New to me compressor: Quincy QT-5 ...

[brickbat]

Nice. So now with the smaller sheave, how much motor current is your VFD displaying at, say 150 psi? And what was it with the larger original sheave at 150 psi?

 

[wquiles]

Nice. So now with the smaller sheave, how much motor current is your VFD displaying at, say 150 psi? And what was it with the larger original sheave at 150 psi?

With the large sheave it was tripping at the max the VFD can give (for its 3HP rating) which was something like 9.2 Amps, and that was down in the 110-120 PSI range. Even now at 150-155 PSI it is not tripping at all now, so of course the draw has to be less than 9.2 Amps, but I don't know exactly how many amps since I have not tried setting up the display to show running amps. I will try to remember and report back what is the current 3-phase amp draw now that I am using the smaller sheave.

 

[65535]

If you can pull the amps off the 220V 1Ph input you could roughly calculate the output amps.

 

[wquiles]

I just checked (on the VFD diagnostic's menu you can show pretty much any value in real time) - the amperage right as it stops at 150-155 PSI was 7.4Amps.

 

[brickbat]

Thanks, Will. That makes sense. It looks to me as if your motor sheave is about 1/2 the diameter of the original one, so your motor sees about 1/2 the torque load as the original design. And it seems like your motor current is now about half of nameplate as well.

I suppose you could run the motor a bit faster if you wanted, or run the pressure up a tad higher with your setup. But unless you need the extra air storage, I think you're wise to run the pressure on the low side. It's still plenty high to regulate down to 100 psi or so, and puts a little less stress on the pump.

One interesting option on a VFD-powered compressor would be to have a higher speed mode that was automatically selected if the tank pressure dropped below, say, 100 psi. That way, in normal day-to-day use, the machine would run at a nice non-nerve jarring speed. But, if you were using a lot of air and the tank pressure dropped, the motor would bump up to the higher speed.

The VFD is perfect for this, since it can operate the motor at a higher speed if the torque load is low, which it would be when the tank pressure is lower...

 

[65535]

That would be slick. Pressure switch 1 trips at 120 psi runs compressor at 50-75%. switch 2 trips at 110 psi runs compressor at 100%. I guess both would reset at 150psi?

 

[wquiles]

Right now I am just using one pressure switch input (logic level) but the VFD I got does support up to 3 different set points in my specific model. There is also a mode for constant torque that I have not played with - I wonder if that would adjust the speed automatically as well within a specific range ...

By the way, although it will change somewhat in the new week or two, here is a quick shot of the regulator (with a built-in small filter), which is set to 110psi to help protect the sub-micron second stage filter that can only take 125psi max:

Will

 

[precisionworks]

There is also a mode for constant torque that I have not played with - I wonder if that would adjust the speed automatically

In CT mode, which is used for just a few limited applications, speed can be anywhere in the range of the VFD but torque stays exactly the same. An example of a CT app is winding wire on a large drum. When the wire starts winding on the small diameter core, speed runs high so the tension on the wire is correct. As the core is covered & diameter increases, speed drops to keep tension on the wire at the same setting.

 

[wquiles]

In CT mode, which is used for just a few limited applications, speed can be anywhere in the range of the VFD but torque stays exactly the same. An example of a CT app is winding wire on a large drum. When the wire starts winding on the small diameter core, speed runs high so the tension on the wire is correct. As the core is covered & diameter increases, speed drops to keep tension on the wire at the same setting.

Couldn't then I use the CT mode (along with setting min and max Hz values) to take advantage of the lower load on the motor when the tank is low on air to run the motor somewhat faster (say up to 90Hz) and then have the motor slow down (say 65Hz) as soon as more torque is demanded? Do I need to then program some "desired" torque value/target which will then be adjusted accordingly to the hi/low Hz values?

 

[brickbat]

That sound like the optimum approach. I'm interested to hear how it works. BTW what VFD are you using? I'd like to read up on the CT mode, as none of the drives I've used have it...

 

[precisionworks]

Couldn't then I use the CT mode (along with setting min and max Hz values)

The CT mode over rides all speed settings, and speed control becomes secondary to torque control. Compressor output is a function of pump speed (assuming that torque is adequate to operate the pump at all desired speeds).

Newer compressors, especially newer rotary screws, use a PLC to ramp up or ramp down the pump speed as demand increases or decreases. The PLC is programmed using a comparator function, where actual pressure is compared to desired (setpoint) pressure. There are a number of inexpensive PLC's available today that will do this, and most have a pressure sensor module as an option. Or you can find a used A-B SLC-500 on eBay.

Without a PLC, I'm not sure that you can ramp up or ramp down unless you can find a differential pressure transducer that has a 4-20 mA output. They are available, but cost nearly as much as a low priced PLC.

 

[wquiles]

Couldn't then I use the CT mode (along with setting min and max Hz values) to take advantage of the lower load on the motor when the tank is low on air to run the motor somewhat faster (say up to 90Hz) and then have the motor slow down (say 65Hz) as soon as more torque is demanded? Do I need to then program some "desired" torque value/target which will then be adjusted accordingly to the hi/low Hz values?

That sound like the optimum approach. I'm interested to hear how it works. BTW what VFD are you using? I'd like to read up on the CT mode, as none of the drives I've used have it...

Well, I am going to answer my own question: Yes, I can set it up for CT control, and it does work exactly like I expected, with full torque instead of speed control - in fact I had to turn down the default torque of 100% down to 80% as it was just simply too much torque to get started. However, as Barry mentions above, in this mode I lost all slow acceleration and ramp - it starts at full torque, at the max speed, so there is always a trade-off. I am back to speed control since it gives the motor/pump an easier, longer life :devil:.

The drive I am using is the AC Tech SMVector Drive, in a NEMA 4x Enclosure, which I got from these guys:
http://www.wolfautomation.com/Product.aspx?ProductID=22376

Will

 

[precisionworks]

in this mode I lost all slow acceleration and ramp

Been there, done that

Most VFD's in a factory are PLC controlled - very few are installed in a stand alone configuration. That's the main reason that there are so many options for external control connection. You can make the drive do exactly what you want, and it isn't difficult, but that requires supplying the drive with enough information so that the drive reacts the way you want.

 

[wquiles]

Been there, done that

Most VFD's in a factory are PLC controlled - very few are installed in a stand alone configuration. That's the main reason that there are so many options for external control connection. You can make the drive do exactly what you want, and it isn't difficult, but that requires supplying the drive with enough information so that the drive reacts the way you want.

It was a good learning experience

I actually used the compressor for real last night on a "job", and the larger capacity tank (stored at a higher pressure) does help a lot - I was able to complete on Mag 1xD re-thread job without the compressor turning on at all. In the past, with the Eaton and the 20 Gal tank, it would turn on at least 2-3 times. I later then keep working on a tailcup mod (internal boring) and the compressor finally came ON, but because of the slow-start, it took me a few seconds to realize the compressor was running at all - basically the actual noise of the air nozzle from the Accu-Lube lubrication system was drowning the Quincy compressor running at 65Hz. Maybe not as quiet as the Eaton, but this will do just fine 😀

 

[precisionworks]

was able to complete on Mag 1xD re-thread job without the compressor turning on at all.

You gotta love that 😀

My three 60 gallon tanks all feed the same trunk line, and that line plus hoses is over 20 gallons of volume, so there are times that none of the three kick on. The first to start (about 100 psi turn on pressure) is located farthest from the machine room. The second compressor kicks in when pressure drops to 95 psi, but it's one room away & still quiet enough. Compressor #3 starts if the pressure drops to 90 psi, which happens two or three times a year, mostly when testing an air tool with a 50 cfm (or larger) motor.

When I win PowerBall, I'll buy three compressors like the one you have

 

[65535]

If you win PowerBall you might as well buy a nice 15-50HP (depending on what you need/want) Quincy Rotary Screw. 😛.

Then again at the theatre We have a 50HP Rotary Screw, dryer, filters, 250gallon holding tank. 😛 Never run out of air.

Too bad it isn't a Quincy.

 

[precisionworks]

50HP Rotary Screw, dryer, filters, 250gallon holding tank.

I worked at a factory that covered about 10 acres (4 hectares). Only one shift ran, from about 0400 until 1500. At the end of the shift the big compressors were shut down and the little 50hp screw ran all night to keep up with leaks & keep the lines pressurized to about 90 psi.

The fastest way to get a trip to the plant manager's office was to forget to kick on the 50 before leaving for the day 😀 Even a 200+100 (300 total hp) would take over an hour to pump up the lines from zero pressure.

 

[65535]

That's sick, 50HP worth of leaks. I hate leaks in my air systems, I always seal them up tight.

 

[wquiles]

I worked at a factory that covered about 10 acres (4 hectares). Only one shift ran, from about 0400 until 1500. At the end of the shift the big compressors were shut down and the little 50hp screw ran all night to keep up with leaks & keep the lines pressurized to about 90 psi.

The fastest way to get a trip to the plant manager's office was to forget to kick on the 50 before leaving for the day 😀 Even a 200+100 (300 total hp) would take over an hour to pump up the lines from zero pressure.

OK, ok - enough talk about my tank is bigger than your tank

Guess what? After 10 years the Pneumatic tank drain still works great - all too well !!!
I had to capture a LOT of water that was there!

So I put an adapter and a hose:

I also had the 120V automatic drain on the bottom of the tank, but it was LOUD as heck, so I removed it and put a simple ball valve and a hose:

Both hoses feed to the grass outside the garage door:

Will

 

[precisionworks]

I hate leaks in my air systems, I always seal them up tight.

I tried to show the plant manager the cost of running that compressor during down time, but he felt the effort to stop the leaks (hundreds if not thousands) was not worth the savings :shakehead