I have some troffers in my basement that I got off Craigslist; I'm very
happy with them (they look much better than the previous shop lights
screwed to the joists with lighting panels in the drop ceiling below
them...) however one had a loud ballast in it. I pulled it apart today
to replace the loud ballast and found that the other ballast was very
hot - hot enough that you can only comfortably rest your hand on it for
10 seconds or so. (I have it wired so each ballast is controlled by an
individual switch, so you can have bright lighting for fine work or
normal lighting for simply being downstairs.)
Am I correct in ASSuming that this is not normal, and that I should
procure yet another ballast? These are typical troffers like you'd find
in an office with four 40W tubes and two ballasts. The tubes connected
to the hot ballast light up fine and I have not noticed any unusual
operation, but it simply seems too warm.
replace "roosters" with "cox" to reply.
well I guess this must be normal, the replacement ballast (scavenged
from another similar fixture) is just as hot after being on for a couple
hours. I guess I never ran them exposed before or paid any attention.
Or do I have another bad one?
I don't have any other fluorescent fixtures to install laying around
although I do have tons waiting to be installed...
replace "roosters" with "cox" to reply.
The older magnetic type ballasts usually get too hot to handle. They should
have thermal protection in them as indicated on the label in case they get
hotter than they are suppose to. The new electronic ballasts don't get as
The more-old-fashioned ballasts are either inductors or "high leakage
reactance autotransformers", and the latter often have lamp-series
capacitors. Inductance (or a proper combination of inductance and
capacitance) limits/controls the amount of current flowing through the
The more-modern "electronic ballasts", at least the ones for non-compact
fluorescents, appear to me to work by:
1. Rectifying AC to DC
2. Using an "inverter circuit" to convert the DC to a much higher
frequency AC (hundreds of times higher)
3. Using inductors or capacitors or both to limit/control current.
At the much higher frequency, inductors and transformers work well from
ferrite instead of "transformer steel" (to achieve lower core losses), the
cores are smaller (helps greatly against core losses), and windings get to
use much shorter lengths of wire (greatly reduces winding resistance
Furthermore, fluorescent lamps operated at power line frequency AC often
have a minor loss mechanism known as "oscillatory anode fall", which is
eliminated by use of AC of a frequency higher than the anode fall
One more thing - narrower 2 and 4 foot fluorescent lamps (typically
powered by electronic ballasts) use premium phosphors whose cost gets more
prohibitive in the wider older sizes.
- Don Klipstein ( firstname.lastname@example.org)
The old, non-electric ones:
1: what's their purpose?
(I suppose one task is to, via a transformer, boost the voltage up enough
an arc through several feet of some ("noble"?) gas -- via what,
turning it into a plasma or the like?)
(And a second would be to try to reduce the AC-flicker somehow?
How would it do that?)
2: Might an aid to thinking might be to understand why they chose
the name "ballast"?
No transformer (primary & secondary coils?) needed?
Phosphors. Hmmm. Maybe *that's* how they reduce the flicker, by how long
it takes them to "slowly" decay, hopefully longer than 1/60th of a second?
Thanks for the interesting explanations!
Largely true. Sometimes a requirement is to provide sufficient voltage
exceeding the line voltage to achieve this, whether continuously or for
A more major requirement is to control/limit/regulate current draw by
the "plasma arc". Fluorescent tubes of the usual hot cathode kind
actually have an "electric arc" within them.
The arc is of large size because the gas pressure within a usual
fluorescent tube is typically less than 1 percent of atmospheric pressure.
This is done because a low pressury mercury vapor arc is only efficient at
producing the UV that makes the phosphor coating glow when at low
intensity and "distended" by such low pressure.
However, this is still an electric arc. An electric arc generally
requires means to control/limit the current (amps).
As an oversimplification in fluorescent lamps (more outright true in
some other cases), an increase in current causes the arc to get hotter and
disproportionately more conductive. This means that unless current (amps)
is controlled/limited, the arc will most of the way approximate a short
circuit, drawing even hundreds of amps, and there is typically quickly a
race to whether the bulb blows or the breaker trips.
That is done by electronic ballasts. Generally, those have a rectifier
and filter capacitor ("smothing capacitor") to convert the power line
frequency AC to fairly steady DC, plus means to change the DC to AC of a
much higher frequency (generally between 20 and 100 KHz), and means to
achieve voltages necessary to strike the arc, and means to limit/control
the amount of current flowing through the arc once it is established.
I somewhat remember the term "ballast" being chosen here to mean a
"stabilizing device". Sometimes ships had "ballast" (in that case, "dead
weight") added to them to lower their centers of gravity to make them less
prone to capsizing or to make them float in a more level manner when the
water is less-smooth.
Often they do use transformers. However, the much higher AC frequency
allows much smaller transformers that have windings of much shorter wire
length and smaller cores. This reduces transformer losses.
Mainly, fluorescents with electronic ballasts have less flicker because
the electronic ballasts nearly enough always have those filter capacitors
after their rectifiers to keep the ballasts putting power through the
lamps fairly steadily throughout the AC cycle.
Magnetic ballasts do get hot and they do buzz. Scrap them. Go to a
electrical supply place (not Home Cheapo) and get some electronic ballasts.
No buzz, slightly brighter because they run much cooler, therefore are more
efficient. They also start up almost instantly.
And, electronic ballasts have a much higher operating frequency, so there is
For me, the reason I went to electronic was mostly due to the buzzing. The
50-year-old ballasts, well, it was time.
Junk electronic ballasts such as those found at big box stores do buzz. I
took them back, went to the electrical supply place and got some that have
absolutely no buzz, for about the same price.
I fully agree -- cooler, more reliable operation, no flicker, no
annoying hum and about a 40 per gain in operating efficiency (i.e.,
100+ lumens per watt versus typically 70 to 75). I use Osram
Sylvania's Quicktronic ballasts almost exclusively, with good results;
Philip's Advance and GE may be equally good, but I've little first
hand experience to draw upon.
One other thing to note: If you change the ballast, don't forget to
change the lamps. Look for good quality "800" series T8s -- i.e., 830
or 835 for a "warm" affect, "841" for neutral (equivalent to cool
white in their colour appearance) and "850" if you prefer something
closer to "daylight". For basement applications where temperatures
tend to be a bit cooler, I would avoid the 25 or 28-watt energy saving
versions and stick with the full 32-watts -- faster to full output and
generally more reliable starting at colder temperatures.
Philip's new Alto II lamps are a good choice, and so too Sylvania's
Octron XP or XPS and GE's SPX series. They're a *huge* step up from
the F40 and F34 cool whites from days of old and the improvement in
light quality alone would easily justify a ballast upgrade.
This is an "instant start" ballast. The usual alternative is "rapid
start", where the filaments are heated during starting and during use.
T8 lamps are generally rated to be suitable for both rapid start and
instant start. Sometimes they had different life expectancy figures for
the two different starting methods, and when there was this difference the
life expectancy is shorter with instant start. Starting causes more wear
on the filaments when the filaments are not heated by current flowing
Keep in mind that in my experience about 99% of failed fluorescent lamps
failed from depletion of emissive material on the filaments, as opposed to
breakage of the filaments or the bulb.
Most fluorescent lamp filament breakage leading to lamp failure in my
experience is caused by extremely severe power surges that cause mass
burnouts. So far in my life, I have twice seen fluorescent lamps affected
by this phenomenon, both times in the same location. I have heard of this
before and it appears to be uncommon.
- Don Klipstein ( email@example.com)
That's true of program start electronic ballasts, but for the most
part longer lamp life can be credited to the lamp itself. For
example, the Philips F32T8/TL800/XLL/ALTO is rated at 40,000 hours in
the case of instant start ballasts and 46,000 hours with respect to
program start; by comparison, with a standard F34 or F40 you would be
lucky to reach even half that.
Better yet, a good quality T8 will maintain close to 95 per cent of
its original light output at end-of-life, something that's just not
possible with older T12 technology. And of course, the CRI of an 800
series T8 generally falls in the range of 85 or 86 whereas a standard
cool white would be 62 (higher numbers are better). The upshot is
that you and everything else in the room look a whole lot better.
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