regarding the led in tail lights

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zybeon

Member - Posts: 8

Joined: August 28, 2009

Location: Virginia, United States

Posted: August 28, 2009 at 11:39 AM / IP Logged

If you just want to do it the easy way(and cheaper way) do the current limiting resistors. What I need to give you the values you should use is: Forward voltage, max continuous current, and how many leds in each series. I just was working on a taillight conversion for my Jeep Wrangler. Though KPierson is right, you will have to play with the resistor values alot to get what you want. But a stupid easy way to do it is test it with potentiometers(1k should do). Here is a circuit for 15 red leds in 3 sets of 5 with 2 volt drop and configured for 20ma at full brightness and about 5ma at dim.

regarding the led in tail lights - Page 2 -- posted image.

Here is a look at one of the lights

zybeon

Member - Posts: 8

Joined: August 28, 2009

Location: Virginia, United States

Posted: August 28, 2009 at 11:49 AM / IP Logged

Since your in India these regulations don't apply to you but may to others reading the forums, besides it took me awhile to find this.

DOT Federal Light regulations Part 571 Just scroll down to Figure 1 as it will give candela min/max values.

For figuring out how many LED's to use in series and parallel use this led calculator and for figuring the resistance total of resistors in parallel or in series use the12volt calculator here.

KPierson

Platinum - Posts: 3,527

This member consistently provides reliable information

Joined: April 14, 2005

Location: Ohio, United States

Posted: August 28, 2009 at 12:55 PM / IP Logged

Be careful wiring a bunch of LEDs in series - if one goes bad you'll lose the entire strip of them, and then you'll increase the current to the remaining LEDs (since you are only using one resistor) which will most likely burn out the rest of them quickly.

If you are going to have paralleled groups at least use seperate resistors to insure that the current can't change if an LED does go bad. If I were doing taillights or brake lights (or anything else that could have an impact on my personal safety) I wouldn't even think twice about using a dedicated resistor per LED just to make sure an individual LED failure wouldn't lead to a catostrophic situation.

Kevin Pierson

zybeon

Member - Posts: 8

Joined: August 28, 2009

Location: Virginia, United States

Posted: August 28, 2009 at 1:00 PM / IP Logged

So you want me to use 30 resistors and 45 diodes....

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: August 28, 2009 at 1:03 PM / IP Logged

Yep, that's how I would do it if I were going to use a current limiting approach to control them. It is a bit excessive, but you won't have to worry about over currenting EVERY LED if one LED were to fail (and with that many LEDs chances are one will fail within 5 years if not sooner).

Kevin Pierson

zybeon

Member - Posts: 8

Joined: August 28, 2009

Location: Virginia, United States

Posted: August 28, 2009 at 1:24 PM / IP Logged

Well figured I won't need 45 diodes but just 17. Thought custom things were suppose to be cheaper

zybeon

Member - Posts: 8

Joined: August 28, 2009

Location: Virginia, United States

Posted: August 28, 2009 at 1:40 PM / IP Logged

Well I still think that would be excessive. I can just wire each set individually.

Mad Scientists

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Joined: February 07, 2004

Location: United States

Posted: August 28, 2009 at 1:42 PM / IP Logged

zybeon wrote:

...Thought custom things were suppose to be cheaper

Heh... figure out how much and how long it'll take to do something. Then, multiply each number by at least 4 to get actual time/cost.

BTDT

Jim

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zybeon

Member - Posts: 8

Joined: August 28, 2009

Location: Virginia, United States

Posted: August 28, 2009 at 1:51 PM / IP Logged

Also just realized that my first circuit had the wrong resistor values. Wired for each led to get about 6.5mA instead of 20mA, though not nearly as bright as I wanted it, if one went dead knocking out a set the others would get brighter but still be far within comfortable operating ranges. For the first one to work at a good brightness I would need to change the 120 to about 50 and the 1k to a 500.

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: August 28, 2009 at 9:37 PM / IP Logged

Thats better, at least you are protecting the other groups if one group fails.

Diodes are cheap - you can get 100 of them for $13. If your component prices are too high, you are buying them from the wrong place.

To "make" something like this should cost about $25 (+ shipping) with most of the expense being in the two circuit boards. The LEDs, diodes, and resistors wouldn't be much at all.

Kevin Pierson

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