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Old 18th May 2009, 19:12   #181
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I want to know whether I am doing is right or wrong. I first created a 3 White LED setup with 142 ohm resistor. I am going to do similar kind of sets like 5 rows or 10 rows of 3 LEDs each. Should I use 142 ohm for each row or is it going to be different ?

Also I want to create these kind of LED setup using AC power. Instead of using AC-DC adapter is there any kind of small transformer which I can connect to it.
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Old 18th May 2009, 19:34   #182
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Quote:
Originally Posted by gopinathann View Post
Also I want to create these kind of LED setup using AC power. Instead of using AC-DC adapter is there any kind of small transformer which I can connect to it.
Buy a 220v to 12 v transformer(should cost around Rs:30) and add a bridge rectifier circuit to get 12 to 14 DC.

Below is a pic of the transformer with the bridge rectifier circuit.
The green wires are input(220v AC), the purple wires are output(12v AC) and the bridge rectifier rectifies the 12v AC to 12v DC.
Benny's first DIY : LEDs on an Ikon-18052009912.jpg

Bridge rectifier schematic:
Name:  bridge.gif
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Diodes - 1N4001 (4nos)
Electrolytic capacitor- 1000mf/35 or 40volts (1 no[s])

Pic source:XCircuit Schematic Capture Tutorial Page

Last edited by badboyscad : 18th May 2009 at 19:54.
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Old 19th May 2009, 14:54   #183
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Thanks BBS, I will try this out.

Any idea about my other question, setting up 10 Rows of LEDs. The LED calculator says 14 ohms 8 Watt. Should I use 14 ohms for each row of 3 LEDs ?
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Old 19th May 2009, 15:56   #184
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gopinathann, that circuit is exactly the same as what is used in adaptors. so if you find it hard to make/get an adapter cheaper, stick with the adaptor

the resistance value seems strange. I'd say 150 ohm resistor in series with 3 LED's in series, and wire 10 of these in parallel

Last edited by greenhorn : 19th May 2009 at 15:57.
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Old 19th May 2009, 16:35   #185
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Quote:
Originally Posted by greenhorn View Post
gopinathann, that circuit is exactly the same as what is used in adaptors. so if you find it hard to make/get an adapter cheaper, stick with the adaptor

the resistance value seems strange. I'd say 150 ohm resistor in series with 3 LED's in series, and wire 10 of these in parallel
Your comment seems to be correct. For the following circuit 150 ohms is the correct value, however I am not sure how other calculator gives those strange values.
Input Voltage : 13
Forward Current: 3.3
Desired Current: 25 mA
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Old 19th May 2009, 16:44   #186
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if this lamp will be run mostly on battery (~12V) and for short durations, you can use 100 ohms

On the other hand , if this is going to be used with the engine on (14.4V) , and a lot of the time , try going even higher, say 180/220 ohms - My numberplate lights have begun to die out - and this is the 2nd time in 4 months, so am planning to increase the resistance to 220.

Am sick and have been advised bed rest, + my soldering iron is dead, So my plans will be on hold for a while :(
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Old 19th May 2009, 17:05   #187
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Good work. It all worth the effort made!
Cheers!
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Old 22nd May 2009, 07:46   #188
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Quote:
Originally Posted by greenhorn View Post
the resistor is kinda like a fuse. it limits the current through the LED's. without it , the LED's will be using up a LOT more current (without much increase in brightness) , and they'll die out soon.
Thanks Greenhorn, I ll change the setup soon and add the resistor. What value of resistor should for my present setup?

Quote:
Originally Posted by ghpk View Post
Using the short glass LED (which are used in china made torches these days) will help attain more illumination.
What are these LEDs called? how much do they cost?





BTW, here is the pic of the same

Benny's first DIY : LEDs on an Ikon-dscn1048.jpg

Quote:
Am sick and have been advised bed rest, + my soldering iron is dead, So my plans will be on hold for a while :(
Uh Oh, take care greenhorn, hope you recover soon.

and you appear online on TBHP early morning??

Thats a perfect TBHP Mania

Last edited by srikant : 22nd May 2009 at 07:50.
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Old 22nd May 2009, 08:16   #189
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srikant, add a 100 ohm resistor in series with each row of 3 led's , and then put them in parallel, like in gopinathann's pic above
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Old 22nd May 2009, 11:54   #190
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Hi,

I tried putting 3 LED's in series with a 100 ohms resistor for the boot lamp and tested the circuit on a 5V adapter. The LED's would not glow but the same setup if made parallel would emit very good light...

Is it something that the current being 5V is inadequate for the 3 LED's in series since I guess each LED's takes around 3-3.5 V. However i have not tried this on a 12V setup.

I am doing the setup tonite by soldering the LED's on a PCB. Any reply before that would be really helpful..Anyways..i am thinking of trying out the same (series) setup on a 12V source..

Regards,

Rahul.
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Old 22nd May 2009, 12:05   #191
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rahul, you're thinking along the right lines

if you have one of them breadboards, try it out on that before soldering

and make sure you get the polarity right while soldering the LED's
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Old 22nd May 2009, 14:14   #192
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Quote:
Originally Posted by rahulya007 View Post
Hi,

I tried putting 3 LED's in series with a 100 ohms resistor for the boot lamp and tested the circuit on a 5V adapter. The LED's would not glow but the same setup if made parallel would emit very good light...

Rahul.
3 L.E.D. in series with a 100ohm or 150ohm resistor would work fine on a 12v source and not on 5volts.
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Old 22nd May 2009, 15:31   #193
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I am surprised to see that the White LED doesn't glow on a 1.5 v battery but the normal bulb glows. Atleast the LED should show some light when connected to a battery. I have a torch which has 6 LEDs and runs on a single battery.
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Old 22nd May 2009, 16:45   #194
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the torches have LED Driver IC's inside which step up the voltage. We dont have that luxury
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Old 22nd May 2009, 17:36   #195
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I have a transparent LCD clock which runs on single AAA battery. I want to use the same battery to throw some light on it in the night. Which LED should I use for this ?
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