Switching / monitoring multiple mains outlets & environmental.

Projects General Guidance
1

Hi,

I'm looking at building a box which will do the following:

Switch up to 50 x outlets using mains rated relays (I've seen a relay board with 10a 230VAC rated relays for sale, does anyone know of a larger one than 8 way?).

Monitor temperature and humidity (dallas 1 wire style ?)

Look at mains voltage (I assume using a AC/AC transformer and applying some simple maths)

Read up to 10 amps current per outlet and two mains inlets

Looks at mains frequency (should be a different way of looking at the AC/AC transformer)

Run a web interface for controlling the ports and looking at the results.

Talk to any SNMP graphing solution with a device MIB, for logging over time.

I realise this is a fairly tall order but isn't beyond the realms of possibility - I understand people have done all the things I've listed using Arduino hardware but I'm wondering if it's a little too much for one box, particularly the web server bit?

I am after some advice on the above - perhaps someone may even like to look at this as part of a paid development project? I've already tried to get this done using rent-a-coder and haven't got very far, with the first guy appointed somehow getting them to release the Escrow payment before I'd verified he'd done any work (which he hasn't)..

Apologies in advance if this post is in the wrong area and feel free to move it (admins)....

regards
Lee

2

Hi Lee and welcome.

50 outlets @ 10 amps each? Yikes! Won't that need a 3 phase supply?

I know there aren't any 1-wire humidity sensors around, I looked. There maybe some kind of Lithium battery charger chip around which measures humidity, thats about all.

What's this monster for?

Paul

3

Hi Paul,

Thanks for the reply!

regarding the 1 wire chips I think I dropped a typo there - I know of the Dallas DS18B20 (temp) and DHT22's which I (thought) did both and were 1 wire as well. I'd happily settle for separate sensors and TBH the humidity bit isn't all that important.

The important part is the switching of outlets and in reality, each outlet is only likely to have 0.5 - 3 amps @ 230VAC on it, but the problem is everything including cabling, switching etc. must be rated at the maximum load which could theoretically be plugged into an IEC C13 outlet...

Another very interesting device thing I'd like to look at is the monitoring of two AC inputs via AC/AC transformers and doing some clever switching between sources within milliseconds...

The "monster" as you refer to it is hopefully going to power computers in a Data Centre rack cabinet - there are lots of these on the market and very little which are good value for money; APC, Geist, Raritan to name but a few.

In terms of commercial viability, I have a number of clients in this industry who would potentially be interested in this and other products. I am a qualified electrician, network engineer, electrical designer and the owner of a Data Centre in the UK......

Feel free to hit me up on PM if you want to know specifics? (I realise mods can sometimes get a little narky at shameless plugs :wink: )

Cheers
Lee

4

Hi there Lee.
I presume, for your project, you want a mains supply with as few drop-outs and spikes as possible. I'm no expert on power supplies, but wouldn't using relays give you more spikes and dropouts? Have you thought about using triacs, instead of relays, for switching the mains current?

5

Here are some of the links

http://openenergymonitor.org/emon/buildingblocks

6

Thanks for the replies chaps,

The use of triacs is something I've considered, but to be honest relays would suffice for the switching on and off of outlets - I would be looking at using the type which fail on rather than off.

Triacs did however conjure up thoughts of something even nicer which could be done on the mains input side and in particular switching of mains sources. Everything connected to these bars would be switched mode AC power supply, so could cope with brief interruptions of power (by brief I mean milliseconds) so it isn't beyond the realms of possiblity one could do some clever switching, have two mains inputs and very quickly switch between one and the other, should a power source become unavailable.

regards
Lee

7

Unless you have a huge UPS or a back-up generator, how would switching between supplies help you?
If a navvy puts a pick into the power cable in the street, all three phases will go down!
An intermittent supply will affect all three phases.
An over or under voltage supply will affect all three phases.
A frequency variation will affect all three phases.
If you overload the supply fuse, switching the overload to another supply will trip/blow that fuse too.
I can't see any advantage in being able to switch supplies unless, as I said above, you've a back-up supply of some sort that is independent of the mains.

8

Take a peek at the AD7763 (one channel current/voltage/temperature/frequency) or AD7816 (adds voltage measurement for six channels). You'll find these types of "energy management" chips from many manufacturers, and this is the type of thing I'd assume you'd find in commercial PDUs. These particular chips have an SPI output so you could string up quite a few outlets with them.

With respect to using triacs, I have an APC rackmount unit with 8 switchable outlets; it uses relays for switching. It seems like a latching relay would be the best way to go -- you'd be able to "reboot" the PDU without affecting power output to all of the connected devices.

Regarding switching power, that's not uncommon in a datacenter, Henry. Being able to power cycle a server remotely is a big advantage in corporate environments when the support is "outsourced". I could tell you stories about on-site support breaking power switches on servers when they were asked to power cycle them.

9

Henry,

Firstly, Define huge? We have both multiple UPS's and generators on supplies A and B. We are fed at 11kV into a private ring main unit and off to separate 11kV to 400V trasnsformers, which feed dual 4000 amp switchgear and off into wraparound bypass, static ties switches etc. and through moderate sized UPS's (550kVA x 4 per side, A & B, 480v DC battery strings). That's one of my own sites, fairly small and simple setup. Customers we have who own other places are fed at 33kV and higher, with sites capacities of up to 30mVA and above. See Dropbox - Error

The problem with having UPS's and generators, ACB changeover switchgear and the like is that it creates multiple single points of failure on each path and, no mattter how good the design is, it's very difficult to guarantee both feeds right down to the dual 32amp commando in each rack, stay on.

Now most clients have dual fed equipment with multiple supplies and A&B feeds into each cabinet, but many still buy servers with a single power supply and some network equipment, even high end stuff sometimes is single fed on the AC side. Some kit is DC @ 48V, so we have many rectifiers and battery banks to cope with that stuff. The usual solution to get around this is something of this ilk: APC, a flagship brand of Schneider Electric - APC USA - They do the job well enough, but rarely have enough ports to power a whole rack, which means you end up having lots of them....

Chagrin, I've encountered these packaged energy management chips before, although not the exact ones you've listed - I'll have a look and do some digging - they definitely look interesting, for sure.. :slight_smile:

I've found a company in India who manufactures a 32amp Thyristor which would be capable of switching full load in a partial cycle, awaiting some feedback now, but paralleling up a couple of those puppies would certainly do the trick as well, at a low cost.

Just a note regarding phasing, we'd never normally feed a cabinet from different phases unless on a 3 phase commando socket (a lot of the newer blade stuff and storage arrays require three phase). Doing so in a single phase rack would expose the equipment and more importantly, the people working in the rack to 400 Volts potential between the two supplies. I've seen a few places where this has been blatantly disregarded, with disastrous consequences.

Lee