10/11/2014 – Bulb wars are over

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.


2 responses to “10/11/2014 – Bulb wars are over

  1. As far as the bulbs not looking bright at 6.3vac, do you think it could have anything to do with the original machines running the lamp matrix at 18vdc but each full “on” bulb only getting 1/8th duty cycle? I have no idea if that would matter… Just wondering?

    • Fine question and I can’t really give a definitive answer. I would need a light meter to measure the output of the bulb at the different voltages. I did end up going back and testing the voltage/current relationship for incandescent bulbs. It is linear from 4V to 12V and probably a little higher, but I was too lazy and the 12V supply was sitting on the table. Because of physics, I assume that it won’t be linear to really high voltages, but I’m not sure where that voltage point is. I have read that you get significantly higher light output with higher voltages, but at a much reduced life of the bulb. Only way to be certain would be to get a light meter on it.

      The human eye integrates light very efficiently. I used to have to go to neuroscience shows, and I’d set up the light source to blink red/green and blue light really rapidly to form white light. If you take your hand and wave it quickly back and forth in front of the light, you can see the component colors. It entertained the kids that were stuck walking the show with their PhD parents.

      Sorry I can’t give any more definitive answer.

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