DIY: 12V trigger outlet to automatically power on/off devices

Hey guys,
I wanted to share the results of a little project I tinkered with for the past few days. I recently got a new sub that doesn't have an auto-signal-sensing mechanism, therefore stays powered on all the time. Sure, it probably doesn't waste too much energy, but since I have 12V trigger outlets on my processor, I wanted to explore options to automatically power on/off the sub as necessary. In the past, I've used something like a Niles AC3. Although it does the job, it's not cheap ($100+) and is rather noisy when switching on or off, as it uses a mechanical relay. I was digging around on the AVS forum, and saw how a fellow made something similar from basic Home Depot parts. I figured I'd give it a shot myself as a relatively inexpensive project.

Here are most of the parts you'd need:

• Metal 1gang square box from Home Depot
• Cover for above box
• Outlet socket of your choice, I picked a nice 20amp version for about $8
• 5-15P 15Amp power plug, I chose a Hubbell model from Home Depot, about $11
• Cable clamp connector for the receptacle box
• Bulk 12 awg/3 power cord, about $1/ft at Home Depot
• .110" Female Quick Disconnect connectors <---- You'll need to order off ebay ($4) or Amazon, as HD/Lowes won't stock this size
• 10-12awg Female Quick Disconnect connectors <---Home Depot should stock these
• Some #4 screws and bolts (I used 3/4") x 2 to screw the relay into the box. Home Depot has these for about $1 a bag
• You may want some ring/spade connectors to attach from the electrical wire to the outlet. You could certainly use bare wire if you want.

You also need a couple of parts from Mouser.com

• 20Amp 12V trigger relay <--This is a nice solid state relay, and is silent in operation
• Female 3.5mm mini-plug connector <--This is where you'll plug your trigger wire into

I decided to buy enough parts to make two boxes. This cut down a bit on shipping cost per average item from Mouser, and some of the other connectors come in packs of 12+. Total parts cost, $~100. And $60 was just the relays and the Hubbell plugs.

I'm not good at writing DIY, so I hope the pictures can speak for themselves. The main thing you'll want to do is cut the hot wire (black) from the power cord and attach it to to the - side of the 120V trigger. The white (neutral) wire from the cord goes to the silver wire on the plug, green to ground on the plug. Now, you'll want to wire up the female 3.5mm connector. It has a tip (short) and ring (longer) connector. Tip is positive and will go to + on the relay, ring goes to -. You'll need some spare wire to make these connectors. I used some CL2 rated speaker wire, and crimped the .110" connectors on each of the ends. The ends that connect to the female jack are a bit tricky because even the .110" connectors are too big. I attached them anyways, and used a bit of solder to secure. I then bent the newly-attached wire (not the connector!) and used a zip-tie to secure to the female barrel plug housing to provide strain relief. Be careful here, I broke the tiny connectors on the first jack I used and had to order another I did use some heat shrink around each of these connections for insulating purposes.

Next, drill some holes in the work box so you can attach the relay inside via the #4 screws/bolts. You can connect the wires as show in my pics. You will also want to attach the Hubbell to the bulk power cord you bought. It is very simple, even if you've never done it before. Instructions are included with the plug.

Make sure all the wires have room to fit when you close the box up, and you're all done! You will likely want to test with a voltmeter to make sure the outlet is getting 120V when the trigger is applied. Now you have a way to turn on/off any 120V device, assuming you have a receiver etc that supplies 12V trigger output

 

Awesome thanks! We can use this at my school!

 

I built something very similar to this except I added a power resistor across the relay load terminals where the 2 black wires attach. When the relay throws the resistor is bypased. Instead of triggering it with a control voltage from a device, I have the input coil of the relay hooked up to one side of my main amplifier's power supply capacitor bank.

The reason I have this is because I added a massive amount of capacitance to the power supply of that amp. The current rush to charge it when drained would be enough to blow a breaker, so I built this to limit that current until the capacitors charge up to the trigger voltage of the relay. When they do, the relay trips, the resistor is bypassed, and it's back to normal operation.

I realize this is totally unrelated to what you were trying to do, but the circuitry is so similar that I figured I'd mention it.

 

^^ Interesting, Doug!

I thought of another way to make my device above more useful, especially if you have older gear that doesn't have 12V triggers per se, but a switched outlet on the back. Heck, gear from 40 years ago has these types of outlets! But you wouldn't typically want to plug in anything with even a moderate amount of current draw into your receiver.

So, you could get something like this: http://shop.emotiva.com/products/et3

Plug the power cord from the ET3 into the back of your older receiver, then the trigger outlet from the ET3 into the relay box like I made. This would allow you to power something off a dedicated outlet (via plugging in the relay box) and still use your switched AC outlets to control as trigger.

 

Well of course all you need is a little 12v transformer or wall wart hooked up to your switched AC outlet to drive the relay box if you don't have a 12v trigger. I'm not at all sure what that ET3 does as it was unclear from what I read from that link. Does it provide cycled triggers so that one trigger can control 3 different devices independently? Perhaps it's just a buffer of sorts so that the trigger output from your device can drive higher current trigger inputs. Generally the more current you're switching, the higher the current required for the trigger, though there are ways around that.

There are other ways to do this as well. Radio Shack used to make a power strip that was controlled by any AC device that was plugged into a special outlet on the strip. It detected the current when anything plugged into that special outlet was activated and that in turn activated the main outlets on the strip. They haven't made that device in years, but it's not too hard to create one with a bit or cleverness.

 

Indeed, you could also just use any old 12V wall wart or 12 V power supply plugged into the same receiver outlet. I've done this many times for stuff that doesn't have 12V trigger outputs, pretty handy, and cheap!

 

Russound ACT-1 is not that expensive. Works for me.

 

^^ Chris and Doug, that would work too.. but those wall wart power supplies don't have a 3.5mm male tip. So you'd need an adapter of some sort. Yes I've seen those "smart strips" too. A good alternative for a bit less $$$.

Interesting, I never came across the ACT-1 in my searches. Looks like the exact same thing as what I built! Only two potential drawbacks, single outlet, and most likely uses a mechanical relay (loud). Certainly not deal-breakers, but something to keep in mind.

 

I don't know about the relay. In my home theater it is behind a wall - behind the equipment in an adjoining room so I wouldn't notice it. I use it to trigger a Vestax amp that drives my (incredibly awesome sounding!!!) homemade Infininte Baffle subwoofer and an old receiver for "zone B" speakers above my pool table. I use a simple splitter to make it power multiple devices.

 

Works like a charm with my new (used) Rotel RSP-976 surround sound processor. Thanks!

 

Excellent!

 

Looks cool. Reminds me of things I used to make all the time years ago, and made me in the mood to do some DIY stuff..!..Cool.

 

I ordered a couple of the same relays from Amazon and both have the following problem: even when there is no input voltage supplied (or even when nothing is connected across the terminals), I am getting 120V power supplied to the outlet. Yes, my black/hot line is across the load terminals of the SSR (I checked both sides of the power supply wire). Do I have defective SSRs or am I doing something wrong? According to a review on Amazon, someone else had the same problem. Checking for conductance across the SSR load pins (with nothing else connected anywhere), I am getting high resistance, but would have expected no connection whatsoever. Thanks for any help.

 

Black needs to go to the relay, first. And neutral from your wire, straight to the outlet. Check my third pic in the original post.

 

Yes, that's the way I have it. Black/hot wire from source (wall) goes into pin 2 of the relay, and pin 1 is connected to the hot/brass side of the outlet. I also tried flipping pins 1 and 2 with no change. I'm thinking the relays Amazon is selling are either different or defective. Here's the one I have: http://amzn.to/1DRAS0M

 

Ya, that's the same one I have. I guess you got a bad one?

 

Ok, figured it out. This relay has a small leakage current on the output/load side. If the actual load that is drawn is negligible, the relay will not reset. Thus, no matter what the input, the relay output was closed. To reopen it, you simply have to connect an actual load to the outlet. I used a lightbulb. Everything works fine now - I should have been using the lightbulb (or fan, or whatever) instead of just the volt meter.

 

Now that you mention this... My receiver, which is 40+ years old has this switched outlet on the back. I have a nak cassette deck plugged into it just because it was the most accessible open outlet at the time, but it is almost never, ever powered on or used. It's not hurting or effecting anything simply by being plugged in, is it?

 

No, it shouldn't hurt anything. However, you can make an almost identical relay switch as I described above, where the 120V outlet on the back of your receiver triggers the relay. You would just need a different relay (e.g. 120V trigger input) and make a "plug" end on the trigger wire instead of a 12V headphone jack. This would allow the same functionality, but you don't have to worry about the deck (or other gear) overloading your receiver, because it would get the power from the relay box, which is of course plugged into a standard outlet.

 

Thanks for the tip. While the deck can be powered on from a switched outlet (and even has a special function for this) I actually do not have it power on with the switched outlet simply because I really never use it. So either way, it's always off. I just press its power button when I do use it, business as usual. But I can always just put it in a standard wall outlet, or leave it unplugged. I figured it may be smarter to leave the real outlet open for something which might require a bit more draw than a tiny tape machine.

 

...intrigued

 

As an update, a few months back I "converted" one of the two boxes I made to a "high current" version. I used a mechanical relay, so I could trigger my subwoofer. As I understand it, the solid state relays are not idea for high-current-draw applications. They can either get hot, or reduce the power draw. Probably not worth stressing over, but I figured it would be an interesting project to compliment what I already did.

Of course I had to get a new relay (Omron G7L-1A-TUBJ-CB, 12V version). Because this relay is bigger than the SSR, I had to get a box extender. Wiring schematics remain the same, but I added a 1N400x snubber across the coil relay contacts to avoid any spikes from the 120V contacts.

 

Ive been wanting to wire up my phono preamp to kick on only when the TT is on. Is there a cheaper way to do this?

 

Yeah, something like this: http://www.amazon.com/Take-Charge-Smart-Power-Strip/dp/B005DTBCD2

But there is no guarantee that your TT draws enough power to activate the trigger mechanism.

 

Oh really? Boo. How would I find out?

I just need something with like 2 outlets on it, everything im finding is a big strip like you linked.