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#7014 01/18/02 11:54 AM
Joined: Jan 2002
Posts: 12
static Offline OP

I have a 70w sodium light on my garage, the light will go on and off on its own. I replaced the light sensor and made sure that it was not pointing at any other light sources. This did not help, on the advise of the local HD store, I replaced the bulb and have the same problem. I noticed the other day that it always goes off when I turn the inside garage lights on or the compressor on (A small one) I took reading when the compressor kicks on and when the lights come on and get 118v as the lowest for a second then back to 122v. I am willing to replace the whole thing is need be, but I was wondering what in the unit would need to be replaced, I understand that the cap is used for starting it but it sounds like the unit is touchy to the volts comming in, once it goes out, it will start right back up and will be fine untill something else is switched on. None of the lights in the garage flicker or anything like that and nothing is overloaded, it has an old 4 fuse box that goes to outlets on the wall, a 4 tube 4ft fluorescent fixture, the compressor is a small unit that pulls about 7 amps. The fuses are the correct 15 amp. I realise that the panel should be replaced, but down the road the garage is going to be replaced so I did not have it done when the house was done.
(One other thing, it looks like that outdoor light is on its own fuse and the inside light has its own with one not used at all and the other for the plugs. )

(Note, the spell checker does not work..looks like they want to charge for it now)

#7015 01/18/02 12:53 PM
Joined: Jan 2002
Posts: 12
This is a tattle tail on a high pressure sodium lamp that it is due for replacement,but you said you did that.Is it the correct lamp for the ballast,are the taps set correctly,maybe this is a bad bunch of lamps.?Will this fixture run fine from another power source?Is the photo cell facing the light causing it to jack on and off?These are some of the most highly efficient types of light next to the low pressure sodium lamp.I can't imagine voltage drop being the problem,unless it is being caused by a bad connection.

#7016 01/18/02 12:57 PM
Joined: May 2001
Posts: 176
What kind of ballast do you have? is a reactor type or a CWA (constant wattage autotransformer)? A reactor is more sensitive to voltage fluctuations than a CWA. Some of the Home Depot, Lowes, etc economy types use the more economical ballast, resulting in these kinds of problems. When you replace the entire fixture, go to an electrical supply store such as GrayBar to get your replacement fixture.

#7017 01/18/02 11:10 PM
Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and
Warren has hit on the most logical culprite - a straight reactor core type HID Ballast.

This is very commonly used for low power H.P.S. lamps, driven from a 120 VAC source. Since the lamp is 55 VAC, the Ballast / Lamp combination works well at 120 VAC without the need of an Autotransformer... Until...

The straight Reactor Ballast will respond Big-Time to fluctuations at 5% and above. This works out to drops / rises of Voltage in the range of 6 VAC on the 120 VAC system becoming a major influence to the light output or operation. Voltage sags in the area of 15% to 20% will cause a H.P.S. lamp to drop out very easilly.

The CWA [Constant Wattage Autotransformer] can withstand Voltage sags of 30-40% before the lamp's plasma dies off [lamp goes out].
The CWA is somewhat linear to fluctuations - 10% [+/-] change in line voltage usualy results in a 5% change in lamp intensity.

CW [Isolated Transformer] Ballasts have the best lamp regulation.

As far as the Capacitor goes, it's only used with the straight Reactor Ballast to bring the Power Factor up from 50% to near 90%. It performs no other function than this.
The same goes for High Reactance [HX] type Autotransformer Ballasts.

When a Capacitor is used in the Secondary of a CWA / Reg-lag Ballast, it improves Power Factor and is also used to "Tweek" the lamp's performance.

From the sounds of things, I would say the Voltage / Current at the HPS lamp comes very close to zero for maybe 1/8 cycle - or drops below 40 VAC for upto 4 cycles when the lamp extinguishes. On Fluorescent lamps, the transient drop is noticed as a brief "Pulse" or "Flash", because they recover rapidly as compared to HID lamps.
Incandescent lamps will do the "Dim then Surge, then recover" deal. They are noticable during the event from the transient drop in light output, which is followed by a rapid overshoot in lamp intensity. This makes the event seem much different than it really is.

HIDs cannot lose their plasma, then instantly re-establish it, so when the plasma becomes too thin, the lamp goes out.
The starting arc cannot be maintained across the arc tube until the tube's temperature is low enough to drop the pressure inside the arc tube.
When the pressure inside the tube drops low enough to allow enough current to be pushed by the available level of Voltage [to jump between the Electrodes] - this will create the initial starting arc and sustain it long enough to produce a nice fat plasma!

Pardon the strange descriptions above [Linked Image]

Scott SET

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#7018 01/19/02 10:05 PM
Joined: Aug 2001
Posts: 332
Your symptoms are the ones normally given by a bad/dying bulb but you've replaced that, and the voltage readings are ok. In my job we maintain 51 schools and there are hundreds of these lights. A long time ago we realized that it just isn't worth the time and trouble to search thru all the pieces to find the bad one. (and yes, we have the meters to test each component separately). Half the time you have to special oreder the individual component after you identify it. We find it quicker and cheaper to just replace the whole dern innerds of the fixture and not spend the time troubleshooting them.

#7019 01/21/02 10:24 AM
Joined: Jan 2002
Posts: 12
static Offline OP
Thanks for all the information!

I think I will just replace it. Now that I think of all the time I have spent trying to get it working I could have saved if I had just replaced it when it first started acting up. I just don't like to give up on something with out knowing the reason that it did not work.

#7020 02/11/02 02:13 PM
Joined: Jan 2002
Posts: 12
static Offline OP

Well, it is fixed. I was just going to take it down when I noticed that the power for it goes stright into a hole in the wall. Turns out that it just connects to the romex up in the top of the garage on the inside using wire nuts. One of them was not tight. So the light has worked for almost a week now with no problems. Now the light needs to come down and get mounted on a box and this whole thing done right, but at least I know that I don't need to replace it. The fun of a 61 year old house that has had 3 owners. The guy that built the garage worked for Detroit Edison and built it out of timber from the top of the power poles, could with stand a tornado but would burn down to poor wiring.
Thanks again to everyone that responded. One question, why did it work at all? If it was not touching it should have just not worked?
The wirs were not burnt or anything so it did not look like it was arcing or anything.


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