NOOB QUESTION: What kind of resistor do I need?

  • Thread starter Thread starter MikieCGY
  • Start date Start date
  • Tags Tags
    Noob Resistor
Click For Summary

Discussion Overview

The discussion revolves around the challenges of powering a large number of LEDs for a costume project, specifically addressing the appropriate resistor values, power sources, and configurations for connecting the LEDs. Participants explore various circuit designs and power considerations related to using a 9V battery.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant inquires about the feasibility of running 500 LEDs off a single 9V battery, expressing concern that the battery may be too strong for the LEDs.
  • Another participant provides specific resistor values and configurations, suggesting a 120 ohm resistor in series with each LED to limit current to around 70 mA.
  • There is a suggestion that each LED may need its own resistor, raising questions about the total number of LEDs that can be powered by one battery.
  • A different approach is proposed, where LEDs could be connected in pairs with a 30Ω resistor, which could be more efficient, although concerns about the total current draw are raised.
  • Participants discuss alternative power sources, such as using six D type cells instead of 9V batteries, and the importance of including a fuse in the circuit for safety.
  • One participant suggests experimenting with lower current levels to determine the minimum required to light the LEDs, which could allow for more LEDs to be used.
  • There is mention of pulsing the LEDs to reduce current drain, though this would require additional circuitry that may be complex for beginners.
  • Another participant emphasizes the need to understand the voltage and current requirements of the LEDs and the implications for battery capacity.

Areas of Agreement / Disagreement

Participants express various viewpoints on the best methods for connecting and powering the LEDs, with no consensus reached on a single approach. Multiple competing views on resistor values, configurations, and power sources remain evident throughout the discussion.

Contextual Notes

Participants highlight the importance of understanding the specific requirements of the LEDs and the limitations of the power sources. There are unresolved questions regarding the exact behavior of the LEDs under different conditions and the implications for circuit design.

Who May Find This Useful

This discussion may be useful for hobbyists and beginners interested in electronics, particularly those working with LED circuits for projects or costumes.

MikieCGY
Messages
2
Reaction score
0
First off.. this is my first attempt playing with this kind of stuff.. please have a bit of patience with me :)


I'm looking to make a costume out of LEDs for burningman.. bought a 1000 of them off ebay and when I connect them the 9V battery I'm guessing is too strong for it and burns the LED out.

is it possible to run say 500 LEDs off of 1 9V battery?

These are the specs of my LEDs (which is another language to me)



WLD : 465-470 NM

IV: 8000-10000 MCD

VF: 3.4 -3.6V



please advise. thanks :)
 
Engineering news on Phys.org
MikieCGY, Welcome to Physics Forums!

It appears you have the blue LEDs made by China Young Sun LED Technical Co., LTD. Their model (part) number is YSL-R1042B5C-D13. The specification sheet is available at:
http://www.sparkfun.com/datasheets/Components/LED/Blue-10mm.pdf

The LED’s output wavelength, intensity, and forward voltage you mentioned were measured with a current of 80 milliamperes flowing through it. The suggested operating current is 65-75 mA, which would consume 180 milliwatts of power.

Using your 9 Volt battery, to energize one LED you would use a 120 ohm resistor in series with the LED (between the battery and the LED) to limit the current to around 70 mA.

No, you cannot run 500 LEDs off one 9 battery! A typical alkaline 9 V battery has the capacity of 565 mAhr, meaning it can supply 565 milliamps for one hour. So if you connected eight circuits like the one described above in parallel they would operate for about one hour. You will have to either use bigger batteries or fewer LEDs, or both. Have a good time!

p.s. I went to Burningman in 1982 and had a fantastic experience! I wore a ball cap with a solar cell powering a tiny dc motor with a plastic propeller on top.
 
Thanks for the quick reply Bobby! Also going to a hobby shop today in hopes of buying some resistors instead of buying them online..

does each LED need its own resistor?

How many LEDs can one 9V battery power?

Can you suggest a different power source?


Looking forward to the burn.. its definitely grown since 1982 ... been wanting to go for a fe years now and finally going this year

I'm pretty crafty but my electronic knowledge is just god awful :(


thanks!
 
You could run LEDs in pairs, connected in series with a 30Ω resistor from 9V, that would be more efficient on your power. You would get twice the bang per buck? Each pair would take about 70mA.
250 pairs would need 17A. That represents 17X9 = 150W+, which would be totally daft and would fry you, even if you could carry all the batteries needed! You wouldn't need anything like as many as that. You could get a good show with twenty pairs, which would draw 1.4A (12w).

Actually, you would be better to experiment with just how little current you could get the LEDs to light up at all then use more. That would depend upon the exact behaviour (rather than the published spec) of the LEDs.
AS a power source, six D type cells would be better than 9V batteries and you can get holders for them. You would be well advised to use a fuse in the circuit - just next to one end of the battery pack. D type cells hold a lot of energy and you don't want to be dressed up in a potential crematorium if you get a short circuit somewhere!

To save on current drain it may be worth while pulsing the diodes and accepting the reduced brightness so that you can use more light sources all over you. But you'd need an oscillator / switching circuit, which may not be straightforward for you.
 


Hi there, it's great that you're getting into electronics and experimenting with LEDs! To answer your question, the type of resistor you need will depend on the specific circuit and components you are using. Factors such as the voltage and current requirements of your LEDs, as well as the power source you are using, will determine the type and value of resistor needed. I recommend doing some research on LED circuits and consulting with experienced individuals to determine the best resistor for your project. As for running 500 LEDs off of 1 9V battery, it is possible but you will need to consider the voltage and current requirements of your LEDs and make sure your battery can supply enough power to run all of them. It may also be helpful to use multiple batteries or a different power source for such a large number of LEDs. I hope this helps and good luck with your project!