Air compressor controls

[allscott]

I've got a 75HP Atlas Copco compressor with a display/keypad that has died. The display also acts as the controller for the compressor. The service company that looks after the compressor wants to retrofit it replacing the controls and the wye-delta starter arrangement with a soft start. This is all fine and dandy but they want $30K to do it.

I am kicking around the idea of doing it myself as this does not seem like Rocket science and having some control tied in with my Scada would be very advantageous to our plant.

What all do I need for control on an air compressor? Obvioiusly HOA, start the motor, load and unload. What am I missing?

 

[Fitz]

I’m not familiar with the Atlas, but long ago I did a project to control several large Joy compressors using SLC and WonderWare. You didn’t say if you’re planning to use a PLC/HMI to control it, but here are some suggestions:


Oil pressure switch if it has one.
Timer to shut down the motor when demand has not called for loading after so long.
Fail to run alarm.
Run time totalization.
Loaded and unloaded time totalization.


Seems like you could do a lot of control for a lot less than $30K for this simple application.

 

[MaintMike]

You should have a electrical print in the door that will give you some of the sensors and switches. Outlet air temp and Air/Oil Dp are monitored on some Atlas Copco compressors. And of course some of the things they monitor aren't "must haves" either. You could monitor the OLs on the motors (fan cooled or water cooled?). Good luck and let us know how it turns out.

 

[Jeff23spl]

do you know the exact type of compressor ?

it depend what the 30k$ include to say if it is expensive or not. If it include a large rockwell plc + color hmi or full 24/7 free service on a foreign area etc...

For the usual screw comprossor the logic isn't that much complicated but you'd better have all the avaivailaible protections. You may request the supplier to know about the tripping level as you probably don't know them since the control is down. As explain, their is loading/unloading but also cooler controls and interlocks + others protections...

I would sugest to install a small local plc that would communicate with your main system instead of having it as a part of the main system to keep a stand alone possibility to make it work.
Will you really gain something from replacing the star/delta for a softstart if it still in good shape and you look for money saving, i won't change that untill being ready for a VFD and reduce speed instead of unloading to save electricity

 

[dginbuffalo]

I would use the Atlas drawings to figure out what you need. You know, you could get a new Electronikon ad a Modbus gateway to fix the problem and tie into your Scada system.

Said the Atlas Copco distributor....

 

[bright676]

Model #?

Do you just need the Display to get it going? I may have one, what is the comp model and p/n of the display? We just got rid of a 75 hp atlas copco comp and I saved a bunch of parts including the display.

 

[allscott]

I'm not at work today but I will get the model# as soon as I can.

I have a print that I can hardly read and it is one of the goofiest things I have ever seen. There is a 24VAC control transformer who's output goes through a set of N/C contacts on the wye contactor on the starter in parallel with the no contacts on the run conctacor then going to the display/controller? It makes absolutely no sense to me why the original Engineer would do that?

Right now I can get it to start but it never switches from wye-delta and it just seems like it would be easier to just redo the whole thing.

I am just wondering if there is some magic to an air compressor that I don't see? What are the general I/O?

This compressor is kind of the back up of two others, it is only started when one of the other two go down. I would like to start it up based on plant air pressure and alarm as such. That is why I would like to tie it into the plant SCADA.

 

[allscott]

Do you just need the Display to get it going? I may have one, what is the comp model and p/n of the display? We just got rid of a 75 hp atlas copco comp and I saved a bunch of parts including the display.

Thanks. The original problem was that the display quit. A colleague took the display apart and replaced a rectifier in it. It lights up now and displays but the compressor still doesn't work properly.

 

[allscott]

do you know the exact type of compressor ?

it depend what the 30k$ include to say if it is expensive or not. If it include a large rockwell plc + color hmi or full 24/7 free service on a foreign area etc...

For the usual screw comprossor the logic isn't that much complicated but you'd better have all the avaivailaible protections. You may request the supplier to know about the tripping level as you probably don't know them since the control is down. As explain, their is loading/unloading but also cooler controls and interlocks + others protections...

I would sugest to install a small local plc that would communicate with your main system instead of having it as a part of the main system to keep a stand alone possibility to make it work.
Will you really gain something from replacing the star/delta for a softstart if it still in good shape and you look for money saving, i won't change that untill being ready for a VFD and reduce speed instead of unloading to save electricity

I am in a small town in the boonies in Saskatchwan. We are in the heart of oil country so I pay big time for any service call. The 30K won't get me anylong term service care.

I guess what I am asking is if I decide to retrofit the unit what do I need to control on an air compressor?

 

[Hefty]

We had the same thing happen here. Replacement cost of upwards 20K retrofit for a broken display on one of our 150hp compressors .
If you decide to retrofit, this is what we did. Purchased an AB micrologix 1400 with an RTD expansion ,plus a an EZD-T8C-S Display form EZ Automation. This for under $2500.
My partner programmed it using this as a guideline http://www.aircompressorhelp.com/supervisor_i_&_ie.htm . Basically monitor the temperature and unit pressure. Most importantly making sure not starting when unit pressure is high. Good Luck .

 

[OkiePC]

OEM compressor controls are expensive and often lack flexibility. At 75HP I would definitely shoot for a soft starter and PLC control. Like you said it is not rocket science. You may have an unload valve so that when demand drops, you can unload the compressor for a short time without stopping the motor, let it run with little or no load and then load it back up when demand picks up. You can program a PLC to "learn" to adapt to the demand and unload times your plant sees on a typical daily basis and that is one of the more complicated features seen with OEM controls as a money saver. Some just use a simple digital output for load/unload, and some use an analog positioner to unload as a percentage. Some have an analog feedback for the load/unload position. I think I have only seen the unload analog controls with refrigeration compressor controls. Each time I had to order a board or deal with limitations I thought "I could do this with a PLC and a week of effort and replace all this junk for the total costs of that one board or display."

Then once you have one on PLC control all ironed out, and you need to sequence several of them, you will not be stuck with some weird comms network and funky sequencer from the OEM.

Since you have a price for $30k with soft starter, you have ammo to use your own and go with a soft starter too. That will be so much simpler and more reliable over the long term than wye/delta contactors, so definitely try to build your project around a common off the shelf soft starter in my opinion. Modern soft starters are just so much better in so many ways, it will pay for itself in fewer headaches and more ability to do predictive repairs by easily (perhaps automatically) monitoring running current and faults and more.