Wiring 12V bulbs in series or...?

[Carolina]

Hope this is the correct forum for this.

I have a chandelier that holds 18 bulbs, it's not in use since ages ago and I was planning to restore it to its former glory. Here's the thing, I also have more than 80 incandescent light bulbs taking up space in my workshop (long story) but they're all rated for 12V and 25 watts, there's obviously more than enough bulbs for this light fixture.

Say I wanted to put all 18 bulbs into the chandelier, what would make more sense, rewiring the whole thing in series so each bulb receives a fraction of the input voltage (240V, I'd use a dimmer to make it 216) or using a transformer/DC power supply (unsure yet) to feed each 12V in parallel?

I was thinking if one of the bulb fails in series then a part of the circuit dies and then the rest basically burn out due to the higher voltage, am I right? so it'd be a terrible idea.

Would a DC power supply work? as far as I know AC or DC is irrelevant when dealing with incandescent bulbs, so it'd be the same if I used a DC PSU or a step-down transformer to make the output 12V AC, just want to be sure on this.

Also would a 12V PSU meant for LEDs work? it outputs the required voltage but perhaps I'm missing something. I did something similar already with another chandelier but used DC LED bulbs and a higher voltage PSU (48V).

Safety inspections are not a problem since they're non-existent in my country (the reason of 60% house fires tho), but I'll replace the ancient wiring inside this thing anyway, and also run new wires to the switch and a junction box.

 

[newfutile]

Wiring in series is a bad idea because mains voltage would be present at each lamp holder also if one blows they will all go out -the likelihood of a shock is quite high.

wiring all in parallel is a better idea as it keeps the voltage down to 12V , however you will need a transformer of 450 watts or more, a led driver will not be able to handle this current.

 

[DPG]

I hope you're not planning to leave it on for long. Half a kilowatt for a light fitting!

But as above, parallel is the way to go.

 

[Lucien Nunes]

Series is a nuisance. When one lamp fails they all go out, then you have to search for the bad one. No harm comes to the other lamps though. You can wire 220V neon indicators across each lampholder in which case the neon across the bad lamp will light, but I can't see it being easy to hide 18 neon indicators in the fitting. One sneaky problem with series connection is that if the lamp manufacturing is even slightly inaccurate, so that some lamps have a slightly different resistance to the others, the ones with the highest resistance receive more than their correct share of the voltage and burn out prematurely.

Parallel is more practical as far as the lamps themselves are concerned, but it makes the wiring harder. 18 x 25 / 12 = 37.5 amps so heavy wiring will be needed, e.g. #8 gauge if it's short, heavier if it's long and you need to minimise voltage drop. AC vs. DC: Lamps can sometimes give a longer life on AC. You might also find that an electronic 12V 40A power supply (although large enough for the running load) would trip into overload protection at switch-on, because filament lamps have a low resistance when cold. The inrush current is around 10 times the running current so the PSU would have to deliver a surge of 400A for a fraction of a second. Some will, some won't. Some will flash on and off a few times for a second until the lamps reach working temperature. This would not be a problem with a wirewound transformer. Finally think about fusing. If you have a 40A transformer feeding #8 wiring that splits into say #16 wiring to each lamp socket, if that shorts it will burn out rapidly, probably without blowing the transformer fuse. You might need to group the lamps and fuse them to say 10A where the wiring splits in the fixture with something like inline blade fuseholders.

Series is cheaper and simpler, parallel is expensive and complicated but safer and works better. 12V makes things hard, hence 100/120/220/230V was normal for domestic lighting in the filament lamp era, not 12V, even though 12V filament lamps last longer and are more efficient. If I had to use 12V lamps I would probably wire them series-paralle. For 18 lamps you could use six parallel strings of three lamps in series, run at 36V from a transformer. That brings the current down to 12.5A, makes searching for the dead one easier and prevents unexpected shocks from a '12V' lighting fixture that actually works at 220V.

BTW if you go all-series and use a dimmer, note that when you get to setting the 216V, many multimeters won't correctly read the voltage output of a dimmer due to the chopped waveform. I have been writing 220V above as much of S. America is officially 220V, but it sounds like you have 240 where you are.

 

[Carolina]

Wiring in series is a bad idea because mains voltage would be present at each lamp holder also if one blows they will all go out -the likelihood of a shock is quite high.

wiring all in parallel is a better idea as it keeps the voltage down to 12V , however you will need a transformer of 450 watts or more, a led driver will not be able to handle this current.

Series is a nuisance.

Thanks that's what I thought, if one goes out then so do the rest that were before it.

I hope you're not planning to leave it on for long. Half a kilowatt for a light fitting!

But as above, parallel is the way to go.

It's in our dining room so only when it's used, right now there's a single holder hanging from the chandelier, it's not pretty but the only bypass I was able to come up with in the meantime. Consumption isn't a big deal as power is reasonably cheap, sure going the LED route would be better but also more expensive considering the price of each bulb.

One sneaky problem with series connection is that if the lamp manufacturing is even slightly inaccurate, so that some lamps have a slightly different resistance to the others, the ones with the highest resistance receive more than their correct share of the voltage and burn out prematurely.

Interesting, I just tried wiring in series two AC bulbs that claimed to be 100W yet upon measuring one was 96 and the other 102 therefore each was receiving a different voltage instead of 50/50. Yet another reason to avoid series, it was an idea sure, but a bad one. Even if I go with 36V and a mixed circuit there's the problem that if one burns then the remaining bulbs will follow due to the voltage spike.

Fusing could be done, I do have inline holders and several fuses so it wouldn't be such a big deal. Same for wiring, if I go for a power supply then I could use thin wiring for sets of 6 bulbs, 12.5 amps each since PSUs come with multiple terminals, otherwise wiring would need to be ridiculously thick for a ceiling fixture ^^

BTW if you go all-series and use a dimmer, note that when you get to setting the 216V, many multimeters won't correctly read the voltage output of a dimmer due to the chopped waveform. I have been writing 220V above as much of S. America is officially 220V, but it sounds like you have 240 where you are.

I'd ask about why exactly but it must be complicated and I'm just getting started with coursework and theory.
Just like the theory I'm reading those 240V are also theoretical, I should get said voltage but due to the power plant being a crumbling relic and me living in a rural area I usually get 200, in fact I've just used the multimeter and I'm getting exactly 206.4, not great not terrible during hot days where everyone uses A/C I only get around 170, terrible for motors I know, some CFLs won't even run at that voltage so that's where AVRs and other mitigating devices come into play, but that's worthy of another thread tbh.
Thanks for the informative reply.

 

[Carolina]

12V makes things hard, hence 100/120/220/230V was normal for domestic lighting in the filament lamp era, not 12V, even though 12V filament lamps last longer and are more efficient.

Hey again, circuit's all done and I went for 2 separate 250W wide input range (to compensate for low mains V) power supplies rather than a single big one due to their smaller sizes. Everything seems to be working though I haven't mounted the fitting to the ceiling yet.

Care to explain why do 12V lamps are more efficient?

One thing I noticed is that the light these emit is a bit different, the tone is still warm yet less orangey than that of AC bulbs. I've checked the voltage under full load and it's 12.01 so it's not like the filaments glows brighter because they're overvolted.
Maybe it's just me being used to AC bulbs browning out due to them never getting full 240V though, who knows.

 

[Lucien Nunes]

Care to explain why do 12V lamps are more efficient?
.....
One thing I noticed is that the light these emit is a bit different

For a lamp of a given wattage, the voltage determines the necessary resistance of the filament. The higher the voltage, the higher its resistance must be, and therefore the longer and thinner the filament. A 240V 25W filament is thin and delicate, easily damaged by vibration and cannot withstand even a small amount of tungsten evaporating from its surface. A 12V 25W one is short, thick and quite robust and can be pushed to a slightly higher temperature for the same lifetime. Even a small increase in temperature dramatically increases the fraction of power converted into visible light, i.e. efficiency, and increases the colour temperature of the light.

Certain applications such as 8 & 16mm cine projectors often used 12 / 24V lamps to get a concentrated, brilliant white light that a 240V lamp could not achieve, despite the extra cost of the transformer. In stage lighting for concerts in the days of large numbers of 1kW parcans, it was quite common in 240V territories to use 120V bulbs and wire them as series pairs, as the 120V filaments were more reliable and gave more light for the 1kW.

 

[DPG]

For a lamp of a given wattage, the voltage determines the necessary resistance of the filament. The higher the voltage, the higher its resistance must be, and therefore the longer and thinner the filament. A 240V 25W filament is thin and delicate, easily damaged by vibration and cannot withstand even a small amount of tungsten evaporating from its surface. A 12V 25W one is short, thick and quite robust and can be pushed to a slightly higher temperature for the same lifetime. Even a small increase in temperature dramatically increases the fraction of power converted into visible light, i.e. efficiency, and increases the colour temperature of the light.

Certain applications such as 8 & 16mm cine projectors often used 12 / 24V lamps to get a concentrated, brilliant white light that a 240V lamp could not achieve, despite the extra cost of the transformer. In stage lighting for concerts in the days of large numbers of 1kW parcans, it was quite common in 240V territories to use 120V bulbs and wire them as series pairs, as the 120V filaments were more reliable and gave more light for the 1kW.

I used to wonder years ago why projectors used a 24V lamp and a huge transformer. Cheers for the info!

 

[Lucien Nunes]

Projector transformers were a thing even before 24V quartz halogen lamps. In the 1950s & 60s when projector A1-class lamps were tubular glass-envelope, inert gasfilled with a planar filament, we used 120V versions and a 240-120V transformer for the same reason. Even so, a 120V 750W A1 lamp gives a duller, yellower light than a 250W 24V one, and the light is harder to collect efficiently because the filament is more spread-out. 240V A1 projector lamps did exist but not in the smaller sizes. Obviously the point-source requirement only applies to projectors, not chandeliers, but the colour, efficiency and lifespan considerations apply to both.

So critical is the relationship between voltage and life that many projectors also had some kind of voltage control for the lamp, typically a 4-position switch with a few taps on the transformer, a variac or similar, to allow a compromise between brightness and life according to what it was being used for. Even things like microfiche readers often had 'normal' and 'high' lamp settings to allow the user to save the lamp life (normal would be something like 11.4V on a 12V lamp.)

The Phoebus cartel of lamp makers that was considered to be fixing the lifespan of GLS lamps in 1930s Europe, kind-of got away with it because of the tradeoff. Makers within the cartel were fined if they were found to be making lamps with more than 1000-hour life, as this would have decreased sales. But shorter life meant higher efficiency so when an enquiry was launched it was accepted that the 1000-hour life was also a sign of an efficient lamp of high colour temp i.e. a mark of performance that was an acceptable compromise for most users.

 

[Carolina]

For a lamp of a given wattage, the voltage determines the necessary resistance of the filament. The higher the voltage, the higher its resistance must be, and therefore the longer and thinner the filament. A 240V 25W filament is thin and delicate, easily damaged by vibration and cannot withstand even a small amount of tungsten evaporating from its surface. A 12V 25W one is short, thick and quite robust and can be pushed to a slightly higher temperature for the same lifetime. Even a small increase in temperature dramatically increases the fraction of power converted into visible light, i.e. efficiency, and increases the colour temperature of the light.

Certain applications such as 8 & 16mm cine projectors often used 12 / 24V lamps to get a concentrated, brilliant white light that a 240V lamp could not achieve, despite the extra cost of the transformer. In stage lighting for concerts in the days of large numbers of 1kW parcans, it was quite common in 240V territories to use 120V bulbs and wire them as series pairs, as the 120V filaments were more reliable and gave more light for the 1kW.

Thanks for the detailed explanation. Chandelier is up and running once again after being dead for who knows how many decades.
Using 120V bulbs in series gave me an idea for yet another home project but I'm not sure if I'll be able to get those in my country as everything is made for 220/240V.

As a side note I've tried LED but all of the AC ones I bought died or started flickering after some months, and they were expensive from known brands cough Phoebus cartel at it again cough, the DC ones are still kicking though.