lower during normal operation.

Alex:
Here is an idea, find a wall transformer that outputs 12V AC, then rectify, filter and regulate if needed. There are many such wall adaptors and this solution will allow you to learn without being exposed to mains voltage.

Here is what I mean, I am sure you can find them locally.

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0458923

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