Super bright Blue LED

I have a viper 791xv. I would like to install a few more (2 volt super bright LED's  DEI #8634). I would like to hook them into the same circuit  the original blue led is on, so they all blink together. Does anyone know how many led's I can put on this circuit with out over loading it? I would also Like to make sure this is a 2 volt circuit, but I don't have the alarm installed yet.  Can anyone help me with this?

i think it's 5

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Kevin Gerry
Certified Electronics Technician
MECP First Class Installer

Owner/Installer
Classic Car Audio
since 1979

So I should be able to add 2 more with no problems? Do you know if this is a 2 volt circuit?

You technically won't overload the circuit, your LEDs will just get dimmer and dimmer and dimmer until they won't light at all.  I had three super brights on my DEI alarm a few years back with no problems.

LED outputs typically consist of voltage, the LED, and a resistor,  The resistor will limit the amount current that can be drawn, so that is why you can't overload it. 

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Kevin Pierson

I'm sorry if I implied that an LED is a resistor.  I was simply trying to state the necesarry parts in the electronic output of the alarm (voltage, the LED, and a resistor).  Without the resistor the LED would draw the maximum amount of current availible from the power source and burn itself out rather quickly.

This is why you need the resistor, but a side effect of the resistor is that it will limit the maximum availible current availible on the output.  Because of this you shouldn't have to worry about overloading this circuit and damaging it.  It just simply won't output any more current no matter how many LEDs you attach to it.  Sorry for any confustion!

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Kevin Pierson

You should always use a resitor with an LED, even when using the 'correct' voltage.  It is more important to drive an LED with the correct current, and the resistor will allow you to do that.  Also, if you are driving an LED with an unregulated power supply any spike in voltage will most likely destory the LED, if no resistor in in line.  Furthermore, LEDs are voltage rated with a tolerance.  Just because one LED can handle 5vdc from a batch doesn't mean that the next three will handle it.  Throw a resistor inline and you won't have to worry about the voltage tolerance.

For more information about this check out:

https://www.superbrightleds.com/led_info.htm

I'm 99.9% sure that ALL comercially availible products utilize resistors when dealing with LEDs.

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Kevin Pierson

Haha, I wasn't referring to that part of the page, I was referencing:

DO NOT use LEDS without a current limiting resistor in series with the LED. The forward voltage rating is TYPICAL and can vary from part to part, so while some LEDS may work fine just connected to a battery of the proper voltage, other will be overdriven and destroyed. ALWAYS USE A RESISTOR IN SERIES WITH THE LED OR LED

There is a link on that page that says something like "why do I need a resistor" and it goes on with further detail.

You lost me on the whole kit thing though, what kind of kit are you referring to? 

 

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Kevin Pierson

The output voltage of DEI alarm's led port is 2V. No resistor needed.
You will be fine with 3 leds running in series off of a DEI alarm.

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Certified Security Specialist
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I would connect the LEDs in parallel, not series.

I never meant that the original poster needed to use a resistor with this application.  I was trying to state that the DEI unit has a resistor built in to it, to drive the LED that comes with the unit.  This is where the 2v output comes from (the voltage drop over the resistor).  The original poster was worried about overloading the circuit and  I was simply trying to explain that it is it impossible to overload an LED drive circuit because they have current limiting resistors on them (evident from the 2vdc on the line). 

If you read the deeper in to the link I posted they touch on the subject of driving LEDs with current, not voltage, as current is much easier to control and more stable when it comes to unstable voltages.  On the site linked to they too recomend to never use an LED without a resistor.  You don't 'have' to use a resistor, but you should.  Most discreet components can be used without resistors, but its not recomended to do so.  In fact, the first circuit I ever built and installed in a  car didn't have a single resistor or capacitor in it, and it worked great (it was a sequencer consisting of a 7805, a switch and a microcontroller directly driving, through internal resistors, three super bright LEDs).  In the circuits that I design today there are countless components added to filter and protect the overall circuit.  We use transistors to protect the microcontroller, resistors to limit current in to the transistor, which in turn limits output of the tranistor, resistors on the output side of the transisors also help limit the total output of the board.  We also use 470ohm resistors on all our LEDs.  Sorry for getting off subject a little there, just trying to illustrate my point that even though the resistor may not be needed, it should still be used.

I've never seen a scanner that you have to use a resistor with, all of the ones I've installed worked off of straight 12vdc.   

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Kevin Pierson

I have a pretty good understanding of ohms law.  However, I'm having a hard time figuring out how ohms law applies to this discussion.

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Kevin Pierson

No, because LEDs are not resistive devices.  Their current consumption is not based on the voltage applied.

https://led.linear1.org/why-do-i-need-a-resistor-with-an-led/2/

This guy graphed current consumption based on voltage alone.  The guy running the test notes that between applying 3.2 volts and 3.4 volts the current rasied 4x.  0.2 volt change and 4 times more current draw, try figuring that out with Ohms Law!  This is why you should have the resistor.  Your LED may work great at 5vdc, but whats it going to do at 5.2vdc?

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Kevin Pierson

PER DEI: You can use 5 Red leds MAX and they MUST be wired in series. Also never mix RED / blue.

If the original poster is worried about possibly blowing the alarm's output, DEI also sells a led sequencer that can support 5 leds per 5 channels for a max of 25 leds. Overkill but still safe and seperate from the alarm.

The blue leds use more current so you can't use as many blue leds but you should be fine at 3. I have been unable to find documentation on Directechs and I lost all of my DEI factory training info, if I find I will post.

This is the answer to the original poster's question PER DEI.

You guys can keep debating.

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Certified Security Specialist
Always check info with a digital multimeter.
I promise to be good.
Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.

Hey Guys  Thanks for all  the info!  I see that I should be able to use 3 blue super brights with no problem. auex, you say that DEI says put in series, I see why they would get dimmer with each led I add. Why  can't I put them in parallel? Wouldn't that keep 2 volts going to each one and keep them from getting dimmer???

Parallel would cause the leds to draw more current then the alarm can put out and cause the alarm's led output to blow.

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Certified Security Specialist
Always check info with a digital multimeter.
I promise to be good.
Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.

Thanks again !!!! auex

And so ends the great LED debate of 2005.....

Gus


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Wherever I go, that is where I end up......

funny

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Certified Security Specialist
Always check info with a digital multimeter.
I promise to be good.
Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.