GT4
Well-known member
- Joined
- 8 Nov 2008
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I too worked out an ideal solution (and the equivalent fractional solutions)
And the one I implemented was the most appropriate to the existent hardware (ie there is a certain beauty in reusing the PCB with the fewest cuts)
You should also consider any array's sensitivity to voltage drift (for me, the brake lights must work both with engine off: 11.5-12.5v and with engine running alternator: 14.5v)
If you run the max current calcs on both extremes on the non-linear LED characteristics, you realise you are better (more tolerant) running external voltage drops across linear reisistors.
Any way, long story short, if you use "normal" 2.5mm diameter resistors (in high power design), the headroom is plenty in the back of the brake light enclosure (cf the 1.5-2mm diameter of the standard wiring etc that already fits in there: just cut the supply cable and run the resistors in series) .
EDIT: just look at the supply tabs (spades) on the track side of PCB, they are circa 3mm off the board, and accept the female spade caps too (adding 1+mm), so you can see the resistors are easily lower than that.
NB: you will need to extend one side of the internal supply wiring/cabling by about 20cm (from memory) anyway, as I flipped one of the original entry/exit supply tabs to be opposite end of the PCB: my current runs from one end of the PCB to the other (via alternating batches of LEDs on the array "ladder"), unlike the original 100% parallel incandescent bulb design (which had a top and bottom/positive and negative supply "bus bars").
PS - I should perhaps have updated this thread, but still wanting more power, I tweaked the current even higher (it was technically on the conservative side of the available 8,000 mcd), so I swapped one pair of resistors for 23R (IIRC).
ie 11.5R effective @ 1.2W max on one end, and 23.5R @ 1.2W max at the other (don't forget to stagger the resistors for most efficient packing).
So a drop from 47R total, to 35R.
You may wish to start @ 47R|47R x 2 too, and see how you go, intensity wise (given current LED output characteristics may be better now any way), and drop down as you see fit.
And the one I implemented was the most appropriate to the existent hardware (ie there is a certain beauty in reusing the PCB with the fewest cuts)
You should also consider any array's sensitivity to voltage drift (for me, the brake lights must work both with engine off: 11.5-12.5v and with engine running alternator: 14.5v)
If you run the max current calcs on both extremes on the non-linear LED characteristics, you realise you are better (more tolerant) running external voltage drops across linear reisistors.
Any way, long story short, if you use "normal" 2.5mm diameter resistors (in high power design), the headroom is plenty in the back of the brake light enclosure (cf the 1.5-2mm diameter of the standard wiring etc that already fits in there: just cut the supply cable and run the resistors in series) .
EDIT: just look at the supply tabs (spades) on the track side of PCB, they are circa 3mm off the board, and accept the female spade caps too (adding 1+mm), so you can see the resistors are easily lower than that.
NB: you will need to extend one side of the internal supply wiring/cabling by about 20cm (from memory) anyway, as I flipped one of the original entry/exit supply tabs to be opposite end of the PCB: my current runs from one end of the PCB to the other (via alternating batches of LEDs on the array "ladder"), unlike the original 100% parallel incandescent bulb design (which had a top and bottom/positive and negative supply "bus bars").
PS - I should perhaps have updated this thread, but still wanting more power, I tweaked the current even higher (it was technically on the conservative side of the available 8,000 mcd), so I swapped one pair of resistors for 23R (IIRC).
ie 11.5R effective @ 1.2W max on one end, and 23.5R @ 1.2W max at the other (don't forget to stagger the resistors for most efficient packing).
So a drop from 47R total, to 35R.
You may wish to start @ 47R|47R x 2 too, and see how you go, intensity wise (given current LED output characteristics may be better now any way), and drop down as you see fit.