resistor for led
Printed From: the12volt.com
Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=122755
Printed Date: May 21, 2024 at 6:14 PM
Topic: resistor for led
Posted By: crazylumpia
Subject: resistor for led
Date Posted: July 19, 2010 at 8:24 PM
Hi, i keep burning out my status LED that I would like to light up when my second fuel pump comes on. I've tried to calculate the resistor i need with several Ohm's law calculator ,but having trouble finding it in Radioshack even if I would need to wire in series.
Car battery is approx 14.5V
LED is 12V
expected current draw on fuel pump max 12A
Which resistor(s) would i need at radioshack and how should i wire them? (series/paralell)
part numbers would be great.
thanks in advance
Replies:
Posted By: i am an idiot
Date Posted: July 19, 2010 at 8:43 PM
I have never seen an LED that would not light up properly with a 1K Ohm resistor. Notice the K, Radio Shack does sell a 1/4 watt 1K Ohm resistor. Wire the resistor in series with the LED. Does not matter if you place it on the power or the ground wire.
Posted By: crazylumpia
Date Posted: July 19, 2010 at 8:56 PM
thank you for the quick reply. Am I correct assuming that i would need a single 1/4 watt 1K ohm resistor for this circuit?
Posted By: i am an idiot
Date Posted: July 19, 2010 at 9:46 PM
1 resistor per LED. Wire resistor in series with LED, if you are using moltiple LEDs parallel the LED/Resistor setups,
Posted By: crazylumpia
Date Posted: July 19, 2010 at 10:51 PM
thank you again. Heading to the shack tonight and soldering in the morning :)
Posted By: crazylumpia
Date Posted: July 31, 2010 at 5:44 PM
i'm still burning out the LED even with a 1/4 watt 1k ohm resistor in place.
Here is a rough schematic of what i am trying to do
note, i actually have a boost activated switch inbetween the positive lead of the battery and the components, It completes th circuit when i reach 10psi. Let me know if there is more information i could provide.
Posted By: i am an idiot
Date Posted: July 31, 2010 at 8:12 PM
Where is the resistor in the above circuit?? The light in the circuit will be on all the time. You have 12v led written by the LED, is it a 12v device?
Posted By: crazylumpia
Date Posted: July 31, 2010 at 9:19 PM
i put the 1/4 watt 1k ohm resistor on the positive pole of the 12v led. I've set this up before but burnt out the led without the resistor. The led's are the 12v prewired type from ebay.
Also i failed to draw in the boost activated switch that triggers a relay to trigger the circuit.
Posted By: crazylumpia
Date Posted: July 31, 2010 at 9:40 PM
here is the full schematic of what i have setup right now.
Posted By: i am an idiot
Date Posted: July 31, 2010 at 10:41 PM
If you have a 12volt LED, you should not need a resistor.
Posted By: crazylumpia
Date Posted: July 31, 2010 at 11:45 PM
i am an idiot wrote:
If you have a 12volt LED, you should not need a resistor.
thats what i thought, but i can't explain why they are blowing out.
Any thoughts on my diagram? does everything look proper? even considering the draw on 12-15A draw by the pump?
Posted By: oldspark
Date Posted: August 01, 2010 at 7:05 AM
Maybe it's a reverse-polarity spike causing the damage (albeit unusual).
Try a reverse biased diode across the LED - eg - something like an 1N4004 (1A 400V) with its Kathode (line end) towards the +12V and other end (Anode) to GND in parallel with LED (whether the LED itself or the LED with inbuilt resistor).
Posted By: crazylumpia
Date Posted: August 01, 2010 at 11:14 AM
would a bad ground on the led cause the damage? i would think a bad ground would only cause it to intermitantly work.
oldspark, thanks for the tip.
Posted By: oldspark
Date Posted: August 01, 2010 at 11:35 AM
For bulbs - yes - intermittents are probably the biggest cause of failure (when people say it's a short - they mean intermittent (think about it)) - other than vibration/shock or poor quality.
Though it's a possibility, it's unlikely for LEDs - ie, no thermal shock; LEDs are often switched at very high frequencies.
Reverse polarity (through inductive spikes) is more probably, but it's worth ensuring a good ground anyhow.
Posted By: t&t tech
Date Posted: August 17, 2010 at 5:21 AM
i am an idiot wrote:
If you have a 12volt LED, you should not need a resistor.
For a minute there you had me wondering. LOL! ------------- COMMIT YOUR WAY TO JEHOVAH AND HE WILL ACT IN YOUR BEHALF.
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