LED light array

[life-saver]

This is pretty simple stuff I reckon, but I'm just having a little difficulty wrapping my brain around the little details. I really don't have a great deal of electronics experience.. I'm more of a "wannabe"? lol.

Anyhow.. I've found bulk LED's on eBay for cheap. I want to be able to build my own LED light modules, which could be used in automotive applications (I'm a police officer and I'm wanting to play around with some ideas).

So.. essentially, I need to figure out the best way to supply power to a light array.. voltage in an automotive application can vary (especially with all the equipment in a police car) so, there will definitely be spikes in voltage supply.

Next.. I need to be able to scale this up and down.. meaning, I may want to build a light array that drives 3 rows of 8 LED's or I may want to drive 6 rows of 6 or different configurations.

Here is some numbers that I'm trying to figure out.. the blue LED's that I will primarily be using are 3.6v, 25mA LED's. As best that I can figure, I could put 3 in series, with a resistor.. and it would require 10.8v, add a resistor to that, and repeat this for however many I would want to run in parallel? is that accurate? so, for example, if I would want ONE module of 3x8 (24LEDs), I would have 8 tied together in parallel.

Am I on the right track and making sense? Or did I go wrong somewhere??

So.. my concerns are (1) to make sure I'm on the right track, and then (2) when I hooked this up to automotive "12v" which can range from 10v to 14v, how do I (a) protect the circuit to keep it working, and (b) provide enough constant power?

I once had a retail purchased YELLOW LED lighthead, which contained (roughly) 44 yellow LEDs (4x11), and you could wire it to a 9v battery and it would power that lighthead for days. literally.

Also, I know these are typically less powerful LEDs, and most public safety applications use newer, 3rd generation LEDs.. but for now I just wanted to play around with some of these older LEDs.. maybe when the newer, brighter LED's come down in price, and I've made a few things successfully, I'll invest more.. but for now this is just in an experimental phase...

I eventually want to turn this into a more substantial project (and learning opportunity for me) to include using a microcontroller (don't laugh; a Basic Stamp maybe?) lol.. and to write programs to control multiple lightheads to create custom flash patterns and effects.

I guess I'm just hoping to find someone who could have a lot of patience with a newbie who is really interested in learning some basic electronics design stuff.

Any help is much appreciated. Thanks for your time.

 

[BaCaRdi]

Have to love that Mr. Ohm, V=IR, P=VI

http://ledcalc.com/

-BaC

 

[audioguru]

A few of your cheap no-name-brand LEDs might work.
A few might have the claimed 3.6V forward voltage.
With 3 in series then most won't light when the battery is only 10V and some will burn out when it is 14V unless you measure each LED and match them to their own resistor.
If You use two LEDs in series then their brightness won't change much with their different voltages and the changing battery voltage.

 

[Oznog]

The no-names are not as economical as you may think.

Typically, better expect major variations and like a 5% DOA rate. Sometimes that happens. And over the life of the array, expect early failures. Or, hell, maybe you'll get lucky and 100% will be good for 100k hours. Who knows?

The thing is, the newer LEDs are so darn powerful that one is equal to a great many small devices without the wiring and regulation problems.

 

[life-saver]

high-power alternatives

okay.. so, y'all don't recommend what I was wanting to try.

the better alternative sounds like I should consider using what?, like the 1w or 3w high power "luxeon" LEDs that come on the heat-sinks?

but with those, I'm still gonna need to wire them in with the drivers, right? the only advantage to these, is that I won't need to worry about a more stable power source, right?

from what I'm getting, I could use (depending on the driver) up to 5 of these per light, with one driver? but if I did, I would need 22v input? not too practical in a 12v environment. Anyway to get around that?? Could these be wired in parallel instead of series off one driver?

here is some example info from one driver:

* Maximum output current: 700mA
* PWM dimming function
* Maximum Load: 1-5pcs Luxeon LEDs, no less than 3 Watt each.
* For example:

Amount 1 White LED 2 White LED 3 White LED 4 White LED 5 White LED
Min Input Voltage 6v 10v 14v 18V 22V

* Preset Current: 700mA, it may vary from 690-710mA.
* Current Ripple: 14mA RMS, 76mA p-p.
* Maximum Input Voltage: 25V DC.
* Suggested Input Voltage: 6-24V DC.
* Efficiency: 78% @ 14V input, 3*3W Luxeon LEDs in serial connection.

 

[Hero999]

https://www.electro-tech-online.com/threads/led-switching-regulator.41375/

 

[Oznog]

Right you need a switching reg and a voltage higher than the total forward voltage of the LEDs plus a bit of overhead (1v-2v), unless you go for a boost driver. Realistically, 3 LEDs in series. The advantage is one of those devices is equal to say 30 or 50 of the 5mm T1-3/4 LEDs, and should be completely reliable when driven and heatsinked properly.

Devices cannot be paralleled without one series resistor per string (with 2 devices in parallel, each is a string and each needs a resistor). With a constant-current driver, this is dangerous in that we doubled the current above what one single device should have and a broken connection will result in all that current going through the other device. But it is still done however.

 

[Ubergeek63]

your best bet as far as quick and easy for the most light is high power LEDs, two in series per buck puck.

If you are looking to do more yourself I can help you with that as well... my recommendation would be an HV9910 circuit.