Do globes care about AC or DC?

Hi,

If I have a 12V globe (or any voltage for that matter), does the globe "care" whether it is run on AC or DC?

"Care" in the sense of: - will it work? - will it last as long (or maybe longer)?

In particular, we're thinking of moving out of town and building a house without connecting to the electricity grid. We like the 12V lights that have now become so popular. These run from mains via a transformer. The transformer converts mains AC to 12V AC.

If we ran 12V batteries for the house, it would make sense to just run 12V DC to all our lighting rather than convert to mains AC via the inverter and then back to the 12V with the above transformer(s).

tia, RR

and

AC or DC is fine for the globes. Just use the same voltage.

If it's a standard incandescent type, AC versus DC means exactly zilch. If it's an LED type, or a flourescent, then it's going to be picky about what it eats. In theory, a flourescent COULD run from either AC or DC, but the use of transformers to play with the starting voltage/current and such means that AC must be used to power it unless you go with something that's built to deal with DC. (which will more than likely simply turn the DC into AC or pseudo-AC via some form of inverter, do the transformer work on it that's needed, and run the light from that) LED-style, of course, will need to run on DC, and will expect the proper polarity. If fed the wrong juice, or the wrong polarity, they tend to leak out all the magic smoke rather quickly.

Again, if it's an incandescent, it should work fine, regardless of whether you feed it AC or DC of the proper voltage. It *MIGHT* last longer if run on DC, or it might not make any measurable/significant difference, depending on the exact filament technology it's built around. I would think it extremely unlikely that the lifespan would be any shorter due to being run on DC.

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Thanks for the replies.

The globes are filaments, and apart from that I don't think they are "special".

I found a picture of the globe type here:

Feed 'em 12 volts of either AC or DC, and they'll work just fine. Going back to your previous message, I would say these guys should last at least as long when run on DC as AC, and likely a bit more besides. But that's just my hunch, with nothing scientific to back it.

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This listing is quite high. Check here:

NAYYY, Tom

:

I wonder if the length of the cabling to your lighting will be an issue - long runs at low volts and 'high' amps mean thick(er) cabling to avoid excessive voltage drop.

Worth thinking about as 32v systems were generally the go in the old days to reduce cable losses

David

RR wrote:

The main thing to worry about here is cabling and switching. If you are using 12V, 50W dichroics thats about 4A per bulb to switch. If you have four that's 16A to switch. Obviously switch will have to be rated higher than that. Or maybe use relays and then there's dimming to consider. None of these problems exist when used with mains transformers/SMPS's as the primary current is small and dimmers are easy to add.

Anyway in just a few years LED's will start to take over and they are about

35% efficient as against 7% for your halogen globes. I would think about using LED's now and just a few halogens where you need good light. More expensive yes, but you will save on cabling and switching costs. Oh there is one drawback with LED's at the moment and that is colour/color temperature and CRI but thats another story.

Cheers.

Do you know how LEDs compare to fluorescents? From my own testing they seem about the same or a bit better (maybe 10-20% better?) but I've never seen this properly tested anywhere.

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Depends on what you mean by "better". Fluoro's produce about 40 lumens/watt against 25 lumens/watt for LEDs. But LED output is constantly improving. Lifetime for fluoro is about 5000 hours compared to 50,000 for LED. Lifetime for LED is when the light output reaches between 70 - 50% of original. Light from LED is concentrated, whereas light from a fluoro is uniform. Colour/color temperatures and CRI vary widely.

Cheers.

and

Your 12v wiring will have to be much heavier than the wiring for 230v. Perhaps you might give some thought to an inverter to convert 12v DC to 230v AC. This will make consumer electrical goods easier to operate. Try a ship/yacht chandler for a suitable inverter and a wind generator to mount on the roof.

R

[snip]

Not exactly. The power needed to melt the contacts is calculated by I squared R, where R is the resistance of the switch contacts. If I is constant (16A), R is constant, then power dissipation across the contacts is constant.

The 240V only comes in to play when worrying about arcing.

Hope that made sense...

Thanks to all who replied! Very helpful.

Quietguy: yes, I'm just looking into the issue of cable thinkness.

Roger Dewhurst: it just doesn't seem to make sense to have 12VDC > If you have four that's 16A to switch. Obviously switch will have to be

rated

Thanks, but aren't switches rated on power? So a 240V switch rated at 10A will be quite happy to switch 12V at up to 240*10/12 = 200A?

Maybe I've still got a lot to learn?

LEDs suggestion....I'll think about that!

-- RR

Not really.

AC may be slightly more stressful on the filament, so possibly slightly longer on DC.

yes, IMO, that would work. check with the maker of the globes.

but if you're making your own electricity you may find that LED or CCFL use less electricity, and so can run for longer.

Bye. Jasen

In , Andy Baxter wrote in part:

Most white LEDs have color rendering index rated to be 70-85, and old tech cool white fluorescent rates usually 62, sometimes 66. In both cases the main color distortions are making most colors - especially reds and greens - darker and duller than "proper". White LEDs are not as bad as cool white fluorescent.

Triphosphor fluorescents, which includes most compact fluorescents, are different. Most compacts, Philips "Ultralume" and the better of the two common grades for T8 (GE SPX, others with color code of 8 followed by a

2-digit abbreviation of the color temperature) have rated color rendering index of 82-86 (82 for compacts). The main color distortion is making most colors brighter and more "vivid" than proper, although reds come up orangish.

Most white LEDs have color temperature around 6000K (icy cold slightly bluish). Most higher power white ones appear to me to be around

5000-5500K - not as bluish to sometimes not looking bluish at all but still icy cold. There are some "warm white" LEDs out there, with color temperature mostly around 3500K. However, I see a tendency for those to be a little less efficient than the higher color temperature ones.

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