A USB Power Controled Plug Strip. With Isolation.

The whole point of this Instructable was to allow me to power on all the accessories for my computer without thinking about it. And then not power all the little power vampire wall warts when I am not using the computer. The idea is simple, you power on your CPU, all of the other parts of the system power up (monitor, laser printer, speakers, etc) When you power off your CPU, they follow suit.Now there products out there that will do this for you, and if you do not have the experience working with line voltage electricity, please stop reading and just go buy one. There are several products that do exactly what we are trying to do here, but of all the ones that I have reviewed have disadvantages over the device that we are going to build. They fall into three basic types:

There are cheap usb controlled power strips, but I have seen several that do not offer any isolation, and if you are creating a possible path for line voltage (120v here in the USA) to your mother board, and its many hundred dollars worth of over-clocked goodness. I would like some isolation.

There are current sensing power strips, One of the outlets is set up to sense current flow. When this happens the electronics in the power strip power on the other outlets. Its a good idea, but sometimes they do not sense correctly, and will not turn on the accesories. Also the electronics require yet another little power supply to be on 24/7, this we are trying to avoid.

There are well designed enterprise grade solutions with isolation, that work very well and have a very hefty price tag as well.

This circuit uses no extra power when it is not in use, and offers some hefty isolation from power surges, and does not cost a fortune to build.

Step 1: What You Will Need

First off if you do not feel confident in your ability to work with line voltage power, please stop reading. If you build this project wrong, you have the ability to destroy your motherboard on your PC. I'm not kidding.

The heart of this system is two things really, the actual switching is done by a DC controlled solid state relay, All the isolation is provided by a pair of fuses and some transient voltage surge supressing diodes (TVSS)

All of the other parts are really up to you, I used what I had kicking around. Which was mostly standard electrical fittings, and an old plug strip, and a heatsink from a junk processor, and a USB cable that was miss ordered with usb "A" connectors on both ends. Feel free to use whatever works for you.

All told the parts that I had to order (fuses and holders, TVSS, and Solid State Relay) were less then $30.00 USD from an online supplier.

Step 2: The Schematic!

The concept of this circuit is pretty simple. The 5 volts provided in the USB connector is used to turn on a large Solid State Relay, which turns on the power to the power strip. All of the power control is done by the solid state relay(SSR). If you have never used and SSR for controliing power it could not be any easier, the designers have taken all of the hard engineering out of thier use. And what you get is a box with 4 terminals. Two of the terminals are for the line voltage. The other two are for the control voltage. When you supply control voltage to the control terminals, the line voltage terminals turn on. Thats it. No, really. Its just a little black box. No further engineering needed. Inductive loads, motors, lighting, resistive loads. They don't really care as long as they are within there rated current range.

The relay I chose was a Z240D10 from OPTO22. It has a maximum rated current of 10 amps @ 120VAC. This should be more then enough for my desk. The control input accepts from 3-32 VDC. So the 5 volts from the USB connector is more then enough. It was also chosen for its low cost. If you need more current capacity you can order a larger SSR.

The protection part of the circuit is three fold:

The first line of defense is the actual SSR. It uses an optical isolation between the power and control rated at a 4000 volts.

The second part of the circuit is a pair of 125mA fuses that will blow if over loaded.

The third part of the circuit is a pair of (1.5KE6.8CA) 7.14v transient voltage surge supressing diodes (TVSS) These are similar to a Zeiner diode. When the voltage across the terminals exceeds a limit. They begin conducting. Except unlike the Zeiner diode, they are bidirectional. So if for any reason the voltage in the control parts of the circuit exceeds 7.14v they act like a short and blow the fuses. The power dissapation for these parts is rated at 1500 watts for 1 millisecond. Which is more then enough to blow the fuses and protect the circuit. Circuits like this one are used in various communication devices that are subject to lightning and power surges.

Step 3: Enough Talking Time to Build.

I chose to mount all of the components in a standard electrical box, for low load situations the box itself is probably enough of a heatsink for the SSR. But I had an old processor heatsink that was pretty good fit. So it was added to the box behind where the SSR mounts. Don't forget to add some heatsink compound between the SSR and the box, and some between the box and the heatsink.

The cord for the Plugstrip is cut in half and run through the electrical box. The neutral (white wire) is spliced with a crimp terminal. The grounds (green wire) are spliced and connected to the metal chassis for safety. The hot wire (black) is connected through the SSR with crimp terminals. This concludes the line voltage wiring.

The +5V and Ground from the USB cable (pins1 and 4) are are connected to one end of the fuse block, and one TVSS The TVSS diodes are simply crimped into the connectors for the fuse blocks. Simple, fast, easy. Then two wires are run from the other end of the fuses (with another TVSS) to the control terminals of the SSR. Most SSR's will have one of the control terminals marked for the positive (+) lead. Make sure to get the polarity right.

Make sure to insulate the other two wires in the USB cable from each other and the metal case. If you do not you can short out the USB buss and cause all kinds of other problems.

This concludes the wiring.

I added a small piece of plastic (recycled blister packaging) to form a voltage barrier between the high and low voltage sides of the case, as extra insurance.

Step 4: Close It Up and Test!

So with the wiring completed. and checked. Its time to close it up and test. I recommend starting with things other then your computer and all its toys for testing. Plug a light bulb into the plugstrip. Plug the power strip into the wall. If everything is correct, nothing will happen. Now DO NOT USE YOUR COMPUTER FOR THE NEXT STEP. Find yourself a USB charger from your iWatever, and plug it into the wall. When you plug the USB cable from the unit into the charger the lightbulb should light. This way if you get anything wrong, the most you should be out is the cost of the charger.

Troubleshooting: If it does not work check the switch on the power strip. Then check if you have the polarity from the USB cable to the SSR correct.

Hope you have enjoyed this. Its a fun little project. And has the side benefits of making your life easier, saving you money on electricity, and doing your part to save the planet.

Keep tinkering,
Richard.

Comments

[BigD145]

Nice instructable, but your computer IS a vampiric wall wart. I just put my computer and peripherals on a single control strip.

[kill-a-watt]

There's a small amount of power that gets supplied to the mobo to do things like network booting. You can actually boot a room full of computers by sending a special packet to an off computer. All in all this has saved the world gobs of energy because backup computers can be booted remotely, and they don't have to run 24/7 just in case the primary breaks. in this case one little parasitic load can switch off a few wall warts

[kill-a-watt]

just checked and the PC seems to be pulling 2 watts. that works out, at 15 cents per KWH as:

(2 * 24 * 365 * .15) / 1000 = $2.63/year

17.52 KWH/year (four loads of laundry in an electric dryer)

I believe that is quite a few wall warts worth of idle juice. Still, it's a pain to shutdown your PC and then flip a switch on a power strip

[BigD145]

If you're using tons of USB peripherals, you're probably not going to need them from a remote location. That USB scanner won't do you much good from across the country. Network booting won't even enter into this. Rooms full of computers tend to be either full on or in standby mode. There aren't too many businesses that do a full overnight shutdown or that use a single power strip. Employees rarely even turn monitors off. I can't even tell you how many offices I've walked into that had the same screensaver on every monitor. They stay on all night long and waste vast amounts of power. This entire project is tailored for single user, private home usage. Unless you're a paraplegic, I'd say it's not that difficult to flip a switch. You'd put more effort into building this particular project than you'd put into flipping a switch twice a day for a few months, assuming your nearest hardware store is inside your living room.

[lopez8675]

what if your computer is tucked in a corner, and the power strip is behind it? then for some people you have to crawl under a counter, pull out your PC, flip theswitch, and push back your PC.

[BigD145]

You could not make it so inaccessible. Mine is under my desk, but that doesn't stop me from getting on my knees twice a day.

[Mack48]

At 74 years old with bad knees, there isn't much I would not do to avoid getting down on my knees even once a day. Actually getting down is not too hard, but getting back up is murder.

[kill-a-watt]

True, the network boot feature isn't too useful for the average person. It is, however, very useful to someone running a Beowulf cluster. I use the feature to reboot my firewall remotely if for some reason a power outage lasts longer that the UPS, and it's built into every modern PC. No one even asked me first, they just put that in the standard. On my PC, it goes like this. I tell the PC to shut down, I wait about 45 seconds, and then I flip the toggle switch. I'm afraid to kill the power strip first because I have storage mounted over the network (NAT and a router) I could leave the router on 24/7 but I'll bet that would take more power than the PC's net boot usage. I'll check that next. Something like this would make my life easier. I like it. Oh and just a note, the test PC that I'm measuring happens to have 2 network cards in it. It use to be my old firewall. I'll see what it draws when I take one of those cards out too.

[milo0is0hot0]

i've tried a few times to remotely start up and shut down my pc's from my laptop so that i do not have to go down stairs and turn it then on and off! however i have never managed it! my software was s**t!!! please can you tell me the software that works for you! i run on a windows enviroment and if you know how to shut down and boot up using ms-dos/cmd i would be happy to know

[kill-a-watt]

this feature is implemented in the hardware, not the OS, so a computer running (really not running, because it's off) anything should boot ok if it gets the magic "packet"

There are plenty of sites on the internet that can send that magic packet for you, try looking http://www.google.com/search?q=%22Wake+on+LAN%22

Here's one: http://www.dslreports.com/wakeup

also, check this wikipedia page: http://en.wikipedia.org/wiki/Wake-on-LAN , perhaps you need a cable to your network card?

[milo0is0hot0]

THANKS, i was aware that it is hardware based and usally you can disable/enable in the bios i just needed the software/program to send the 'magic' packet anyway thanks for the links should solve my problem...

[smmiller506]

Nicer computers and most power supplies (like the Thermaltake Toughpower I used) in DIY computers have a switch on the back of the PSU that's connected into the line voltage. When that switch is off, there truly is no power draw. Therefore, there is no power draw anywhere in the computer or power strip.

[BigD145]

Now you're talking about a rocker switch, exactly like what's on a power strip. We're back to just using a single power strip and one switch to do the job.

[smmiller506]

You're right, but I was thinking more of convenience - the computer is more likely to be closer to you than the power strip than the USB it's plugged into. Also, it would be safer to use multiple USB controlled power strips form one computer power switch, than plug multiple strips into one main strip. You are likely to overload the main strip whereas multiple strips can be plugged into different outlets, and still be controlled by the computer.

[BigD145]

This entire project involves a single power strip, so let's stick to that. If you can overload a power strip, you're not really interested in saving power.

[thermoelectric]

It would usually take something like a small welder to blow a power strip

[alpha1040]

I have blown them before... its a bit easier than you would think. I was running 7 computers (300w x3, 600w x2, 450w x2) and it completely fried the unit. Luckily I had others around. I do computer repair and I have had up to 18 computers running in my workshop at once lol (obviously not all on one strip!).

[crazy-blender]

do you need the heat sink and what would happen if you didn't use it ?

[Mack48]

As Richard mounted the SSR on a metal box using heat sink compound, that is likely all that is needed as long as the surface of the box is smooth and clean. He used one because he had it already laying around and thought "If a little heat-sinking is good , more might be better". And that is generally true, but only if the fins of the heatsink are arranged so as to induce convective air flow through the fins. Without the airflow all it does is add some thermal mass which will slow down the temperature rise a bit. Having said all that, the power switching device inside an SSR is either a TRIAC or two SCRs which are switching from either full on to full off. When off they dissipate almost no power, and when on they dissipate only a small amount, basically their forward voltage multiplied by the amount of RMS current flowing in the circuit. That is about 1.5 X .707(10) at 10 amps or about 10.6 Watts in the case of a 10 A load. Try to imagine how hot a 10 watt incandescent lamp would get if you were holding it by the envelope. Ouch! Okay, I do not have a ready reference for how much thermal resistance a 4 " square connection box has to ambient air, or what the ambient air gradient desired is, or what the load current really is, but those things greatly affect the answer to your question. If his load current is really 10 Amps, and he wants it to stay cool to the touch (and definitely within the ratings of the given SSR) and he wants it to last a really long time, he may not only need a heatsink, but also a fan to force convection through its fins. The only way to be sure is to instrument the case with a temp sensor and then try it out with the real load over a range of ambient air temperatures. You cannot assume 25 degrees C. either since most ambients vary quite a bit over time. Having said all that to try and answer your simple question you may get a sense of why engineers hate simple questions. The answer to most engineering questions is "It all depends..." followed by some long winded answer that most non-engineers cannot bear to hear. Many folks like the "Try it and see" approach, otherwise known as the empirical method rather than the other way because they don't like the math. As long as you can afford all the burned up parts, that may be okay. You may burn up a few either way, but there should be fewer the "other" way.

[Mack48]

A very nice project, one that solves a problem, and uses up a few of those parts that you had laying around to boot. Your writing style was straight forward and understandable, Having said that I offer a couple of observations that would augment your grammar a bit. There, their and they're are three words that sound alike but mean totally different things and are not interchangeable, Some sentence fragments may illustrate this better than some long winded rules, so here goes... There is a lot of confusion about this... Their car is out of gas... They're going to get more...! There is an adjective which modifies a noun. Their is also an adjective that shows possession of something (a noun usually but possibly also verbs). They're is a contraction of They and Are. Contractions are usually a device used to indicate a relaxed, less formal way of speaking such as normal people do in conversational speech. It happens when folks speak quickly enough that it is hard to tell when a word ends and the next one begins. Another problematic word is it's because it might be a contraction of "it is" or a noun form of "it" meant to show possession, i.e "that is it's own ball" perhaps speaking of a dog or some indeterminate thing (an alien?). Also, Then and Than are often mixed up, but the grammar rules for these words I'll leave for you to research. I'm not an English teacher or anything like that but certain words catch my eye when I'm reading and they are misused. I guess I could be a proof reader (as all of us should be of our own writing whenever writing for others to read) but that is also something that I have not done professionally. I guess where all this comes from is 40 plus years of professional engineering where writing has always been a part of my job. I mean no insult, but offer the above comments in an intended constructive way. Again, a nice project. Thanks for sharing it.