Quote:
Originally Posted by meelis11
Check out this led calculator: LED series parallel array wizard
You should check your led specs for voltages/current, typical voltage is 3.3V, and current is 10-20mA
Seems that 10K resistor is resistive enough - more resistance, dimmer the LED. So minimum 1.2K |
That calculator says my 12V forward voltage is suspiciously high, but I swear it was bought as a 12V, and it worked OK with 12V on the test bench.
I found Ohm's law somewhere in my highschool notes:
R=(Vsup-Vfor)/I
So if I take Vsup=15V (just to be safe), Vfor=12V and I=2mA (very liberal) then R=600. Gee, a 10k resistor seems like overkill, but I could still handle 15-20k, since I don't mind if the led is dim. I guess I could just use a 3.3V led, since they seem to be standard. It's the max amperage I'm concerned with (
Mein Ammeter ist kaput), I'll have to ask in the store.
Quote:
Originally Posted by NiHaoMike
If there's an inductive load, it might be causing voltage spikes. Connect a diode in inverse parallel with the LED after the resistor.
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You might be right. From what I remember, the led burned out right after I pushed the button to close my grille block - the closing mechanism is a power lock motor. I wonder if that motor could effect anything else in the car?
I'll test the voltage this afternoon, maybe I'll see if the meter registers voltage spikes when fiddling with the grille block.
EDIT: Checked and don't see any surges. The reading is 13.95V with engine on, and it drops to 13.4-13.6 when the grille block motor button is pressed (<half second). Other than that - nothing. Just after starting the engine I may get 14.05, but I guess that's normal.