leds aren’t lighting up, stumped
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=133722
Printed Date: May 10, 2025 at 1:40 AM
Topic: leds aren’t lighting up, stumped
Posted By: a10100101001
Subject: leds aren’t lighting up, stumped
Date Posted: February 28, 2013 at 12:04 AM
I have to ask; is a car battery charger wildly different than a car battery when used as a power supply?
here's the issue as simply as I can put it: I wired up some strobe LED's to be used as turn signals along with resistors. When I tested my system out on my desk using a car battery charger as a power supply everything worked perfectly. As soon as I wired it up on my vehicle, the LED's won't light up. If I look closely I can see a little bit of light, I mean i'm putting the led 2 inches from my eyes and I see something. When I connect the LED's to the car battery charger, they are extremely bright and blinding.
I went so far as to connect the LED's wires directly to the car battery, same result. Everything electrical on the vehicle works perfectly.
My multimeter shows 12 volts on the battery , and 13-14 volts with the vehicle running. Battery charger shows around 10 volts on the 10 amp setting
My battery is a lifeline agm battery
vehicle is a chevy express 3500
Any ideas?
polarity is definitely correct
I am using resistors to limit current
Led's light up everytime when using a car charger
I tried connecting the led directly to the car battery of my wife's car, same result, won't light up properly
Replies:
Posted By: oldspark
Date Posted: February 28, 2013 at 1:36 AM
It depends on the battery charger.
Older cheap and small types were a very unregulated voltage.
Many old types also have a high ripple content (no capacitors).
Newer SMPS types often have pulsating charge modes.
IOW, very few have a smooth 14.4VDC etc output.
If you designed your system by trial and error rather than calculating for 12-14.4V etc, then you are seeing the effects of that ripple which can read up to 30V on an AC scale.
Posted By: a10100101001
Date Posted: February 28, 2013 at 2:06 AM
Thank you Oldspark, yes I made the mistake of designing the system by trial and error. After reading your response I used a adjustable power supply until the LED's lit up, 18V made them light up. I'll never use a car battery charger again :(
thanks again, i'm sure the ripple you're talking about was making my LED's light up.. back to the drawing board for me. part of the problem is I have no specs on the LEDs (ecco 3510a led strobe) I assumed 12v would do the trick, the inline control module must be doing something completely different than what I thought.
Posted By: oldspark
Date Posted: February 28, 2013 at 2:41 AM
Hi 529 (or 1321?).
You're lucky it was only LEDs. The number of people that connect 12V electronic devices thinking chargers are 12V.
Even with a battery connected (which filters out most ripple), the voltage is often over 14V...
LEDs are usually 20mA unless of the square high current types.
Hang on, you supplied their type... google google...
Ah ha - It's 24 1W LEDs (hence 24W) and "Works with 10-16 volts DC; .75 amp draw". (Check: 12V x .75A = 9W. 16 x .75 = 12W. 24W should be 2A @ 12V. So which info is wrong?)
POST EDIT - Ecco claim it's 12V .75A & hence 8W. Hence 24 LEDs of max 1/3W each ignoring control circuitry consumption.
The point is, assuming the 12-16V is correct, they'll be fine on a normal automotive 12V system no resistor required.
Care is required when buying "12V" rated stuff. Does that mean a 12V regulated supply (ie, 11.5-12.5V) or an automotive of battery 12V supply which is 12.6V with a normally charged battery, no more than 14.4V long-term, but can be up to 15-1/2V etc. (Usual design specs for 12V battery/automotive equipment is up to 16V. Lower limits should be ~8V but can vary higher or lower.)
LEDs do not vary much with voltage; they are current devices. IE - whereas a normal bulb may vary almost linearly with voltage, LEDs don't.
But you may not want to vary brightness. That module includes flash & strobe circuitry which won't like normal dimming techniques (namely PWM).
Posted By: a10100101001
Date Posted: February 28, 2013 at 9:36 AM
I have 6 of these in various locations, two that are on either side of the box at about the center I was wanting to use as turn signals as well.
like you said, the control module didn't like PWM at all (fisrt thing I tried)  , so I attacked the led array by itself with 7 diodes; the pcb has 4 wires coming out of it, I followed the traces and found out that one wire is (+) and the other three are (-). I soldered the diodes in line so that the (+) and three (-) would only flow from the control module to the LEDs. I then tapped the positive wire on the LED side of the diode, and tapped all three (-)s on the LED side of the diodes and joined them together to run a single ground wire to my relay set.
Four SPDT relays connect and disconnect ground from the control module and connect PWM ground directly to the LEDs... these relays are activated by the headlights (+).
Two positives are then wired to the LEDs, first positive is coming from the turn signals, second positive is coming from a different relay that's controlled by a switch activating all emergency lighting; this one goes directly to the control module.
The LEDs are square, i'm assuming high current type. I'm also assuming the control module needs to control the 3 lines of LEDs individually for strobe purposes, but I could be wrong.
Unfortunately the control module is encased with melted rubber, even if I can melt the rubber off to see what's in there, the components will be desoldered as well i'm sure :(
Thanks Oldspark :) 529 is fine 
Posted By: a10100101001
Date Posted: February 28, 2013 at 10:30 AM
Forgot to specify that I tapped the three LED (-) wires with diodes to keep them separate to the control module. Also activating the control module does make the LEDs light up normally.
Posted By: a10100101001
Date Posted: February 28, 2013 at 10:38 AM
Sorry for multiple posts, i'm a bit on the slow side. I wanted to ask if you recommend implementing a voltage regulator to future 12v automotive projects to avoid surprises like this one?
Posted By: oldspark
Date Posted: February 28, 2013 at 11:58 AM
No worries Hex.
Don't worry about a regulator because vehicles don't have them and you may strike worse problems. (Although alternator voltage regulators endeavor to keep a constant voltage, the vehicle supply is not the same as a electronic voltage regulated supplies.)
You need to design for normal voltages of say 12V or lower, and up to ~14.5V, but preferably allow for short durations of 16V or 15V, and below 12V when idling with lights and wipers on etc, and maybe down to 9V or 8V when cranking. Plus spike protection.
The normal voltage at the battery with the engine running should be ~14.2V, and no more than 14.4V long term.
A good test bed is to use a battery charger, but with a battery connected.
You can switch off the charger for "off the battery" testing (noting that a full battery is ~12.7V but will take time to drop from its post-charging "surface charge" voltage of up to ~13.7V) and turn on the battery charger to simulate normal vehicle operation (noting that that simple transformer-type chargers can exceed the normal max battery charging voltage of 14.4V when the battery is (near) fully charged unless loads are added).
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