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Author Topic: mercury vapor bulb question  (Read 12277 times)

Offline mr_big

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mercury vapor bulb question
« on: February 04, 2005, 04:01:15 pm »
Is there any way to run a mercury vapor bulb from a fluorescent ballast

Offline pSlawinski

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Re: mercury vapor bulb question
« Reply #1 on: February 04, 2005, 05:18:07 pm »
No, fluorescent lamp ballasts have an open circuit voltage lower than that of most mercury vapor lamps.  Most florescent ballasts are designed to be used with pre-warm fluorescent lamps which have special electrodes that heat up to aid in starting the lamp.

Offline mr_big

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Re: mercury vapor bulb question
« Reply #2 on: February 04, 2005, 05:38:02 pm »
thanks for the help I will see what I can do about obtaining a ballast for one

Offline Zelandeth

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Re: mercury vapor bulb question
« Reply #3 on: September 27, 2005, 04:36:29 pm »
Not strictly true.  Due to the starting electrode in many high pressure mercury vapour lamps, the striking requirements aren't too high.

It is possible to run an 80W MB lamp from a 56/65W fluorescent ballast (at least here where the line voltage is 230V anyway).  Running it for long like this isn't advisible as the ballast will get rather warm rather rapidly as I recall.  An 80W lamp running on a 70W fluorescent ballast will light and run okay, but the ballast does a really good impression of a radiant heater after a few minutes.

It's *certainly not advisible*, no.  But if you're just wanting to grab a photo of the lamp or something, it'll work for that purpose.  My suggestion is to connect it up to a wattmeter first, then you can keep track of how much power's going in and kill it if it starts to run away with you.

It's worth mentioning I guess that the ballasts for fluorescent lamps in 110-120V areas, as if I remember rightly they've got seperate windings for the heaters and such.  Whereas the ones I have here just have one wire going in, and one coming out.  I still want to know where all these F70 ballasts came from...I have no idea when I got them!  (make good door stops and paperweights though).

Offline mr_big

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Re: mercury vapor bulb question
« Reply #4 on: September 28, 2005, 02:03:04 pm »
I have tried this before and it worked finee except for a little bit of flickering but was able to get that fixed
I have run one from a fluorescent ballast before but could not get the arc to go to the other electrode
At least not that I could see

Offline Mónico González

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Re: mercury vapor bulb question
« Reply #5 on: September 29, 2005, 11:03:14 am »
Here in European countries where the voltage of 50 Hz lines are fixed up within the limits of 220 to 240 volts, depending upon the countries, both mercury and fluorescent ballasts are simple self-inductances or choke coils which are simply connected in series with the charge (in this case, the lamp itself), because the starting peak voltage at open-circuit are as high as 310-340 volts, enough to cause the ionisation, by means of the third auxiliary electrode, of the low pressurized argon within the arc tube.
Power range of mercury lamps in American countries differs a bit from European ones.
Here the smallest lamp that you can get are the 50 watts type, followed by the 80 and 125 watts lamps, instead the 100 watts minimum power mercury lamp usually found in American countries.
Fluorescent ballasts for 110-125-130 volts, also are simple choke coils for tubes up to 20 watts, but larger tubes, from 36-40 watts on, does need reactive or dispersive self-transformers to rise the output voltage up to the right ionizing values when the starter does open the heating circuit, acting also as current limiters.
Furthermore, mercury lamps as other hot-cathode discharge lamps, must not be powered at  current/voltage characteristics different from those for which they were designed, or a shortened lifespan and/or a lower efficiency than expcted could be obtained from them. Keep in mind that for most discharge lamps (unless cold-cathode types), any deviation in plus or minus from its nominal value never could be considered for long period running. Only for experimentation or short time testing purposes, a different way to power discharge lamps must be attempted (including ballasting by means of incandescent lamps).
In any case, ballasts for mercury lamp powering, are often a cheap and easy-to-find device, that can be purchased from almost any electrics store. Here in Spain, mercury ballast from 50 to 1000 watts are "each day" things, especially those for 80 and 125 watts, so, I never would consider the idea of use any other limiting device with my valuable clear mercuries.
Otherwise happens with clear mercury lamps, which (at least in Spain) must be ordered outside here, because in Europe are a strong aversion (I don't understand why!) to high colour temperature light sources, so, all mercury vapour lamps that can be found here, are fluorescent Ytrium vanadate coated ones that casts a 3800-4000? Kelvin light (slightly pinkish-white) instead the 5800-6000 (green-blueish-white) usual in clear non-corrected ones (my favourites).
Best regards.

Offline Max

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Re: mercury vapor bulb question
« Reply #6 on: September 29, 2005, 12:54:52 pm »
Hi Monico,

In the US, lamps of 40/50W are also available - the 100W rating is not the lowest. The reason for this double power rating is that these small lamps can be run on two different ballasts, with a ten watt difference in dissipated power.

From you message it is clear that you really favour clear-mercury lamps. But what do you think of the aspect of skin under their light? Don't you think that the lack of red gives a ghastly rendering of people? As far as high-color temperatures are concerned, I find that Tc>6500K metal halide lamps are far better. Interestingly, if you strongly overdrive a high-pressure sodium lamp, you can reach a light color close to that of a clear mercury source, but the peculiar thing is that red objects will appear saturated under its light.

Max

Offline mr_big

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Re: mercury vapor bulb question
« Reply #7 on: September 30, 2005, 01:17:02 pm »
I really prefer the clear ones anyway becuase you get more light and the bigger the bulb is the brighter unless it is coated

Offline James

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Re: mercury vapor bulb question
« Reply #8 on: October 03, 2005, 02:41:38 pm »
It's worth remembering that the first mass produced European fluorescent lamps were actually developed specifically to run on the ballast of a high pressure mercury lamp.  Although the concept of the fluorescent lamp originated at the labs of Osram in London, it was GE in USA who perfected the design and first came up with a mass produced version.  It was the famous F40T12 4-foot 40-watt tube, launched in 1938.

When European manufacturers came to adopt this format, the continent was on the point of plunging into war, and few resources were available for setting up production of this new lamp.  It was intolerable to consider investing resources in developing a new ballast as well as the lamp, thus the first European lamp was developed around the next best thing - the 80-watt mercury choke.  The tube length was increased to 5-feet and was rated 80 Watts.  Furthermore it was equipped with ordinary bayonet caps as used on incandescent lamps, since these components were readily available and required little development effort.  An example can be seen at http://www.lamptech.co.uk/Spec%20Sheets/Philips%20MCFE80.htm

Soon after this, the 8-foot tube was introduced, to run on the standard 125W mercury ballast.  After the war the lamps were down-rated and new ballasts were developed to run them at more appropriate loadings of 65W and 85W respectively.  The bi-pin cap was also introduced at that time. 

So yes, a fluorescent ballast can be used to run many mercury lamps, certainly in Europe.  It will of course not run the lamp at the specified current, but will do no harm and certainly light it reasonably well.

James.

Offline Mónico González

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Re: mercury vapor bulb question
« Reply #9 on: October 04, 2005, 05:39:10 am »
Hi, James!
Of course, when I said that it's a wrong method to ballast mercury lamps using regular fluorescent chokes, I was speaking about mutual lamp-ballast power mismatching. In other words, that isn't recommended to power an 80 or 125 watt mercury lamp through a tiny inductance rated for a single 56 or 65 watt FL tube, as I understood from mr_big's post, because the current through the arc tube would be insufficient for the complete mercury vaporisation, so, the voltage drop between electrodes couldn't be adequate (higher than normal), also originating an uneven underheating of electrodes with the subsequent sputtering effect.
No mention are done about the overloading of the ballast choke itself!, A good moment for taking the bread and butter? :-D
Perhaps a 50 watt lamp could work reasonably well with one of these simple 40 w devices, or so, an 80 watt one, will run OK (slightly overdriven) along an 85 watts FL reactor,  but in both cases, the purchase of one or another of these ballasts, would cost as much, or perhaps more, than an specific mercury vapour choke.
Obviously, a self-inductance coil is only that: a coil, regardless the use of it could be done.
I've heard previously some about the development in UK of 80 and 125 watts fluorescent tubes at those days previous to WWII, to take advantage of existing mercury ballast, even the amazing tale of use of B22d caps for these oversized tubes!. But obviously these lamps were calculated and sized according the volt-ampere characteristics of existing 80 and 125 watts ballasts. (typical values are: 0,8 A/115 V for 80 watt  and 1,15 A/125 V for 125 watt operation).
Also obvious is the fact that these tube socketing and unfitting could't been done in the same way we know in our days, by means of a 90 degrees rotation, Hi!
Best regards.