DIY LED floodlight
Hi all, I have been amazed at the different types of DIY lights on this forum and wish I had found these threads earlier when I was making mine. I have been interested in ledís and decided to build a bike light as I thought it would be a simple task, famous last words as they say. My original idea was to use MR16 LED light globes as used in home down lights. I visited local light shop, they were extremely helpful and had a dark room in their shop to test light bulbs. They showed me various 2, 3 and 5 watt MR16 type LEDís.
After some thought, I settled on something completely different, a 240 volt LED floodlight. The light gave a very nice broad spread of light. I thought this would make a good base for my new bike light. Details as follows:
The type of light bulb is normally called a PAR 38 flood light but in a LED variety. The light comprises of 130 x 5mm ledís and had a rating of 6 watts when run at 240V. It cost $40 Aus. After cutting the lens and back off the light, I found the 240V ac seemed to be rectified to approximately 340V DC, which was applied across the ledís connected in series. After a few tests, I removed the lights circuit and rewired the ledís to run 33 parallel 4 series connected leds. 4 series connected ledís was chosen so the light would run at around 12 to 13 volts.
The leds are arranged in six rings in a conical shaped reflector. The original glass lens was replaced with Perspex to save weight.
The original main body of the housing was reused. A 50mm electrical connector (Clipsal 50mm Rigid PVC Conduit Fitting Screwed Converter) was glued to the rear of the housing to form a new body. A Cateye spacer and handlebar clamp was used as the mount. The body was painted to hide the surgery scars.
Power source is 14.4V via 2500mAh AA NiMh batteries.
A buckpuck 3023 regulator (1000mA) was used. The light is configured with an on/off switch and a low/high power switch. A low battery indicator is also used. The led at the back of the light will change from green to red when the battery voltage drops below 13.8 volts. The two light levels are set via trimpots, 6 watt (0.48A @ 12.5V) and 13 watt (0.93A @ 13V) post regulator I cannot seem to get a full 1amp out of the buckpuck.
The light unit weighs 330g, the handlebar clamp 20g, and the battery pack with a soft case weighs 440g, total 790grams.
Being a floodlight the light spread was not pointy but around 30 degrees of the main centre bright light with quite a reasonable amount of secondary peripheral light. I have been toying with the idea of adding another buckpuck and running it at a higher power level. It may mean adding another pair of NiMH batteries to the power supply to boost the input voltage. I have run it on the bench off a variable power supply at this level but I am a little precious with the unit currently and concerned that I will get carried away and may end up melting the unit. Hence, those plans are currently on hold.
That’s an interesting light apostolos, thanks for posting and welcome to MTBR!
Just out of curiosity I’m wondering if the individual LED’s are mounted on any form of PCB to help dissipate the heat, or are they just held in place by the reflector? Heat isn’t usually thought of as an issue for 5mm LED’s, but when you have a huge array with over a hundred LED’s it does start to become a significant consideration, especially if you’re thinking of driving them a little harder.
With your regulation you mention that you can’t get a full amp out of your buckpuck, is this the case when it’s powered by both your battery pack and power supply? I was just thinking that it may be possible that your cells can’t cope with such a significant power draw.
Do you have any beam shots at all, perhaps a comparison with another light?
I love these posts with the DIY lights.
Way beyond my ability to create myself, be vvery interesting and cool to see you guys create.
Keep up the good work.
With a little bit more reading and asking a few questions, it might not be quite as hard as you think. Itís certainly fun playing about, if nothing else!
Originally Posted by Mr .P
Be sure to make an entry in the database (in my signature) too!
Originally Posted by apostolos
Hi Dave, the ledís are soldered into different sized donut shaped PCBís with the centre one being a disk. The PCB mounting allowed for relatively easy resoldering into the 33 parallel x 4 series configuration. The PCB/led unit then fits into the reflector with individual holes per led.
In relation to the buck puck, I remember testing it off the bench power supply and noticing the maximum of 0.93 amps. I tried to fix the problem by replaced the original potentiometer with normal resistors at around 5K but still couldnít get more current out of it. I tried turning the input voltage up and down to see if it made a difference. In the final configuration the small 0.07A doesn't make much of a noticeable difference with the light output hence its not an issue. The problem may be a measurement one and I note that instructions on the buckpuck indicated a special way to measure the current. I just use my multimeter and connect it in series with the load in all cases for current measurement.
As an aside the buckpuck is about the 4th serious circuit I have tried on the light. Sorry to get technical for a minute, but the first circuit was when I connect the ledís straight to 10x1.2v NmH batteries. Great light output to start with at 13.5 volts under load but would gradually fade. The second circuit was suppose to be a fancy switching circuit but was beyond me, as I couldnít get it to work on the bench and gave up. The third was a Ďkeep it simpleí, switching circuit (LM2576 regulator chip, up to 3A) and worked quite well at around 85% efficiency, however I needed 16.8V battery (14x1.2 NMH) to get the light to work at high power over the full life of the battery as the input power needed to be about 1.5 volts above the operating voltage for control. The above was however a voltage regulator circuit and I noticed that at the higher power setting the current would ever so slowly creep up when the light was run on the bench for long periods of time. This was not really a problem on the bike due to the air passing around it. Eventually, I grasped the concept of current control over voltage control for ledís and tried the buckpuck. The puck runs at a measured 93% efficiency in this configuration and only needs about 0.5 to 0.8 volts above the operating voltage for control on this light. Itís a very clever little controller. The voltage applied now by the puck, may slowly drop over time when running at the higher power as its keeping the current constant. The voltage will eventually stabilise. Hence I wish I found all these threads earlier as it would have save some time, money and effort but I am much the wiser for the journey.
I will do beam shots but it may take a little longer as I am preparing for a 100km ride this weekend and providing I survive I will sort something out.