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Old 08-25-2010, 06:04 AM   #1
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


I have a 20-40 year old Mercury Vapor light fixture in my yard above the stairs that lead up to my house. It was non-functioning when I moved in. If I had to guess, based on it's appearance I would say that it is a 175Watt fixture.

I can hear that the dusk to dawn feature is still working. (It makes a vibrating sound for about 2 minutes every dusk/dawn, followed by a "CLICK" sound)

I am assuming that the bulb is burned out, but I suppose the ballast could be fried also.

I am very frugal with energy. My monthly electric bill runs about $60 (or less) a month. I am not willing to waste 175W, 100W, or even 65W for a light that stays on all night, but at the same time, I need a LITTLE light out there to illuminate the stairs leading up to my house. I have been using a series of battery operated LED motion detector lights, dispersed at intervals along the stairways/path leading up to my hillside house, but these run out of batteries every few months, and don't really put out a lot of light.

I have calculated that it would actually be CHEAPER to operate a GE 14Watt CFL Outdoor Bug Bulb (with 60W incandescent light equivalent) from dusk to dawn than it would be to keep changing the batteries in the LED motion lights. It would also be more convenient and safer to have a light on all night.

Unfortunately the area light fixture in my yard is pretty high up, and difficult to reach without death-defying effort using my ladder that is not tall enough. I can however buy a bulb changing tool and an extension pole to replace the bulb without killing myself, but opening the top of the unit to rewire the socket directly to the dusk/dawn sensor, bypassing the ballast would be very difficult to accomplish.

SO, here are my questions:

#1: Can I install a self-ballasted 14 watt bulb into a 175 watt, ballasted Mogul socket, and expect it to work? (using a mogul to medium socket adapter) The ballast merely LIMITS the wattage from EXCEEDING 175 watts, correct?

#2: Worst case scenario is that the ballast is fried. If this is the case, what is the likelihood that it is still passing power to the socket?
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Old 08-25-2010, 08:10 AM   #2
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


The old mercury vapor lamp ballast may or may not pass at 14 watts a voltage within tolerances taht the CFL will operate on.

At full brightness, the mercury lamp is actually running at a lower voltage when drawing its 175 watts.

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Last edited by AllanJ; 08-25-2010 at 08:15 AM.
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Old 08-25-2010, 08:51 AM   #3
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


No they are not compatable! You could rewire the fixture to work, however that would violate the UL listing.

Without rewiring the wrong voltage would be supplied to the CFL.
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Old 08-25-2010, 09:05 AM   #4
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


Why would the voltage change? Is that how the ballast limits the wattage? By reducing the voltage when the wattage tries to exceed 175watts?

Would that still apply if the wattage does not exceed 175?
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Old 08-25-2010, 10:16 AM   #5
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


A ballast is basically a transformer which either steps up or down voltage and current. You would be putting 2 in series if you tried doing what you suggest so there for your voltage and current would be wrong.
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Old 08-25-2010, 11:39 AM   #6
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


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A ballast is basically a transformer which either steps up or down voltage and current. You would be putting 2 in series if you tried doing what you suggest so there for your voltage and current would be wrong.
This still doesn't make sense to me. I am trying to understand the science here.

A ballast is basically a self-adjusting transformer, that variably steps down the voltage to produce a specific wattage, correct?

In the case of a 175Watt bulb, the job of the ballast would be to make sure that the bulb ONLY receives 175Watts in order for it to function properly, agreed?

An unballasted 175Watt bulb will actually try to pull as much amperage as it can, until it burns out, thus requiring the NEED for the ballast.

If we use the formula: Watts = Amps * Volts, we get 175 = Amps * Volts, we could change the volts to respond to the amps which would be variable, in order to obtain our goal of 175 watts.

Therefore, if the bulb tried to pull 3 amps, the ballast would step down the Volts to 58.3, in order to achieve 175 watts, correct?

SO, this also means that if the bulb only tries to pull 1.46 amps, exactly 120 volts would be required in order to achieve 175 Watts, correct?

Thus, if the amps fell BELOW this threshold of 1.46 the ballast would do NOTHING, correct? The ballast wouldn't be configured to automatically reverse itself in order to STEP UP the Voltage above 120 Volts, correct?

If all this is correct, it should therefore stand to reason that a 14 watt SELF-BALLASTING bulb would only pull .14 amps (at 120 Volts), well below the threshold required to engage the ballast.

Does this make sense or am I crazy?
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Old 08-25-2010, 11:55 AM   #7
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


Would that CF bulb even fit in there? Don't M-V bulbs have a fatter base? Maybe I'm thinking of something else, but I thought they made the screw-in part a different size so you don't go putting the wrong bulbs in the wrong fixtures.
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Old 08-25-2010, 12:13 PM   #8
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


There are CFL bulbs that have a very large base
I think the same as the larger mogul bases
I'd simply bypass or remove the ballast
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Old 08-25-2010, 01:02 PM   #9
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


@hyunelan2
As I indicated, I would be using a socket adapter to make a standard bulb fit in a mogul socket. They are available at any hardware store (or on Amazon) for a couple of dollars.

@Scuba_DaveThe CFL bulbs that are designed to replace standard MV bulbs, and fit in mogul sockets are usually unballasted, designed to work with the existing ballast.

Due to the location of the lamp fixture, removing the ballast is not an option unless I also want to purchase a $300-$400 ladder. (See images below)

Unfortunately I am confined to a very tight budget to try to get this light working.


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Old 08-25-2010, 01:03 PM   #10
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


check out this site and maybe it will help you understand

http://www.ehow.com/how-does_4927509...ast-works.html
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Old 08-25-2010, 01:11 PM   #11
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


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Originally Posted by codeone View Post
check out this site and maybe it will help you understand

http://www.ehow.com/how-does_4927509...ast-works.html
Thank you codeone. I guess that answers my question. A ballast WILL step up the voltage, as well as step it down. Bummer! This means if I put in a self-ballasting bulb that only pulled .11666 amps, the 175 watt ballast would try to step up the voltage to 1500 Volts to compensate! Yikes!
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Old 08-25-2010, 01:16 PM   #12
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


With any type of bulb that uses a gas vapor it takes a high starting voltage to ignite the gas. Also with any transformer there is no physical connection between the primary wires and the secondary wires, therefore you would not have the correct line voltage to fire your CFL bulb.
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Old 08-25-2010, 01:19 PM   #13
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


I see what you mean about access. Looks like you need a sky hook .

Be careful whatever you decide to do.
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Old 08-25-2010, 01:53 PM   #14
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


Yeah, that's a tough spot
I think I'd be inclined to install a new fixture lower, just above that little junction cover
Would make it much easier to change bulks
While CFL's are supposed to last a long time...I find when installed outside they only last 2-3 years depending upon use & weather exposure
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Old 08-25-2010, 02:18 PM   #15
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Can I install a self-ballasted CFL bulb into a ballasted fixture?


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Originally Posted by Scuba_Dave View Post
Yeah, that's a tough spot
I think I'd be inclined to install a new fixture lower, just above that little junction cover
Would make it much easier to change bulks
While CFL's are supposed to last a long time...I find when installed outside they only last 2-3 years depending upon use & weather exposure
Thanks Scuba_Dave!

I was thinking exactly the same thing. Not only would a lower location make it make it easier to change bulbs (or remove ballasts), if I am going to replace a 175W bulb with a 14W bulb, it is not going to throw light nearly as far, and thus SHOULD be closer to the ground. Right at the junction box seems like the perfect height to get the stairs and a decent section of the hill below. (I still plan to use motion sensor lights at the bottom of the hill)

So, I guess my focus needs to shift to how to remove the existing fixture, instead of trying to remove the ballast from it. This actually looks like it will be an easier task than the latter, although STILL not possible with my existing ladder.

Hmm, maybe I can rent a ladder...

Once I get the fixture down, I can crack it open and see how easy it would be to bypass the ballast, then remount it right above the junction where it protrudes from the wall, eliminating the extension pole altogether.

And if that doesn't work, I suppose it wouldn't be that expensive to just replace the whole thing. (once I get past the ladder issue) Frankly, the existing fixture is kind of ugly anyway. Although, unfortunately all of the less expensive area lights I have seen are just as ugly as this one! It kind of defeats the purpose of my plan to save $60 a year in electricity if I have to pay $200 for the light fixture and its installation!

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