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.

Comments

[mantasxxi]

Hi lads,have read all this,i know is such of old thread,but like to ask how these tvss diodes working? How its proctecting circuit and blows the fuses? And why there are two of these on each side of fuses? Thanks

[toymotorhead]

Ok, TVSS diodes are are also known as avalanche diodes. Under normal operation they do not conduct. When the voltage rises to a designated amount they begin conducting. So in this case we are using 7.4 VDC diodes, in a circuit tht is powered by USB power at 5 VDC. So as long as the voltage does not rise above 7.4 VDC they do nothing. If the voltage does rise above that, they begin conducting. This will overload the fuses, and make them fail open, disconnecting the two sides of the circuit.

Its probably a bit of overkill in this circuit as the solid state relay already has quite a bit of isolation built in. But its a second line of defense, which is good, as computers are quite expensive.

[mantasxxi]

sorry once again for my silly questions,but is this protection in case relay fail and starts give an AC power to pc usb port? is this possible? can't understand why should be another reason that usb power should rise above normal 5V?

[mantasxxi]

tell me,can be used one diode and one fuse? or this won't work? is the zener diode will do the same thing as these tvs ones?

[nickroche]

Hey Richard,
This type of project is always going to draw comment from 'concerned people' and I have to admit doing a little data sheet checking myself when I first read it. Of course, people will come up with dozens of ways in which you should have made it safer or with more isolation etc, but I reckon this design is a good balance between isolation, function, safety and cost - there will always be tradeoffs and other ways to achieve the same thing or make improvements. UL, CE, EN standards, isolation transformers, circuit breakers.....hey, what about some thermal fuses in case things run away, or some fuses for the fuses, just in case they don't work?! There is always a 'whats reasonable' line and I'm sure you're well within it, especially for a non commercial, DIY project.
Anyway - good instructible, well made and I like it. Nick

[crazy-blender]

i made this and i found a relay that was 40 amps i think but witch way do you install the diodes silver or black side facing + or -

[crazy-blender]

this is pretty cool but where can you get a relay that is 30 amps

[toymotorhead]

You can find solid state relays that will switch 30A with ease. The one chosen was selected for its low cost, and small size You can look up the OPTO22 120D45 http://www.opto22.com/site/pr_details.aspx?cid=3&item=120D4

Its a larger form factor part, and is rated up to 45A. At those levels of power you are definitely going to need a heatsink, and you should do a little experimenting to make sure its large enough to handle the heat dissipation, or check with the manufacturer of the device you are using to make sure you have a large enough heatsink, or what they recommend. If you don't, if you are lucky, you will just make your device fail prematurely, if you are unlucky, you could cause a fire.

[crazy-blender]

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

[jlongton]

I just gathered all the components to build a similar device when i realized that the +5vdc delivered to the USB port remains on when in standby mode. I have an HTPC that I connect to my TV. I rarely turn it off. Instead I use a wireless mouse and keyboard to put it in and out of standby. I would like to be able to turn off the peripherals when in standby. It seems like I might have to connect to a 5v power supply plug inside the PC instead. anyone know of a better solution?

[toymotorhead]

I can think a few possible fairly simple workarounds to try.

1) Check read up on the motherboard in your HTPC. On some motherboards the USB power can be selected either with jumpers on the Mainboard, or in BIOS as to weather they have power when shutdown or in standby.

2) If you have the room you can install a cheepo PCI USB interface, that should power down when you go to standby, you don't need anything fancy, I would suggest eBay.

3) Check if your power supply powers down the +5v supply to the diskdrives when it goes into standby, the red wire is +5V and the Black is ground. There are usually a couple of extra connectors available.

[jlongton]

thanks for the suggestions.

1) I need to have at least 1 port powered while on standby to wake it with my wireless keyboard. so this likely won't work, unless there is a separate jumper for front and rear ports.

2) This is a possibility. If i can find a cheap one, and nothing else works, I might do this.

3) This is another possibility, but requires a bit more work and makes it more permanent to this PC.

It would be nice to have an outlet on the box you made where the PC could be plugged in. Then when the PC was turned on or woken up it would trigger the relay to turn on the strip. I'm not sure how the relay would be triggered though. it would have to detect the current or something,

[abishur]

Wow so you made this a pretty long time ago, but I used this as a basis for my own USB activate power outlet. I needed a single outlet rather than full strip (and I don't really have room for a full strip), but it's still a really great instructable! I did forgo the extra isolation as optical isolation is pretty "fool-proof" so there's (practically) no risk of it jumping back down the USB line and my deal plugs into a surge protector so there's the AC line is also protected from surge back.

Thanks again! Without this guide I definitely wouldn't have had the courage to set up my own system and would have ended up shelling out $30+ bucks for a pre-made "smart" power strip

[nickboy98]

pretty good, a good use for this would be in a caravan, buy one of those usb smoke lighter thingy's and you could power a whole caravan with 5 volts of power, even one of those usb solar thingys power an entire caravan with tiny solar power

[joshnosh]

no mate this just turns on whatever you have plugged into the strip when you turn your pc on like an automatic switch
it dosent make the power from the usb
usb is is only 500ma so you would get virtually nothing if you converted it to mains (you might be able to power a tinny tinny light bulb)
and if you plugged a tiny solar cell into an inverter (a box that makes mains ac from a dc supply ) nothing would happen because its tinny.
you can convert a 9v battery to give you 100,000v but you wouldn't be able to replace a power station with a 9v battery because the output is very small

[krisumsnz]

Hey Rich
Far to much negative comment above! I built this device. Now my HTPC client running mediaportal has a single "on" button - the amp, TV, subwoofer and remote controller power up. Wife and kids happy.
To finish up the whole shebang shuts down with no activity detected with "amp WinOff" and so when a song, DVD etc ends the whole lots switches off again.....(or the off button is used....)
It is fantastic and was simple enough to make

Thanks so much for the idea!
regards
Neville

[saadmanna]

i have worked on similar Project with Parallel port and serial port.
i am searching some thing like this but much more advance...so that i can control  at-least 8 switches with USB.

[cboy2us]

This provides isolation?!?!?!?!, first lightning strike, you will pay for.

[nforge]

Isolated ground can mean a few different things depending on who you ask.  But typically the requirements for an isolated ground are that it's wired directly back to an electrical panel, not relying on conduit or other metal items to link it back to a panel.  But when it's in a residential application, this is as good as an isolated ground, it would be a straight run back to a panel, and as long as the box is grounded it's as safe as you'll get.  http://www.mikeholt.com/technical.php?id=grounding/unformatted/ig1&type=u&title=Isolated%20Ground%20Reference%20One

[cooldudeintown]

I love the retro Pentium 2. I tend to forget that we all owned one of those at one point. Great Instructional keep up the good work.

[Arbitror]

So what's the Pentium II for?

[toymotorhead]

I just used the heatsink off the back of the Pentium II to give me a little better cooling. It was in the junk drawer, and about the right size.

[Arbitror]

Those good 'ol slot CPUs are good for many things!

[criggie]

Yep - I have one as a business card holder.  Works great.

[Arbitror]

It's like a paperclip, useful for almost anything...

[Blackice504]

some computers like mine have usb power always so for those people who like this project and have the same setup you can control this fuction by two ways one is the bios the other is physical jumpers to to allow or turn off usb power when the computer is off this is because some keyboards how power button on them or to wake up on mouse so if you have any problems remember to this step good instructable. thanks for sharing and love the case you made.

[2schnauzers]

I want to turn on/off a power strip when my TV is turned on/off. Does anyone know how to create a circuit (similar to this article) that would accomplish that? My thought is when the TV is on (via the remote control) it would draw power, somehow that fact could be used by a circuit to turn on the SSR. Thanks!

[rea5245]

toymotorhead, I hope you can give me some advice on this. I bought the parts for this, including a 1.5KE6.8CALFCT-ND (DigiKey part number). This is apparently a bidirectional TVS. It doesn't have a polarity marking on it. Can I use this part in place of your diodes, or do I need to go shopping again? Thanks.

[toymotorhead]

It looks like they should work fine. The bidrectional version should work fine, and polarity should not matter. Hope that helps Richard

[toymotorhead]

Clarification, the polarity that you install the TVSS should not matter, the polarity to the SSR still matters.

[toymotorhead]

I need to start thinking more before I comment, the breakdown voltage is a little lower on that part, but I do not think I will be a problem. You can start with one of the TVSS just on the SSR side of the fuses, that way if it starts conducting it will just blow the fuses, and not cause computer problems. Cheers RIchard

[bwanaaa]

for some reason that link doesnt work- search for this part at digikey: SA12CALFCT-ND

[toymotorhead]

If the supply voltage is 12vdc you should look for a rating that is higher then that. I would look for something in the 16-20 volt range. A lot of 12 volt supplies actualy run closer to 14 volts. You want a bit of headroom before the TVSS clamp down on the power supply,.

[bwanaaa]

ok, this is great, but i want to build something like this so my audio receiver can control a powerstrip. The receiver has a 12 v switched miniplug. Would the design be the same? The only thing i'd have to change is the diode so that it has a 12v rating instead of 5 (like this one http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=SA12CALFCT-ND). The failure voltage of these diodes is 13,3v

[billth87]

UL would want you to put a fuse or a circuit breaker in the hot line before any of your circuitry. If your SSR shorts to ground you could start a fire with this design. It's a 10A SSR, so a 10 Amp fuse would be appropriate.

[radon222]

Is there a reason to use an SSR instead of a mechanical relay? Relays seem to be a lot cheaper.

[toymotorhead]

SSRs offer many advantages, first of all they can use very low voltages on the control end of things to control large amounts of power. Its hard to find a 10 or 20 amp 120 volt rated mechanical relay that will run on 5 volts. Open the SSR catalog and you can find a hundred different ones. The one specified also has optical isolation between the control and the power. It also is a zero crossing type, so it only switches on and off at the zero voltage state of the 60hz sine wave. Where as typical mechanical relay switches off in any point in the sine wave, and causes da'arcin' and da"sparkin' on the contacts when it opens and closes. Which can lead to failure. But most importantly. There is no problem with voltage spikes on the control side when the coil of the relay is disconnected. These can actually be much more powerful then you might imagine. You could probably get away with a diode wired reversed biased across the coil as a spike supressor. But pretty much all of these flaws can just be avoided by using a SSR. Hope this helps. Rich.

[rocketman221]

yeah those voltage spikes from the relay coils are quite strong. i got a good enough zap from one to make me drop it and that was only running at 3 volts.

[technodude92]

This may work well with plug and play devices, but older peripherals, especially ones that take long to start, should be powered up before the CPU. I, as a rule, always power the peripherals before the CPU.

[amjadk]

The second that you turn on the computer, the CPU starts :P