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Server-controlled power strip

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mightywombat

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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
 
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justDIY

Active Member
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.
 

mightywombat

New Member
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!
 

justDIY

Active Member
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.
 

mightywombat

New Member
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...
 

mightywombat

New Member
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?
 

MikeMl

Well-Known Member
Most Helpful Member
I use one similar to this. It is controlled via the USB port.
 

Mike_2545

Super Moderator
Now, I just need to find one that can pass 120VAC and is triggerable with 5VDC...


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


 

iflymyhelishigh

New Member
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 ;)
 

Mike_2545

Super Moderator
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.
 

mightywombat

New Member
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.
 

mightywombat

New Member
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.
 

iflymyhelishigh

New Member
Ahh. I didn't click on the link. The picture says 24VDC ;)

wombat, you might want to do something like me, I actually am wondering if its possible to request a reboot from an arduino.

Now, cause I am going to start a small dedicated server company, possibly shared too, I know that these servers can NOT fail. That is why I have been researching for a while now, complete network controlled strip, DIY UPS interfaced to a generator, it'll be pretty awesome. The area where I want to host the servers is known to have power outages often, hence the reason for the generator. Plus running the fibro lines to the area is going to be expensive.

I don't think its best to just cut power lol. Windows hates it when you do that, and a reboot if possible would be MUCH softer ;)

What kind of server are you running? If its UNIX then I think we can work together on this ;)
 

mightywombat

New Member
Iflymyhelishigh: I'm running a Linux server on an old HP Pavilion I found on the curb. :) As to requesting a reboot from an Arduino, I'm intending that the Arduino should only be responsible for restarting the server if the computer has frozen and is unresponsive, in which case you would have to powercycle the PC anyway. Since I'm not running a commercial server just an at-home internet sharing setup, and since my cats don't use the internet, I only have one client: my wife.

At this point in the design process I don't have a circuit diagram, but as soon as I figure out what relay to use I'll be just about ready to wire the thing up. If you're interested in a collaboration you can email me at mightywombat @ gmail.com
 

justDIY

Active Member
regardless of the coil voltage, I don't think 2A is a suitable rating for powering "servers" or anything with a decent sized SMPS power supply ... the inrush current to charge up those hungry capacitors is quite high, even though the constant operating current might be low
 

mightywombat

New Member
JustDIY: That's what I'm concerned about, but I'm having a little trouble finding a relay, normally closed, that can A) handle the current requirement and B) doesn't cost $6+ each. The ones I'm finding will require a driver circuit as well, which adds a little bit of additional price to the already more expensive relays. I'm just trying to keep my cost down, since I'm building this to save money over buying a commercial unit.
 
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