[Novalug] Home power monitoring

Greg Faust gregfaust@gmail.com
Wed Feb 20 19:17:10 EST 2008


it's amazing that nerd heaven only has 100 amp 3 phase.... I always
dreamed nerd heaven has perpetual energy is always at the perfect voltage
and never fluctuates or goes out and nobody needs backups because nothing
ever crashes or gets "fat fingered" by the admins.

On Wed, Feb 20, 2008 at 7:00 PM, <ethan@757.org> wrote:

> Howdy,
>
>   I'm new to the list, but checked out the archives to determine the
> traffic. I noticed a somewhat recent thread regarding measuring the power
> consumption.
>
>   A few years ago I had an office / "hacker space" in Virginia Beach, VA.
> I had a setup that was doing something similiar. I wasn't logging it to a
> computer because I never got around to it. Knowing what I know now, then,
> I think it would be easy.
>
>   The current is measured with something called a Current Transformer.
> It's a doughnut looking coil. There is a variety called a split-core
> current transformer (they seem to call them CT's in the industry). These
> are ideal because you can put them on a wire without disconnecting it.
> This is what the clamp on meters are.
>
>   The coils come in a ratio, like 100:5 ... I *think* it means at 100 amps
> 5 volts will show up on the terminals, but I forget.
>
>   In my setup there, I had a main panel with 3 phases of 100 amps (208). A
> normal house has single phase delivered on two wires, with a neutral. In
> the three phase setup, it's like 110-120vac from a leg to neutral, but 208
> between legs. In a house it's similiar from legs to neutral, but 220-240
> between the two legs. I had a 60 amp breaker that was 3 pole (3 phase)
> that had the wires coming out, went through 3 of the current transformers,
> then went into a disconnect switch. The disconnect switch fed a 18,000
> watt (18kva) UPS, which in turn fed a sub panel that fed the racks of nerd
> heaven.
>
> I took the output of the 3 CTs and fed a meter I got from eBay. The meter
> is made by Square D, under the brand power logic. I originally wanted to
> use the meter on a single phase house style setup, but was told all the
> numbers will be off. I remember having to configure the meter with the
> ratio of the CT's I was using, and it would show the current load on each
> leg.
>
> It should be very trivial to read the CT with a ADC chip (Analog to
> digital converter), and then read that on a computer. This would eliminate
> the need to have two RS232 connected DMM meters tied up all the time.
>
> A huge issue is going to be adding CT's to an existing circuit breaker
> panel. Definitely consult an electrician unless you are very very familiar
> with that stuff. There is no way to disconnect the power coming into the
> panel (the two 110 feeds that should be 100 amps per leg or so, unless you
> have a baller McMansion that has 400 amp service). Also, we talked about
> it before when my stuff was setup -- and I'm not sure what the electrical
> code is regarding running low voltage cable in a breaker panel (the wires
> to read the CTs). I think it's a huge no :-(
>
> I actually found out about the powerlogic panels as when I worked at NASA
> they were included on the MGE PDU units in our data center. They retail
> for about $2600 each, but I think I got mine for $180 on feeBay. The
> powerlogic panels are absolutely wonderful, it's a shame they are 3 phase.
> You could still use one to pull the data from the CT, read the power
> frequency, and ThD and stuff... but the power consumption #s will prob be
> wrong. They speak RS485 or RS422, and use something called Modbus which is
> common with industrial controls platforms (I'd love to get paws on Allen
> Bradley panelview LCDs to monkey with).
>
> Pic of the powerlogic showing THD from 5KW cheap generator during
> hurricane isabele:
> http://users.757.org/~ethan/pics/geek/unsort/IMG_1151.JPG
>
> Arrgh. I was wrong, no cut off switch between the breaker panel and UPS:
> http://users.757.org/~ethan/pics/lasers/laser-office/IMG_2033.JPG
> The CT's are in the grey box to the right of the painted breaker panel. I
> can't find a picture with the cover off, even though the thing was open
> half the time (the wires had no break in them, they just went through the
> coils).
>
>
>
>
> --
> Ethan O'Toole
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