Photo sensor to control compressor

[Bas]

There is a similar thread on Woodnet, but that one has already degenerated into petty bickering.

I plan to soundproof the closet in my workshop and use it to house the DC and compressor. Of course, being out of sight, out of mind, I'm pretty sure that one day the compressor will come up in the middle of the night. If I do a really good job with soundproofing it, I won't hear it, but chances are that at 3am the droning will penetrate the walls. A simple solution (that still involves sufficient nerdyness with high cool factor) would be to use a photosensor tied to a relay. Light in the shop means power to the compressor. No light in the shop, compressor is off.

Most photosensors I've seen are for prosaic, light-weight applications such as turning lights on and off (boring!). Anyone know a good source for something that can handle 20A@110V?

 

[kooshball]

Not as cool but have you thought about running a relay from your shop lights instead so that if they are energized you will have power in the DC room?

 

[dlrion]

I am sure you could find a photosensor that would handle your power... but a much simpler way to do it is to have a small DC photosensor control an AC relay. I did something similiar for a solar heater I made for my shop. I got a photo sensor that can tell when there is light falling on the solar array, and hooked it up so that the fan I had blowing heat into the shop would only run during the daylight. The relay I used was one repurposed that I had previously bought in California, and it was only a 10 amp model. But the cool thing was it was designed for a 12 volt system, but I found a simple 9 volt battery powered it successfully for a year or more.

The photosensor does not have to be capable of 20A just the relay... that happens everyday!

 

[dlrion]

Try this one

http://www.alliedelec.com/search/productdetail.aspx?SKU=8860142

Then its a pretty simple matter of hooking up the photo sensor in series with the a small DC power supply. I love old computers for this... the DC power supplies are great... but a 9 volt battery will work too. No light, no DC electricity, no magnetic field, no AC electricty.

 

[ehpoole]

I would second the suggestion to power a contactor (relay) directly off your lighting circuit. It will prove considerably more reliable -- and less finicky -- than the photo cell approach. As an electronics enthusiast I love projects like this, but we should also be aware of the tendency to needlessly complicate a simple task! That said, don't be afraid to throw a microcontroller in their just for the heck of it (why use a simple transistor/triac circuit when you can add a MCU to the mix :rolf.

You don't mention what size/type compressor you're intending to switch, but many of the smaller compressors are designed to bleed excess pressure from the piston cylinder to reduce stress on the motor during startup. Without bleeding the pressure off the motor is force to draw a much greater initial stall current to overcome the resistance offered by the piston, greatly accellerating wear and tear on your motor. As such, you may need to install your own bleeder solenoid (another good argument for driving everything directly off a properly rated DPDT contactor -- one throw activates the compressor, the other the bleeder valve) to automate this.

Regardless of the approach you choose, I wish you success in your quest!

PS - Just a reminder, if you use an electronics circuit (even a photocell) you will need to address the back EMF created by the contactor/relay when it is deenergized. Diodes work great for DC coils, back to back zeners or MOVs or gas discharge tubes work great for AC coils. Alternately, you could opt for a solid state contactor provided it is adequately rated for the startup surge/HP your compressor requires. I don't recommend driving the compressor directly with a triac due to the voltage drop and the fact it is a highly inductive circuit (plus the back EMF from the compressor).

 

[bob vaughan]

Hooking a photo sensor to the coil of a magnetic starter might work. The coil doesn't take much power. The mag starter would feed power to the compressor's pressure switch or simply feed power to a receptacle that the compressor is plugged into.

 

[Bas]

Thanks for the input everyone, great discussion!

but a much simpler way to do it is to have a small DC photosensor control an AC relay.

That was my first idea as well, but sometimes it's easier to get it all-in-one. Certainly would take up less space. The smaller photosensors are pretty darn cheap though, which is always a plus.

I would second the suggestion to power a contactor (relay) directly off your lighting circuit.

I actually have three lighting circuits in my shop. One runs off the main panel in the house, the other two off the subpanel. That way, should I ever overload the subpanel, I wouldn't suddenly be in complete darkness (I'm in a windowless basement shop). So orchestrating the relay would be complicated.

You don't mention what size/type compressor you're intending to switch

Well, eventually I'm sure I'll get a big 60 gallon upright. For now, it would be for a smaller hot dog style compressor. I know it's harder on the motor, but with the low usage the compressor sees at my shop, the tank will most likely rust out before I wear out the motor... But a bleeder solenoid is of course extremely cool :gar-Bi


Nothing like mixing electronics with woodworking.... :icon_cheers

 

[Chipper]

I've got a bunch of Allen Bradly power contactor relays NOS and I need to sell a few. 120vac coil and double pole double throw 20A 300v contacts. I'm thinking in the $15 range. I'll try to post a pic. PM if interested.

 

[scsmith42]

Bas, I too prefer the "contactor triggered by a light switch" option. Alternatively, you could use a simple water heater timer to control the compressor.

 

[Bas]

Bas, I too prefer the "contactor triggered by a light switch" option. Alternatively, you could use a simple water heater timer to control the compressor.

You know what, I have one of those. I think it's called the Little Gray Box. Easy, simple, cheap, effective, easy to clean, low water usage, two for the price of one, low VOC.

Where's the fun in that!!!! :rotflm: :rotflm:

 

[DonDeJ]

Do you want the compressor to come on whenever the lights are on? Could you just put a heavy duty toggle switch somewhere you would notice it? Maybe put a pilot light on it? If you made a point to drain the compressor every day, you could get into the routine of draining the tank and shutting off the compressor.

If you have to go high tech, you could always get somebody to write an iPhone app for it. :gar-La;

 

[Sully]

Dude! Shop elf. Simple, effective, reliable, low maintenance. :gar-La;

 

[Rob]

I've always wanted a switch next to the door, with a large red light that is on when the compressor is. 60 gal tank, 220V. Haven't thought much about it, but not sure what parts to get that would handle the load. Not much of an electrician other then adding a breaker or wiring a socket.

 

[mkepke]

X10 motion detector with an x10 20A receptacle.

You can also buy x10 controlled 120V and 240V switches.

-Mark

 

[DonDeJ]

Consider a couple of performance issues associated with your plan to hide the DC and comp in a closet. A dust collector needs to freely circulate air. Air in has to equal air out, and if there are restrictions to the flow of air, efficiency go down hill. An insulated closet that shuts out the noise will certainly restrict air flow.

As for the compressor, the little Senco should be fine in the closet, but when you get your big compressor, it will generate a lot more heat (if it runs a lot), and it will suck in more air. Don't smother the compressor in a small closet.

As for the photo cell idea, if you want to use a relay, why not just use the lighting circuit to power the relay. You would need to power the photocell anyway, why add unnecessary parts that can cause problems. Keep it simple.

 

[bobby g]

Bas,

For really cool, consider a microswitch under your matress! You could control the coil of a contactor with it.:rotflm::rotflm::rotflm:

bobby g

 

[Bas]

Consider a couple of performance issues associated with your plan to hide the DC and comp in a closet. A dust collector needs to freely circulate air. Air in has to equal air out, and if there are restrictions to the flow of air, efficiency go down hill. An insulated closet that shuts out the noise will certainly restrict air flow.

I plan to cut a 12"x12" opening in the drywall between two studs near the ceiling in the closet. On the outer wall, I'll also cut a 12"x12" opening, near the floor. In theory, a 6"x6" hole should be sufficient to match the 6" ductwork, but that doesn't take into account resistance, so I'd rather go a little bigger.

Of course, along with the air, the opening will provide sound with a path back to the shop, but because it has to travel along an 8ft chute it will be lessened. If I wanted to get really fancy I could create a "slalom course" using pieces of 2x4 inside the chute to further eliminate sound, but that would also impede airflow. Plus, I'm looking for "good", not "perfect".

 

[bobby g]

Bas,

The 12 X 12 hole will probably not be enough area to prevent pressure build-up in the room. Oneida was willing to calculate the requirement for my present setup. At my old shop, with a 2 HP Delta blower, I had 2 - 20 X 20 grills in the wall and still had some pressure build-up in the room.

Bob

 

[Bas]

Bas,

The 12 X 12 hole will probably not be enough area to prevent pressure build-up in the room. Oneida was willing to calculate the requirement for my present setup. At my old shop, with a 2 HP Delta blower, I had 2 - 20 X 20 grills in the wall and still had some pressure build-up in the room.

Bob

Wow, that much! I suppose I could make four 12x24 holes, but now I'm rethinking things. My plan was to add a second layer of drywall on the inside w/ green glue to add some soundproofing, and perhaps use some of the other ideas discussed last year. But if I'm then cutting 8 big holes, I wonder whether that's a misplaced investment. I'm sure it would still help, but it's like caulking a door and then leaving a window open.

Thanks for the feedback Bobby. Much easier to do this right from the start than cutting extra holes afterward.

 

[bobby g]

Bas,

As you may recall, the dust collector closet at my shop has a full louvered, 3 X 8
door on it. The area provided met the Oneida criteria for my 5 HP system. The louvers help some with the noise too.

Regards,

bobby g