DrZarkov wrote:I still have a resistor-problem I think. I've testeds my 18 V transformator, it has 18 V. I've tested the LED-array, it is working. Connected to the circuit, I get a faint glowing, by far not enough. At the LEDs something between 10.4 V and 11 V arrive. Unfortunally I haven't such a good equipment like an oscilloscope to test. So now I have to start debugging in a more conventional way...
Did you get this working? Assuming (say) strings of 3 LEDs each, at about 3.5V each, that would be 10.5V (in your range). Is the 18V you measured the DC voltage after passing through your rectifier? If so, then the voltage across the resistor for a single string would be (18-10.5) = 7.5V and for a current of (say) 25mA that would be 7.5/.025 --> 300 ohms. So each string should have about a 300 ohm resistor, and if there were 48 LEDs in total that would be 400mA -- too big for the diodes, I think. Also, I wonder if your power supply can deliver 18V @400mA ?
How about cutting the LEDs down to 12, or 24, to see how it behaves?