On my analog DC layout, the headlights and reverse lights on my Athearn SD40-2 require the loco to run at very high speed in order to allow enough voltage to power them. This loco is DCC ready without the typical post mount cab/head light as found on older Athearns. I’m using (2) 1.5V grain of rice bulbs wired in parallel, attached to the [inside] posts on the respective ends of the light board. The [outer] posts connect directly to the poles on the power trucks and carry the entire votage load supplied to the loco from the tracks and will blow out these bulbs instantly if I were to connect them here.
Before attaching the wire leads from the bulbs, I measured 1.3 volts at the inner posts with the loco running at about 20 percent power (+/- 3 volts applied) up to 1.6 volts at 100 percent power (+/- 15 volts applied). Enough to power the bulbs, right? That’s what I thought too. But, when I connect the wire leads from the bulbs, voltage drops to 0 and doesn’t rise until I’ve applied at least 75 percent power and then I only get about 0.5 volt. It’s not until I’ve got it at just under full-power that the lights are as bright as they should be (1.5 volts).
What’s going on here? Why is power dropping when I connect the bulb leads? What can I do so that I can sell this thing with working lights?
I’d really appreciate the help.