Plastic enclosure for power supply?

[theundeadelvis]

I know it's not recommended but is there anyway to safely use a plastic enclosure for a power supply? Can I shield it with foil like the method on Geo?

Thanks,
Ahren Owen

[Joecool85]

Not sure, but I was wondering this the other day also...

[bancika]

Can someone tell me what's wrong with plastic, I planned to make one too, just to know
Thanks

[BrianJ]

Personally, I think plastic for a power supply would be the best bet, be sure to get a durable one.  I build all my projects in metal boxes for durability, but I trust my wiring with my life.  A metal box could end up as a conductor if a wire breaks and it could kill you.  Please don't shield it.  Heatshrink everything.  I prefer transformers with leads on the primary so I have a more durable connection the power cord.  When I first started out, I would use transformers with solder tabs and connect them to the power cord with inadequate guage/voltage solid core wire.  Don't make these mistakes.  Also, avoid pc mount power transformers for diy projects.  Mouser P# 41FG100 is a great little 12.6v CT @ 100mA transformer.  Long leads and mounting ears included.


It seems like most DIY pedal supplies don't include one but never run off of line voltage without a fuse.  I like IEC (computer style) power entry modules with the fuse holder built in.  Output current limiting for the 9v supply is not the same thing as a fuse for the primary. I would also recommend not installing a power switch in line with the primary.  Get an entry module with a switch or put the power switch in line with the 9v rail.  The fewer 120v connection you have, the better.

I hope it doesn't sound like I'm preaching.  I wish you the best of luck.

[bancika]

Thanks, so I'll make it in plastic as I planned (it's just less expensive than metal and looks cool, like black powdered metal )
I'll use 12V xformer salvaged from old genius speakers, large and looks sturdy

[theundeadelvis]

I could be wrong here but I believe that with a metal enclosure if there is a short a large portion of the current is directed to the earth ground. So, if you get schocked I don't think you absorb all of the current. With a plastic enclosure if there is a short it doesn't necissarily (spelling?) go to the earth ground and if you touch something metal (switch, led holder, etc.) that the current is travelling through you become the earth ground and all the current travels through you. I could be WAY OFF but this is how I imagine it in my head. So, this is what spawned my question. Thanks for the input though.

[BrianJ]

I apologize.  I was assuming in my explanation that this is a beginner's project.

Yes, IF the enclosure is grounded properly it should provide a preferable current path.  IF it is fused then the fuse should blow almost immediately.  IF everything is done properly a metal enclosure will be safer.  All the exposed metal components should also be grounded even if the enclosure is not.  Better yet, if this is your first mains powered project, don't use any metal parts.  

Like I said, I make all my stuff in metal.   I use crimp connectors and a big dedicated chassis ground lug with a lock washer on every project.  When I got started it was recommended that I build using plastic.  Is a safer default choice if you are inexperienced in such matters.  Whichever method you choose, please be safe.

[theundeadelvis]

Thanks BrianJ! I appreciate the input. I have built a number of power supplies before, always in metal enclosures. Its just that I have this really nice plastic box that would be perfect for another. That's why I was curious. Thanks again as always!

[BrianJ]

Thank YOU, theundeadelvis.  I just finished painting my first enclosure as per you're advise.   It came out fantastic.  I even bought a $15 wallmart toaster.  Maybe I'll post pics in the Pictures thread...

[Mark Hammer]

I think the answer to the "Is it safe?" question comes in the form of what you're using a power supply to replace.  Ever see metal wallwarts?

[smallbearelec]

For many reasons, even if you don't buy my kit, please see my article on building a Small Wart 60:

http://www.smallbearelec.com/Projects/SmWart/SmWart.htm

You will be interested in the plastic version. PLEASE note the safety precautions, and the care required with the mechanical design. If you don't do it exactly as I did, do remember above all: NO exposed metal parts!!

Regards
Steve Daniels

[theundeadelvis]

Thank you Mark and Steve. Actually it was Steve's small wart project that spawned my question. That is why I was wondering if you lined the box with foil for shielding and used a three prong cord if it would essentially be like using a metal enclosure? I'm building a modified ultra clean ps from GGG. Thanks again guys!

[smallbearelec]

I was wondering if you lined the box with foil for shielding and used a three prong cord if it would essentially be like using a metal enclosure?

I would not recommend this. Any shielding effect that you get from the foil is not going to reduce hum. Presumably you won't be putting the supply right next to a preamp stage, so you are depending on good circuit design and filtering to deliver clean, quiet power. As to construction: I would NOT put a supply designed to provide up to one amp (which the Ultra-Clean can) in a plastic case of any sort. My caution on this point stems from some failure-mode experiments that I did when designing the Small Wart; if the output is shorted, the regulator chip will protect itself. But that will not stop the transformer from overheating and possibly causing a fire hazard. Even a fuse on the transformer primary might not blow. If you build the Ultra-Clean, build in metal. If you don't have the tools (or the construction chops) to work a metal case correctly, buy a commercial PS and pick an easier project. If you don't have moocho experience in modding power supply designs to your purposes, GET HELP! I'm not trying to be mean...I would like to help avoid what Dr. Hammer has referred to as a "blue light special," i.e., an ambulance taking someone to the hospital. Line voltage will bite, and without warning.