What's in a Fluorescent Ballast?? (magnetic, instant start, single pin/duplex bulbs)

I'm trying to find a schematic for a magnetic ballast that would power a bank of twin 8' F96T12 instant start bulbs.
Is the ballast simply a high voltage transformer? Are there any other components like a capacitor or inductor?
Is the secondary isolated from the primary?
The secondary has a lead for each of the two ends of the bulbs Does this mean that the secondary winding has a center tap to neutral with each end powering a seperate bulb? Or are the two bulbs simply connected in parallel?
Im trying to determine how to bench test a ballast and also understand if a ballast can be at fault if one bulb is lit and the other isn't. (yes, I've substituted known good bulbs with the same result).
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Simple answer.

No.
Yes.

No.
http://home.online.no/~oddvarde/elektro/lysror.jpg
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Isn't that a pre-heat type ballast? IS circuitry is quite a bit different...check out http://misty.com/~don ...
wrote:

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On Wed, 24 Dec 2003 19:50:18 GMT, "Amelia M. Samples"

Microsoft Outlook Express 6 behavour!
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I don't claim to know much about fluorescent lights, however I have dozens of the cheap shop lights that seem to only last a couple years in a cold damp inviornment.
One thing that I notice (i addition to their failure in cold weather) is that the pin sockets don't always make good contact with the tube pins. I don't know if it is poor construction or that the contacts corrode.. Initially you can twist the bulb a it and it will light but eventually the whold damn thing fails.. I suspect that poor contacts in the sockets cause premature failure of the ballast or other electronic components or ever the early failure of the bulb..
I finally starte replacing my 14 cheapo shop lights with the slightly more expensive electronic cold weather shop lights from HD. About $17 plus bulbs but they work flawlessly and are much better built than the older $8 ones I got from Lowes.
Steve
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- davefr -

- Nehmo -
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/lighting.html#c2
'The "slimline instant start" system produces light instantly by employing a transformer in the ballast to produce a voltage about three times the normal operating voltage to "strike the arc" in the bulb. Preheating the filaments is not required for this kind of system.'
Schematics and explanation:
http://www.advancetransformer.com/literature/pdf/FLB_Pocket_Guide.pdf
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* Nehmo Sergheyev *
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Thanks!! That second link is excellent and answers all my questions.
On Wed, 24 Dec 2003 20:31:47 GMT, "Nehmo Sergheyev"

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A ballast MUST have a current limiting element in series with the lamp. For a 60Hz ballast this current limiting element can be an inductor or resistor, but the resistor will have a substantial power loss. At high frequency, above about 3 kHz, you can also use a capacitor as the current limiting element.

Sometimes, but usually not.

No. The lamps are wired in series but a very small capacitor is placed across one of the lamps to force all the starting voltage to appear across the OTHER lamp when neither lamp is lit.

Discharge lamps, including fluorescent lamps can NEVER be operated in parallel. So-called "parallel" ballasts have a separate current limiting element for each of the "parallel" branches.

What type of ballast? If series connected instant start it is possible that the small capacitor I mentioned above is shorted. Exactly what are the symptoms? Is the lamp completely dead or just operating at lower than normal output?
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Vic Roberts
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Reverse the red and the blue wires. In other words, if the reds are on the right, and blues on left, put the reds on the left, and blues on the right. This sounds silly, but it is a very common problem, except most people dont know it, and trash a perfectly good ballast because of it. Some ballasts actually state this on their label, but most dont. The problem you describe is what happens too.
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On Sat, 27 Dec 2003 09:57:47 -0600, snipped-for-privacy@my.com wrote:

Why should it matter which side of the fixture the read and blue wires go to? In fact, in many two-lamp fixtures they go to the same side, with the yellow leads going to the other side.
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On Sat, 27 Dec 2003 18:01:51 GMT, Victor Roberts

I have never understood the reason for this myself, except that I know for fact the problem exists. I do know though, that the yellow wire has nothing to do with it. It's the relation to the neutral (white) wire, and the hot (black) one. Like I said this sounds silly, but I had to deal with this at work.
I am a maintenance man, and we got a brand new 8 foot fixture. This new fixture did not work..... One bulb would light, the other would not. I called the company and they shipped out a replacement ballast. I installed it, and had the same problem. I tried 4 pairs of NEW bulbs. I used a multimeter to be sure each wire was actually conducted to the socket ends. I double and triple checked we were using the proper bulbs, and that the wiring was correct. I checked to insure the line voltage was correct. I bought more bulbs and a different brand,,,,,,, A half day was wasted when I finally ran out of ideas. I mean, what else is there..... a ballast, 4 sockets, two bulbs, a line cord, and the metal housing.
I called the company again, and requested a complete new fixture. They had me talk to their customer service manager. He grabbed another ballast off the shelf, and started asking me where the red wires go, the blues, etc. He too was puzzled, and had another guy get on the phone. That guy asked me if the red wires were on the same side as the black, or white (which ever it is). They were NOT. I reversed them, and the light worked fine, and has ever since. The apologized, and said they would contact the manufacturer, and said the manufacturer had wired the fixture wrong.
For all my troubles, they told me to keep the extra ballast. This mistake probably cost my company at least $50.... However, I learned something I never knew before. This only affects magnetic ballasts, not the electronic type, and appears to not be a problem with the 4 footers, just the longer fixtures (and maybe others).
So, I still have no idea why this happens, but it is FOR REAL !!!
It's easy to swap the red + blue. Just pull the two sockets out of their clamps, and reverse them.
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On Sat, 27 Dec 2003 23:52:47 -0600, snipped-for-privacy@my.com wrote:
[snip]

I missed the part in the first message were you said these were 8 foot fixtures. I assume then that these were instant start lamps and ballasts. Is that correct? Does the ballast have any yellow leads? If the ballast is instant start then this does make sense. I am looking at some wiring diagrams for magnetic instant start ballasts. For these ballasts, one end of one or both of the lamps is connected to the white or black power lead. For these ballasts the ballast manufacturer shows the red lead connected to the other end of the lamp that it connected to the white power line lead.
However, for many ballasts, including all rapid start ballasts I know about, the lamps are never connected directly to the power input leads. For these ballasts, switching the read and blue leads should not make any difference in lamp operation.
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writes

In a fixture with two inductive ballast's and the usual starter arrangement, if the wires are mixed so that one tubes "A" cathode is wired through the starter to the other tubes "B" cathode, then it creates a kind of flip-flop condition where the first tube to light stops the other lighting.
If the starters were removable, then the removal of one would show a single electrode glowing on each tube during the starting attempts.
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another poster gave this pdf:
http://www.advancetransformer.com/literature/pdf/FLB_Pocket_Guide.pdf
if you scroll down to page 26, "troubleshooting", they describe the exact problem me@my reported. the text makes clear that it is a common problem with unpredictable operating results, that range from almost normal (intermittent?) operation or one bulb operation, to not working, to premature lamp and ballast failures.
some of the RCM'er have described these very symptoms, drives them crazy wondering what the hey is happening. this pdf is worth the download for anyone using flourescent shop lites. --Loren
ps. followup-to set to sci.engr.lighting
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