Greetings all,

I have a couple of questions regarding 50 watt mercury vapor lamps. First question is, is it possible to run them on 120V using a resistive/incandescent ballast? I know the running voltage is around 80V, but I don't know if the 120V is enough to initiate the arc.

Second, I've heard that although it is possible to run them on a preheat or rapid start F40T12 ballast, they'll be slightly underdriven, at around 35 watts. Will this significantly shorten the life of the lamp? Would a lamp rated for 40/50 watts handle it any better than a lamp rated for just 50 watts?

And finally, can an electronic ballast be used?

The reason I ask is because I'm looking at two 40/50 watt lamps on eBay that I'm seriously considering getting. In fact, I think I will try and go for them. I've been really wanting to try some MV stuff, but self-ballasted lamps are expensive, and the 50W regular ones are uncommon to come by.

Thanks.

Greetings all,

I have a couple of questions regarding 50 watt mercury vapor lamps. First question is, is it possible to run them on 120V using a resistive/incandescent ballast? I know the running voltage is around 80V, but I don't know if the 120V is enough to initiate the arc.

The 120V won't be sufficient to ignite (and here I mean carry the cold cathode discharge with very high cathode fall voltage before the cathodes warm up and so reach the thermionic emission), neither to run the lamp, it has to reignite each time the circuit current crosses zero. And the latest aspect is, what is asking for the 200V minimum OCV of the ballast.
So at 120V mains, the lamp will most likely not ignite, nor establish an arc and if so, it will extinguish once warming up.

Second, I've heard that although it is possible to run them on a preheat or rapid start F40T12 ballast, they'll be slightly underdriven, at around 35 watts. Will this significantly shorten the life of the lamp? Would a lamp rated for 40/50 watts handle it any better than a lamp rated for just 50 watts?

At first the efficacy will fall way short of the rating.
The life itself could be somewhat shortened (I assume the lamp is designed for an optimum at the rated power), but I don't think it would be significant at all.
And there is some theoretical risk (it depend on the ballast characteristics) of the lamp "locking" itself in a low temperature saturated vapor mode (where the voltage is so low, the real dissipated power is not sufficient to heat it up further) not reaching the operating temperature.
Definitely it will take "ages" for the lamp to warm up...

And finally, can an electronic ballast be used?

Not a HF type, as that can drive the arctube into it's resonance, cause standing waves in the arc intensity and so locally overheat the arctube...

MH ballasts would detect the higher arc voltage of an MV as a "failing" lamp, shut down, so do not operate it either.

The reason I ask is because I'm looking at two 40/50 watt lamps on eBay that I'm seriously considering getting. In fact, I think I will try and go for them. I've been really wanting to try some MV stuff, but self-ballasted lamps are expensive, and the 50W regular ones are uncommon to come by.

Thanks.

If you get 240V (a step-up transformer,...) and two 75W lightbulbs in series, it could work well as an experimental and/or showcase setup...

Thanks, good to know. All right, then, what if I were to take two identical F30T12 ballasts, or two identical residential F40T12 ballasts, and run them on parallel? I know this can be done with choke ballasts, but what about autotransformers?

I've also determined that I could also use an F40T12/HO ballast, but getting a hold of one of those probably isn't very likely, or likely to be inexpensive. At any rate, I've bid on the lamps, so if I get them, I'll figure something out, even if in the end it's just finding a full-power F40T12 ballast and using that.

Thanks.

Thanks, good to know. All right, then, what if I were to take two identical F30T12 ballasts, or two identical residential F40T12 ballasts, and run them on parallel? I know this can be done with choke ballasts, but what about autotransformers?

Both should be exactly of the same type, to ensure the phase and OCV are the same.
And you should check and make sure the lamp current is 0.6A or slightly below. Do not overpower the lamps...

I've also determined that I could also use an F40T12/HO ballast, but getting a hold of one of those probably isn't very likely, or likely to be inexpensive. At any rate, I've bid on the lamps, so if I get them, I'll figure something out, even if in the end it's just finding a full-power F40T12 ballast and using that.

Thanks.

i have got mine running in a remote ballast box, using a 50W Advnace MH ballast, see here for details

make sure if you use a MH ballast the input power into the ballast isn't more then .7A as a 50W MV runs at .6A  or 600mA

I'm proud to announce I won the lamps:

http://www.ebay.com/itm/H46DL-40-50W-DX-mercury-vapor-lamp-bulb-/291003061189?autorefresh=true&_trksid=p2047675.l2557&ssPageName=STRK%3AMEWAX%3AIT&nma=true&si=snZDOoujlRwioLDU36nwvaHco1o%253D&orig_cvip=true&rt=nc

I think this is a pretty lucky find, two NOS 40/50 watt units (and high quality ones at that) for such a good price. I'm pretty happy.   When they arrive, I'll give them a quick run - just a few seconds - on my F30T12 strip light just to make sure they work.

I've been thinking a lot about what sort of a fixture I should actually set up for them. At first I was just thinking of a lampholder on a piece of board, since that would be cheap and simple to set up. But it just occurred to me that the last time I was in the local surplus and salvage store they had stainless steel barn light-like fixtures for $10 a pop. That would work pretty well, although I don't know where/if I could place the ballast on one. I saw fluorescent and HPS wallpacks there that I could convert, but at $50 a piece I would have to hope that I could make my money back on selling the included lamp and ballast, and then, again, hope the new ballast would fit in place. There's a lot of variables I'll have to figure out.

Alights: Regarding your setup, what model of Advance ballast are you using, and where did you put it in the fixture?

Medved: A setup like Alights' slightly overdrives the lamp, at around 58 watts. Would this be better or worse for the lamp than a fluorescent ballast, which would underdrive it at around 35 watts?

Thanks guys.

Medved: A setup like Alights' slightly overdrives the lamp, at around 58 watts. Would this be better or worse for the lamp than a fluorescent ballast, which would underdrive it at around 35 watts?
Thanks guys.

The overdrive will for sure shorten the lamp life quite significantly (although it increase the lamp efficacy), so better to never go above ~0.65A.
If the lamp is rated "40/50W", I would not fear as much the underdrive - the 40W rating mean the lamp design count on currents 0.4..0.5A, so full power F40T12 ballast (0.43A) should still be OK (but it would mean about 35W drive, so mainly lower efficacy).

To check for the possible low temperature lock up, try the lamp on a ballast with ~20% lower current than you intend to operate it (e.g. try it on a 0.3A ballast, when you want to operate it on 0.36A). If the lamp warm up and the arc voltage reaches the normal 90V level after stabilizing (on the 0.3A; but it will take way longer time), your intended level (0.36A) should be still fine.
But if the arc voltage stabilize way below the desired 90V (on the 0.36A for our case), desired current (0.36A) is too low.

I would try the MV lamp on 39 watt MH ballast with no ignightor.  Magnetic ballast this size is not too common
50 watt ballast do show up on EBay but rarly.

Thanks guys, I really appreciate it. It looks like I'll be grabbing myself a preheat 40 watt fluorescent lamp ballast around Christmas time. The way I see it, as Medved also mentioned, is since the lamps are rated for 40 and 50 watts, a 5 watt underdrive will probably be better than an 8 watt overdrive. I'm not worried about efficacy, just as long as I do no unnecessary harm to the lamps. Not to mention that the fluorescent ballast can be had easier and cheaper than an MH ballast, and I don't have to worry about making sure I get one without an ignitor. I looked at the 39W MH ballasts, and it seems the great majority of them are electronic, and the current is only negligibly higher than a fluorescent ballast.

I came home today, and received and tested the bulbs. Photo here. They both work beautifully.

Medved, get a load of this. I decided to run them up as far as they would go on my F30T12 ballast while monitoring a multimeter across the lamp. The arc voltage went all the way up to 105V! Could that ballast really have slightly overdriven them?

If the lamp voltage went all the way up to the ~100V, it mean all the mercury has evaporated, so it operates in the correct mode.

If it was single lamp F30T12, it won't overdrive it.

If you connect two channels in parallel, it may overdrive it.
To test that, just measure the lamp current...

Thanks. So the arc voltage will never go higher than the 100 or so volts even if it is overdriven? Yeah, it's s single lamp ballast. Unfortunately I don't think either of my multimeters are capable of measuring AC current. I tried one, and on the current mode it just read 0, so I think it's DC-only. Heck, I would try wiring my Kill-A-Watt meter in series with the lamp, but unbelievably that got stolen by someone working on the house.

The arc voltage depend mainly on the mercury pressure. And once all of it evaporates, the pressure, so the voltage does not change anymore.
So if all the different ballasts are able to evaporate all of it, the voltage would be the same (well, almost, so +/-5V I still call as the same).