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Buy it now or pass? Commercial compressor

Sincerd

Aluminum
Joined
Jul 22, 2023
Have an option to get this compressor for 4k. My issue is it's 3ph. I have a 20hp rotory, if I had a phase perfect may not be an issue, but I don't constantly want to running the rotory. Seems like the electronics are pretty advanced. Wondering how much I will be missing, by running a vfd directly to motor? My guess is it will be difficult if not impossible to run the vfd through the electronic system of this machine? Is there another option I'm not thinking of? It's a pretty nice unit and I've always wanted a screw compressor. I have no current need for a compressor this large, but I do see several cncs in the future.

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Usually these are coupled with receivers so that they don't run continually. A vfd sized for this unit would certainly cost more than starting a rotary as required!:ack2: If you actually see future capacity, then why hesitate?
 
You think? 5hp I wonder how efficient

The raw performance of a 5hp screw is pretty comparable to a 5hp piston. It's just that the screw should have a 100% duty cycle, and the good ones are much quieter than a thumper.

Agreed that 5hp is awfully small. I'd wait until a Home Depot compressor can't keep up with your needs, then move on to a 10hp screw or bigger if needed. Screws are much more PITA, and not worth the hassle if your usage is so small.
 
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Screw is a lot nicer to have to sit next to all day.

This is only a 5hp compressor. You can get a single phase to three phase VFD for 5hp, no trouble. A bit of wiring and you're up and running. A bit more and you could have it running variable speed.
 
I have the "T" version at work. It's an awesome machine! That seems to be a good price, and I'd love to have it for my personal shop! :D
 
The raw performance of a 5hp screw is pretty comparable to a 5hp piston. It's just that the screw should have a 100% duty cycle, and the good ones are much quieter than a thumper.

Agreed that 5hp is awfully small. I'd wait until a Home Depot compressor can't keep up with your needs, then move on to a 10hp screw or bigger if needed. Screws are much more PITA, and not worth the hassle if your usage is so small.
My "at work" 5hp screw is way more capable than my own 50(?) yr old 5hp two-lung thumper, which is "ok" adequate for my needs, and a noisy s.o.b.
 
I have a couple of small Kaeser screw compressor. They are nice. But to actually take care of a screw compressor is more involved than a piston. You do have maintenance costs. And they do just want to run. If you have low or intermittent loads, you really need a healthy size receiver so the compressor has enough time to run, fill the tank, and get up to temperature. On my SX 7.5 I have a 500 gallon receiver. It takes about 3 minutes to bring the tank from 125 to 155 PSI and then the compressor idles (motor running unloaded) for about 5 minutes.

The motor is wired as star delta. So that is why it has so many contactors.

Also note that compressor isn't substantially more than $4k new. I just bought a high pressure SX 7.5 compressor for $9800. I would imagine the SX 5 new is maybe $7k. With warranty and they come out and start it up. Kaeser also has the ability to offer discount. I recall a multi thousand dollar discount on my Aircenter I bought from them a few years ago.
 
Also, don't think about redoing the electrical on this compressor. There's a bunch going on that is controlled by the computer. Unless you are going to fully understand what they are doing and then reimplement it in a PLC, it just doesn't make sense. This thing is German, so it has a lot going on. Get a dumber screw compressor if you want to retrofit something with a VFD.
 
My thoughts on Kaeser compressors:

 
Do you hear those 2 or 3 brain cells in the back of your head telling you you should get it?
Well listen to them and one day you will be standing in front of that compressor staring at it thinking those are the best 3 brain cells you have.
 
I would never buy a three phase compressor for single phase service. I know our bigger IR screw compressor has a lot of control valves and doesn't just start and stop the motor. For 5HP just buy a high end piston compressor and keep it as a backup.
 
I think that's about the most expensive way to get 20cfm of compressed air that you'll find. It's all been said here about noise so no need to repeat that. My IR T30 piston compressor is bigger (7.5hp, about 27 cfm I think), paid $750 for it used. Single phase, stuck in a closet so noise is not bad. It just runs. And when something does quit on it the part that's needed is generally pretty cheap and simple. Once I had a check valve go bad- grainger, once I had motor start contacts go bad- local motor shop, once I had a motor cap go bad- Grainger.

Better for those of us using phase converters to save 3 phase power for stuff that really needs it.
 
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Buy a cheap HF or Home Depot compressor and save the money. If they feed a reciever, then you don't need a lot of cfm.

I have a 3hp, 20 gallon (home depot) + 10 gallon reciever that can more then keep up with 2 fadals plus air tools.
 
I would never buy a three phase compressor for single phase service. I know our bigger IR screw compressor has a lot of control valves and doesn't just start and stop the motor. For 5HP just buy a high end piston compressor and keep it as a backup.

I sure as hell will. single phase motors SUCK. I've replaced probably a dozen start caps in 20 years.

A 3 phase motor on a VFD from single phase is a way better setup than a single phase motor, especially starting against a load like an air compressor.
 
I want a nice, quiet screw compressor as much as the next guy but, for something with a fixed load like a compressor, no way would I try to run it on a phase converter unless it was the absolute last way on the planet to do the job. Or maybe you plan to move to a new location with 3-phase service in the next year or so.
 








 
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