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Old 17th December 2008, 09:10   #31
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3 blue LED's means 3*3.7V which is approximately 11.1V. The car provides 12V to the bulbs.

I'm not sure how much current these can handle. You may need the current limiting resistor.
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Old 17th December 2008, 11:07   #32
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Originally Posted by Rocky_Balboa View Post
Benny,
Nice job man, are you not thinking of disco lights for headlamps?
Rocky.
Nopes, thats not even an option.

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You've forgotten to mention an important step, Ben:

How does one go about convincing one's wife that a blue light in the car is a cool thing?
Get her to watch FnF.

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benny boy thats a very nice DIY, one question here last time i tried something like this the lights heated up too much on leaving the cabin light on for a couple of minutes . How is you setup doing with respect to the heat ?
Would LEDs generate so much of heat? I doubt it. Someone please correct me, if wrong. I havent left the cabin light on for long durations, as i have the switch placed at the door open position.

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Originally Posted by vid6639 View Post
3 blue LED's means 3*3.7V which is approximately 11.1V. The car provides 12V to the bulbs.

I'm not sure how much current these can handle. You may need the current limiting resistor.
I was advised to use a limiting resistor, but decided to just try it out this way. Lemme see.

Been really busy with work that it leaves little time to fiddle with this for the time being.
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Old 17th December 2008, 11:32   #33
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Quote:
Originally Posted by hellstar View Post
one question here last time i tried something like this the lights heated up too much on leaving the cabin light on for a couple of minutes .
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Originally Posted by vid6639 View Post
I'm not sure how much current these can handle. You may need the current limiting resistor.
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Originally Posted by benbsb29 View Post
Would LEDs generate so much of heat? I doubt it. Someone please correct me, if wrong. I havent left the cabin light on for long durations, as i have the switch placed at the door open position.
Yes they can produce heat before burning off. That is exactly why i keep stressing to use a resistor.

Please dont do LED circuits without resistors because by getting the LEDs over nominal current you make them overheat and rob them their extraordinarily long lives. A 20mA LED working at 50mA will be giving out slightly below double its normal light emission (the overheating makes it far less efficient), but it will only live between 100 and 500 hours (4 to 20 days), contrary to its theoretical mean life of 50,000 hours (5.7years).
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Old 17th December 2008, 12:36   #34
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Yes they can produce heat before burning off. That is exactly why i keep stressing to use a resistor.
Just curious. How would you connect the resistor? Parallel to the LEDs or in series?
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Old 17th December 2008, 12:42   #35
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Just curious. How would you connect the resistor? Parallel to the LEDs or in series?
i connected the resistor in series with the LEDs(in my DIYs). But parallel connection can also be done.

Last edited by badboyscad : 17th December 2008 at 12:45.
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Old 17th December 2008, 12:44   #36
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Now that badboyscad has spoken with reason, i will do accordingly.
The other problem for me is that in order to buy a resistor of a different rating, i will need to go all the way to SP Road.

OT : Do any of the Bangy guys know a place which sells these electronic items near Marathalli?
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Old 17th December 2008, 14:03   #37
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Folks, it is a bit more complex than that.

First of all you need to connect a resistor in series to the LEDs. Job of the resistor is obviously to bring down the current to the optimum operating current rating for the LED.

For any electrical circuit, OHM's low is applicable, which says

I = V/R

where I is current, V is potential in Volts and R is resistance.

Unfortunately, in a LED, the rule doesn't apply, and LEDs doesn't seem to offer any real resistance. So, bottomline is, any variation in Voltage could bring an exponential variation is current (unlike Ohm's law) if LED alone is connected across the potential. In Car batteries, Voltage does vary.

Here is a good source to calculate the Ohms for the resistor.
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Old 17th December 2008, 14:29   #38
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Originally Posted by badboyscad View Post
i connected the resistor in series with the LEDs(in my DIYs). But parallel connection can also be done.
You mean a resistor parallel to LED ?
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Old 17th December 2008, 15:36   #39
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best way to connect is a resistor for each led in series to it and put them together for maximum life. going series with all leds powered by a single resistor is not recommended by experts, but i know it makes the whole thing whole complex. did you keep the lights on for sometime with the engine running, quite possible they will fail in a day or two. my experience.
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Old 17th December 2008, 16:03   #40
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did you keep the lights on for sometime with the engine running, quite possible they will fail in a day or two. my experience.
Nopes, i have had the lights turned on with the engine running, but not for prolonged durations.
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Old 17th December 2008, 22:39   #41
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I tried out an arrangement this evening using white LEDs in series.
I connected the 3 white LEDs in series with a 47 ohms resistor. Didnt click any pics as this was a crude arrangement as well. Will try and get a PCB this weekend and fabricate a better set-up.
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Old 17th December 2008, 22:48   #42
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Originally Posted by benbsb29 View Post
I connected the 3 white LEDs in series with a 47 ohms resistor
no no. use 82ohm 1/4 watt resistor for white LEDs.

Last edited by badboyscad : 17th December 2008 at 22:55.
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Old 18th December 2008, 12:59   #43
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Quote:
Originally Posted by WhiteKnight View Post
Folks, it is a bit more complex than that.

First of all you need to connect a resistor in series to the LEDs. Job of the resistor is obviously to bring down the current to the optimum operating current rating for the LED.

For any electrical circuit, OHM's low is applicable, which says

I = V/R

where I is current, V is potential in Volts and R is resistance.

Unfortunately, in a LED, the rule doesn't apply, and LEDs doesn't seem to offer any real resistance. So, bottomline is, any variation in Voltage could bring an exponential variation is current (unlike Ohm's law) if LED alone is connected across the potential. In Car batteries, Voltage does vary.

Here is a good source to calculate the Ohms for the resistor.
But in my experience R=V/I works very well where V=Voltage drop across the resistor and I = working current of the LED.

If we connect a LED of 3v with 20mA of nominal current across a 12 Volt source then the Value of the resistor should be (12-3)/0.02 = 450ohms with 1/4watts.

Also I think the voltage may vary between 11.5-12.5 or 13.0 I believe depending on the battery and alternator output.
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Old 18th December 2008, 13:04   #44
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Benny, that's a neat and sweet job. It does look cool. Does it feel cool too

About the resistor and LED. Yes, its always suggested that they should go both hand in hand. Do not separate them and make any sin. Lol.
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Old 18th December 2008, 13:22   #45
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Originally Posted by benbsb29 View Post
I might think in terms of changing the silly green color of the speedo console.
That would be interesting. What colour do you think will look good on the console, considering yours is front lit ?
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