I am building a computer-controllable power strip for my home server. The goal is to make the system capable of automatically resetting any peripherals - or the server itself - if there is a detected error or fault of some kind. It will have a microcontroller managing the power outlets based on instructions from the server. The micro will also monitor a "heartbeat" from the server and powercycle it if there's a problem. The server will monitor its peripherals - wireless, internet connection/modem - and call for a reboot of that device if it fails a check.

This should be a pretty straightforward build, but I'm not that familiar with AC power management so I'm having trouble coming up with the component tio use for switching the outlets. It should be noted that each outlet on the power strip will be controlled individually, and should be normally closed so that the default state is to pass power to the connected devices in the event of a system failure on the micro.

The other requirement is that the component should be activated by logic-level power. This isn't a hard and fast requirement, but would make the design a great deal simpler.

So, in summary:

120VAC comes in from the mains power, through a digitally-adressable component (relay, MOSFET, whatever), smoothed out with a cap if necessary, and on to the device. A microcontroller, probably an Arduino or similar device, will be in charge of switching the outlets off when necessary, so the power available to drive the gate will probably not be more than 5VDC. It will only need to keep the power cut off for about 30 seconds at the most, timed by either the server or the micro - I haven't decided yet.

Any recommendations or comments on the design are welcome and encouraged. Thanks for your time and effort!

Ed

 

search out the product "pdu" or power distribution unit. the majority of them use SSR's to switch power, some of the old school use good old mechanical relays. Real expensive ones implement current transformers on each outlet as well as on the input, and provide fancy graphics on power usage. typically these devices are managed by a embedded computer, which handles interfaces such as ethernet, telephone modem, GSM/CDMA modem, WiFi, etc - it all depends on how expensive it is.

it is insulting how much these things cost retail, so I can definitely see the attraction in building your own. perhaps for home use, it would be acceptable, but if it's something for a business, I don't think the bosses would be sold on something from a workshop when the bottom line relies on the servers.

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For a simple power cycle, a good old fashioned mechanical relay will do the trick.

 

JustDIY: Thanks for the advice! I am building this just for personal use, so it's not incredibly necessary to make it conform to industry requirements, but id like to make a nod to them at least. That said, do you have any thoughts on how to build an AC switching circuit that can be controlled by a DC signal? Should I look for an SSR, or can I do this with a MOSFET? I really am starting from zero with respect to my AC electricity knowledge.

Thanks again!

 

A solid state relay

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it all depends what your budget is and what you've got access to. an ssr is the cleanest way to go, and most can be driven directly from a microcontroller (low voltage dc). however, a mechanical relay is a LOT less expensive, most 120vac relays use a 12+ volt coil, which means you'll need to use a relay driver between your low voltage and the relay. you'll also want to consider opto-isolation in there somewhere, in case something should go bad inside the relay.

__________________
If you don't have a planet, what good are gold bars?

want to contact me directly? gmail gordonthree
check out my project website: http://projects.dimension-x.net
Favorite numbers:
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

 

Blueroomelectronics: I had not actually considered the humble yet venerable relay for this application until you mentioned it. I suppose that, since the switch would not be tripped often, a mechanical disconnect would work nicely. Now, I just need to find one that can pass 120VAC and is triggerable with 5VDC...

 

JustDIY: I have never used opto-isolation in a circuit. How is it accomplished? Would the isolation point go between the relay driver and the relay? Forgive my ignorance, but I appear to have bitten off a little more than I can chew with this project. But, hey, how else will I learn anything, right?

 

I use one similar to this. It is controlled via the USB port.

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Mike ML.

 

Here is one that does not brake the bank 5VDC DPDT DIP RELAY | AllElectronics.com

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Mike2545

 

mightywombat, I'm doing a project JUST like this, but with a couple differences. All it is is a remote power switch, no monitering at all, monitoring is done by a separate unit that has the power to request a system reboot, or cut power to that port, then reapply power then perform normal startup.

All of it is programming, I'm just looking for the right solid state relay

 

Mike2545: That relay is triggered by 24VDC. That isn't 5VDC and I doubt the OP wants to buy a power supply just for that. haha

 

Look again it states: Kest# KS2E-M-DC5. 5 vdc 130 ohm coil. DPDT contacts rated 2 amps. Small sealed case, 0.80" x 0.38" x 0.40" high. Fits 16 pin IC socket DIP pattern. UL, CSA.

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Mike2545

 

iflymyhelishigh: It looks to me like the relay he linked to has a 5VDC coil. I'm in the same situation as you WRT the relay - I want to find one that is normally closed, DPST, and which can handle the maximum current draw of my server.

 

iflymyhelishigh: Also, the microcontroller is going to need a DC power supply anyway, so it would be a relatively simple matter to start with a higher voltage supply and bring it down to power the micro, or to use a step-up regulator to bring up the micro's supply voltage to that required by the relay. It would, naturally, be easier to just power the micro with a commercial wall wart and let the micro power the relay, so of course I would prefer to be able to do that.