[APD] Metal Halide lights on timers

[Andrew Mitchell <andrewm at cse_unsw.edu.au>]

Hi all,

I have 4 150w metal halide lights (and 2 double 4ft flourescents) on
timers on my 300+g tank.

I have been keeping these for over a year now on those cheap $5-10
timers from the local hardware/department store. (I use 2 timers, each
for half the load)

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.

Now, I'm starting to get sick of replacing these things under warranty,
and am fearing that perhaps there is a problem with one of the lamps,
fittings or ballasts and no problem with the timers.

The lights are plugged into the timer through a powerboard with the
2400w overload cutout, and the timer to the powerpoint similarly. At the
switchboard everything is on 20A circuits with ground fault protection.
(240V in Australia). The house itself is 2 years old.

Has anyone else had a similar problem or have any suggestions?
The best thing I can think of is to try 3 $5 timers (one on each MH and
one on the flouros) to see which is causing the problem. But then what?

thanks,
-- 
Andrew Mitchell <andrewm at cse_unsw.edu.au>

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