[Wswss] Ballast for high pressure sodium lamps

[Lance Collister, W7GJ]

Hello Mike,

After graduation from college, I worked at General Electric as a lamp designer in the 
high pressure sodium group.  The ballasts themselves are simply inductors to limit 
the current to current in the arc inside the lamp.  Although the principle of the 
lamp itself is to produce light from a bright arc between two electrodes breaking 
down a sodium/xenon gas, I suspect your problem is related to either the 
photoelectric controllers or an improper "starter circuit".

I think you should try to locate the problem lamp, as it should not be a problem 
during the daytime when the photoelectric controller is supposed to keep the lamp 
turned off.  Typically, the noisy part of the operation of such a lamp is when it 
turns on.  To do this, a "starter board" circuit applies high voltage spikes across 
the arc tube electrodes to break down the inert xenon gas that fills the arc tube. 
Once this arc starts, the electrodes heat up, and warm the sodium that has 
precipitated in a reservoir near the electrodes.  As the sodium heats up and goes 
into a gaseous state, the current in the arc tube goes up and the lamp becomes 
brighter.  The starter then turns off, and the noisiest part of the lamp operation 
disappears.  However, for some reason, it sounds like your lamp(s) may be trying to 
start during the day, so something in the control circuitry appears to be defective.

A more common problem is for the noisy startup phase to repeat itself whenever it is 
dark out. That is due to the fact that the mode of failure at the end of life for the 
lamp is for the arc to increase in voltage, causing it to draw more current.  Since 
the current is limited by the ballast, the arc goes out.  The starter circuit, 
sensing the loss of current through the lamp, starts providing high voltage spikes to 
break down the gas in the arc tube again, but it cannot re-start the lamp until the 
gas in the tube cools and some of the sodium precipitates out.  Once started again, 
the starter circuit turns off until the lamp voltage increases to the point where the 
lamp goes out again.  This "cycling" will go on indefinitely until the old lamp is 
replaced, and this source of interference can be easily identified as a light that is 
repeatedly warming up, becoming bright, and then going out.

The situation you describe sounds much harder to spot visually, although you may be 
able to see some faint white glow in the lamp during the daytime if you look closely 
at it.  That would be the xenon being broken down by the starter, which is firing but 
not being permitted to fully release current to the arc until dark.

Good luck and VY 73, Lance



On 9/20/2010 1:31 AM, Mike Goshay wrote:
> Does anyone have info on these ballasts causing interference on our Ham Bands? Hp
> Sodium Lamps are creating a terrible racket on HF and to some extenton VHf as
> well.It disappears when lamp comes ON at dusk. These are on a residential property
> and are not in utilities jurisdiction.
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-- 
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: (406) 626-5728
URL: http://www.bigskyspaces.com/w7gj
2m DXCC #11/6m DXCC #815

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