lighting help needed

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Phantom
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lighting help needed

Post by Phantom »

hi all,

ok im new to all this lighting stuff so i need your help, i have just bought these 3mm LED's and want to know how many of them i can chain together whilst using a small square battery with out having to buy resisitors...see links below for LED and battery information.

LED's

http://www.ebay.co.uk/itm/121255201707? ... 1497.l2648

battery

http://www.tesco.com/direct/maplin-extr ... 6-1206.prd
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brt
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Post by brt »

You have a 9 volt battery. Did you buy more than 1 color? The chart for the LEDs shows the voltage range for each color.
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Phantom
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Post by Phantom »

brt wrote:You have a 9 volt battery. Did you buy more than 1 color? The chart for the LEDs shows the voltage range for each color.
yeah i bought a dozen white and a dozen blue 3mm LED's
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Redag
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Post by Redag »

I would encourage you not to try to use a system that hopes to balance without resistors. Theoretically it can be done, but your work will be much tougher. Just learn how to use resistors. All it requires is Ohm's Law and some extraordinarily cheap components.
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Tchail
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Post by Tchail »

With a 9V battery, you can string together three white/blue LEDs without needing a resistor.

9V / 3V per LED = 3 LEDs.
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Post by Madman Lighting »

Ummm.. thats not such a good idea.

LEDs are really current mode devices which means that they may happen to have X volts across them while running, but that can change with temperature and other things.

For a really simple circuit, add a resistor, even if its just 100 ohms, to limit the current to a safe value.

A better way is to control the current in the string, which is more complicated but thats how my controller does it.
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Mr. Engineer
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Post by Mr. Engineer »

+1 for Madman

The current limiting resistors are there to protect the LEDs from burning out.

Each colour of LED have their own voltage and current rating, here are some general ones:

RED = 1.8v, 20mA
GREEN = 2.2v, 20mA
White = 3.2~3.5v, 25mA
Blue = 3.2~3.5v, 25mA

You can put almost three White LEDs in series for the 9volt battery (square battery) but whatever you do, they still need a small resistor. IMHO, I always prefer parallel LEDs and with it, their own personal resistors. I then do not have to worry about extra energy loss (the excess 5.8volts the resistor has to waste as heat.)
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