Variable speed and/or under driving a compressor.

[spoolin01]

You guys must be looking at some big compressors. The RIX 3cfs model requires 3HP (11A@220V single phase), the 5.5cfs only 5HP. For the 3 I just put a pigtail on an unused 30A breaker at the secondary panel since I can wheel the compressor nearby. It would be nice to live where better service is available, I'd like to convert the 5.5 to electric.

 

[iain/hsm]

You guys must be looking at some big compressors. The RIX 3cfs model requires 3HP (11A@220V single phase), the 5.5cfs only 5HP. For the 3 I just put a pigtail on an unused 30A breaker at the secondary panel since I can wheel the compressor nearby. It would be nice to live where better service is available, I'd like to convert the 5.5 to electric.

The motors fitted on the SA units are chosen the nearest size up from the maximum BHP required.
By example the SA-6 requires 4.87 BHP (3.63Kw) at 5000 psi and considerably less at lower pressures. Hence the 5 BHP (3.72 Kw) motor fitted.

In addition the motor contactor overload relay (cut out) is also calculated at the relief valve pressure setting that is around 15% over the maximum rated working pressure for additional built in safety.
Having both the relief valve operating lift pressure and the electrical overload relay switch setting operating at the same time offers additional safety options.

 

[iain/hsm]

Rix, splash? The familiar small ones are oil-less. Like to know if there's any reason not to under-drive those.

Pretty much everything under 5 BHP is oil-less design.
6 to 10 BHP (10 to 40 scfm) are splash lubricated. oil free design
20 to 50 BHP (20 to 50 scfm) are gerotor pump shaft driven oil lubricated. And again oil free
75 to 300 BHP (100 to 1500 scfm) are external pressure fed oil pump and oil free

All are oil free in that the upper area and pistons as the gas parts are separated from the oiled lower parts
by a distance piece and oil sealed on the piston rod. The rod length being greater than the piston stroke
effectibly separates the lower oiled parts from the upper oil-free parts, hence oil free compressor.

 

[iain/hsm]

Is anyone using a variable speed drive on their compressor? What are your reasons?
Thanks!

In Europe it's the law for any compressor built after January 2017 to have either an efficiant EFF3 motor design or if you choose to use the older cheaper EFF 2 motors over 0.75 BHP it needs to be controled either with your variable speed drive by varying the voltage to control RPM or by a Variable Frequency Drive method by altering the Hz or frequency to control the RPM.

The year before (2016) it was any motor rated above 7.5 Kw (10 BHP) needed to be either EFF3 or VFD drive
The older DOL or Direct on line starters are still manufactured but mostly for export and to be fair most are not aware of this legislation. also historically 10BHP (7.5Kw) was the largest motor we could run DOL in Europe
all motors larger than 10HP were wired Star delta. In Europe our voltage is 400V and 50Hz for 3 phase and 230/240 volt 50 Hz single phase with 50Hz motors running slower than the 60Hz US motors. 3000 RPM as opposed to 3600 RPM 2 pole and 1500 RPM for 4 pole as opposed to 1800 RPM for the equivelent US motor at 60Hz.

 

[BRT]

In Europe it's the law for any compressor built after January 2017 to have either an efficiant EFF3 motor design or if you choose to use the older cheaper EFF 2 motors over 0.75 BHP it needs to be controled either with your variable speed drive by varying the voltage to control RPM or by a Variable Frequency Drive method by altering the Hz or frequency to control the RPM.

The year before (2016) it was any motor rated above 7.5 Kw (10 BHP) needed to be either EFF3 or VFD drive
The older DOL or Direct on line starters are still manufactured but mostly for export and to be fair most are not aware of this legislation. also historically 10BHP (7.5Kw) was the largest motor we could run DOL in Europe
all motors larger than 10HP were wired Star delta. In Europe our voltage is 400V and 50Hz for 3 phase and 230/240 volt 50 Hz single phase with 50Hz motors running slower than the 60Hz US motors. 3000 RPM as opposed to 3600 RPM 2 pole and 1500 RPM for 4 pole as opposed to 1800 RPM for the equivelent US motor at 60Hz.

Ain't regulation great. Here we commonly start 100 hp across the line.