Johncfii
Solar Enthusiast
- Joined
- Nov 24, 2020
- Messages
- 265
I’ve been operating submersible well pumps for more than four decades. I’ve installed, repaired, and replaced many pumps. The reason for this post is to encourage anyone operating, or planning to operate a submersible pump on solar power, of the significant benefits of powering the pump with three phase, 230 VAC power. For a new or replacement install, it isn’t costly, and it isn’t especially complicated. You don’t need three-phase mains power. A Variable Frequency Drive generates the three phases.
The benefits:
1. NO starting surge current to overwhelm or stress your system. The variable frequency drive (VFD), that converts your 230-volt single phase power from your solar inverter to three-phase 230 VAC, is fully programable to provide a slow, linear, ramp up of motor speed. (I have mine programmed to steadily accelerate to full speed over 20 seconds). This is far superior to “soft-start” single phase motors.
2. NO high starting torque that has damaged many long down pipes, and many power leads over time.
3. Better motor efficiency. For any given HP rating, a three-phase motor is about 15% more efficient. A typical 1-1/2 HP single-phase submersible pump motor draws 10 amps at full load, which is 2300 watts at 230 VAC. A typical 1-1/2 HP three-phase motor draws 5 amps at full load, which is 1992 watts. (The formula to calculate three phase power is: 1.732 x amps x volts).
4. You will have fully variable motor speed that will allow you to reduce power draw in times of low sun energy. You can easily set your VFD to run the pump motor at 3/4 of full speed, or 1/2 of full speed. Water pumped is fairly linearly proportional to power consumed, down to about 50% of full speed. Some pump motors can even be operated with reasonable efficiency down to 25% of full speed if you are REALLY short on power reserves, and can make do with a smaller volume of water during hard times.
5. You can use smaller conductors down to the pump. Three-phase motors generally allow the use of one size smaller conductor. If your single-phase motor would require 10 ga conductors, a three-phase motor, all other things being the same, will only need 12 ga conductors. (This potential saving can be offset if your single-phase motor is 1-1/2 HP, or less, and is of the “two-wire” variety).
6. You can install your water system with a smaller, or even without, a pressure tank. This is possible because you can install a $130 pressure transducer that will send a 4-20 milliamp control signal to your VFD that varies linearly with system pressure. You program your VFD to maintain your chosen system pressure, and the pump speed will ramp up and down to maintain that constant pressure, as it reads the input from the pressure transducer. But this refinement is optional.
7. Three-phase motors cost about 10% less than single phase motors of the same HP. This is because their lower current demand allows the build with less total copper in the windings.
8. Most of these modern Variable Frequency Drives do not require a pure sine wave input. Whatever AC waveform you input is first converted to about 320 volts DC anyway. (Verify with your VFD vendor.)
The disadvantages:
1. You have to install an extra component in the form the VFD. But these are now amazingly affordable and reliable. A VFD rated for 3HP costs less than $300. I recommend selecting a drive rated for twice the HP rating of your motor. The incremental cost is very small. This increases reliability because the system runs cool, with little stress. I have both Fuji and Hitachi drives that have been in daily service for eight years with no trouble.
2. Some VFD manuals will recommend that a “line reactor” be installed at the drive output for long wire runs. Not a big deal. A $50 to $100 added cost.
3. As a DIY system, this can save you a ton of money compared to buying prepackaged system of the same components from Grundfos. But it does require some study, and some electrical understanding. If you managed to DIY your solar system, you can DIY this.
4. 1-1/2 HP is about the smallest size three-phase submersible motor available.
We have three wells on our property, all with three-phase pumps running off of VFD’s. Before my conversion to three-phase motors and VFD’s, we had to pull and replace some system component, in one well or the other, about every two years. It was always either a pump motor, a pump, cracked PVC down piping, or damaged lead wires. It was so frequent that I built an A-frame for my tractor that allows my wife and I to pull and install any pump ourselves - by running a steel cable over a pulley at the top of the A-frame, and connected to the bumper of our pickup. She would drive forward 20 feet to pull 20 feet of down-pipe up out of the well. We got to be very fast at it.
But since my conversion to three phase pump motors, we have not pulled a single pump in the eight years since. I am convinced that this is because of low starting torque, no surge current, and a pump motor than runs cooler at higher efficiency. (We do have hot well water which is not good for long component life anyway).
In the summer, when we have an excess of solar power, the domestic water pump is set to run from our solar panels during daylight hours. This is when we do our garden/lawn watering.
Here is a link to one source for the VFD’s. Note that they come in a flavor that requires 3-phase input, and a flavor that will accept single phase input:
Here is a link to a pressure transducer that can be used to replicate the Grundfos tank-less system:
These are line reactors:
Feel free to send me a direct message if you would like some help in getting past any confusion about this approach to water pumping using solar power. I’ll try to help, to the extent that work allows.
The benefits:
1. NO starting surge current to overwhelm or stress your system. The variable frequency drive (VFD), that converts your 230-volt single phase power from your solar inverter to three-phase 230 VAC, is fully programable to provide a slow, linear, ramp up of motor speed. (I have mine programmed to steadily accelerate to full speed over 20 seconds). This is far superior to “soft-start” single phase motors.
2. NO high starting torque that has damaged many long down pipes, and many power leads over time.
3. Better motor efficiency. For any given HP rating, a three-phase motor is about 15% more efficient. A typical 1-1/2 HP single-phase submersible pump motor draws 10 amps at full load, which is 2300 watts at 230 VAC. A typical 1-1/2 HP three-phase motor draws 5 amps at full load, which is 1992 watts. (The formula to calculate three phase power is: 1.732 x amps x volts).
4. You will have fully variable motor speed that will allow you to reduce power draw in times of low sun energy. You can easily set your VFD to run the pump motor at 3/4 of full speed, or 1/2 of full speed. Water pumped is fairly linearly proportional to power consumed, down to about 50% of full speed. Some pump motors can even be operated with reasonable efficiency down to 25% of full speed if you are REALLY short on power reserves, and can make do with a smaller volume of water during hard times.
5. You can use smaller conductors down to the pump. Three-phase motors generally allow the use of one size smaller conductor. If your single-phase motor would require 10 ga conductors, a three-phase motor, all other things being the same, will only need 12 ga conductors. (This potential saving can be offset if your single-phase motor is 1-1/2 HP, or less, and is of the “two-wire” variety).
6. You can install your water system with a smaller, or even without, a pressure tank. This is possible because you can install a $130 pressure transducer that will send a 4-20 milliamp control signal to your VFD that varies linearly with system pressure. You program your VFD to maintain your chosen system pressure, and the pump speed will ramp up and down to maintain that constant pressure, as it reads the input from the pressure transducer. But this refinement is optional.
7. Three-phase motors cost about 10% less than single phase motors of the same HP. This is because their lower current demand allows the build with less total copper in the windings.
8. Most of these modern Variable Frequency Drives do not require a pure sine wave input. Whatever AC waveform you input is first converted to about 320 volts DC anyway. (Verify with your VFD vendor.)
The disadvantages:
1. You have to install an extra component in the form the VFD. But these are now amazingly affordable and reliable. A VFD rated for 3HP costs less than $300. I recommend selecting a drive rated for twice the HP rating of your motor. The incremental cost is very small. This increases reliability because the system runs cool, with little stress. I have both Fuji and Hitachi drives that have been in daily service for eight years with no trouble.
2. Some VFD manuals will recommend that a “line reactor” be installed at the drive output for long wire runs. Not a big deal. A $50 to $100 added cost.
3. As a DIY system, this can save you a ton of money compared to buying prepackaged system of the same components from Grundfos. But it does require some study, and some electrical understanding. If you managed to DIY your solar system, you can DIY this.
4. 1-1/2 HP is about the smallest size three-phase submersible motor available.
We have three wells on our property, all with three-phase pumps running off of VFD’s. Before my conversion to three-phase motors and VFD’s, we had to pull and replace some system component, in one well or the other, about every two years. It was always either a pump motor, a pump, cracked PVC down piping, or damaged lead wires. It was so frequent that I built an A-frame for my tractor that allows my wife and I to pull and install any pump ourselves - by running a steel cable over a pulley at the top of the A-frame, and connected to the bumper of our pickup. She would drive forward 20 feet to pull 20 feet of down-pipe up out of the well. We got to be very fast at it.
But since my conversion to three phase pump motors, we have not pulled a single pump in the eight years since. I am convinced that this is because of low starting torque, no surge current, and a pump motor than runs cooler at higher efficiency. (We do have hot well water which is not good for long component life anyway).
In the summer, when we have an excess of solar power, the domestic water pump is set to run from our solar panels during daylight hours. This is when we do our garden/lawn watering.
Here is a link to one source for the VFD’s. Note that they come in a flavor that requires 3-phase input, and a flavor that will accept single phase input:
Hitachi Drives - Buy AC Drives at Wolf Automation
AC Drives in stock, ready to ship! Authorized stocking distributor offers great pricing and service plus free shipping for online orders over $100.
www.wolfautomation.com
Here is a link to a pressure transducer that can be used to replicate the Grundfos tank-less system:
Sensor, Pressure, High Accuracy, Standard, NPN, 30
Sensor, Pressure, High Accuracy, Standard, NPN, 30x30mm, Connector, 1,000kPa,
www.wolfautomation.com
These are line reactors:
Line Reactors/Load Reactors | Wolf Automation
Line Reactors/Load Reactors in stock, choose from top brands. Great pricing, easy to order, loyalty program and great service.
www.wolfautomation.com
Feel free to send me a direct message if you would like some help in getting past any confusion about this approach to water pumping using solar power. I’ll try to help, to the extent that work allows.
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