Sunday, February 22, 2015

testing fluorescent fixtures - 40 watt

My first test in a series is this old florescent fixture with magnetic ballast and big T12 40 watt tubes which had been on my shop ceiling for years. It used 90 watts to give 60 footcandles illumination in my test jig at room temperature of 15C. The power factor was excellent. The ballast caused no FM interference. In spite of the leakage of potting compound, it had given an excellent 25 years of service.

Although this wasn't the first test that I did, I thought I would present it first since this is representative of old magnetic ballast and T12 fluorescent tube technology. I had four fixtures like this one on the main shop ceiling.

click any pic to enlarge

This is the condition of the test ballast, an old Canadian General Electric "Gold Label" 17A240E. It works but you can see that the potting compound has been leaking. At room temperature, the black potting material is hard. In fact, it was somewhat difficult to remove the fixture cover since the potting had effectively glued it shut.

I found a reference to this ballast which says that GE sold their ballast division to Alliance in the late 80s. On the back of my GE ballast, I found the code "9002" which might translate to Feb 1990. Elsewhere on the fixture, I found "4 90" which might mean April 1990. My readers will know my fondness for mature technology which stands the test of time. Although this fixture shows it's age, I am impressed that it seems to have given almost 25 years of good service!

The lamp holder posts in this fixture were dirty but in fair condition. There is no broken plastic and the contact fingers did not seem to be distorted or burnt. If I refurbish this fixture, I will likely clean these posts or replace them with new ones. I used them for this test.

It is worthwhile to examine these posts carefully if they are going to be reused since people who try to remove and replace tubes can easily damage these posts if they do not understand the correct way to do this.

The bulbs I used were from the fixture. They are older Sylvania 40 watt T12 Cool White tubes that show some blacking at the ends opposite the lables, shown in the bottom half of the picture.

I did three runs with this ballast at three different temperatures. This involved a run early in the morning when the shop was cold (room ambient temp about 1C). Then another later in the morning about an hour after the wood stove was lit (average temp abut 6C). Finally a third run mid afternoon when the stove had been running for several hours at an average room temperature of about 15C.

The graph shows that the light output (in footcandles) increases as the lamps run over the first ten minutes and then levels out at some steady value. As the temperature of the ambient air increases, the lamp output increases also.

I was pleasantly surprised that the lamps even lit at 1C since in my experience, some cold morning days in the shop, some of the lamps would not light up, or would not light up for some minutes.

The label on the GE claimed a power factor of 90%+. My measurements showed that the power factor was indeed greater than .90 within 5 minutes of startup. At room temperature of 15C, the power factor reached 0.97 after ten minutes. At the lowest temperature, power factor reached 0.93.

The label on the GE ballast claimed line current of 0.8A and this was certainly close except in the start up situation (less than 5 minutes operating) when it used slightly more, up to one amp.

The instantaneous power use was remarkably constant at the different tempertures and times, varying between 84 to 88 watts, as measured on the Kill A Watt meter.

My actual raw test data is available here as test10.pdf.

A troubling result of these tests was that the temperature of the old GE kept rising, up to 51.6C by the end of an hour from an ambient starting temperature of 13C. It was so hot in fact that more of the black potting compound had started to ooze out of the ballast by the end of the test and it was quite gooey in viscosity. Clearly there is something not quite right about this ballast and it will have to be scrapped. I wonder what it might be like after several hours operating in the summer, when the ambient temperature is more like 30C?!

Some older ballasts contained PCBs. I found this GE document which states that ballasts manufactured after January 1979 do not contain PCBs so this one does not. Further, it describes the potting compound as a mixture of asphalt and sand so the black ooze is no more hazardous than pavement.

One good thing about this old GE ballast is that it did not create any FM radio interference - none. This was even without having the fixture grounded which I found gave better interference results with some of the newer electronic ballasts.

In summary, this old technology magnetic ballast and T12 40 watt tubes, admittedly not new tubes, used about 90 watts to give 60 footcandles illumination in my test jig at room temperature of 15C. The power factor was excellent. The old ballast caused no FM interference. In spite of the leakage of potting compound, it had given an excellent 25 years of service. I did not attempt to measure anything about the color of the light produced.

The condition of this magnetic ballast should make us think carefully about products which claim to "retrofit" older magnetic and T12 lighting with newer versions by means of an adapter like this one. Better to assess the condition of what you have in case you discover ballasts like this one that really should be replaced?

I have a series of tests to post in the coming days comparing different fixtures as alternatives to this one. This old fixture will be the reference against which the others will be compared.

For background, this interesting article "The Fluorescent Lamp" with many pictures traces the history and workings of fluorescent lighting, from the Edison Tech Center.

Thank you for your interest.
George Plhak
Lion's Head, Ontario, Canada

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testing fluorescent fixtures - 40 watt (this article)
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