The pump was a hand-me-down that was way too powerful for the drippers,
Sump pumps don't typically make more than 13 psi or so. I don't see how it could be too powerful. I can't imagine your drippers wanting less than 13 lbs. Shut off the return valve and the motor will just be idling as opposed to pulling max amps moving a lot of water.
Really? I don't understand how that could happen, since most sump's just don't make pressure, they are a volume pump.
What pressures were these drippers and sprayers supposed to operate at. Most of the ones I'm familiar with like 40 plus PSI.
This is an indication of engineers taking the "design life" too literally.VFD's are getting cheaper but, they are not reliable. It is the exception to see one that has lasted 20 years, not the norm. Any that I have seen that lasted 10 years, did so by virtue of several repairs.
See the following link, that is from a company who sells VFD's. http://www.powerqualityanddrives.com/payback_analysis_vfd/
"They don't consume any power when the "pressure switch turns off" since you can use a regular pressure switch to disconnect power to the drive." Bill Arden
There is only one company that makes VFD's for pumps that uses a switch instead of a transducer.
"I agree that a CSV is a good choice due to the price, but Brush-less PDC motors are going to get better and better..." Bill Arden
You were just talking about the "sine wave" so surely you know that they do not use DC motors with AC, pulse width modulating (PWM) VFD's. I guess we could go back 30 years and start using DC drives again. Even though VFD's are AC and use AC motors, the technology IS getting better and better. It has been getting better and better for 30 years, and is still not right. There are still some "laws of physics" as you claim to understand that cannot be changed. There are Resonance frequencies, harmonics, "ringing" which causes voltage spikes, "affinity law" which reduces the head by the square of the speed, and many other things that mother nature won't let a VFD correct.
However, I disagree that because a pump is larger than 10 HP a VFD would save energy.
True "sine wave" VFD's don't have "harmonic current" losses since they have inductors and capacitors after the H-Bridge to create a smooth Sine wave voltage.efficiency losses from the harmonic current
OK, I was trying to let this thread die because it will take me a long time to explain and most people don't understand what we are talking about anyway. That is the one of the main problems. Volts to hertz ratio, sign waves, harmonic currents, switching frequencies, inductors, H bridge, even the guys who sell this stuff don't know what all that means. The average home owner is supposed to just believe that a Variable Speed Pump is a "magic" box that saves energy and therefore is worth the added expense, short life expectancy, and all the trouble that goes with it. There are lots of good applications for variable speed equipment. With fresh water pumps however, VFD's are being used as a marketing tool to get more of your money, and to be able to get more of your money, more often.
quote-"With the price of copper rising and the price of electronics falling I am going to guess that it gets to the 1hp well pump market in approximately 8 years (4*moore)" Bill Arden
Copper wire is something that will last, electronics is something that will not last. Which would you rather spend your money on? Grundfos already makes these small pumps and motors that work with "permanent magnets" and the Moore's law is how they finally got them this far. Just because a technology exist, doesn't mean that it is the best way to go..
quote-"Then look at the power draw at startup and what effect that has on other equipment. That is why I say it's generally cheaper to buy a 3 phase motor and a VFD at larger power levels." Bill Arden
Single phase motors use a lot of power at startup. However, when used with a Cycle Stop Valve there are very few startups which usually makes starting currents unimportant. At larger power levels a 3 phase motor is preferable but, it doesn't need a VFD. With submersibles you can use the longest length of the smallest wire possible to create a natural soft start. This works with single phase and three phase. The smaller wire limits the inrush currents on startup, which naturally reduces the starting torque, without needing any complicated electronics.
quote-"True "sine wave" VFD's don't have "harmonic current" losses since they have inductors and capacitors after the H-Bridge to create a smooth Sine wave voltage." Bill Arden
Active and passive filters do help but, some of the harmonics get past the capacitors and H-bridge to add harmonic content to the power supply. Faster switching also helps but, they are still not able to produce a smooth sine wave from pulsing DC.
Moore's law does not override the principle of Occam's Razor.
"All other things being equal, the simplest solution is the best."
The Cycle Stop Valve is by far the simplest solution to the problems.
Screw compressors are positive displacement or PD. PD pumps are one of the good application for VFD's. Grundfos is already trying this with their helical style pumps. Helical style pumps were tried 40 years ago. They work great until the controls don't turn them off when they should. Then something is going to blow up. Liability was one of the reasons these pumps were taken out of production 30+ years ago. We have experienced this problem with the Grundfos pumps already. Something in the electronic controller malfunctions and the pump does not shut off when the faucets are closed, BOOM!!!
I have been watching it continually improve for 30 years and it is still not right. The CSV will stay the same because there is no reason to fix something that works beautifully.
lolI have heard the new heating/AC units with Variable Speed Fans use very little energy. I was told that this is because they are down for repair a lot, and therefore are not using any energy much of the time.
"The waveform does not have to be exact to reduce "eddy currents in the laminations". It's the high frequency edges that cause problems. Note: These frequency's can exceed 1Mhz." Bill Arden
High frequency edges, yep! Exceeding 1 Mhz, yep! And other Problems!!!
I was told the same thing 20 years ago. I am still waiting. Some things mother nature just won't let Mr. Moore fix.
This is awkward, but...
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