120V --> 12V Project: Case and Grounding

[DigiTan]

This is for a typical 120V --> 12V project

Most of my projects up to now have been battery-powered or used wall wart adapters for DC input. As I'm branching into other areas, I need to run some stuff of the 120V AC line to operating things in the 1 - 25 Watt range.

I already committed to the basic precautions like fuses, grounded chassis, bleeder resistors on capacitors, and never touching a live circuit board. What I'm looking for is help on finding cases constructed with 120V use in mind. What I'm picturing is an aluminum flange with plastic on the outside. So I think my first question is:

What should I look for a good 120V project casing?
Who sells it?

You could say something like this would try fit as an IEC Class I appliance.

Also, if anyone had any general advice on working with AC mains, you can post it here.

 

[dknguyen]

It the stuff actually running off 120V? Because it seems to me it's probably going to run off 24-48V at most. In that case you could just use a step-down transformer and that would solve the vast majority of your concerns including voltage and isolation (that is what is used in wall warts after all). In addition, use a plastic enclosure.

 

[MikeMl]

When I need a 120V powered project box, I go to the Surplus store at my University, and buy an external hard drive or floppy drive case for ~$5. It comes with a on-off switch, a fuse, an LED, a 5V and 12V SMPS power supply, a line cord, line-filter, is UL approved, and some even have a boxer fan. What is not to like?

 

[DigiTan]

It the stuff actually running off 120V? Because it seems to me it's probably going to run off 24-48V at most. In that case you could just use a step-down transformer and that would solve the vast majority of your concerns including voltage and isolation (that is what is used in wall warts after all). In addition, use a plastic enclosure.

Realistically, it'll probably be a stepping down to 12V, 6V, or ±12V DC. One thing I wanted to know is when I use the isolation transformer--will it be necessary to also ground any metal bezels, screws, or cooling surfaces that reach the outside.

When I need a 120V powered project box, I go to the Surplus store at my University, and buy an external hard drive or floppy drive case for ~$5. It comes with a on-off switch, a fuse, an LED, a 5V and 12V SMPS power supply, a line cord, line-filter, is UL approved, and some even have a boxer fan. What is not to like?

That could probably work too. Would definitely save the time of tracking them all individually. I'll still need some kind of layout plan in case this goes outside the size or style I can find otherwise.

 

[Reloadron]

I like Mike's approach as to finding used or surplus cases as cases, especially good ones can get expensive. If I do buy a case for work related projects I like cases made by Bud and Hammond to name a few. You buy a case or chassis based on the project as to dimensions and shapes. Most major distributors carry those names.

Bud Industries.

Hammond Manufacturing.

Anyway, again surplus cases and enclosures are a good bet when they can be had.

Ron