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Basic Electronics » wallwart safety?

April 25, 2009
by tbagman
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Hi,

I'd like to power my breadboard with a wallwart, so that I don't need to worry about battery lifetime. I found one from sparkfun electronics that outputs 9V / 650ma.

I'm a little nervous about powering from a power outlet, even though it'd be through a wallwart. Do I need to be concerned about safety if I were to use this? e.g., if I were to brush against power and ground, and get zapped, does this kind of power supply have enough kick to do damage?

Thanks...

April 25, 2009
by digiassn
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You always need to be concerned about safety, no matter if its from a wall wart or a battery. Batteries can explode, as can electronic component on a circuit board from a battery. I just popped a capacitor with a battery, got hot enough that the plastic melted and it spewed the dielectric everywhere.

The long answer is that kind of supply can provide enough current to kill you. You can feel pain with as little as 10 mA, and the heart can start to fibrillate with as little as 60-100 mA and cause cardiac arrest. It all would depend on the amount of current flowing at the time of contact, so its not a simple question to answer. This is why I always laugh at Taser ads that advertise X number of volts coming out of them. It also has to do with the kind of workstation you have, if you have proper grounding straps, breakers in the circuit, if your wearing insulated shoes, and a whole slew of other safety dos and don'ts.

To address your concerns, that depends on a lot of circumstances. The simple answer is probably not, your probably safe, the most you would feel is a slight tingle or burn. I've been electrocuted with 120 V out of the wall before, and it just caused nasty convulsing in my arm. I also used to work on circuits that had over 480 V with well over a 100 A, and that is some scary current. Just be careful not to touch anything while the circuit is live :)

In my opinion, it sounds like you need to read up on proper workbench safety. Theres tons of materials out there that explain setting up a safe workbench. Taking a wall wart and splicing the wires into a breadboard really isn't a safe way to prototype circuits as wires can slip out of the board. Its not to say I haven't done that myself, but its not the safe way to do it. If your worried, and your serious about electronics, you should look into getting a benchtop regulated DC power supply that you can control better than a wall wart and a power strip. Better ones will let you adjust the amount of voltage and current. They even sell breadboards that have terminals for plugging in power supply and supply electricity to the rails with no additional wiring. You can find decent ones for a good price on Ebay. Thats probably your safetst bet, but it will cost you a little more.

April 26, 2009
by tbagman
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Thanks, digiassn -- I appreciate the detailed reply!

May 31, 2009
by luisgarciaalanis
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I don't want to die :S

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