Author Topic: 100w clear merc trouble starting  (Read 3750 times)
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100w clear merc trouble starting « on: November 29, 2017, 07:10:36 AM » Author: 589
Got some cheapie 100w mercs off of fleabay a while back and been running one of them for a month or two. It's gotten to the point where the lamp won't start without operating it like a switch start fluoro, switching it on and off quickly several times. I'm guessing the starting electrode is no bueno, like maybe the resistor is open circuit possibly? Thoughts?
« Last Edit: November 29, 2017, 07:13:00 AM by Andy Sodium » Logged

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Re: 100w clear merc trouble starting « Reply #1 on: November 29, 2017, 01:08:26 PM » Author: Medved
What is the lamp operating position?
If the starting electrode is at the bottom (and mainly when you do not let the lamp fully warm up before shutting down), a bead of mercury may short it towards the main electrode (it is the lowest point in the burner, so mercury may have a tendency to run there when condensed) and that then prevents the auxiliary electrode to form the initiating discharge.

Operating the lamp horizontally usually does not cause such problems, as the critical point (the seal edge between the main and auxiliary) is not anymore the lowest point in the lamp, regardless of on which end is the auxiliary probe.

This is the main reason, why some higher end makers used two electrodes: When one is down, so susceptible towards this problem, the other must be up, so very immune in that matter. And for a reliable ignition one working electrode is sufficient.
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Re: 100w clear merc trouble starting « Reply #2 on: November 29, 2017, 01:49:08 PM » Author: 589
Its operating base up @10deg tilt. I'll check tonight to see where the starting electrode is.
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Re: 100w clear merc trouble starting « Reply #3 on: November 29, 2017, 10:14:12 PM » Author: 589
Yea the starting electrode is on the base side so it is facing upwards when in the fixture. Funny thing, it started working again today now that I'm talking about it  ::)
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Re: 100w clear merc trouble starting « Reply #4 on: November 30, 2017, 04:32:48 AM » Author: Medved
So the starting probe is on the upper end? Then the fault could be indeed either bad resistor, or more likely some cracked weld connection within the lamp assembly.
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Re: 100w clear merc trouble starting « Reply #5 on: November 30, 2017, 01:06:32 PM » Author: 589
Correct, the probe is upwards. I'll monitor it over the next few weeks to see how it fares. If the lamp is indeed faulty I'll try to get it warrantied somehow. Then maybe bust it open to measure the resistor.
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Re: 100w clear merc trouble starting « Reply #6 on: December 07, 2017, 08:40:53 PM » Author: 589
So roughly a week goes by with nothing wrong and then the past two days I come home and the backyard is dark (not working again) now I'm almost thinking its something to do with the remote christmas lights PC I'm using for it. Well, at least it has some involvement in some way. Reason being if I cycle power just once to the light post PC (while already on) it fires up the first time, however doing it via the switch on the PC yields nothing. FYI it is a relay based PC with an electronic countdown timer rated to 1300va ballast or 1500w. Its not really that old either. weird...
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Re: 100w clear merc trouble starting « Reply #7 on: December 07, 2017, 09:51:59 PM » Author: HomeBrewLamps
perhaps replace the timer... if the merc still gives you trouble after tht, what i usually do is throw them temprarily on HPS gear... after that for whatever reason they seem to work fine...
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Re: 100w clear merc trouble starting « Reply #8 on: December 08, 2017, 01:20:48 AM » Author: Lodge
Are you using a med or mougal base merc ?
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Re: 100w clear merc trouble starting « Reply #9 on: December 08, 2017, 04:58:23 AM » Author: 589
Medium. It in a small cooper yardblaster that mounts the lamp in a downward angle.
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Re: 100w clear merc trouble starting « Reply #10 on: December 10, 2017, 07:10:10 PM » Author: 589
It quit working again so I've replaced it with the other lamp I have and have contacted the seller. I've only ran it for a month or so D2D.
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Re: 100w clear merc trouble starting « Reply #11 on: December 10, 2017, 09:01:57 PM » Author: 589
Ok, I can now confirm that the starting electrode is open circuit. I gave the lamp a hot supper on the fulham WH3 and now it will fire on the proper h38 ballast. I also found out that if you attempt a hot restrike on a fully warmed up MV lamp on the fulham the bad boy creates a glow discharge in the outer envelope and starts warming up the arc tube support elements until the arc tube cools enough to strike an arc :o. That could be a potentially dangerous situation for sure for long term use. Also what I noticed is that it would not arc from the starting electrode at all when hot restruck, however a known good lamp would sustain an arc between the starting electrode and main (during which time it would also have a glow discharge in the outer bulb just less so) until the lamp cooled enough and then you could see the discharge spread towards the other main electrode until it restruck. I don't know the starting circuit on these fulham ballasts, but it will give a lamp the business.

Since giving the faulty lamp a hot supper on the fulham ballast I'm hypothesizing that it moved all the stuff around enough to allow the proper h38 ballast to strike the lamp on OCV alone it seems then. I'm guessing that over time the stuff inside migrates around to the point that OCV isn't enough to strike the lamp anymore until you give it another hot supper.
« Last Edit: December 10, 2017, 09:06:38 PM by Andy Sodium » Logged

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Re: 100w clear merc trouble starting « Reply #12 on: December 10, 2017, 10:33:47 PM » Author: HomeBrewLamps
Ok, I can now confirm that the starting electrode is open circuit. I gave the lamp a hot supper on the fulham WH3 and now it will fire on the proper h38 ballast. I also found out that if you attempt a hot restrike on a fully warmed up MV lamp on the fulham the bad boy creates a glow discharge in the outer envelope and starts warming up the arc tube support elements until the arc tube cools enough to strike an arc :o. That could be a potentially dangerous situation for sure for long term use. Also what I noticed is that it would not arc from the starting electrode at all when hot restruck, however a known good lamp would sustain an arc between the starting electrode and main (during which time it would also have a glow discharge in the outer bulb just less so) until the lamp cooled enough and then you could see the discharge spread towards the other main electrode until it restruck. I don't know the starting circuit on these fulham ballasts, but it will give a lamp the business.

Since giving the faulty lamp a hot supper on the fulham ballast I'm hypothesizing that it moved all the stuff around enough to allow the proper h38 ballast to strike the lamp on OCV alone it seems then. I'm guessing that over time the stuff inside migrates around to the point that OCV isn't enough to strike the lamp anymore until you give it another hot supper.
Is "hot supper" like putting it on a higher wattage ballast? or is that putting it on a ballast with an ignitor? or what does that mean??
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Re: 100w clear merc trouble starting « Reply #13 on: December 11, 2017, 07:26:10 AM » Author: 589
Sorry, I've been watching too much AvE lately... Being instant started and ran hard for a short amount of time. I don't know the OCV on the Fulham workhorse, but I imagine it is quite high.
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Re: 100w clear merc trouble starting « Reply #14 on: April 07, 2018, 12:08:55 PM » Author: d3anio97
Sorry, I've been watching too much AvE lately... Being instant started and ran hard for a short amount of time. I don't know the OCV on the Fulham workhorse, but I imagine it is quite high.
For a fluro ballast it should be about 600v... for a merc that's a high voltage to start it with, but it's noting compared to starting one on a 2.5kV starting pulse from some SON gear.
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