Backup Power Schemes

Joseph C. Pistritto jcp at
Sat Aug 9 07:14:57 UTC 1997

At 09:26 PM 8/8/97 -0700, Tony Li wrote:
>> That takes us back to UPSi on equipment, and generators. Technologies
>> available are:
>>	....
>Don't forget cogeneration equipment.
>One would think that local power, UPS, and one flavor of generator should
>suffice.  For the "reasonable".  ;-)

Having built a large datacenter recently (PointCast's), I can say that we
planned for local power failures that lasted up to about 48 hours.  If it's
worse than that,  you have A Big Problem.

We made our system completely automatic since it might have to operate when
there was no operator to initiate a transfer (although for the first year
we didn't have this).  One thing to watch out for is the problem of utility
power "coming back" and then dying again.  This caused at least one ISP
accident since they had insufficient battery power to transfer from
Utility->Battery->Generator and back to Utility and then do it again.  This
is especially a problem if you manually initiate your generators (which is
by far the most common situation).

These kinds of multiple transfers are actually more common than you think.


Joseph C. Pistritto                        jcp at               
Belmont, California              

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