So in the last post, I had thought that I messed up the silkscreen on the incandescent driver boards. Turns out that I had accidentally hooked the voltages to the test fixture incorrectly. The silkscreen on the card is correct. The incandescent driver board contains two spade terminals for VBulb (voltage for the bulb). There are two terminals so the bulb voltage can be daisy chained between the cards. Since I hooked the voltage up incorrectly, the LED test fixture was backwards and I also had to fix that.
So the light output from incandescent bulbs was anemic at 5V. I thought this was due to the fact that I was running them at 5VDC vs 6.3VAC. Of course I couldn’t do any side by side comparisons, so it was mostly me remembering how bright the bulbs should look.
This weekend, I built up a test fixture to do some side by side testing of both LED bulbs and incandescent bulbs. The test fixture involves a DC-DC converter with a potentiometer so I can get voltages from 2VDC to around 11.8VDC. I took one of the old bulb boards from Shaq Attaq, and hooked that up to the voltage output. Next I added a .1 ohm current sense resistor so that I could accurately measure the current.
First thing that I noticed was that the incandescent bulbs at 5V were anemic. Strangely enough, the same bulbs at 6.3V were also anemic. It seems that in my minds eye, incandescent bulbs are much brighter than they are in reality. Since the load of the bulb is reactive, the equivalent in DC is 6.3VAC/sqrt(2) = 4.54VDC. Strangely, 5vDC should be a little bit brighter than 6.3 VAC. I then applied 12V to the incandescent bulbs, and they looked nice. They probably wouldn’t last very long at that voltage.
Next I moved onto doing all the measurements. Dave was kind enough to lend me a bunch of different LED bulbs. Seems like most of them are Ablaze bulbs. Here is a link to the document: BulbMeasurements.
LEDs have a very steep current to light output curve, then it flattens and additional current is converted into heat, not light. LED bulbs have a current limiting resistor inside of them. The value of that resistor determines the location on the curve. After doing the measurements and looking at the light output, I’m certain that the LED bulbs will look good being powered at 5VDC.
Next up will be adding wiring for all the feature lights on SS2.