this seems to be the best place for answers on everything so here goes. I'm trying to have a little electrical fun with my dashboard lights and I have some questions about resistors. If you run batteries in series you get more voltage if you run in parallel you get more current. What happens to when you run resistors in parallel or series? does parallel just allow them to handle more current? What's the deal with the wattages on resistors? is that the max wattage you can run through one? I'm planning on replacing my dash bulbs with much brighter LEDs. I need resistors to step down the voltage of the power source. Thanks for the help.
Resistor Questions
- Thread starter carrera79
- Start date
- Status
- Joined
- Sep 28, 2002
- Messages
- 39,798
Equal resistors in parallel cut the resistance in half. Equal resistors in line double the resistance. Look at them as pipes. Two 1/2" pipes will provide double the flow at the same pressure. One 1/2" pipe double the length will have double the resistance to just one 1/2" pipe of a given length.
You need a Zener diode I would think to assure that you reduce the voltage to the right amount. It can be done with resistors ..but it could require some trial and error (unless there is a preferred method that someone has already come up with for this mod).
A Zener diode provides the same voltage output over a wide range of input voltages. It's the priciple voltage regulation device in the Delco 10SI altenator (antiquated I'm sure).
There you are ...clear as mud!
You need a Zener diode I would think to assure that you reduce the voltage to the right amount. It can be done with resistors ..but it could require some trial and error (unless there is a preferred method that someone has already come up with for this mod).
A Zener diode provides the same voltage output over a wide range of input voltages. It's the priciple voltage regulation device in the Delco 10SI altenator (antiquated I'm sure).
There you are ...clear as mud!
Thanks Gary. I'm going to look for that diode you mentioned. right now I was using some assumptions about the maximum and minimum voltages that the LED would see and I was going to wire up some resistors to put me in the correct range. thanks a lot for your input.
Most LED's have no built in resistor or any kind of current limiting. If you apply car battery voltage across the LED, you will have a super bright laser for a few millionths of a second, then nothing. You need to have a series resistor with the LED. The LED has a polarity and you must connect it up the right way. Take a look at the LED data sheet to figure out the correct polarity.
What you need to find out is the forward voltage drop of the LED's you choose, typically around 2V for a red LED, more for blue or white. Your cars electrical system will be around 14V (13.4V). With 2V across the LED, you will then have 14V-2V = 12V across the series resistor. If you want, say, 10mA current through the LED, the resistor will need to be (from Ohms Law, V=IR):
R=V/I = 12V/0.01A=1200ohms (1.2Kohm).
Keith.
[ February 02, 2004, 02:59 PM: Message edited by: keith ]
What you need to find out is the forward voltage drop of the LED's you choose, typically around 2V for a red LED, more for blue or white. Your cars electrical system will be around 14V (13.4V). With 2V across the LED, you will then have 14V-2V = 12V across the series resistor. If you want, say, 10mA current through the LED, the resistor will need to be (from Ohms Law, V=IR):
R=V/I = 12V/0.01A=1200ohms (1.2Kohm).
Keith.
[ February 02, 2004, 02:59 PM: Message edited by: keith ]
Keith's method works. You can even connect an LED across 115 volt AC. Radio Shack still carries little stuff like LED's and resistors. They are in the back.
Hummmmmmmmmmmmmm. I should have made that an LED and a resistor.
Actually, it changes from a Light Emitting Diode (LED) to a Dark Emitting Diode (DED). budda bing
A quick look at power (for the above 1.2KOhm resistor):
P = VI = 12V X 0.01A = 0.12 Watts
So a 1/4 Watt resistor should do. If it runs hot, use a 1/2 Watt resistor.
What Keith said. Go outside the acceptable voltage of LED's and poof.
I have a couple of UV LED's I purchased from Nichia 4 years ago (Had to sign release forms and took 4 months to get). I believe nichia leads the world in Blue, white (really blue with yellow phosphor to make white), and UV. They also produce blue and UV lazer diodes. Also, some cool long persistant phosphor for glow in the dark applications.
Hey all, thanks for all of the help. I put in the LEDs last night and they look great. They are bright blue and they run through a green tint fiber optic to get to the mirror that reflects onto the instruments, so I get a blue green reflection that looks great. It also seems to react with the instruments and it glows.
- Status
Similar threads
