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Old 08-22-2012, 05:54 PM
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Question on 12 volt LED's and current regulation?

I have recently purchased a qty of 4, of 3 watt LEDs to mount as pairs in each tail light housing. They will operate as dual element lamps, such as 1157's.

I also purchased qty 10 of 5 smd 5050 LEDs for the instrument lamps.

I have read of similar LEDs burning out early as they are for 12 volts, and not really designed for the 13.8-14.3 Volts automotive. As they may use fixed resistors there is no current regulation if a higher voltage is applied.

Has anyone encountered this? I see that 12 Volt voltage regulators are less than $1, and it would not be hard to incorporate. Has anyone done this, or felt it was necessary.

By the way, the way I have configured these visually is to look almost as conventional bulbs, but without the heat. These won't look like I need a Light Sabre with me for my Star Wars Vehicle, like some I've seen.

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Old 08-22-2012, 06:47 PM
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I just use the 1157 led bulbs from SUPERBRIGHTLEDS.com
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Old 08-23-2012, 01:09 PM
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Quote:
Originally Posted by grobb284 View Post
I have recently purchased a qty of 4, of 3 watt LEDs to mount as pairs in each tail light housing. They will operate as dual element lamps, such as 1157's.

I also purchased qty 10 of 5 smd 5050 LEDs for the instrument lamps.

I have read of similar LEDs burning out early as they are for 12 volts, and not really designed for the 13.8-14.3 Volts automotive. As they may use fixed resistors there is no current regulation if a higher voltage is applied.

Has anyone encountered this? I see that 12 Volt voltage regulators are less than $1, and it would not be hard to incorporate. Has anyone done this, or felt it was necessary.

By the way, the way I have configured these visually is to look almost as conventional bulbs, but without the heat. These won't look like I need a Light Sabre with me for my Star Wars Vehicle, like some I've seen.

The problem is that a regulator needs an input that is ~2 volts, or more, higher than the regulated output voltage. So it would need to see a continual ~14 volts just to get output from the regulator..., not so good if the engine is off.

You could add an additional "outboard" resistor to each LED. Maybe go to RadioShack and get some 10+ watt resistors (typically for speaker crossovers), of maybe 16 ohms or such, and wire one in series with each LED.

BTW, the 16 ohms is based on:

(12 volts x 12 volts) / 3 watts = 48 ohms (effectively)

(13.8 volts x 13.8 volts) / 3 watts = 63 ohms (effectively)

63 ohms - 48 ohms = 15 ohms

So I would try a 16 ohm resistor. But this is actually for incandescent bulbs and LED behave differently. Still.... any added resistance will help prolong the life of the LEDs. BTW, the resistors could get quite hot, so mount them appropriately.
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