Homemade LED Rearlamp

[Ian]

As promised for John and anyone else who's interested here's details of my extremely bright rearlamp. It consists of 14 superbright 5mm LED's and 1 standard flashing LED inserted into 5mm holes drilled in a cateye rack mount reflector (4 of the LEDs are behind the lens and not visible in the photos) I did try the LEDs behind the lens but light transmission through the lens was poor, hardly surprising as it is designed to reflect . The LEDs are simply wired in series, I did originally include a resistor but have since replaced it with 4 more LEDs as the flashing LED serves the same current limiting function.
The extreme brightness of this lamp is shown below. The LEDs are red, the orange appearance in the photo is a result of over exposure.

The last photo shows the connections to the LEDs. They are wired in series, the cathode (denoted by shorter lead and flat on body) being connected to the anode of the next LED and the ends of the chain to the battery, cathode (short lead / flat on body) to negative, anode to positive. Polarity is important as LEDs will be destroyed if its reversed. I connect to the battery through the charger socket, although an alternative will have to be sought with lithium batteries. My system with 14 + 1(flashing) LEDs is for 36V, 8+1 or 9+1 would be suitable for 24V.
I used these LEDs , and the flashing LED is from Maplins, stock number QY96E

 

[flecc]

Neat job Ian, very nice, and leaves the reflector still fulfilling it's legal function. Perhaps an idea for manufacturer's to pursue, neater than a separate rear light.
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[JohnInStockie]

Ian, thats a really good light. Its exactly what Im looking for for my bike too (although I am yet to figure out how to wire to the battery, still nervous). I will have to order those parts. My battery is 24V, so I guess the smaller no of leds then (8 + 1)

I think its the most important light on the bike, and the one that can get enough of the drivers attension to get them to turn the stearing wheel right a bit.

Can I ask a coupe of Q's

Where did you get the cateve reflector, is it a standard one?

Why didnt you put more of the flashing LEDs on, what was your thinking there?

Thanks

John

 

[Haku]

Looks good, digital cameras are notorious for not being able to photograph red light sources, the only way to make the LEDs red and so make it a true to life photo is to edit it with a paint package

Is that globs of glue from a glue gun over some of the LEDs on the back? it doesn't look like you've completely covered the LEDs legs so I'd be a bit worried about shorting in wet weather, especially as you're drawing power from the bike's battery.
My current lighting setup is 1 LED in the rear reflector and 3 in the front, powered from a 4-AA battery pack with a DC-DC converter putting out exactly 3v for the LEDs so no resistors required and it stays the same brightness right till the end of the batteries life.
Even though I haven't specifically made sure it's all waterproof (because it's only 4-AAs) it has survived being in some really bad weather, both riding in heavy rain and sitting out in heavy rain without any shorting or damage, I was quite suprised. When I eventually power them from the bike battery I'll be double checking that nothing can short anywhere, even going as far as putting a fuse in.

One thing I discovered with LEDs and reflectors is that yes putting them behind the reflector doesn't work too well because of the reflecting angles on the back, however if you put use some glue gun glue on the back of the reflector before pressing the LED into it then it'll make the light disperse better and be visable from all angles.

 

[Ian]

Where did you get the cateve reflector, is it a standard one?

Why didnt you put more of the flashing LEDs on, what was your thinking there?

John, the cateye reflector came as standard with the bike, but cateye is a well known make and they must be available somewhere.

The single flashing LED is in series with the rest and therefore causes all the LEDs to flash in time with it. In actual fact the flashing is slightly irregular but if anything that makes it even more noticeable.

Those LEDs are very bright indeed and I'm sure a smaller number on a 24V system would still be highly visible, even in daylight. I haven't used mine properly in the dark yet, my only concern is that it might be too bright .

 

[Ian]

Is that globs of glue from a glue gun over some of the LEDs on the back? it doesn't look like you've completely covered the LEDs legs so I'd be a bit worried about shorting in wet weather, especially as you're drawing power from the bike's battery

Don't worry Haku, all the bare wires are coated in epoxy, transparent at the moment but no doubt will turn grotty brown in time.
The idea of using glue to transmit light through the reflector is a good one and a neater alternative to drilling the lens

 

[JohnInStockie]

Sorry guys, a bit of clarity please, do you mean that instead of drilling into the red reflector, use glue on the inside and stick them to it?

Would they still be visible?

John

 

[Haku]

Yes, my current back light is a reflector with a bright LED inside, I drilled a hole in the black plastic back of the reflector, dabbed some hot glue onto the LED and pushed it in so it stuck to the back of the red plastic of the reflector.

No LEDs poking out of the reflector, still works as a reflector, the light is dispersed fairly evenly in all directions and what I think is important is that it's not shining a direct narrow beam of light so car drivers will still clearly see the light but won't be dazzled by it.

This is what my reflector/backlight will look like, the LEDs are just held in by the 5mm hole in the black plastic back with no glue, it's so bright from all angles that I might not need the hot glue to help disperse it, the digital camera picks up the bright red as white but there's no white light coming from the reflector at all:

 

[Ian]

Sorry guys, a bit of clarity please, do you mean that instead of drilling into the red reflector, use glue on the inside and stick them to it?

Would they still be visible?

John

The back of the lens is made up of lots of pyramid shapes, the angled sides of which do the reflecting. By filling the "valleys" with glue Haku has eliminated the angled sides and prevented the light being reflected back to the LED.
This does have the advantage of giving some dispersion to the light, something my lamp doesn't do, however car drivers can easily avoid being dazzled by keeping an adequate distance away

 

[prState]

After I lost my store bought rear light, I made a new one from one of those blinky lights Santas that people wear on their clothes sometimes at the holidays here.

Instead of the tiny disposable watch style batteries it came with, it runs on 2 AAA batteries, and I added a toggle switch and battery case. The led is completely bare, but I rarely ride in rain, so it's not a problem. All held together with careful applications of superglue.

 

[Haku]

Yesterday I added 4 more LEDs to my front reflector, it's the scrap one I'm testing with as I have a brand new one ready to be drilled when I've finished testing, the 4x rechargable AAs drained pretty quickly and I suspect they weren't fully charged anyway, so I hooked up the Adjustable Switching Regulator from dimensionengineering.com to the bike battery and it worked perfectly first time.

I checked with a multimeter and found they're only drawing less than 90mA from the bike's battery which is practically nothing compared to what the motor draws.

I'm planning on doubling the front LEDs to 14 or 15 and with the new reflector drilled in a proper drilling/milling machine the LEDs will all shine their beam directly forwards unlike the test reflector where I just drilled by hand so there's a bit of a beam spread, but even with the test reflector I can see along dark and dimly lit roads really well.

The pics were just taken in shade in daylight, at night they're very bright. The LEDs in the back reflector aren't glued to the back of the reflection part and they still glow well.

 

[flecc]

Nicely done Haku. Anything which can bring a wince of pain from the manufacturers of lights costing more than bikes earns my respect.
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[Haku]

The current setup is pretty much finished and in great working order but the wiring etc. looks like a real McGyver job at the moment because it's still in the development stage.

The bolt came off the front reflector fixing so I used a couple of cable ties to hold it in place (works suprisingly well), the LEDs in the front reflector are only held in by the 5mm holes and all the legs being directly soldered together at the back (which is then covered up with duckttape), the back reflector is held in by wedging it in place then sellotaping it to stop it falling out (no problems after a few days use over bumpy roads & cycletracks!) and gluegun glue holding the LEDs in place.

The power cables are going to all be re-done, for now the power from the battery is going to a DC-DC converter to cut the bike battery down to 5v which is then fed directly to the back 2.5v LEDs, and another DC-DC converter converting the 5v down to 3v for the front LEDs all wired in parallel.
Using two DC-DC converters might be considered unnecessary or overkill but it means there's no resistors in sight which makes things so much easier to wire up, and the LEDs will receive exactly the right voltage for them (can be precicely dialled up or down if need be) no matter what voltage the battery is at.
Furthermore the first DC-DC converter providing 5v is just right for also being able to charge my mp3 player or mobile phone at the same time.

The trickiest part now is getting a waterproof switch for the lights and a waterproof socket for charging external devices (though it wouldn't be used when raining). Mounting the electronics & switch to the handlebars is covered, I have a spare handlebar reflector mount I can use for holding the box of electronic bits.

Would anyone be interested in seeing the final build in step-by-step pictorial form? wondering if it's worth spending time photographing the final construction of my setup.

 

[Miles]

Would anyone be interested in seeing the final build in step-by-step pictorial form? wondering if it's worth spending time photographing the final construction of my setup.

Yes, it would be a great contribution to the new technical section.

 

[Haku]

Ok! but it's not going to be an overnight thing, weeks maybe a few months as I intend to get things done right.

Some great advantages of doing lights like this is that you don't have to worry about batteries for them, or worry about them being stolen because they don't look like normal lights so they're always there when you need them, you can switch them on easily and conveniently (I've never used any commercial bike lights with switches that are easy/convenient to operate), finally you can make the front light brighter than most off-the-shelf solutions that don't cost more than most whole bikes (as flecc mentioned).

It also give me a reason to give my bike a proper clean if it's going to be photographed

 

[flecc]

It also give me a reason to give my bike a proper clean if it's going to be photographed

There's cleaning and there's cleaning.

One way is the hard way with soap and water.

The other is in a photo editor in the comfort of your home!
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[Haku]

Oh, well, photo editing I can do (StarDwarf, DoctorK, WizardofHoth, Hostage, MarsLander, Gollum, DrunkMorph, Fozzie, Penguins) but my bike is a shade of dirt beyond editing

 

[flecc]

Nice work there Haku.

You should have released the "Hostage" one to the BBC though, they have ignored the Queen's bad mood faking with that in their hands to use.
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[Ian]

Love the Mars lander Haku, NASA could have saved a fortune by going to Toys R Us.

 

[Haku]

Thanks guys the Bigtrak in the Mars lander is actually my own one, always wanted one as a kid but we weren't rich enough for such expensive toys, eBay is fun
Those are just a few of a slew of pictures I make for fun for posting on b3ta.com that I've been registered with for over 4 years and have had 23 images posted on the front page, be warned, it's not a site for the squeamish, faint hearted or easily offended.



Back to the LEDs, I've been having second thoughts about powering my lights from the bike's battery, twice now I've done exactly the same journey with exactly the same battery charge level, at the end of the journeys the battery was flatter than I expected (as far as I can tell from the 4 power level LEDs - why can't we have a decent power level meter for ebikes?) when previous times doing the same journey with lights using their own battery the bike's battery level I felt was higher at the end of the journey.

I'm not sure if this is some sort of placebo type effect where I think the battery may be lower due to the drain from the LEDs or wether they actually are draining more than I thought.
I don't know how I'd do reproducable tests with lights drawing power from the main battery and not drawing power from the main battery, because each ride is different in how much pedal power you add into the mix, and trying to judge the true power left with a 4 LED display is difficult at best.

As for mA consumption of the LEDs I've heard a cheap multimeter isn't very good at measuring amp usage which I can quite believe, but I know someone who has a bench power supply that will more accurately tell you the amps being drawn so I'll be doing tests with that outputting 26v to 29v next week.