Power LED Backpack Lighting System

by mackstann

28K8215

Intro: Power LED Backpack Lighting System

There have been many LED instructables, so I will mainly focus on what's different about mine and leave you to fill in the details by reading elsewhere. I won't go into calculating resistor values, series vs. parallel, or things like that. Partially because I did this a while ago and don't remember some of the stuff.

First, the rationale: I don't want lights on my bike because they're theft magnets, are more fragile, and more cumbersome. I want a single battery pack that powers a tail light and one or two headlights, and I want to turn it all on or off with one switch. The backpack is the best way to go for me, since I also like to carry my lock in the backpack anyway and always have it with me.

I used two Luxeon Rebel Stars (145 lumens @ 700mA) for the headlights, and two Luxeon III red-orange side emitters for the tail light. I made a little 555 timer circuit (google it) and encased it in epoxy, and rigged up a switch so that the tail light is always blinking, but the headlights can blink or be solid. Due to my electronics half-assery, the headlights actually blink very slightly when "solid." You can't really tell when riding, though.

I went the resistor route instead of using a buckpuck, which I somewhat regret. A buckpuck is especially cool because you can later upgrade to a Li-ion battery pack (much more convenient to charge, and lighter) and it'll still work the same even though the input voltage is different. And it wastes less juice and thus produces less waste heat.

The switches I used are waterproof E-Switch 100AWSP1's, mouser part # 612-100A-A1422 / manuf. part # 100AWSP1T1B4M2RE.

A good place to go for 555 circuit:
https://www.instructables.com/id/EP8RPXKLVPEXCFLXNH/

STEP 1: Wiring

I thought it would be really cool to make all of the wiring really modular so that I could add/remove the blinky circuit or switches or lights or whatever down the line... but the sheer number of connectors needed ended up being ridiculous and I wouldn't do it that way again. It would be much cleaner and more robust to put the blinky circuit and the circuit to connect the battery/switches/blink all together in one little box, and then just plug the battery and lights and switches into the box.

I also used fairly heavy gauge speaker wire which made it a little more clunky than necessary.

STEP 2: Tail Light

I used the lens from a cheapo Bell light and a bunch of heatsinks JB Welded together as the backing. JB Weld conducts heat well but not electricity, so it is perfect for attaching the LEDs and resistors to the heatsinks. I "vented" the light by having some empty wire insulation go through the JB Weld seal as a snorkel of sorts. This way it is rainproof (the ends of the "snorkels" face down) but not airtight. I was worried about air pressure and/or condensation caused by the heat from the LEDs. This may have been an overly paranoid precaution.

Even though the color of the LEDs is called red-orange, it's pretty much red. It's the same color as a car tail light. Red-orange is more visible than "real" red. The two Luxeon IIIs make for quite a bright tail light, although the headlights get all the compliments. On to those...

STEP 3: Headlights

The headlights are Luxeon Rebel Stars from http://luxeonstar.com . They say that no lenses are currently designed to work with them, and I have no idea whether you could get some to work well enough. Having these on my backpack straps, the lenses would be really bulky anyway, and I don't have a particular need to see far ahead. If I'm riding under city lights at night then I just care about being seen, and I'm satisfied with how far ahead I can see with them in dark areas. It's pretty much a 180 degree blast of light, though. In the city, the street lights all around in front of me are always blinking along with my lights. They blow away every other bike headlight I've been around, and people are always amazed by them. Sometimes I wonder if they're actually too bright and unfocused, but I've gotten no negative reactions of any kind, except when I accidentally turn them on right in front of someone.

The Rebel Stars I used put out 145 lumens @ 700mA. You can get ones up to 180 lumens @ 700 mA. Compare this to a Luxeon III which is 80 lumens @ 1000mA, or Luxeon K2s putting out 75 Lumens @ 700mA or 130 Lumens @ 1500mA. And you can actually run the Rebels at 1000mA, which could get you up to maybe 200 lumens. As I said in the intro, I don't remember exactly what kind of juice I wired them up for, but I believe it was in the neighborhood of 500mA each.

The headlight on the right was the first, and crappier, iteration. I tried using epoxy and that didn't work so well. The left is how I would do it if I were to make another set of these. They're pretty much completely exposed, but they seem to be ok with that. The actual Rebel LED part has this little clear rubber bubble thing, which is pretty fragile and soon was ripped off of each one. But it didn't noticeably change the optics. JB Weld holds them on and seals off the contacts. For each light, I pressed the spiky sides of two heatsinks into each other, which then gave me these slots that I could run zip ties through to attach them to the backpack straps with.

And that's pretty much it!

15 Comments

selvam12345 10 years ago

Hi, I am building a battery powered LED torch with 4X1.2V 1200mA batteries, and 3X3W LEDs I am trying hard to find a driver which could do the job of connecting them together

the LEDs I have are,
LED, HIGH POWER, 5000K, 70CRI, 275LM
Series: LUXEON TX
LED Colour: White
Luminous Flux @ Test: 369lm
Forward Current @ Test: 1A
Forward Current If Max: 1.2A
Forward Voltage @ Test: 2.86V.

could you please help me what should be the specifications of the driver??

H3xx 14 years ago

I'm surprised nobody's gone there yet but... BULLY BLINDERS!!! The gooneis were the first thin to come to mind...

Udon 14 years ago

I like it. Clunky is good. I'm planning on building a backpack power/lights/charger/... thing, but I haven't thought of where everything would actually go. This instructable helps.

lavert31 15 years ago

Hello, It's look neat and full light. about the star, did you use current regulator or just connect each star directly to the batteries? Etay

insanityideas 16 years ago

Thanks for drawing attention to how simplified you can make the LED bike light... many people seem to fret endlessly about keeping water out or having huge heatsinks. didn't realise JB Weld was non-conducting. I have a question... did you find that the 555 timer was ok with switching two Luxeon LED's?? Thats quite a lot of current for a 555 to be passing and switching!! Or does it tend to act as a built in current limiter?

mackstann 16 years ago

I linked the timer up with a transistor that could handle some huge amount like 60w. I don't remember where I saw how to do this but it's pretty simple. Basically, the high current goes through the transistor and the timer circuit just switches it on and off. You might also be able to use a relay for the same thing.

mackstann 15 years ago

Yeah definitely. It's as bright or brighter than any other blinky I've seen. I haven't really done many side by side comparisons though.

insanityideas 16 years ago

Yes I was planning to use a suitable transistor, was just checking to see if you had successfully bodged it without. I intend to use a decade counter IC (basically has 10 output pins and advances an "on" signal through each of them in turn in response to a timer pulse) to generate a custom flash pattern rather than just a regular on and off. Was thinking something like flash, flash, long pause, flash. Want to use a high speed time signal so its more of a strobe than a flasher, which would prevent the use of a relay.

John Culbertson 15 years ago

Sounds like you are using a 4017 decade counter. They are really simple to use, just google 4017 tutorials and you will find plenty of info. Good luck

insanityideas 15 years ago

I was going to use a 4017 decade counter, but in the end used two 555 timers to create the effect I wanted. The first timer has a long on-off cycle which turns on the second timer which has a very quick on-off cycle. The output of the second 555 timer switches a MOSFET to turn on and off the LED's (as they exceed 200ma power draw). In retrospect this was much easier than messing around generating a time signal for the 4017 and then deciding on a pattern of on-off's, because I didn't require a specific flash pattern and the 555 timers allowed me to vary the duration of the "on" and "off" phase of the flash more precisely (using 4 variable resistors). The 4017 would be more suitable for people who want a particular 10 step flash pattern and less control over length of flash pulse (as this is always tied to the clock pulse). A 555 timer can be used to generate a timer input for the 4017. And your right the 4017 is easy to use... does exactly what it says it does!

bullet_proof 15 years ago

Does anyone have any more detail on how to do this? I've got a spare white luxeon and want to turn it into a forward-facing blinking light running at, say 500ma - but all the 555 chips I've found max out at 200ma. I've looked around but as I'm clueless with circuit design, I might have missed the configuration mackstann pointed out.

insanityideas 15 years ago

I recently did this with a 555 timer, have not got round to doing a proper write up, but I can give you the quick answer. You need to connect a mosfet to the output of the 555 timer, and then use the mosfet to switch the LED on and off. The mosfet must be rated at a high enough current for your use (most are). Connect the source pin on the mosfet to the negative pin on the LED, the Drain pin on the mosfet to the negative rail for the circuit, and the gate pin of the mosfet to a 100K Ohm resistor which is connected to pin 3 on the 555 timer. You could also do this with a regular transistor, assuming you can find one that will switch 500ma or above. You don't need a heatsink on the mosfet, but you will need a way of limiting current through the LED, any of the circuits for controlling Luxon LED's will work.