fluorescent ballast question

Hi,
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.
thanks
nate
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Nate Nagel wrote:

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...
nate
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Dump them in the shit can and get some CFL's. That heat you feel is your electric meter spinning wildly from the inefficiency of the ballasts.

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A better idea would likely be to replace the existing ballast with electronic ones (which are what the CFL use anyway.
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Joseph Meehan wrote:

For sure, when it comes to waste/efficiency magnetic ballasts are the SUVs of fluorescent lamp control.
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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 hot.
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What *are* these electronic ballasts? How do they work -- as compared to the other ones (get hot)?
Thanks!
David
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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 lamps.
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 losses).
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 oscillation frequency.
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 ( snipped-for-privacy@misty.com)
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The old, non-electric ones:
1: what's their purpose?
(I suppose one task is to, via a transformer, boost the voltage up enough to blast 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!
David
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Don't you mean non-electronic?

Largely true. Sometimes a requirement is to provide sufficient voltage exceeding the line voltage to achieve this, whether continuously or for starting.
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.

- Don Klipstein ( snipped-for-privacy@misty.com)
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THANKS!
David
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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 no flicker.
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.
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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.
Cheers, Paul
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Paul M. Eldridge wrote: <snip>

... and bulbs last (almost) forever with electronic ballasts.
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This I've not heard before. Why do they last longer? It seems the filaments are still being subjected to the stresses of current inrush when turned on.
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Bob M. wrote:

I don't know why, but I do know I haven't had to change a bulb since I switched to electronic ballasts quite a few years ago.
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The cheap electronic T8 ballasts I've been using have one wire that goes to both filaments pins at the end of a tube, so current never flows from one pin to the other through the filament.
Nick
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wrote:

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 through them.
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 ( snipped-for-privacy@misty.com)
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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.
See: http://www.nam.lighting.philips.com/us/ecatalog/fluor/pdf/p-5794.pdf
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.
Cheers, Paul
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