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).
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
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.
- Nehmo -
'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:
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?
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.
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.
On Sat, 27 Dec 2003 23:52:47 -0600, email@example.com wrote:
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.
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.
another poster gave this 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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