Periodic Daily Crash

[Mark Terribile]

Jason Watkins writes:

> I've got a machine that's crashed now twice in a row around 3 am. I'm
> assuming this is being triggered by something periodic daily is
running.

>I'm only remote access to it, so right now I'm waiting for someone
> to reboot it so I can get back in... what should I look through
> to identify the problem?

Does it happen every morning, or every Tuesday and Thursday (or Monday
and Friday, or ...)?  Is the machine on a good, voltage-regulating UPS?
If not, can you see if you can put it on one for a while?

I once worked around a machine that crashed every morning at about
06:15 .  We never were sure why ... but it was an old machine with
a dodgy power supply and at that hour the main elevators were turned
on in the building.  That entails starting a very large motor-generator
set for each elevator, and the equipment was three-phase and the motors
were almost certainly induction motors, which can draw enormous current
when the rotor is not turning.  I suspect they turned them on one right
after the other without waiting for each to come up to speed (could a
seismograph on the building have detected the torque effects?) and the
resulting voltage drop caused the power supply to work too hard and
overheat or else shut down from undervoltage.

(The MG set was used to produce DC of variable voltage and polarity,
which was used to operate the lifting motor of the elevator.  The
voltage and polarity are controlled by controlling the current in the
field winding of the generator.)

    Mark Terribile


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