12 volt trigger circuit for cabinet fan - AVS Forum
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post #1 of 23 Old 02-02-2010, 08:14 AM - Thread Starter
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I hope this is the correct location for this question.

I will be installing my receiver in a cabinet that doesn't leave much space (approx 1" above and each side) and I am wanting to install a fan to help move the air.

The receiver has a 12 volt trigger that I want to use to switch a 5-12 volt wall-wart to power a computer case fan so it turns on/off with the reciever. Is this going to be a diy venture? Are there schematics available?

I have looked around via google and other forums, but I can't seem to find what I'm looking for. Thanks for any help.
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post #2 of 23 Old 02-02-2010, 08:25 AM
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Quote:
Originally Posted by SilentJ20 View Post

I hope this is the correct location for this question.

I will be installing my receiver in a cabinet that doesn't leave much space (approx 1" above and each side) and I am wanting to install a fan to help move the air.

The receiver has a 12 volt trigger that I want to use to switch a 5-12 volt wall-wart to power a computer case fan so it turns on/off with the reciever. Is this going to be a diy venture? Are there schematics available?

I have looked around via google and other forums, but I can't seem to find what I'm looking for. Thanks for any help.

Google for "12 volt trigger power strip" or outlet and you can find items in the $100 - $200 range. Does your receiver have a switched outlet that you could plug your fan into?

Also, there have been a few threads lately mentioning a "power sensing smart strip" which is less expensive than the 12 volt trigger options.
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post #3 of 23 Old 02-02-2010, 08:32 AM - Thread Starter
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MurrayW,

Unfortunately, my receiver does not have a switched outlet. That would have made things too easy.

If the 12 volt switching power strips are between $100-200, that seems like a lot of money to switch one fan.

I knew about the current sensing power strips, and they are more affordable, but I was hoping to still not pay $30 to switch a small fan on/off. I may have to resort to one if I can't find a cheaper way, though.
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post #4 of 23 Old 02-02-2010, 09:09 AM
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Quote:
Originally Posted by SilentJ20 View Post

MurrayW,

Unfortunately, my receiver does not have a switched outlet. That would have made things too easy.

If the 12 volt switching power strips are between $100-200, that seems like a lot of money to switch one fan.

I knew about the current sensing power strips, and they are more affordable, but I was hoping to still not pay $30 to switch a small fan on/off. I may have to resort to one if I can't find a cheaper way, though.

I am not sure how DIY you want to get, but I am sure there are home-brewed ways to accomplish what you want to do...but I don't know how. Good luck and report back if you find a solution. I am looking to do something similar to trigger a back light for my TV when it is powered on and so far the smart strip seems the cheapest and easiest solution for me.
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post #5 of 23 Old 02-02-2010, 06:29 PM
 
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Why don't you just use a relay?
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post #6 of 23 Old 02-03-2010, 05:17 AM - Thread Starter
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Quote:
Originally Posted by duvetyne View Post

Why don't you just use a relay?

Because I'm not sure that's all that is needed? Is the 12 volt trigger signal a constant voltage or a pulse of some kind? If it is constant, then I guess I could use a relay (maybe a resistor, too). I'm still waiting on the receiver shipping, so I can't test the trigger signal myself, yet.
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post #7 of 23 Old 02-03-2010, 05:44 AM
 
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Why would you need a resistor?

You could use an electromechanical relay, a solid state relay, a transistor or an optoisolator...all of which are much cheaper then those power bars above.
If the trigger is constant, and they usually are, connect the trigger output to the relay coil, ssr input, base/ground or diode input, depending on what you use.
Let me know if you can't find a schematic online.
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post #8 of 23 Old 02-03-2010, 05:54 AM - Thread Starter
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I wasn't sure about what would happen with only a relay in the loop. Wouldn't that be pretty much a direct loop, or short? I know connecting the positive and negative of a power supply/battery directly with a wire is bad, and I didn't know what a relay added to the circuit. Electronics noob

Something like this should work: 12VDC/125VAC RELAY

The 12 volt draw is 30mA, and the receiver 12 volt switch is 0.1A (100mA) max. So I should be fine.

Thanks for the help duvetyne, it ended up being a lot simpler than I thought. I wonder why it was hard to find?
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post #9 of 23 Old 02-03-2010, 07:31 AM
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Quote:
Originally Posted by SilentJ20 View Post

I wasn't sure about what would happen with only a relay in the loop. Wouldn't that be pretty much a direct loop, or short? I know connecting the positive and negative of a power supply/battery directly with a wire is bad, and I didn't know what a relay added to the circuit. Electronics noob

Something like this should work: 12VDC/125VAC RELAY

The 12 volt draw is 30mA, and the receiver 12 volt switch is 0.1A (100mA) max. So I should be fine.

Thanks for the help duvetyne, it ended up being a lot simpler than I thought. I wonder why it was hard to find?

There is next to nothing about this relay on the RS site and the picture is just a blue rectangle. How exactly would this work? How would you connect the 12V trigger signal and where would you plug in the fan?

Sorry for asking what are probably basic questions, but I too would like to find a better solution than the smart power strip.

thanks,
Murray
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post #10 of 23 Old 02-03-2010, 07:59 AM - Thread Starter
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Yeah, the picture shows very little except for the important detail that it is, in fact, blue

Here is a bit better picture of a similar relay:



Below is some info I have found myself that I shall pass along for future reference:

There are 6 legs total for this type of relay. Two of them are for the incoming 12 volt signal (somewhat dependent on the specific relay, I think), and the other pins are for the contacts to be switched.

Good description here.

The relay from RS can be used to switch something on/off that uses up to 125V and up to 10 amps. So it could switch a 120VAC cabinet fan, or a wall wart for powering a 12V or other fan. The packaging usually contains the schematic as far as what pins are what.

Let me know if that makes sense, or someone else with better knowledge than me can step in.

It seems odd to charge $200 for a 12V triggered power strip, when the key item that does the switching is only $5 from radio shack.
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post #11 of 23 Old 02-03-2010, 08:37 AM
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Quote:
Originally Posted by SilentJ20 View Post

Yeah, the picture shows very little except for the important detail that it is, in fact, blue

Here is a bit better picture of a similar relay:

Below is some info I have found myself that I shall pass along for future reference:

There are 6 legs total for this type of relay. Two of them are for the incoming 12 volt signal (somewhat dependent on the specific relay, I think), and the other pins are for the contacts to be switched.

Good description here.

The relay from RS can be used to switch something on/off that uses up to 125V and up to 10 amps. So it could switch a 120VAC cabinet fan, or a wall wart for powering a 12V or other fan. The packaging usually contains the schematic as far as what pins are what.

Let me know if that makes sense, or someone else with better knowledge than me can step in.

It seems odd to charge $200 for a 12V triggered power strip, when the key item that does the switching is only $5 from radio shack.

It's getting clearer...but I still need more basic information on the physical connections.

1. How do connect the mini-plug from the 12 Volt trigger to the appropriate 2 legs of the relay?
2. How do you connect the 2 prongs of the electrical cord for the fan to the appropriate 2 legs of the relay?
3. How do you connect the appropriate 2 legs of the relay to the house AC?

Sorry for being so dense.

thanks,
Murray
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post #12 of 23 Old 02-03-2010, 09:33 AM - Thread Starter
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Cut the wires, strip the wires, solder the wires

Depending on the relay you may be able to use some sort of crimp connector, too.

Different receivers can have different connections on the back for the signal wire. Mine has what is essentially a headphone jack, but in mono (2 contacts instead of 3 for stereo). Solder the 2 trigger wires to opposite ends of the coil on the relay (should be marked). On mine, I will probably skip the soldering of 120V wiring, and instead use the relay to switch the wall-wart/power supply instead. I just feel better about soldering and messing with low voltage stuff. The downside of this means the wall-wart will always be plugged in and using some--although small--amount of power.

Here is what I will try to do:



In theory, this should work. Anyone see any issues?
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post #13 of 23 Old 02-03-2010, 12:39 PM
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I've made two of these... one to turn on/off lights for different inputs and one to turn on/off my sub amp. they work great and fairly easy to put together. cost about $15.
LL
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post #14 of 23 Old 02-03-2010, 08:20 PM - Thread Starter
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Quote:
Originally Posted by mhebig View Post

I've made two of these... one to turn on/off lights for different inputs and one to turn on/off my sub amp. they work great and fairly easy to put together. cost about $15.

I like that! What kind of box is the outlet and relay in? Did you use a similar relay to what I'm thinking of?
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post #15 of 23 Old 02-03-2010, 09:29 PM
 
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Quote:
Wouldn't that be pretty much a direct loop, or short?

Only if you connect wrong.

Follow the schematic, it's a very simple circuit....it's just a switch.
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post #16 of 23 Old 02-04-2010, 07:22 AM
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Quote:
Originally Posted by SilentJ20 View Post

I like that! What kind of box is the outlet and relay in? Did you use a similar relay to what I'm thinking of?

the box is just a normal, all plastic junction box from any hardware store. I found one without holes pre-punched in it. then just drilled my own where I needed them. there happened to be just enough room under the outlet to fit the relay, so its a nice neat package.

the relay i used is the one mentioned above from the shack The soldering of everything was a bit tricky, cause everything is small, but it not too bad.

then I picked up a replacement power cord, one with bare wire on one end and a 3-prog on the other. A mono mini connector like this one. and used some 2 conductor audio cable I had lying around.

hope this helps.
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post #17 of 23 Old 02-04-2010, 07:27 AM - Thread Starter
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mhebig,

That helps a lot, thanks. Did you do anything to insulate the 110V lines at the relay? Heat shrink or anything? I'm worried about the connections being close together...
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post #18 of 23 Old 02-04-2010, 08:09 AM
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I did put some heat shrink on the ends. be sure to post some pictures, if you end up making one. thanks
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post #19 of 23 Old 05-24-2010, 08:40 PM
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If the receiver has a USB port, why not use something like this:

USB Fan
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post #20 of 23 Old 05-26-2010, 01:11 AM
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I posted this on the other 12vdc trigger thread but here goes. The AVR's 12vdc trigger out is a current limited small switching transistor circuit. It is NOT designed to switch inductive loads. If you use a mechanical relay, a 1N4001 diode (from RS or other supplier) should be across the relay coil with the banded end (anode) connected to the 12VDC output and the cathode end to the ground and the relay's other coil connection.

Solid state relays are cheap at MPJA.com.
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post #21 of 23 Old 05-30-2010, 07:48 PM
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I just bought a pioneer elite and I noticed that it says it has a 12 volt trigger. So if I need to put a 12 volt fan in my enclosure to cool things down a bit do I just plug one one of the 12 volt fans into the receiver as a power source?
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post #22 of 23 Old 05-30-2010, 09:16 PM
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As Gizmologist said, it is not designed to power a fan (which is an inductive load) nor is it likely to have enough current capacity to drive a fan (50 mA max on my Pio SC-27). Get one of the switching power strips shown above, build a relay circuit (use one of the solid-state relays from Gizmo's link), or try the X10 controller (what I did for my subs but overkill for your case).

For your situation, if you do not care to build a relay box, I would purchase a quiet 120V fan and use the switched power strip MurrayW posted.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #23 of 23 Old 09-08-2010, 01:38 PM
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Does anyone think a diode is necessary with the use of the relay? I've read that the coil can release voltage back to the AVR (or Projector) when the trigger is turned off. Is this significant enough to damage the equipment?
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