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JazzDad
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Mecury Vapor yard light
08/14/08 11:37 AM
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Yo! Anyone know the output voltage of the transformer in one of these common 175W "yard light" fixtures? My normal troubleshooting method would be to put a new bulb in and see if it comes on. I don't want to invest the money for a new bulb, if there is something wrong with the X-fmr or the photo cell. Thanks for all your knowledgeable answers and wild guesses. (Please be specific as to which you are offering.  ) Bret
All kids are gifted; some just open their packages earlier than others.-Michael Carr
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egon
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Re: Mecury Vapor yard light
[re: JazzDad]
08/14/08 07:03 PM
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Carbon negative Jazz. Solar panel, battery and LEDs! 
Egon : 
Edited by egon (08/15/08 06:28 AM)
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jml755
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Re: Mecury Vapor yard light
[re: JazzDad]
08/15/08 07:31 AM
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First off, No, I don't know the output voltage. These will probably qualify as somewhere between something educated and a SWAG:
- I would think the xformer would have a primary/secondary rating tag on it (SWAG)
- Check to see if you're getting ANY voltage out of the secondary.(somewhat educated).
- Take the photocell out of the circuit and check it with a meter for continuity when it's covered/uncovered. (somewhat educated)
Anyway, the above is what I would do. Of course, it's a lot easier to go through troubleshooting when it's on a bench than when you're up on a ladder (depending upon your installation)
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JazzDad
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Re: Mecury Vapor yard light
[re: jml755]
08/15/08 09:09 AM
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Fortunately, it is not mounted.
I was most concerned about putting a volt meter on the output of that transformer. If it's over 600 volts, I'll have to use the meter with high voltage leads. But then again, at what voltage will that gas excite?
And Egon, I should have expected an answer like that from you, what with all the grief I always give you.
All kids are gifted; some just open their packages earlier than others.-Michael Carr
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eccentricfarmer
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Re: Mecury Vapor yard light
[re: JazzDad]
08/15/08 02:53 PM
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WILD!!
As far as the sensor, usually there is a glass or plastic cover you can look thru. If you look really, really careful you can see a little guy in there on the toilet reading a newspaper or magazine sometimes. When it gets so dark he cannot read anymore then he reachs over and hits the lite switch to continue his musings. If you cannot see your little guy then the sensor is out to lunch and must be replaced. 
You should hear the explanation for what goes on in a copy machine!!
No fun, change the rules!!!
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egon
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Re: Mecury Vapor yard light
[re: JazzDad]
08/15/08 04:57 PM
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Ah Jazz, just trying to bring you up to snuff!
Egon
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Pat
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Re: Mecury Vapor yard light
[re: egon]
08/20/08 04:54 PM
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Actually it isn't a transformer in the usual sense. It is a ballast (or transformer type ballast as opposed to electronic.) If you have another similar light or a friend with one try your bulb in the other light. If it works that way replace your photocell.
There are other approaches but they require significantly more electronics ability.
Ballasts typically outlast several bulbs.
If your bulb was good and the new photocell doesn't fix it then buy another light that takes the same photocell and you have 2 spares. (Some stores won't let you return a photocell)
While you have the bulb out, inspect it carefully. If you tap on the glass (give it a fair thump) and look carefully at the filament, does one side of the filament move independently from the other. If yes, then the filament has gone bye bye.
If you are buying a new fixture, consider low pressure sodium if color rendition doesn't matter at all compared to electrical economy and high pressure sodium for a golden white light that will reproduce greens and blues fairly well and still be more economical lumens per Watt than mercury. Mercury lights do put out a lot of UV which is not always a good thing.
White LED's are a consideratioin.
Pat
"I'm not from your planet, monkey boy!"
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JazzDad
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Re: Mecury Vapor yard light
[re: Pat]
08/22/08 08:26 AM
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Hmmm. Putting a VOM in the mogul base socket shows the same voltage as what's coming in from the mains; 120VAC.
The fixture was a salvage, with no lamp, so I don't want to invest money into it if I need to be replacing multiple parts.
All kids are gifted; some just open their packages earlier than others.-Michael Carr
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jml755
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Re: Mecury Vapor yard light
[re: JazzDad]
08/22/08 08:34 AM
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JazzDad,
After reading Pat's reply, I did a little research on ballasts. I always thought they were a transformer as well. But research indicates they are a current regulator, so the voltage would be the same. Learn something new everyday.
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egon
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Re: Mecury Vapor yard light
[re: jml755]
08/22/08 09:04 AM
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Just a note of caution! Pat spent some time living on small boats that were in the water. He may get lead or concrete or even stones mixed up in the Ballast thing!
Egon
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Pat
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Re: Mecury Vapor yard light
[re: JazzDad]
08/23/08 07:59 AM
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Sorry Jazz but... Your test didn't prove much about the status of the fixture, beyond that it was hooked to power and the internal wires were not burned open.
Again, it is NOT a transformer per se as in the sense of isolation transformer, step up or step down transformer, it is a ballast transformer or just ballast.
Recall the "job" of the ballast resistor in ignition systems back in the 60's? This is similar.... but different. (High power to start then reduced power to run.)
The lamp is a gaseous discharge design. It requires a high voltage to ionize the gas to initiate current flow through it. The ballast provides that. Once the "arc is struck", so to speak, the ballast must limit the current flow to prevent the lamp from self destructing. The ballast acts as a "choke coil" where its X sub L (inductive reactance) is an AC resistance that limits the current flow through the lamp. In fact a resistor could be used for the ballast action but would dissipate much more power.
Power in Watts in an AC circuit depends on resistance as well as reactance (Impedance.)
In an AC circuit the power is computed by multiplying the current (Amps) times the Volts and then times the cosine of the phase angle. If the voltage and current do not peak together during an alternation of the AC current then less power is produced. The inductance of the ballast shifts the phase of the current vs voltage so the power is reduced and the lamp doesn't act like a flash bulb.
Electric type folk use the mnemonic device "ELI the ICE man." where E is voltage, L is inductance, and C is capacitance. This is to remember that in an inductor (L) the voltage leads the current and in a capacitor (C) the current Leads the voltage.
(This material may be included on the mid term exam.)
If all this just sounds like a new age version of Jaberwocky then put away your VOM and follow my previoius post's instructions or just go buy a fixture.
Pat
"I'm not from your planet, monkey boy!"
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