caddyroger
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Graham, WA |  Auto alarm led light
what would be the brightest led or setup I could get for a alarm?
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SparkChaser
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| said by caddyroger  :what would be the brightest led or setup I could get for a alarm? That's kind of an open question. Could you be more specific, what do you mean set up? There are a lot of bright red LEDS out there now. |
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caddyroger
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Graham, WA | By the setup could you use resistors or relays to get a very bight light?
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SparkChaser
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clubs: | What is driving the LED. You have a signal from an alarm? Is that why you mention relay? |
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leibold
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Sunnyvale, CA
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| reply to caddyroger
Is this intended to replace the led for an existing alarm or do you want to build a theft deterant (a blinking led to make it appear that there is an alarm) ?
Most LEDs will vary in brightness depending on the forward current through the led. If you are replacing the led of an existing alarm device you may be limited by the current that the output circuit can supply. However it could also be that all you need to increase the brightness of the existing led is to reduce the resistor that is undoubtedly in line with the led.
Even if there is no such limit, keep in mind that a super bright led will draw a higher current and therefore be a bigger drain on the car battery. That is not going to matter with a good battery in warm climates but can make the difference between being able to start the car on a cold winter morning or not.
I'm not sure what you mean by "setup" in your question, but for a typical alarm led you probably want it to blink. Unlike most leds, blinking leds (where the blink circuit is integrated within the led itself) require a constant voltage and don't offer the ability to vary brightness by increasing the current.
If brightness is that important, I would avoid blinking leds and use regular (high intensity) leds and an external blinking circuit.
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caddyroger
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Graham, WA | reply to SparkChaser
The alarm is what driving the led. I was just wanting the brightest but after I posted I realized that using a relay could drain the battery. I don't think I go that way.
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leibold
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join:2002-07-09
Sunnyvale, CA
clubs:
| Do you have a schematic for the alarm or are able to tell from tracing the connection to the led what is driving it ?
That would tell you whether or not it is save to increase the current without causing damage to the alarm. Otherwise, can you at least tell which way the led is currently wired ?
alarm (resistor) -- led -- +12V
or
alarm (resistor) -- led -- ground
or
alarm -- led -- resistor -- +12V
or
alarm -- led -- resistor -- ground
It should be simple enough to boost the output current with a small transistor.
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Kringle
Dr.D
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Pierrefonds, QC | reply to caddyroger
Definitely a modification of this circuit: »Re: Detecting an open in a circuit without current. |
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Jason
Dear Penthouse Forum
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| reply to caddyroger
said by caddyroger :The alarm is what driving the led. I was just wanting the brightest but after I posted I realized that using a relay could drain the battery. I don't think I go that way. One of those ultrabright red LEDs shouldn't need more than 20 mA, A blue, or white ultrabright may need more, but we're still talking 30-40mA. I dont think you'd need to add any other sourcing device, more than likely the internal LED driver in the car alarm can handle that much current.
I replaced the stock red LED on my silencer car alarm with an ultrabright blue LED and a limiting resistor. System has worked fine for years.
-Jason
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SparkChaser
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| reply to caddyroger
said by caddyroger :The alarm is what driving the led. I was just wanting the brightest but after I posted I realized that using a relay could drain the battery. I don't think I go that way. If you are just replacing an existing LED you shouldn't have any trouble popping in an ultrabright as Jason says.
If it is a control signal from an alarm and not meant to drive an LED you'd be better off adding a transistor. It won't draw any appreciable current like a relay. It will just be the current of the LED. If the latter is the case they you have to know what the output is, positive/negative pulse.
You might want to think of other colors, since a lot of us have trouble seeing red.  Also, if you are looking for something that will be visible from the side don't select something with a narrow viewing angle.
The current draw seen by the battery is going to be the LED current times the on time/divided by the off time.
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leibold
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Sunnyvale, CA
clubs:
edit:
October 5th, @03:45PM
| said by SparkChaser :The current draw seen by the battery is going to be the LED current times the on time/divided by the off time. Close, but not quite correct. The current draw seen by the battery is the LED current times the on-time divided by the cycle-time (that is on-time + off-time).
That applies regardless whether or not an additional transistor is used to boost the signal from the alarm since the current through the transistor flows through the LED.
However the current that needs to be handled by the led driver in the alarm device is the full current of the LED unless a transistor is added to the circuit to boost the output power.
said by Jason :One of those ultrabright red LEDs shouldn't need more than 20 mA, A blue, or white ultrabright may need more, but we're still talking 30-40mA. I dont think you'd need to add any other sourcing device, more than likely the internal LED driver in the car alarm can handle that much current. Given that a standard led has a rating of 20mA, you make it sound as if replacing it with a super bright led would not be much of a difference. However for signal purposes (like an alarm indicator) a standard led may be driven with just 3 to 5 mA which is sufficient to clearly see it, but by no means bright. On the other hand a 1W super bright led may draw as much as a 700mA current (about 200 times more) and even more powerful leds are becoming available. Your figure of 30-40mA (should probably be 30-50mA) is about right for regular high intensity leds, but keep in mind that the OP explicitly asked for the brightest led (which is likely to be overkill for the application).
Edit: Here is a PDF for the 1W Super Bright LED Specification which is available at »www.superbrightleds.com.
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SparkChaser
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| said by leibold :Close, but not quite correct. The current draw seen by the battery is the LED current times the on-time divided by the cycle-time (that is on-time + off-time). You're right, I was trying to simplify it for the guy. I'm basing it on mine (which is the only one I've ever looked at) which is about .5 to 4. So, it's about 12.5% vs 14%. Sorry for the misunderstanding, I'll follow the book from now on.
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SparkChaser
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| reply to leibold
said by leibold :Given that a standard led has a rating of 20mA, you make it sound as if replacing it with a super bright led would not be much of a difference. However for signal purposes (like an alarm indicator) a standard led may be driven with just 3 to 5 mA which is sufficient to clearly see it, but by no means bright. On the other hand a 1W super bright led may draw as much as a 700mA current (about 200 times more) and even more powerful leds are becoming available. Your figure of 30-40mA (should probably be 30-50mA) is about right for regular high intensity leds, but keep in mind that the OP explicitly asked for the brightest led (which is likely to be overkill for the application). I think Jason and I were talking about something like the RL5-R8030 in the link you gave. At 20 ma it has 8000 mcd @ 630 nm with an angular FWHM of 30 degrees.
I'd still pick green 
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Jason
Dear Penthouse Forum
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Yeah, I think we all were on the same page about the superbright LEDs.
Replacing the LED with the high-flux LEDs you speak of (Luxeon, Et.Al) would be no trivial task (Installing the correct driver, thermal management, etc.), and I suspect way outside the scope of the OPs question.
I kinda thought it was a given we were discussing the standard 3mm plastic "bulb" package LEDs.
But, I guess I need to be more thorough in my responses?
-jason
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sdgthy
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said by leibold :Given that a standard led has a rating of 20mA, you make it sound as if replacing it with a super bright led would not be much of a difference. Max rating, bad design practice to design for max rating. I try to keep a 20mA max to LED no more than 15mA. That assumes PWM isn't being used. The max current rating is nearly always at some unlikely temp that won't be seen. Not to mention that an LED run at max current will loose half it's brightness in less than half it's rated lifetime. |
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