# Led in 24v circuits

Discussion in 'General Electronics Chat' started by cloudmaker, Jul 30, 2009.

1. ### cloudmaker Thread Starter New Member

Jul 30, 2009
2
0
I would like to use some 12v .5w LED replacement globes in a 24v lighting circuit. Each unit has 6 LED's and they are designed to plug in to a 12 downlight system. (2 pins). They replace small incandescent units.
I know this is a naive question but if I put two 12v .5w in series would there be enough resistance to cope with the 24v?

I'm guessing not, but since I have a Solar 24v system it would be nice to find some way to use these 12v units. I have an inverter to use 240v stuff and also acquired a transformer to step down from 24v to 14v if needs be. So far I have not really used the last and if I did so it would be rather inefficient, hence my interest in using the readily available 12v LED units to reduce power consumption. Any suggestions would be gratefully received.

2. ### t06afre AAC Fanatic!

May 11, 2009
5,936
1,227
What you need is a series resistor
Effect in Watt=voltage*current
So your LED unit draw .5/12=0.042 Ampere
If you have a 24 volt system, you will need a resistor that give a 12 volt voltagedrop. The size of this resistor i given by the formula voltagedrop/current. 12/0.042 is equal to 286 ohm. Your local store will not have a suited resistor equal to 286 Ohm. But by connecting two resistor in series you may create a resistor very close to 286 ohm. I also suggest you use resistor rated for 1 Watt.
In which country do you live? Perhaps I can point you to online elctronic store

3. ### Wendy Moderator

Mar 24, 2008
21,502
2,962
Actually you can do what you suggested. If the units are both equal in resistance (I would assume so) they would each drop 12V of the total 24V. The only proviso I would add is they don't have any dimming circuits, that might change the basic assumptions.

As with a Christmas tree, if one blows both go dark. LEDs have a very long life, so this is negligible also.

4. ### t06afre AAC Fanatic!

May 11, 2009
5,936
1,227
I will also add that if you chose to as resistor, as I suggested or two LED units in series you will have the power consumption. If you use a resistor the energy is radiated as heat, and not as light, as if you use two LED units . (this is somewhat simplified )

Jul 7, 2009
1,577
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I second what Bill said -- put them in series. No other parts needed.

6. ### cloudmaker Thread Starter New Member

Jul 30, 2009
2
0
I live in Australia and we have 240v light sockets with bayonet fittings.
There is an adapter for the bayonet fitting to connect the two pronged incandescent (now LED), as seen here http://www.onlinelighting.com.au/product_info.php?cPath=60_169&products_id=5334

So I'm using the 240v fitting on a 24v circuit.

What I don't understand is how would my proposed setup be different from having several of the same lights on a given 24v circuit.
Is it just that I'm making sure that I always have two 12v units switched on via a given switch circuit?

Thanks again.