Re: Hall Effect for outlet strips

David Lesher <wb8foz@xxxxxxxxx> wrote:
>So on the NANOG list, there's a thread on where to find a rack-mount
>outlet strip with per-outlet measurement, for bill-back purposes in
>a server hotel environment. The data so far is grim: [Baytech RPC5/6
>4 outlets for $644] And it's not UL-approved.

This may have come up before, but:

Buy a regular outlet strip and n Kill-A-Watt single-plug watthour meters,
about US$35 each. These meters don't have data output, but this can be
somewhat fixed by 1 to n cheap webcams and creating a web page for someone
in the billing department to look at this month's reading, last month's
reading, and doing the math. For more automation, there is a single-plug
watthour meter with serial port, the Watts Up Pro. About US$125 each.

I think some UPSes (APC Smart-UPS?) report the current load, even when
they're not on battery. Maybe you could buy a cheap, small UPS for each
server, and use its built-in monitoring. You're not after the UPS
functionality - that is still provided by the big UPS and generator for
the whole data center.

If the hotel owner can run their own code on the servers, you might be
able to do it by proxy. Temporarily install a watthour meter and note
its reading for the server in each of three states: idle, running all
the disks ('find /'?) only, and running 100% CPU (Seti@Home?) on all
CPUs only. Then use something like MRTG to collect stats from each
machine and compute electrical usage based on the disk and CPU load and
the measured energy consumption.

I've only bought co-lo space, and not sold it, but I wonder: is price so
important and margin so low that the ability to charge a customer less
if they use less electricity is that important?

>So I was thinking; is there a Hall-effect package that could
>cheaply tell you raw amps at least on each of n outlets?

Digi-Key sells a Melexis MLX90215 Hall-effect IC that looks like it might
work for $11/1 and $7/50. There is a page on the data *** about using
it for current sensing. I don't know anything about it other than it
exists.

Matt Roberds

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