On 3 March 2011 10:17, RussellMc wrote: >> Everyone's comments so far are suggesting that the short life of my >> LEDs is caused by over-current/spikes. > > That was one of the reasons. I should have said many, rather than everyone. > But also note: > >>> The best LEDs operated correctly can have lifetime in the 50k - 100k >>> hours range to 70% output. >>> The worst manage under to well under 1000 hours. > > This is when driven properly. > > And > >> - Use LEDs from a reputable "big 5" LED maker OR one using technology >> from a maker who knows what they are doing. There are many small LED >> makers worldwide but I am unaware of any that have managed long LED >> lifetimes by themselves. I'd risk saying that ANY Asian LED maker who >> cannot show a direct technology link from "big name" LED makers does >> not make quality product. =A0There is now a substantial cross linking of >> licences. Some (not all) competent LED makers are (in no order) Cree, >> Osram, Lumiled/Luxeon. Nichia, Avago, Sharp, Seoul semi ... > > ie - you can drive them as well as you want, but if they are junk they > will still be junk. > Essentially any LED without a traceable path to the technology of the > big-few is Junk. > If fixing the current source doesn't improve the situation then I'll assume the parts are junk and follow up on some of the links Jesse provided to try to source better quality. The oznium.com one looks promising. Thanks Jesse > If you were rolling your own then a trivially easy current source can > be made with an LM317 + one resistor. > BUT The LM317 requires 1.25V output drop plus about 2.5V "headroom" for t= he IC. > Too much for 3 LEDs on 12V. > > A 4 channel current source can be made with eg an LM324, 4 x MOSFETS, > 1 x TL431, 4 x current sense resistors and a few other r's and c's. > Very cheap. > LED current flows to ground via MOSFET and =A0sense resistor. > Op amp section monitors resistor voltage wrt reference voltage and > drives MOSG\FET gate to maintain V_R_sense at same voltage as Vref. > Works well. > > =A0 =A0R > Cheap sounds good. I'll have to spend some time working out how to put all that together but that's a learning exercise for me. Thanks again. Patrick > > > A constant current supply has >> been recommended by a few people so I duly went to wikipedia the great >> source of information and mis-information to get some ideas in that >> vein. Before I ask for advice on how to implement this idea I should >> provide some more information on the set up as it is, and why I put it >> together that way. >> >> The LEDs are powered from the side-lights circuit on the bike by >> splicing the line coming in just under the headlight assembly. =A0This >> means they are only powered when the ignition is on and they can be >> switched on and off using the normal handlebar switch along with the >> other lights. >> There are 2 each of white and yellow LED strings each with 24LEDs, >> 24cm long mounted on the sides. =A0There are also 3 strings of 12 white >> LEDs mounted around the top. >> The top strings are driven directly from the light supply and the >> white and yellow side strings are driven via a pair of relays. =A0When >> the turning indicator is inactive, the white string is lit (normal). >> When the turning indicator is lit, the yellow string is lit and the >> white string is not. >> I set it up this way because I thought having lots of white lights >> facing forward and very little area of indicator visible from the >> front, it might be difficult for oncoming traffic to see when I'm >> indicating to turn. >> If anyone has a better idea than the relays for the indicators part >> I'd be glad to hear it, by the way. >> >> Providing a single constant-current source for the whole set up might >> be problematic when indicating as I expect my relay will have a breif >> moment of not powering either of its connected 24LED strings meaning >> the current source(tuned for normally driving 84 LEDs) would be shared >> between 60 instead. =A0Is this something I should be concerned by? >> =A0If so, perhaps I should have 3 separate constant-current sources. >> One for the top 36 LEDs and one each for the side sets with their >> relays. =A0The next thing I need to know is what's the correct constant >> current. =A0I plan to determine this by measuring the current drawn >> using a clean 12V supply prior to re-installation. >> >> I'll also need to build and weatherproof the new circuit(s) and >> preferably have them all together in as compact a package as possible >> along with the relays. =A0This will be tucked into the space just under >> the headlight and secured with cable-ties. This package would have 10 >> connections, 2 for the incoming supply, 2 for top LEDs and 3(x2) for >> white/yellow/ground on each side. I plan to use the standard 2 and 3 >> way connectors similar to those found all over the rest of the bike. >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .