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Incandescent lamps on 230 V DC?

Incandescent lamps on 230 V DC?

Incandescent lamps on 230 V DC?

(OP)
What are the problems (if any) if one wants to run normal 230 V lamps from a DC voltage with 230 V tension?

Of course, the switches and fuses may be a problem, but the lamps as such? Is there any knowledge out there?

RE: Incandescent lamps on 230 V DC?

Based on my understanding, it shouldn't be a problem.

The explanation for RMS voltages always mentioned the equivalence for heating (and obviously incandescent lighting).

RE: Incandescent lamps on 230 V DC?

(OP)
Yes, that is understood. But otherwise? Better safe than sorry. That's why I ask. I mean, the glowing wire is quite thin and what happens if you have a DC voltage across the filament? Do the ions migrate from one pole (+) to the other (-)? With AC that doesn't happen. But DC?

RE: Incandescent lamps on 230 V DC?

There seems to be consensus that supplying incandescent lamps from a DC source shortens lamp life.
Try googling for:

filament electromigration lamp

RE: Incandescent lamps on 230 V DC?

I don't think there would be much of a problem.  The filament failure mode might be a bit more exciting than an ac system since you have no zero crossings to help extinguish the arc.  

You could check with lamp manufacturer.  

RE: Incandescent lamps on 230 V DC?

To counter any possible 'ion migration' effects, perhaps once a month you could reverse the polarity of the applied DC voltage...  

More seriously, if you're worried about bulb life then drop the voltage ever so slightly.

RE: Incandescent lamps on 230 V DC?

(OP)
Thanks benta. There seems to be a problem - but not quite the one I thought. Does material migrate IN THE FILAMENT? Or have I misunderstood something? I thought that the ions could be moving in the vacuum.

RE: Incandescent lamps on 230 V DC?

There is no significant ion migration; filaments "burn out" due to evaporation of the filament (the black stuff that collects on the walls is tungsten).  There is anecdotal evidence of light bulbs surviving much longer on DC than they can on AC (see stories of the Edison bulb); the explanation is that the AC current causes the filament to vibrate and subsequently fail due to fatigue.

RE: Incandescent lamps on 230 V DC?

It's an interesting questions considering that Edison developed incandescent lights using DC...

But it seems that running a lamp on DC will live only 20% of it's AC operated counterpart.


This from Tektronix:

AC VERSUS DC OPERATION

Since lamp life is primarily a function of filament evaporation, there is a minimal life loss from ac or intermittent operation. Failures under ac operation are generally due to "crystallization", although some filament evaporation is present.

However, because of filament evaporation, lamp life under dc operating conditions is around 1/5 the rated average life specified. Hot spots are developed as the filament evaporation accelerates from localized increased resistance.

Electromigration on the tungsten filament results in "notching" or a sawtooth surface.

Most Tektronix incandescent lamp applications are under dc operating conditions. The increased filament evaporation causes a substantially lower life expectancy so provisions must be made for easy replacement.

Figure 2 illustrates, among other things, the tradeoffs between applied voltage and average life ratings for lamps operated under ac conditions. This graph is accurate only for lamps at 5000 hours or less rated life. Applying 125% of rated voltage will yield 0.07 x rated average life hours of operation.

For dc applications the suggested formula for life hours is:


life = 1.8 x 104 hours x (d2.5) EXP(f/KT)

where d is wire diameter/N CM
f = 2.72
K = 8.6 x 10-5
T is filament temperature in °K

In general, ac operation is recommended with a maintaining current to avoid high inrush current.




Andy

RE: Incandescent lamps on 230 V DC?

"...running a lamp on DC will live only 20%..."

Sounds rather bleak...

If this is really true, then the lamp manufacturers should include within their incandescent lamps a small IC to switch the DC into (square wave) AC.  A five-times (?) improvement in life span might, for some applications, be well worth the cost of such a trivially simple and super-cheap IC.

This subject has me thinking about those ultra-expensive lamps used in video projectors. Those bulbs retail for as much as Cdn$600 (~US$500). I wonder what the trade-off is between using raw household AC (with its obvious voltage variations), or using more tightly-regulated DC, to power the lamp?

RE: Incandescent lamps on 230 V DC?

My instincts tell me that design operating voltage might have a large effect on ion migration. While a lamp designed for 12 volts could possibly work equally well on ac or dc, 230v is a whole different matter.

My only practical experience with this was with a 240v system in Australia that used batteries to provide emergency lighting in the event of mains failure. The biggest problem was variation in battery voltage, especially when the batteries were taken straight off charge, and placed under lamp load. Contactor controlled diode voltage droppers were used to reduce the initial voltage.

As an emergency lighting system hopefully only has to operate for short intermittent periods, overall bulb life is probably not a huge issue. If you plan to run lamps continuously off high voltage dc, a lower design operating voltage might present fewer problems.

RE: Incandescent lamps on 230 V DC?

If the incandescent lamp is rated 230V RMS, then there shouldn't be a huge difference in the filament life, IMHO.  If the lamp is rated 230V Peak to Peak, then the operating the lamp from 230 VDC will indeed shorten the lamp's lifespan.

Back in the early days of Edison lamps, one of Edison's workers noticed that after some hours of operation, you could see the "Shadow" of one of the filament supports on the inside of the envelope.  Edison was a proponent of DC power for household use.  Tesla championed AC.  Anyway, the carbon filament early Edison lamps used "Boiled" away and the carbon condensed on the inside of the envelope of the lamp...except where the filament support connected to the positive side of the supply collected the carbon, leaving the shadow.

Edison did an experiment, placing a second electrode within the envelope and noticed that current flowed through the otherwise unconnected "Plate".  As his system was DC, he had no idea that he had discovered a rectifier, saw no commercial use for the interesting phenominon and did nothing with it.

How much tungsten boils off the filament?   I haven't ever done a study, however I would guess, running your lamp off DC might indeed cause a "Shadow" to appear on the lamps envelope.

You didn't mention your reason for operating the lamp from a DC source.  Whatever that may be, good luck.

I remain,
The Old Soldering Gunslinger

RE: Incandescent lamps on 230 V DC?

Quote:

If this is really true, then the lamp manufacturers should include within their incandescent lamps a small IC to switch the DC into (square wave) AC.  A five-times (?) improvement in life span might, for some applications, be well worth the cost of such a trivially simple and super-cheap IC.


Or, they could use an LED, which runs really well on DC....








A

RE: Incandescent lamps on 230 V DC?

Gas lights and candles have none of these problems hehehe.

RE: Incandescent lamps on 230 V DC?

(OP)
Ever tried to run a gas light on DC?     Or a candle?

RE: Incandescent lamps on 230 V DC?

Quote:

Ever tried to run a gas light on DC?     Or a candle?

There are those who think I've been in broadcasting since the time you used a wooden match to light the TV set's pilot light.

RE: Incandescent lamps on 230 V DC?

The bulbs in cars seem to work ok on DC and they have to contend with continuous vibration and environmental temperature excursions as well.

RE: Incandescent lamps on 230 V DC?

logbook: sure, bulbs do "okay" on DC, but those same bulbs would last up to 5 times longer on AC.


Here's an idea - why not take the car alternator's AC output and use it for the lamps? Probably never have to change a bulb...


A

RE: Incandescent lamps on 230 V DC?

(OP)
I don't know if a measly few hundreds of hours is "to do OK". A car isn't in use for many hours/year and I think that I have to change bulbs at least once a year.

Also, I still think that ionisation plays some role - and that gets worse with higher voltage. 230 V is a lot more than 12 V.

RE: Incandescent lamps on 230 V DC?

"...gets worse with higher voltage."

Hmmm...

The voltage divides itself across the length of the filament. Doesn't that mean that each section of the filament would 'have no idea' what the overall voltage is?

One can imagine making shorter filaments with proportionally less voltage and the conditions on those shorter filaments would be identical to the full length filament with the full voltage.

This equivalence might not apply during start-up.

RE: Incandescent lamps on 230 V DC?

While what VE1BLL says is true, for equivalent wattage lamps the lower voltage lamp carries more current and its filament is made from thicker material.

The surface area, which directly affects ion migration, to volume of metal varies in proportion to diameter, while the volume of metal varies in proportion the square of diameter.

Hypothesis: the thick wire can support material loss in the form of ion migration for longer than the thin one before the wire reaches the point of mechanical failure.

----------------------------------

If we learn from our mistakes,
I'm getting a great education!

RE: Incandescent lamps on 230 V DC?

(OP)
My original thinking was this: A voltage gradient between the more positive and the more negative end of the filament creates an electric field that moves ions (which I believe to be positive) so that they drift from the positive end towards the negative end. That field is - still in my thinking - intenser in a 230 V lamp than in a 12 V lamp. And if it is an AC field, the net movement is nil - I think.

I have got a lot of interesting answers to my first question. Som have asked why I ask - and that is also an interesting answer. The reason is that more and more people start thinking DC distribution instead of AC. Mostly to avoid the harmonics issue, but also to facilitate common UPS functions in "distribution islands" and to avoid losses and costs due to local rectification in every computer, TV, herd and other appliances in the house. It is therefore good to find out what influence DC can have on different components in an electric installation. Fuses, breakers, outlets and so on are also being discussed.

RE: Incandescent lamps on 230 V DC?

"...DC distribution instead of AC..."

'Tom' and 'Nick' (Thomas Edison and Nikola Tesla) had a period of debate on this exact same question many years ago.

Nick won the debate, but Tom ended up much wealthier.

RE: Incandescent lamps on 230 V DC?

(OP)
Yes, we know about that. But that was about hundred years ago. Not many computers and other non-linear loads at that time. And the need for UPS almost non-existent. A short blink didn't matter much.

RE: Incandescent lamps on 230 V DC?

The filament will act as a diode. The negative end of the filament will conduct electrons to the conductor holding the positive end of the filament.
The electrons leaving the negative end of the filament will cool that end of the filament.
It would be an interesting experiment to operate the lamp and check the temperature at each end of the filament, and then reverse the polarity and check again.
I have been told that lamp life using DC is much less than when using AC.

RE: Incandescent lamps on 230 V DC?

I agree. With dc, one end will always be at a high positive dc voltage with respect to the other end, and there will definitely be current flow across the vacuum.

This has all sorts of implications. The anode end would probably run considerably hotter, and then there is the problem ion migration.

In a thermionic diode the directly heated cathode is going to run at low voltage (typically 4 to 10v) and high current, and be a fairly massive structure compared to the skinny filament in a high voltage lamp. The anode would be even more robust.

Another probably more serious problem is what happens when the lamp finally gives up. With ac, the dreaded "plink" and sudden extremely bright flash at cold turn on, is actually an arc. The momentary half cycle fault current can be very high indeed, but at least with ac it will most likely be extinguished at the next zero crossing, (provided there is minimal series inductance).

With dc, a continuous arc might form which could possibly grow to frightening proportions at a high dc voltage with minimal series impedance, until the main fuse/breaker finally trips.

Interrupting large dc currents at high voltage is a very serious business indeed, as the fuse and circuit breaker manufacturers are well aware. What happens if a massive continuous dc arc escapes from inside the glass envelope ?

RE: Incandescent lamps on 230 V DC?

Wow, is this ever interesting. Who would have guessed that something we have all come to take for granted has so much to think about...

I have a question to add to this however. I have used, on lamps in very difficult access areas, a small "lamp saver button" that was inserted into the mogul base socket ahead of the lamp. This button was a diode, so the lamp would recieve 1/2 wave AC, which can be thought of as variable potential DC. These devices would make the lamps last 3-5 times longer than normal. I know it was true because I did my own test of sorts. I had a multi-lamp fixture that needed a 20ft ladder to get to. 1/2 of the lamps got the bulb saver, the rest did not. The ones with the lamp saver had roughly 2/3 of the lumen output (tested with a light meter), but lasted 5 years, opposed to 18 months without. If DC shortens the life, how do you explain this? Was it just because at the reduced output, the filaments ran cooler?

"Venditori de oleum-vipera non vigere excordis populi"


RE: Incandescent lamps on 230 V DC?

Most definitely, even a 10% decrease in operating voltage will dramatically increase lamp life. The biggest killer is thermal shock at turn on, the cold inrush current can be up to ten times the rated running current. Lamps rarely fail when running, it is that "plink" at turn on.

In my home, every incandescent lamp is now operated from a lamp dimmer instead of the usual on/off switch. Just the act of twisting up the knob which takes maybe half a second, will all but eliminate thermal shock. If it can be run at slightly less than flat out, that helps too.

I have no actual figures, but from memory,lamp life now seems to be several times what it was years ago when I only had switches fitted. It is not the cost of the lamps, but the damned inconvenience.

RE: Incandescent lamps on 230 V DC?

when we used to use bulbs (in the days before LED lamps became so cheap) we used to run 130V bulbs on 110V supplies, i seem to remember bulb life went up by 2 or 300%

RE: Incandescent lamps on 230 V DC?

Those lamp savers are a resistance that decreases is value when it heats up.  This reduces thermal shock on the lamp filiment that increases in resistance (about 8 times)and prevents it from acting more like a fuse.  These buttons are not diodes.  While the 20% of life is a little shocking, empirically the effective lamp life is probably only shortened by about 30%.  There are many other factors that shorten lamp life.

RE: Incandescent lamps on 230 V DC?

Those negative temperature coefficient thermistors are an excellent idea, they are used extensively on slide projector lamps to limit inrush. Suitably specified they should work well on any lamp to extend it's life

OperaHouse, you wouldn't by any chance have a connection with the Sydney Opera House ?

RE: Incandescent lamps on 230 V DC?

Hi OperaHouse,

I have seen the diode variety of 'lamp saver' too. A horrible product causing lots of even-order harmonics. Imagine a large housing estate or a commercial / industrial facility fitted with them! I guess the diode orientation is probably random so there would be some degree of cancellation. The NTC sounds a better way to do it if the additional heat can be safely got rid of.

----------------------------------

If we learn from our mistakes,
I'm getting a great education!

RE: Incandescent lamps on 230 V DC?

I have a 15W lamp that I use to illuminate that stairs so my dog can go out the dog dooe at night.  That has a diode in series so it doesn't ruin the dogs night vision and the lamp lasts longer.  I used to have it on a timer till I figured out the timer consumed just about as much as the lamp.  I should use a cap after reading all this, it lasts about a year and a half.

The Opera House actually comes from Nantucket.  There is a building there from the old whaling days called the Opera House.  Time has a way of cleansing things. I think it wasn't much more than a brothel in its day.  They still have sailboat races there for the Opera House Cup.  And it might just have something to do with my having a 12 rank pipe organ in my garage. I'm up for a trip down under.  I loved "Deckchair Danny."

RE: Incandescent lamps on 230 V DC?

The Reason I asked was that I was involved with the design of the emergency lighting system at The Sydney Opera House. This was (and probably still is) the largest dc installation in the southern hemisphere.

The house lights normally run on 240v three phase mains power, but if the mains fails, all three phases are switched over to a 240v (nominal) nickel cadmium battery supply. It was what I was referring to in an earlier post on this thread.

I was employed as the electronics design engineer by the contractor that supplied the batteries, chargers, and diode voltage dropper. Unfortunately I was only involved in the battery room part of the project, and have zero knowledge of the lamps, or any of the problems that may have resulted with that side of it. Your handle suggested to me that you might have been in some way connected.

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