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Some notes/tips Posted by Randy Thatcher [Email]  (#22)  [Profile/Gallery]
(more from Randy Thatcher) on Wed, 10 Oct 2001 16:15:49
In Reply to: Blue LED dash pic, post, Tue, 9 Oct 2001 23:15:12 Members do not see ads below this line. - Help Keep This Site Online - Signup |
After 18 hours of work Monday travelling to and from the Mercedes Plant in Alabama for meetings, I decided to work at home today (wake up at 11, put on Homer Simpson slippers, get on conference call, write a proposal, surf the net, etc). After cramming 8 hours of work into 3 hours (hahahaha) it's time to work on the Saab.
I looked at your website and have a few comments... You wish the thing would light up brighter. I say the same about my stock lights. A few things to do without having the actual I-V curves of the LED's.
1. Run 2 LED's in parallel. This puts your Imax to 60mA and keeps voltage the same. So, cut your resistance in half, and make sure the power rating on the resistors is OK.
2. Run the single LED's a bit hotter (higher current).
I used 15V for the Vmax of the car.
For a single LED you must use a resistor > 377 Ohms
For parallel LED's you must use a resistor > 188 Ohms
If you figure you want 20mA, pick the typical operating point of the car.
I've read that 12V @ Idle and about 13-14 is typical when driving.
Let's go with 13V, then.
For a single LED: (13V - 3.7V)/.02A = 465 Ohms
Power @ 30mA = Imax * Vdrop = .03A * (13V - 3.7V) = .28W For safety's sake, go with 1/2W resistor.
For parallel LED's:
(13V - 3.7V)/.04A = 232.5 Ohms
Power @ 30mA = Imax * Vdrop = .06A * (13V - 3.7V) = .56W For safety's sake, go with 3/4W or 1W resistor.
Running Hotter (as hot as possible witout going too low with resistor):
Single @ 24mA R = (13 - 3.7) / .024 = 388 Ohms
Parallel @ 48mA R = (13 - 3.7) / .048 = 194 Ohms
FYI, I grabbed a 430 Ohm 1W resistor from my audio stash and I'm going to head over to the rat shack for LED's. I hope to install this mod, check my alternator brushes, AND run some more silicone vacuum line tonight. Wish me luck!
Randy
1990 SPG
2000 9-3
posted by 66.32.4...
, Wed, 10 Oct 2001 21:27:59, Wed, 10 Oct 2001 16:15:49 <-- Viewing This Message
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