Series Connection of Bulbs

Hello prasobh83

Yes, both the 12 Volt bulbs must be the same wattage, that ensures they are of equal brilliance when lit.

Please ensure that your transformer is capable of running the 2 No. 12 v 75 watt lamps in series, without damage to the transformer.

Kind Regards....

Thank you for your kind reply.That means i can connect 12V bulbs in 24V transformer if they connected in series.

Hello again, prasobh83

Yes.

But as I said earlier, ensure your transformer is capable of supplying the current required.

If you run the 2 No. 12 volt 75 Watt bulbs in series, be aware that the required current from the 24 volt transformer will be doubled - you will also have approximately twice the light output.

To keep the transformer current and light output approximately the same as your 1 No. 24 Volt 75 watt bulb, then the 12 volt bulbs wattage would need to be halved.

So the safest way (if you do not know transformer capacity), would be to use 2 No. 12 volt 40 watt bulbs in series, which transformer current and total light output is approximately the same as the single 24 volt 75 watt bulb.

Kind Regards....

Yes - you'll be burning 150W with your new bulbs - see if your transformer can supply that. If you could find 12V, 35W bulbs (70W for two), you could run it from your transformer for sure.

it's a series circuit. current won't be doubled - if anything current draw will be less because the 2 filaments in series will probably have a greater resistance than the single 24v filament.

We are talking wattage here not current. Current is sonstant in a series circuit but if you have two 12V 75W bulbs in series across a 24V source your source seens an effective 150W load or 6 Amps, as opposed to a single 24V 75W bulb which would be 3 Amps.

Shawn

Not only equal brilliance but both will be at 12V. If they are different wattage the voltage drop on them will differ due to different current (resistance). If they are different wattage one will be at greater than 12V and one will be at lower than 12V ( at least until the one at greater than 12V burns out.

Generally 12 V lamps give longer life than 24 V. Both lamps should be of equal wattages and combined wattage be less than 75 W.

Oh yes !

Damage to the transformer is likely ! you are asking for about 12 Amps from a supply that was originally putting out 3.125 Amps . It should cook , lose output voltage , distortion to the sine wave (not relevant here) and so on .

You see it was putting out 75 watts, now you ask for 150 watts - going to be tough .

Sorry there wasn't an easier fix .

Chas.

Just remember that if the one bulbs burns out, both will stop working. Keep spares for testing on hand.

Not always safe. Pl remember voltage drop across the bulbs will be proportional to each of these's resistance (and hence related to actual wattage). Since these will not be exactly equal, nor will be the sharing between them, and a bulb may be sharing more than the other, resulting in faster burn-out.

Hello sb

Not the case, in practice.

Earlier Street light circuits were always series fed, around 2200 volts, with a small overvoltage puncture disk parallel with each lamp.

If a lamp overcircuited (blew), the voltage across that lamp's disk rose to the supply voltage, punctured the thin insulation, and effectively short circuited that "blown" lamp.

Also airport runway lights are always series run, on the same basis, on circuits around 2500 Volts for the series string, with special current limiting transformers.

Kind Regards....

Interesting news, this runway lights business .

The only advantage I see is a saving on copper wire diameter in this area .

Is that correct, or is there more ? Thanks,

Chas.

Hello Idodeclare!

There are three reasons:

1. High copper wire volt drop along such a length of wire if in parallel - as you say above.
   
2. Lamps can be lower voltage, thus the filament is more robust, lasts longer, and is less prone to vibration failure.
3. Insulation cost for the higher voltage is far cheaper than copper for the much heavier wire needed if lamps are in parallel.

Kind Regards....

Thank you Sparkstation, very much . Don't know how i got labeled idodeclare-must have

clicked on something-? now i'm using some poor chap's ID - not fair, yet unintentional .

Series runway et al : a fistful of sensible, practical reasons there ! forgot about the longer lasting lower voltage filament factor - kind of explains everything incl. v-drop .

Thanks a heck of a lot for the complete and comprehensive answer .

Chas, i used to think, but now idodeclare for some reason .