Lighting up an LGB92490

N

NigelP

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I recently acquired an LGB 92490 which had already been fitted with a 55021 chip. Being part of the Toy Train range the headlights aren't installed but inspection shows that cable runs shouldn't be an issue. Question is this, what are the voltages like across the function terminals of a 55021and will I need to wire any resistors into the LED circuits I install?

TIA

Nigel
 
Default is full track voltage. Lights be dimmed by setting CV50 [values 1 to 32] - use 5 for 5v, 26 for 19v, 32 for full track voltage.

(F1 can be dimmed using CV49 values as for CV50).
 
I always think its best to stick to full voltage for function outputs and fit a suitable resistor. That way if you ever replace the decoder or reset the function output voltage CV you don't end up blowing the LED!
 
I'd say a 1500 ohm (1k5) resistor is usually a good starting point for the average LED with say 24V supply. That should give you around 15mA current, taking into account the typical LED forward voltage drop around 2V, which is well within safety limits.

I usually keep a selection of resistors to hand as they're so cheap, start at 1k8 and if that's too dim try the next one down. For bright LEDs I often end up at 1k or even less, but then again my DCC system is only 18V track voltage, and you get voltage drop in the decoder as well as the LED forward voltage drop.

Handy online LED resistor calculator is here:
http://led.linear1.org/1led.wiz
 
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