12v to 3v
Printed From: the12volt.com
Forum Name: General Discussion
Forum Discription: General Mobile Electronics Questions and Answers
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=26538
Printed Date: May 01, 2024 at 6:40 PM
Topic: 12v to 3v
Posted By: nevek
Subject: 12v to 3v
Date Posted: February 15, 2004 at 5:07 PM
does anyoen have a diagram on how to convert 12v to 3v for led's
Replies:
Posted By: uncpaul728
Date Posted: February 15, 2004 at 6:04 PM
Wouldnt that call for a resistor?
Posted By: nevek
Date Posted: February 15, 2004 at 8:30 PM
what resistance resistor?
Posted By: packmouse
Date Posted: February 15, 2004 at 11:14 PM
Hi, I am yesterday new to the group. I am just learning but I think a 9 ohn resistor might be correct. I have just started learning about LEDs they are cool. If you ran 3 leds in series each one would depending on the LEDs voltage which some are about 3 volts after lighting the 3 leds 3 volts would be left over and you would have 3 LEDs telling you the power was on. They wouldnt use much battery if it a car battery. Hope this helps John ------------- Don't throw it away! Ill take it.
Posted By: superchuckles
Date Posted: February 16, 2004 at 11:28 AM
actually - the resistor would only work, if you know the amount of current being drawn at 3 volts first. the proper way to do what you're wanting, is to get a voltage regulator - and it just so happens they make a standard regulator, fairly common so it's easy enuf to get one, that is 3.3volt positive output. the LM2937-3.3 or the UA78M33 should work for your application.
Posted By: MielGibson
Date Posted: February 16, 2004 at 8:34 PM
Posted By: packmouse
Date Posted: February 16, 2004 at 10:48 PM
https://www.theledlight.com/ledcircuits.html I didn't see the for leds at the end of your message. This link should clear it all up regardless of how many you want to hook up. Superchuckles is right I learned from his post. I think the 9 ohm would be for a device that uses 1 amp. Thanks John ------------- Don't throw it away! Ill take it.
Posted By: speakerman
Date Posted: February 17, 2004 at 10:05 PM
I did a lot of led's in my car and I use a 249 ohm resistor on them. It was the lowest I had and tel all work great.
Posted By: markcars
Date Posted: February 24, 2004 at 8:57 PM
you can always put four LEDs in series directly to the 12 volt supply (assuming each of your LEDs takes 3 v). If you have more than 4, then group them by 4's and put each group of 4 in series. Each group having two wires that go directly (or with a switch or whatever you prefer) to the 12v supply.
12 v + ---------------LED-LED-LED-LED-----|
|----------LED-LED-LED-LED-----|
|----------LED-LED-LED-LED-----|
|
12 v -ve-----------------------------------
Sorry about the ugly "drawing". I dont have any
diagramming software yet.
Posted By: packmouse
Date Posted: February 24, 2004 at 10:43 PM
Hi, You should have a 3v a 6v and a 9v tap between each LED like a voltage divider circuit I think. If I am wrong I dont mind being told so. I am always a student and if someone corrects me and they are right then I learned. And that is good. Later ------------- Don't throw it away! Ill take it.
Posted By: markcars
Date Posted: February 24, 2004 at 11:01 PM
You won't need anything if you put the LED's in series. When in series, the current (amperage) that flows through each LED is same whereas the voltage gets divided. So if you have 12volts and 4 LEDs then each LED gets 12/4 which is 3 volts. However if you put them in parallel(meaning every LED's + touching every other LED's + and every LED's - touching every other LED's -), they all get the full 12v but the current/amperage gets divided. To prove this theory, you see "Christmas lights" that are connected directly to a 110v supply without any circuits. Same principle. They have either 10 12volt lights in series (120 volts) or 50 3volt lights in series (needing 150 volts). LED's are more sensitive than cheap "Christmas bulbs" so the tolerance is less however you get the idea.
Posted By: packmouse
Date Posted: February 24, 2004 at 11:40 PM
Hi, Yes, If you only put 1 LED you would need an appropiate resistor. All I am saying is if you decide to series the LEDs is you have the advantage of the votage drops for something else. Example if you have a device that runs on 3 6 or 9v then it is near by. The tap would have to be paralled to ground. Or maybe Im wrong? John ------------- Don't throw it away! Ill take it.
Posted By: markcars
Date Posted: February 25, 2004 at 5:50 AM
yes John, you're right. However if you use LEDs in series to any device for a voltage drop, you are more than likely running the risk of burning out your LED. These LEDs take very little current (about 7 to 20 milliamps). If your device that is needing the voltage drop is a discman for example, it will need about 300 mA and 3V, thereby frying your LEDs since it will get 3 volts but 300 mA across the LED, thereby burning it out.
Check the link that you posted before, it has some details.
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