Author Topic: How are NPF fluorescent ballasts designed to accept a wide range of arc voltages  (Read 853 times)
WorldwideHIDCollectorUSA
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How are NPF fluorescent ballasts designed to accept a wide range of arc voltages « on: March 19, 2021, 03:30:42 AM » Author: WorldwideHIDCollectorUSA
Often times, whenever I look at posts involving running F34T12 fluorescent tubes on F40T12 ballasts, I often read that NPF ballasts without power factor correction capacitors are able to run fluorescent tubes with a wider range of arc voltages than HPF fluorescent ballasts with power factor correction capacitors. I wonder how NPF fluorescent ballasts are less prone to overheating with lower arc voltage tubes compared to HPF fluorescent ballasts that are more likely to overheat with lower arc voltage tubes?

For example, I often read that an HPF F40T12 ballast will overheat when it uses an F34T12 tube while an NPF F40T12 ballast is less likely to overheat with an F34T12 tube in it.
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Re: How are NPF fluorescent ballasts designed to accept a wide range of arc voltages « Reply #1 on: March 19, 2021, 04:04:16 AM » Author: dor123
Read here: https://www.lighting-gallery.net/index.php?topic=10920.0

And again: Power factor don't affects lamp performance. It is the ballast factor that affects it.
« Last Edit: March 19, 2021, 04:58:27 AM by dor123 » Logged

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Re: How are NPF fluorescent ballasts designed to accept a wide range of arc voltages « Reply #2 on: March 19, 2021, 05:16:26 AM » Author: Medved
The typical HPF difference from a typical NPF is not ay PF correction capacitor (usually there aren't any), but the ballast topology (that itself has no direct influence on the robustness) and dimmensioning.
The real difference related to the problem are not that much HPF vs NPF, but differences related to commercial vs home use. At the end it all boils down to the cost.
For commercial use you need a lot of light over a large area, so have high amount of fixtures, consuming high power in total. So the aim is to make the fixtures as bright and as efficient as possible (without sacrificing the life) so you wont pay for more fixtures and more power than necessary. That means the commercial grade fixtures are mainly operating the lamps at full power, so getting maximum light from each lamp, so what the lamp designs are optimized for. Plus you want the wiring to be ac cheap as possible, so you want each fixture to draw as little current as possible, so you are willing to pay some premium for ballasts yet still save $$$ bottom line. Therefore the commercial ballasts are designed as high power factor, even when that means extra complexity so cost. Plus these will be operated almost nonstop, so will gain a lot of hours "on their belt", so accumulate a lot of wear.

In contrast home installations typically need way less light from that single fixture than is the typical F40 output, the intention is to utilize the diffused light nature. So the same lamp are operated at reduced power (around 20..25W). Plus the purchase cost is a big factor there, which mandates the use of the cheapest (because most common and already mass manufactured) bulbs, but because are operated just few hours a day, the lower efficacy is not that problem. Hence using underpowered F40 instead of developing special lamp for that use (there won't by by far not that great demand for such laps, compare to the F40, so the lamp cost would be way greater). And with home installation we are talking about few fixtures, most likely even each on its own circuit, where current draw is of no issue at all, so a simpler, cheaper LPF ballast format. Because used just for few hours a day, these have way shorter runtime "on their belt" than their commercial counterparts, so even when of the same age, less wear.

So the typical LPF vs typical HPF difference is not the power factor, but mainly the power they are feeding the lamps, related to which are the losses so operating temperature margins. Plus when speaking about used ballasts, the commercial ones (so HPF) are way likely be way more worn out than the home use (LPF) ones of the same age.

Now the reduced arc voltage lamps pose greater stress on both ballast types, just because lowering the load voltage causes higher currents. This effect may be worse on ballasts optimized for lower losses, which are more likely the commercial, so HPF ones.
So if you add higher hours so being closer to EOL, less thermal margin, higher influence of the lower arc voltage all adding up with the commercial grade (so HPF) ballast. Plus the fact the HPF needs capacitors in order to work while LPF does not need any and the capacitors being known to be the most temperature sensitive components, adding the difference even more.
 Not much wonder the extra stress of the lower arc voltage lamp becomes the last straw killing industrial (so HPF) ballasts at higher rate...
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