Homemade *bright* LED light setup

[frank9755]

Haku,

Your light set-up looks really good; I'd like to have something similar myself!

Have you connected it to your bike's battery, or have you gone for a separate battery box? If the former, how did you do it?

Regards,

Frank

[Haku]

I started off by powering the few LEDs in the front/back with a 4x AA pack (alkalines lasted much longer than rechargables - a voltage thing) connected to a DC-DC converter, then after a lot of thinking about how to tap the power from the bike's battery I hit upon a solution that wouldn't invalidate the warranty by having to dismantle anythnig, and it was really simple.

My Urban Mover battery has two counter-sunk contacts on it's base which press down on two heavy duty sprung loaded 7mm or so width pins. I made a couple of springs with a width slightly smaller than the contact pins (and soldered wire onto them), so when you twist them onto the contact pins they grip tight.
The great thing is the springs don't get in the way of the battery or the contacts, inbetween the battery base and the bike is a gap of 3mm or so which is enough to bring the wire out without it getting squashed, and it can all be removed very quickly and easily if need be. I'll add a picture of the setup to this post tomorrow.


I'm this close to acquiring all the bits to finish, just need a single 15ohm resistor for the back LEDs (wiring diagram & details in posts will be altered accordingly when fitted as this is all still a work in progress).

[Haku]

Got problems with the LEDs

One of the white LEDs has died and another is flickering, indicating it's going to die. Somewhat fed up because it means I'm going to have to rip them out and replace them, not an easy job when they're superglued in and the legs are soldered to the other LEDs.

I think problem is they're being overdriven, their specs say 3.0v to 3.4v, I've been running them at 3.15v and they get a bit warm, indicating they're getting more power than they can handle so I've set the DC-DC regulator down to 3.0v output and also setup a small experiment - running 6 LEDs on a breadboard being powered with another DC-DC converter at 3.0v for a week non-stop to see how they cope.

[allotmenteer]

Just seen these on ebay:

ADJUSTABLE TRANSFORMER - 12-28V IN TO 3-15V OUT - BMW - eBay Battery Chargers, Batteries Battery Chargers, Consumer Electronics (end time 04-Nov-07 15:51:46 GMT)

They look just the trick for powering lights from a spare 24V battery. My li-ion is about 28.4V fulled charged so it should be ok.

[Haku]

Looks ok for making a fairly foolproof setup, though slightly bulky compared to the Dimension Engineering one, a bit more expensive and not as adjustable.

When doing some eBay searches for Luxeon's I found this listing: Step up - down voltage regulator which looks like an ideal chip to power lights off *any* ebike battery because it can take up to 48v input, however extra components must be needed to make it work properly and that's a little out of my terrortory.

[allotmenteer]

I've found another source for step down regulators:

http://rswww.com/cgi-bin/bv/rswww/se...eID=uknetscape

Only 0.5A so not good for my 12V 15W halogen bulb.

Could be good for LEDs though.

[Jeremy]

This thread has given me the idea to make my own LED lights, so I've spent the last evening playing about. To ensure reliability and longevity for the white LEDs, I've used a proper constant current source. This is dead easy to build, just a single LM317L adjustable voltage regulator IC, a single 56 ohm resistor plus I added a 1N4001 diode to protect the circuit in case I accidentally swap the leads over (!).

I've wired 9 high brightness white LEDs in series (see circuit below) which works OK from 34V to about 55V. For use on lower voltages the circuit can be modified to use series/parallel strings of LEDS, as described in this application note: http://www.onsemi.com/pub/Collateral/AND8109-D.PDF

For the rear light I'm using a flashing LED in series with seven high brightness red LEDs. This needs a constant voltage drive, so I'm playing about with easy and reliable ways to do this. I may post the results back here later.

Jeremy

Edited to add the rear light circuit diagram, which works a treat and is nice and simple. The flashing LED I used is voltage driven, so doesn't need a constant current source. To allow the array to work at 48V I used a zener diode to limit the available voltage - the value of this will need to be changed for a different supply voltage or different number of series LEDs.

Once I've finished gluing all the bits together I'll try and post a picture.

[Grandad]

I have been admiring all the work that has gone into making these LED lamps, well done.
My expertise may now be out of date however I have been puzzled by the use of Voltage regulators as LEDs rely on current control for optimum use. Unless there is an internal resistor, an external one (or a current regulator), should be used to limit the current. (IMHO)

See:
Light Emitting Diodes (LEDs)
Powering Light Emitting Diodes (LEDs)

Here is the spec for one range of high output LEDs

[Jeremy]

Exactly why I opted to use constant current drive for my front light described above. The "voltage regulator" in my circuit is actually used as a constant current source in this configuration (set for 20mA, by the 1.25V reference drop across the resistor).

The rear light is slightly different, as the flashing LED has an integral IC that automatically limits the current, so this string of LEDs can be driven by any suitable voltage. The flashing LED spec gives an operating voltage of 3.5V to 14V. This is increased by the forward voltage drop of each of the series connected LEDs, in this case to about 16V to 26V. The 28V zener diode increases the operating voltage range again to about 44V to 54V, making the unit suitable for my 48V battery.

I believe that the reason the white LEDs showed signs of early failure in the original posters design was because they were not adequately current limited.

Jeremy

[john]

Now that it is dark on the way home and being inspired by this thread I thought it was time to add some more lighting to my bike.

I'd been looking at LED's for a while but my criteria were:

- I didn't want to spend a lot of money
- I didn't want it to take a lot of time to put together

Taking some of the ideas from this thread, I went home last night and started playing with an MR16 12V LED bulb I got from ULTIMASTORE - Energy Saving Lamps, LED'S, LED recently. I don't know exactly what is in these but they seem to work happily on 12V AC or DC. I measured the current at about 35mA when connected to a 12V battery and then connected it in series with 820 ohm resistor to connect it to my 36V supply. (actually I used 4 820 resistors in series/parallel - if you know what I mean - in order to handle the power )

I cut a piece of galvanized steel and drilled two holes in it. One for the mounting bolt and a larger one for the bulb. This would then be mounted in place of the front reflector. I used a reamer to make the bulb hole big enough and fixed it in with silicone. Leave overnight to dry and connect the wires to the battery. Bob's your uncle. A really bright light for about half a hour's work and a few quid.

I think it should be OK in the rain as the bulb appears to be totally encased in glass.

The bulb consumes about 0.5 w and the resistors waste about 1W. I'm not too happy about the waste but it's not going to affect my range by more than a few yards so what the heck.