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[APD] Re: Metal Halide lights on timers

About a month ago one of them failed. I replaced it. 3 Days later the
new one failed. I replaced it with a different brand. That lasted about
another 2-3 days. Each failure was the case that I got up in the morning
and the light was still on, despite all indications on the timer itself
that the light should be off... the relay in the timer appears to have
welded shut!
So I went and spent $40 on a "high-current" heavy duty timer,
specifically designed for such applications as "mercury-vapour
lighting". It failed similarly after 2 days.
All the timers were rated at 2400w, well above the 376w total load I was
giving it.
Your timers are most likely having problems switching the large *inductive* loads of the ballasts. What you need is a heavy-duty timer that is rated for switching motors. Motors are also inductive loads so timers meant to control them should be better able to deal with your ballasts. Most of the usual "heavy duty" timers are specified for use with large *resistive* loads like incandescent lighting and are not necessarily capable of handling the inductive voltage spikes that are present when the MH lights are turned off (and the very high currents when they're turned on).

If you remain unable to find a timer that can run your lights, you can try getting a "definite purpose contactor" from an electrical supply house. These are basically just extremely heavy-duty relays made for switching large motors and should have no problems with your ballasts. Get a contactor with a suitable voltage coil that you can use a normal timer to run it, and use the contactor to actually switch your lighting load on and off.


***************************** Waveform Technology UNIX Systems Administrator

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