Low voltage AC Power Supply?

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makerkid13
 
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Low voltage AC Power Supply?

Post by makerkid13 »

I am a young person interested in electronics looking to do more with AC current without dangerous amounts of electricity like 120V outlets and such. My parents are worried that AC current is more dangerous than DC current, even at low voltages. Bridge rectification and conversion from AC to DC fascinates me but I don't know where to go. Is there a way I can easily generate AC current at a safe level? I do not know where I can find a low voltage AC power supply (not DC adapter), and would like to know whether AC current is any more worrisome than DC. Please help, Adafruit has been a blessing to all of my projects.

Thanks from the Midwest.

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adafruit_support_bill
 
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Re: Low voltage AC Power Supply?

Post by adafruit_support_bill »

Both AC and DC can be dangerous at sufficiently high voltage and current levels. For safe experimentation, I'd recommend a function generator. These are low-current/low-voltage sources of alternating current. They will also allow you to experiment with the effects of different frequencies and waveforms. Both Velleman and Elenco have reasonably priced signal generator kits:
http://www.amazon.com/Velleman-MK105-Au ... B000TA3FKS
http://www.amazon.com/Same-as-FG-500-Ki ... -1-catcorr

makerkid13
 
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Re: Low voltage AC Power Supply?

Post by makerkid13 »

Thank You!

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philba
 
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Re: Low voltage AC Power Supply?

Post by philba »

If you need AC, probably the cheapest way is an AC wall wart. They do exist, I have several in my junkbox, 12VAC is pretty common. You should be able to find them at thrift stores for like 50 cents. Just sort through them - the specs should be printed somewhere on the WW.

Use all precautions. AC is not more dangerous than DC but note that it is the current across the heart that kills you, not the voltage.

I'm not saying a function generator isn't a good purchase but it's definitely more than you were asking for.

uoip
 
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Re: Low voltage AC Power Supply?

Post by uoip »

Agree with all that's been posted here, but I'll add one more suggestion. Take a look at the Elenco XP-720 power supply. If you search around a bit, you can find the instruction manuals, which includes schematics and detailed assembly instructions. Even if you don't buy that power supply, it's good to look at the schematic, because that power supply uses a very straightforward classic design common to lots of linear power supplies and wall warts. Basically a transformer, rectifier, capacitors, followed by linear voltage regulators.

Most of the supply is dedicated to producing DC outputs; 5VDC @ 3A, plus two 1A adjustable outputs, one negative and one positive. But the supply also has a 12.6VAC output that's center tapped, meaning you can tap one side of it for 6.3VAC or use both sides to get 12.6VAC. The AC output provides up to an amp. It looks like the AC output was almost an afterthought, like they used a transformer that had some extra windings and just ran the output to the output jacks.

It's not too bad as a general purpose hobby DC power supply, but it lacks an adjustable current limit and it lacks meters to monitor voltage and current. But not a bad value for the price, if you'll be using the DC aspect of it. The regulated 5VDC at 3A will power a lot of digital electronics, and the adjustable + and - rails are convenient for op-amps and other analog experiments.

If you only want the AC output, finding a low voltage AC transformer is definitely much cheaper. I know low voltage AC transformers are very commonly used for irrigation systems, doorbells, and low voltage landscape lighting. If you can find a pile of wall warts at a thrift store, you'll probably find one that outputs AC, but you'll have to sort through a lot of the more common DC ones to find it.


Oh, and if you're comparing similar voltages and currents, AC and DC have nearly the same danger, or lack thereof. But if you look at the most common examples of AC and DC around the house, DC is normally low voltage and low current, while AC is often higher voltage and current.

Rukbat
 
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Re: Low voltage AC Power Supply?

Post by Rukbat »

"My parents are worried that AC current is more dangerous than DC " That was Edison's ad BANNED against Tesla, and it was as meaningless then as it is now.

The two dangers are surface burns (caused by the voltage) and disruption of the nervous system (including heart attacks), which is caused by the amount of current flowing (amperage). At power-line frequencies, there's very little difference in either case - the right voltage will burn your skin and the right amperage will kill you, AC or DC. Experimenting at the 6-12 volt level may give you a tickle, but the only danger is "electrician's elbow" - jerking your hand away from the circuit and smashing your elbow into something hard enough to hurt you. We used to work with 67 volt, 90 volt and 135 volt batteries back in the days of vacuum tubes and, although a 135 volt shock bites, I've lived through hundreds of them.

Even if there's 100 amps available, at 12 volts the human body will draw something on the order of half a thousandth of an amp from a finger on one hand to a finger on the other (passing through your heart) - not enough to be aware of. Lightning a couple of miles away probably induces more current flow in your body, and human beings have been living through that since there have been human beings.

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