Resistor calculations for low voltage bulbs on DCC
Posted: Mon Apr 13, 2015 9:57 pm
I am fairly new to DCC, and am installing a Digitrax DH165AO into a Genesis SD70 (pre-DCC socket) loco. The replacement board clips in place and the loco moves. However I have successfully blown the headlamp bulbs by connecting the lamp wires to the same connector tabs on the ‘replacement’ DCC board. Digitrax tell me that I should have connected them to FOF and blue (+ common) using a resistor (obviously?).
Looking at various web sites and using ohms law the resistor value required appears to be:
13.7v – 1.5v = 12.2v @ 15mA = 813 ohms 0.25 watt resistor required in series
where
Track voltage = 13.7v (from the display on the DT402 controller)
Replacement headlamp bulbs: Miniatronics 1.5v 15mA incandescent bulbs
Maplins have 820 ohm resistors available to fit in series with each bulb. Could somebody please just confirm that I am heading in the right direction?
In case anybody is wondering, I am using bulbs and not LEDs because a) they fit in the headlamps hole b) I have lots of bulbs.
thanks,
Tony Harris
Looking at various web sites and using ohms law the resistor value required appears to be:
13.7v – 1.5v = 12.2v @ 15mA = 813 ohms 0.25 watt resistor required in series
where
Track voltage = 13.7v (from the display on the DT402 controller)
Replacement headlamp bulbs: Miniatronics 1.5v 15mA incandescent bulbs
Maplins have 820 ohm resistors available to fit in series with each bulb. Could somebody please just confirm that I am heading in the right direction?
In case anybody is wondering, I am using bulbs and not LEDs because a) they fit in the headlamps hole b) I have lots of bulbs.
thanks,
Tony Harris