12V Halogen light - AC ? DC ?


Old 03-11-08, 01:26 AM
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Join Date: Feb 2008
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12V Halogen light - AC ? DC ?

Hi all,

This is a very stupid question, appoligies in advance.

Can anyone advise if the 12V Halogen lights used for home lighting is AC or DC ?

I am wiring up the transformers (specific type for halogen lighting) currently, and on the transformers for the primary and secondary connections, there is no indications of AC or DC (or if the connections need to be wired to live/neutral).

I would imagine that if the transfomers is a DC output, it would note on the output which connection was "ground" and which was 12V.

I am 99% sure that this is all AC, but I thought it best to ask here before proceeding.

Cheers !
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Old 03-11-08, 03:55 AM
Join Date: Oct 2006
Location: Wilmington
Posts: 4,219
AC, to get the AC to DC requires a filter/clamping circuit. A transformer only steps AC up or down, so the output is always AC.
Old 04-13-08, 07:11 PM
Join Date: Apr 2008
Posts: 5
Actually, if it's a magnetic transformer it's definitely AC. If it's an electronic transformer it could be either AC or DC.

Older magnetic transformers (which are large and reliable) just step down AC to lower voltage AC...but there are lot of transformers on the market now that are electronic. These less expensive (and less reliable) transformers are typically AC...but can also be DC. These DC electronic transformers are typically used in cable lighting systems and other systems where voltage drop (which occurs when running low voltage AC over long distances) can be a problem (since voltage drop is less of a problem with DC systems.)

Long story short, if your transformer is relatively lightweight and operates with a very high pitch whine (rather than the common 60 cycle hum) it's probably electronic. After that, unless it says 'DC' on it...it's probably still AC since DC models usually specify that explicitly.

Pretty sure the wiring should be the same either way.

Hope this helps...
Old 05-03-08, 02:40 AM
Join Date: Mar 2008
Posts: 14
Go get yourself one of those beeping voltage detectors. Those things beep only when they're around AC voltage.
But connect wires to the xfrmr's output wires to get the beeper away from the transformer itself; it may pick up the 120VAC inside the transformer housing. Also, some less-expensive beeper testers (I call them AC detectors, which is exactly what they are) may not beep when around only 12 volts AC. Too low of a voltage, possibly.
Or just use a multimeter. That's probably your best bet.
Set the meter to AC & check that first. If nothing, then you've got a DC output.
OR..... what I would do if I didn't have a meter..... Google the transformer's manufacturer & model number, see what shows up.
HOWEVER, if your transformer is just a chunk of metal & wires (in other words, it's not inside of some kind of case), then it is definitely putting out only AC. Transformers work on only AC.
Of course, you could also have a transformer (that is encased) that puts out what's called half-wave DC. Only 1/2 of the input AC's sine wave is flattened out. But that is still generally considered to be a sort of DC voltage, simply due to the fact that the voltage's sine wave as seen on an oscilloscope will be seen either above a zero-point, or below that same zero point. True AC will have sine waves both above AND below the zero point. For a 120VAC voltage, the wave above the zero point is approx 60 volts and the wave below the zero is approx 60 volts. Together, they're 120 volts relative to the zero point.
Old 05-03-08, 02:54 AM
Join Date: Aug 2004
Location: Vancouver, Canada
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Originally Posted by kevin-in-idaho View Post
I call them AC detectors, which is exactly what they are
Used them for years, didn't know that. Thanks!
Old 05-03-08, 08:07 AM
Join Date: Sep 2002
Location: welland ontario
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The transformer is giving you AC. The lamps can be used on AC or DC. They work on both.
Old 05-03-08, 08:43 PM
Join Date: Mar 2008
Posts: 14
AC Detectors

Originally Posted by Kobuchi View Post
Used them for years, didn't know that. Thanks!
Yep... only AC.
Full-wave AC, definitely. Half-wave AC, dunno. I need to test that out sometime, just to see. My eduguess says no, though. Half-wave electrons don't go back & forth in half-wave, only in a smoothly-pulsating single direction (theoretically, anyway). And so, though there is electron movement in half-wave, I'd say that there's not enough to make the conductor material radiate enough energy to be picked up by the standard AC detector that is structurally oriented for standard, ubiquitous full-wave AC.
Relative to Edison's boring DC, Tesla's full-wave AC radiates alot of electromagnetic energy, which is picked up by a gizmo inside the detector called a Hall Effect device.
I love 'em.
I've heard lots of guys on jobs say to NOT depend upon those things for safety reasons, which is a very valid concern for stuff above 120, IMO.
The brand I prefer using, the red-colored GB Instruments "Circuit Alert," can be tested for LED-blinking & beep announcement by pushing down on the detector's shirt-pocket clip. That lets me know that the batteries are good. Alot of others I see can be tested with the generation of electrostatic radiation by vigorously stroking the detector on clothes or one's own bare arm, even. But I like my battery-powered one. And the GB's are inexpensive, yet of good electrical-construction quality I have learned over the years. Fairly tough, too. NOT waterproof, however. However, when testing results seem odd, I take no chances at all with anything above 120. None.

And BTW, RE: those AC-detecting phillips screwdrivers ya see for what... $30 or so? I decided to get one last year. WAY too sensitive. And something that is way too sensitive can give inconclusive or incorrect or misinterpretable results. So I don't use that. It's pretty much just a very expensive phillips screwdriver to me now.
Old 05-03-08, 09:08 PM
Join Date: Apr 2007
Location: Near Buffalo, NY
Posts: 4,239
May I intrude for a couple of comments?

Originally Posted by Just Bill View Post
AC, to get the AC to DC requires a filter/clamping circuit.
Actually conversion from AC to DC requires a rectifier, which could be one diode, two diodes, or a "bridge rectifier" which contains four diodes. A filter (capacitor) isn't necessary, but it does help reduce so-called "AC ripple" that rides on the DC voltage. Another device that's used quite a bit in DC supplies is the voltage regulator, which is usually an IC chip.

Originally Posted by lightingguy View Post
voltage drop (which occurs when running low voltage AC over long distances) can be a problem (since voltage drop is less of a problem with DC systems.)
Are you sure you didn't accidentally swap the terms? DC voltage drop over distance is one of the main concerns in low-voltage systems design. It's the main reason why the pocos chose Tesla/Westinghouse's AC system over Edison's DC system when power distribution was first introduced in the USA.
Old 05-04-08, 03:28 AM
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Originally Posted by Rick Johnston View Post
DC voltage drop over distance is one of the main concerns in low-voltage systems design. It's the main reason why the pocos chose Tesla/Westinghouse's AC system over Edison's
DC system when power distribution was first introduced in the USA.
RE: DC electricity: Yep. A workshop experiment will confirm that.
Plus the fact that AC can be easily stepped up or down in voltage, as all us electricians know about. Volts can be generated at high levels for transmission purposes, and then tapped off & transformed down in voltage for end-use purposes. MUCH more practical than DC.
Edison had a "stick-in-the-mud" mentality, IMO. Besides that, Edison was a 2-legged snake with regards to his dealings with Tesla. Envy, that's all it was with Edison. Edison sure didn't deserve such a fine wife as he somehow got for himself. Tesla was a visionary and much more of a paragon of originality than was Edison, no question about that. In fact, I wouldn't doubt one bit that Edison was in fact pathologically jealous of Tesla's very unique capabilities & of his ability to have very spectacular insights into electromagnetic radiation.

And yet, as the world tends to work in such a way alot of times, Edison is better remembered and became much more wealthy than Tesla. Because after all, it seems that what is desired by many is something really unique & powerful but those many don't particularly want to cotton up to the kind of mind that created such original things in the first place. Too "strange" for the status quo mentality that grovles in mediocrity of thought, just 'cause to be so doesn't take any effort, mostly. But more importantly, such originality of thought requires an awareness of a level of responsibility that requires imagination & principled adherence to concepts of "good" and "bad," put simply, in order to properly deal with the newfound power. Which many found uncomfortable also. Tesla was eventually relegated to the public opinion of being "a kook." HA! Unbelievable, isn't it? wow.....

Yaknow, in my personal opinion, I think Tesla may have REALLY liked AC because he could generate some REALLLY cool & HUGE sparks. I know I do! I've made ~50kV Jacob's Ladders by series-wiring HV transformers (secondaries on one wired to primaries of another, etc.) with the source voltage being only 120. Made my first one, a neon xfrmr 15kV, when I was just 14. (My mother was NOT happy.)

Interesting note here about Tesla: Before actually physically building any electromechanical machine, he would build it in his imagination first. Everything, down to the sizes of bearings for shafts, turns of wire necessary, all of it, from what I've read in historical accounts. Then he'd build it exactly as per what the finished machine became in it's "completed state" in his mind. And it would work perfectly, according to accounts. Genius.

In my opinion, all of the world's current technology can be traced back to Nikola Tesla's passions.
Which is debatable by many in terms of their supposed inherent negative consequences of course, and perhaps rightly so when considering mankind's general love of misanthropy towards "the other guy." The paradox is, "the other guy" is us. But Tesla, I believe, was much more mature spiritually than the average person & so had respect for the negative & destructive potentials of his created visions & their offshoots and would not "go there." Except for his resonance-creating earthquake machine, perhaps. And his admittedly crazy "death beam." Those were purttty bizarre. But his world-changing inventions were put into hands that would eventually abuse the power of those inventions. Such is the fate of mankind though, I suppose. Until we get smart(er) & kind(er), anway.
Tesla died alone in a New York hotel room, nearly penniless, in 1943.
This is a picture of him in late 1942, just months before his passing:

LINK: teslasociety.com: Nikola Tesla Obituaries

Let's see what 12/21/12 has in store.....
Old 05-04-08, 02:59 PM
Join Date: Aug 2004
Location: Vancouver, Canada
Posts: 1,210
Edison truly exemplified the "evil genius for a better tomorrow".

He wanted to scare governments away from AC, and attacked it by staging the public electrocution of animals by AC. This culminated in his invention and sly promotion of the (AC) electric chair, to be used on humans, with full media attendance. Westinghouse refused to supply the AC generators for that, so Edison had to make his own. Then criminals could be hung, or, "Westinghoused", as it was called. Wicked!
Old 05-06-08, 02:03 AM
Join Date: Mar 2008
Posts: 14
Originally Posted by Kobuchi View Post
Edison truly exemplified the "evil genius for a better tomorrow".
I wouldn't want to have played cards with him.
He'd probably try to cheat.....

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