If a single LED were to die creating a short it would increase the voltage to the others possibly by even 10%.
My fear is when you have a run of 10 LED's in series costing $5.00+ each and one dies with the resistance system will you end up replacing all 10 of them? Looking at the spec sheets for most LED's you find that 10 % change in Voltage will cause the Current to Change by as much as 100%. With a target of 700ma we may find the ideal voltage but if it rises by 10% on any one LED we may be finding ourselves with 1,400 ma on that LED roughly 40% over its maximium safe limit.
TropTrea: I agree that more needs to be done to protect the LEDs. Now, my thought runs a little against the grain of the "budget build" thread, since it
adds about $.60 per LED. Placing a
shunt on each star will protect the series string against voltage/current spikes caused by failed LEDs, there-by protecting the other strings, in parallel systems.
I first saw this idea in Nuclearheli's build-V.2 [page 33 of "210 Upgrade Build with LED Build"] sorry, I don't yet see how to post links within RC. The shunt is made with a PLED6S (by Littlefuse) on each star. the PLED's are surface mount but can be modified. nuke did it and so did Mike Dani. Wish the suppliers would offer it right on the star....are you listening Cutter, Rapidled,et.al.??
Kcress pointed out the fact that DIY'ers can easily replace failed LEDs, blown fuses and the like- which by the way can cascade to multiple strings in big parallel systems. but not all canopies and fixtures are that easily removed for soldering,etc. Plus a multi-string failure won't wait long and the fuses are not cheap either. Just ask someone who has had a single blown LED take out the fuses in all the parallel strings on a big driver system. With shunts, a failed led is a tiny problem that
will wait, or can be ignored. In a 48 or 72 LED system you will never notice one missing LED.
as far as the cost increase goes, look at the $$ spent on
extra LEDs (to compensate for driving below max.),
oversized expensive heatsinks, fans, temp controllers and the like, to extend the life of LEDs.
IMHO, I don't feel this shunt idea is
CRITICAL for diy builds, but it is a relatively simple way to avoid trouble in the long haul.
If these LEDs really do last 50,000 hours, then we could have years of trouble/maintainence free service from our creations. Note to Those companies charging thousands of dollars for their fixtures: YOU better be on top of this or there will be a backlash.:furious:
Kcress, I'm not dissing your opinion of PLEDs, I just want people to know the option is out there, cause it has not been talked about very often- so I will beat the drum just a little longer:deadhorse: I surely value your expertise in EE and your experience with DIY. The amount of help you provide
and the patience you display is staggering. keep up the good work.:beer: