Air Dryer Controller

[Reds]

I am installing an air dryer. I want to plumb it so that it only dries the air to the doors so that it doesn't have to run all the time. I need help with turning the dryer on & off (110v). There are 2 24vac signals sent to each door - one to open it and one to close it. I have 4 doors so I need to turn on the dryer any time that any one of these door signals turns on. That would be a total of 8 inputs, all of them used to turn on a single dryer, and several of them could be sending a signal at the same time. Can anyone help me figure out how to do this? Will an Idec Smartrelay do this? Or something else? My electronics knowledge limited. Thanks for any help.

 

[troyberry]

You could use relays. Each input that comes back would be wired to a separate relay coil. Then the contact side of the relay would be wired to your air dryer. You could also use a multiplexor. I build one for our stuff here in Calgary, but I am sure you can buy a ginsan one from Kleen-Rite as well. I think that the relays would be less expensive.
Hope that helps.

Sorry, should have read the post closer...an Idec smart relay would work, but I think it would be quite a bit more expensive than 8 separate relays, and you would need to program it as well.

 

[pitzerwm]

A small PLC would also do it.

 

[Reds]

If I used separate relays, what would happen if 2 of the relays that were both connected to the dryer were energized at the same time? Would that cause a short ?

 

[thoffmanjr]

An “air dryer” is more or less an air conditioner or a heat sink. The humidity in the air is transferred into the holding tank with the warm or hot air that is pumped by the compressor. Warm air can “hold” more humidity. Cold air “holds” less humidity. Turning on your air dryer when the door goes up or down will not be effective because the air dryer needs a little bit more time to cool down before the air starts flowing through it. The humidity in the air condenses and drains out within the cold air dryer. Imagine turning your car’s air condition on after it has been sitting in the sun. The air in your car doesn’t cool down instantly does it? In my opinion you need to connect your air dryer to your air compressor, and then feed a small compressed air holding tank with a drain, and then feed only your doors. One more thing: A 1/2hp air dryer uses about .86kwatts which at 15 cents per kilowatt hour is only 13 cents per hour running and I don’t think your application would have it running continuously. You could also google “heatless desiccant air dryers”. They use very little power, if any, to dry air. You just need to know your air consumption to size them properly.

 

[Reds]

Before buying an air dryer I did some homework. The refrigerated dryers dry the air to a 32? dewpoint. My air cylinders are right inside the door and while the bay is heated to 40? they get some cold air that leaks thru the weatherstriping, plus gusts of cold air while the door is open. This causes the air in the cylinder, line, and regulator to get below 32?. Consequently I bought a regenerative heatless air dryer which has a dried air dewpoint of -40?. This type of dryer has 2 towers that the air flows thru. The air flow alternates from one tower to the other. While one is drying the air the other is purging itself. Due to this method of drying the air it consumes about 2cfm of air in the process and runs non stop. So it is always consuming air and dries the air as it flows thru the dessicant chamber(s). That's why I only want it on when the doors are operating - I don't see any point on having it run during the night (along with my compressor), or between washes on slow days. My only issue with moist air is in my door air cylinders. I had a piston come unscrewed from the rod, and when I took the cylinder apart it had more than a cup of water above the piston. I don't believe that the water above the piston can get exhausted thru the blowhole in the bottom. That would trap that water in there. My doors are extremely slow and sticky when the temp is single digits or lower. I am busy during those times and have to get these doors working right. I had a lot of discussions with the folks at Twin Tower Engineering (the manufacturer) about sizing the dryer for my application and my compressor. They were very helpfull.

 

[troyberry]

If I used separate relays, what would happen if 2 of the relays that were both connected to the dryer were energized at the same time? Would that cause a short ?

No, because all of the coils from the relays are isolated. The contact side would all share the same common and be connected to whatever you will use to turn the dryer on.. No Short-Circuit possible.

 

[Reds]

Thanks to everyone for the input. I'm going to see if I can make it work with relays.

 

[Ric]

Lot of techie info going on here. All I know is when I spent about 600 bucks and added an air dryer to my tunnel wash it solved all the problems being mentioned here. My main gripe was my air doors. It also provides dryer air to your air (flojet etc.) pumps, etc. which leads to better performance. It was an all around good investment. I would not do a wash without it.