Author Topic: 25W "shoplight" lamps - OK for F40/F34 RS?  (Read 6048 times)
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25W "shoplight" lamps - OK for F40/F34 RS? « on: August 29, 2013, 02:10:38 PM » Author: nicksfans
I've been meaning to ask this for a while, but what happens if a 4-foot 25-watt T12 "shoplight" fluorescent lamp is operated on a rapid start ballast for F40 and F34 lamps? I assume it will result in ballast damage on a full-power preheat ballast, but what about the .73A/.78A "energy saver" RS variety? I think I've tried this before and it seemed to work, but will it cause problems in long-term operation? As far as I know, the only magnetic ballasts that will run these lamps safely are the junky normal power factor shoplight ballasts (which I never really understood the purpose of).
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #1 on: August 29, 2013, 02:36:34 PM » Author: Powell
It will be OK, but with full brightness and reduced life.
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #2 on: August 29, 2013, 02:48:09 PM » Author: DetroitTwoStroke
From what I understand, the 25W Shoplite lamps have the same gas fill as a 40W lamp, but the electrodes are designed to run at 25W. So they should operate safely on a full power ballast with reduced lamp life (as little as 6,000 hours).
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #3 on: August 29, 2013, 03:30:00 PM » Author: Medved
The electrodes would both overheat (due to the filament wire carrying larger current, so nearly 4x the Joule losses), as well as the emission layer overloaded (higher current for the emission).
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #4 on: August 29, 2013, 05:17:56 PM » Author: Powell
Actually have had one here at WKDK at one time and it lasted a long time in HPF RS operation. 
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #5 on: August 29, 2013, 10:06:28 PM » Author: nicksfans
Good to know. Thank you. The reason I ask is because I have four of these lamps and wasn't really sure what to do with them. Since they're almost the same as F40s, will they work fine on preheat then? I'm especially curious about compatibility with lead-lag "tulamp" ballasts, since they usually don't like low-wattage lamps. Even if they can't run on preheat, I'm glad to hear I can still run them on a HPF RS ballast. While we're on the low-wattage-lamp topic, I might as well ask what exactly gives 34w lamps different electrical characteristics. Something to do with the gas fill? And if they burn up full-power ballasts because they pull too much current, how exactly do they save energy? Wouldn't they pull more power through ANY ballast?

On another note, I bought some cheap 2-lamp F40 strip lights some time ago (I needed shoplights that were more reliable than the LOA junk I had and I hadn't found my preheaters yet) that came with Keystone T12 electronic ballasts. I've since installed HPF RS ballasts in these fixtures, but the original ballasts were clearly not instant-start (2 wires per socket) though they came on almost instantly and the lamps ran in parallel, and were rated not only for F40s and F34s, but also for the aforementioned 25W lamps AND F32T8s! Here's the kicker: the 25W lamps ran very bright on these ballasts, almost as bright as F40s on HPF RS. I didn't use these ballasts for very long, so I can't speak to the longevity of the 25W lamps, but they seemed to be overdriven. Not bad performance for a "residential" ballast with a power factor somewhere in the 0.70s, if I recall correctly. Unfortunately, these ballasts weren't at all more efficient than HPF RS ballasts, which made them pretty pointless. In fact, they consumed a full 1.0 A when running F32T8s :o They also seemed cheaply made, but I thought they were good performers. I just like rapid start better ;D

For those curious, the Keystone ballasts were close to these: http://keystoneballast.com/kteb-240-1-tp although they didn't have exactly the same specs.
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #6 on: August 30, 2013, 01:50:43 AM » Author: Medved
The 25W is of the same arc voltage as the F40, so on the same ballast it would run at the same power, with the same brightness.
These lamps are intended into home grade fixtures with RS ballast, whose run the (even the F40) lamps at about 25W only. On these ballasts the F40 filament is overrated and so consume quite a lot of power for the auxiliary heating. The "25W" were optimized in this way - the filament was made thinner, so it's power consumption correspond to the 25W real power of these low ballast factor ballasts.

Power factor is a value completely unrelated to whether the ballast run the lamp at full, or reduced power.
It was only a coincidence with the F40T12 RS ballasts (although it became more a standard driven only by cost optimization for the home units vs HPF requirements for the industrial ones), than the home 25W ballasts were of normal power factor and the full power units were of the high power factor, there is no functional reason.
So it is no wonder some other ballast concept is full power, but still normal power factor.

The connection you describe correspond to the classic arrangement of a HF ballast (by the way used in virtually all electronic CFL's): Upon power ON, the circuit is in resonance, heat up the electrodes by huge current (usually about 2..4x the final arc current) and at the same time apply high voltage across the lamp (about 1kV). Once the electrode heat up, the arc voltage drop and that cause the Q of the output circuit to drop, so the heating current reduces to a negligible value (typically about 1/3 of the arc current).
So in fact it operate the lamp in the same mode as the Rapid start (so technically it would belong to the Rapid start), although all the heating up happen almost instantly (so from the user perspective it would be an instant start).

The "single wire per socket" IS ballasts heat up the electrodes only indirectly via the cathode loss of the glow discharge mode. The principal circuit difference on these is, the two wires going to the lamp socket in your ballast are in the IS ballast connected together inside of the ballast box and then form only one lead. But this is quite a simplification: The internal connection mean the resonant circuit stay complete even when there is no lamp, what require some extra features in the circuit to prevent overstress in such case. With your ballast, the missing lamp mean there is no resonant circuit, so no high currents, nor high voltages, so no stress. And if the lamp wear out, the huge current flow there for longer time for each start, till it blow the lamp filament and by that effectively shut down the section.
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #7 on: September 10, 2013, 11:28:21 PM » Author: arcblue
I have seen 25w lamps work quite well for years on near-full-power HPF ballasts.

At my home, I settled on using 40w lamps on all the HPF 2-lamp ballasts, F34's on 30/40w single lamp ballasts (they seem to work better on those than on 2-lamp ballasts) & the rare 34w-optimized LPF 2-lamp ballasts, and F25 on the cheap shoplight choke-cap-ignitor ballasts. With T8's & T5's, I only use the full-wattage lamps, never the krypton energy-savers.

The 25w lamps are also good for old/weak rapid-start or preheat ballasts that have trouble starting F40's.
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #8 on: September 14, 2013, 06:32:09 PM » Author: Powergroove
The 25w utility shoplite in an epact exemption for residential LPF ballast. No different than a 12,000 hour F40. I logged 37,000 hours on a pair of these with a HPF ballast. This labeling is because a LPF ballast will run a labeled F40 @ 25w. The label also says "NOT FOR COMMERCIAL USE" because on a HPF commercial ballast it is a F40/CW which was banned.
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #9 on: September 14, 2013, 08:41:58 PM » Author: nicksfans
12,000 hours is pretty good. Nice to know that these things are basically undercover F40CWs.
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #10 on: September 16, 2013, 02:31:33 PM » Author: Powell
BUT I read from the manufacturer if you ran a 25 watt "40" on a HPF ballast, then the 12,000 hour rated bulb was derated to 6000 hours, but if you run the lamp a LONG time between starts the life is extended.

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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #11 on: September 16, 2013, 03:56:07 PM » Author: Medved
I would guess the 25W lamp life will be shorter than the 40W one on the 40W ballast. With some regime it may be still longer than the original rating, but under this regime the 40W lamp will last even longer.
There are really two ways, where the 25W 4footers may come from: As relabeled F40T12 (these will last long on 40W ballast) and as optimized for the 25W (thinner filaments, lower operating temperature,...). The later will have shorter life on the full power ballast (the reduction by factor of two is reasonable estimate) and I would even guess many will have lower efficacy due to too hot operation.
Ideal for them would be the HPF 25W ballast, but I don't know, if something like that was ever made...

What you may do is to get 3.5/3.5V transformer and a capacitor, so to make something like this adaptor.
It will make sure the lamp is not overpowered, while the filament will get what it need...
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #12 on: October 20, 2013, 04:45:22 PM » Author: buddyboi1979
I've been meaning to ask this for a while, but what happens if a 4-foot 25-watt T12 "shoplight" fluorescent lamp is operated on a rapid start ballast for F40 and F34 lamps? I assume it will result in ballast damage on a full-power preheat ballast, but what about the .73A/.78A "energy saver" RS variety? I think I've tried this before and it seemed to work, but will it cause problems in long-term operation? As far as I know, the only magnetic ballasts that will run these lamps safely are the junky normal power factor shoplight ballasts (which I never really understood the purpose of).
Ive been using GE and Sylvania 25 watt 48"ers with HPF ballasts for years now . Same light output as 40 watt , lasts the same as the old 40 watt 12,000 hour shoplight bulbs.
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #13 on: November 17, 2013, 10:55:26 AM » Author: toomanybulbs
i guess i could go get one at our small town hardware store.
and then measure the resistance of the cathode.i have several old f40 tubes to compare to.
its likely the same as selling full mercury full wattage tubes with the note for cold weather only.
knowing that prompted me to buy several cases at home depot on clearance.tired of this efficiency at all costs performance be dammed tactic!
i am all for better efficiency but not at the cost of performance and durability!
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Re: 25W "shoplight" lamps - OK for F40/F34 RS? « Reply #14 on: November 18, 2013, 12:30:26 PM » Author: Powell
Running a 25 watt shoplite on a full powered 40 watt ballast will drive the lamp at 40 watts. It won't hurt the ballast, but lamp life will be a lot shorter.
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