We have been experimenting with VFDs to run conventional AC Pumps using DC power of solar panels as in previous post (HP Size Solar Pumps) This is because there are a couple of good quality Solar MPPT VFDs easily available at fair prices.
However the VFD requires relatively high DC input voltage, 290 to 360VDC to run a single phase AC pump, and 440+VDC to run a three phase pump.
At sub-HP power levels the solar panels in commercially available sizes (250 to 330 Watt and 36 to 44 VDC each) are most often not going to add up to the input voltage requirements even for a VFD that will run a single phase AC pump.
To deal with this issue, there is a thought process that some kind of DC to DC boost converter can be used from low voltage DC source to raise the DC voltage in the acceptable range for to the VFD.
As a quick check a small experiment was carried out involving following components.
DC source from 8 x 60 W 36VDC array of panels but on a fully cloudy day. The open circuit voltage at the panel output was around 24 to 34 VDC.
A low cost inverter board that runs on SG3524 chip and MOSFETs, it produces approximately 50 Hz square wave AC output.
3. Salvaged transformer from a household inverter, 12-0-12V to 230V centre tapped, this is rated for around 700VA.
4. Frecon make solar VFD for single phase AC output.
The overall assembled setup is shown in the next picture.
To measure the output voltage and to view the wave pattern, a hobbyst’s oscilloscope (DSO138) was used. At the high voltage side output of the transformer a voltage divider comprising of 22kohm, 1.6kohm and 22kohm was connected. The measuring probes of the oscilloscope were connected across the central 1.6kohm resistor, thus the voltage measured on the oscilloscope is scaled down by a ratio of 1.6 : 44 (i.e. 1 : 27.5). Or in other words, the measured voltage on oscilloscope need to be multipled by 27.5 to get the actual voltage level at the transformer output.
Observations
When the DC power was applied to the inverter and VFD was connected to the transformer output, but not yet switched on, the output from transformer showed as in below picture. Oscilloscope showing 8V means the AC output was +220/-220 V peak to peak and 6.84 x 27.5 = 188 VAC RMS. The DC voltage at inverter input was seen to be in range of 12V.
In this case, the LED display of VFD showed a DC input voltage as 172 VDC. This is not really adequate for a single phase solar VFD, while it requires 290 to 360VDC input for normal operation.
When VFD was switched on, the output voltage from transformer was seen to be reduced. Oscilloscope showing 7.04V means the AC output was +193/-193 V peak to peak, and 2.21 x 27.5 = 61 VAC rms. The DC voltage at inverter input was at 6V. More importantly the waveform is highly distorted and is most likely due to not enough driving power for the transfomer of the inverter, suggestive of shortfall in power available from solar panels.
It would be fair to conclude that this conept as such is ok but the voltage levels and power efficiency need to be experimented further and evaluated.
Adequate power and volage from Solar panels need to be made available on a bright sunny day.
May be, high frequency switching with suitable ferrite or equivalent transformer need to be used.
Centrifugal pumps running on normal AC power supply are very common, fairly efficient and most importantly they are locally available from wide range of manufacturers. Their use and operation is more or less hasslefree, they are easily serviceable at nearby workshops and pricewise also they are affordable. These points are specifically important in comparison to a classical solar pump system that is available in market these days, and which potentially uses a BLDC 3 phase DC motor/pump with permanent magnets and all stainless steel body.
These standard AC pumps are available in 0.5 HP to 10s of HP of power rating, able to run on single phase (220V) or three phase (415V) AC power supply and available in formats like monoblock pumpset, openwell submersible and borewell submersible pumps.
Monoblock PumpOpenwell Submersible PumpBorewell Submersible Pump, motor and pump shown separated from each other.
This article discusses the use of such standard AC pumps using Solar Panels as the source of electricity.
Since solar panels generate DC voltage, it is important to have some mechanism or device to convert the DC electricity from the panels to AC power so that the pump can run on it.
A standard AC motor consumes large amounts of current during startup for a few seconds, this current can be 2 to 6 times of the normal operating current at full load. On the other hand solar panels are a current limited source of power i.e. the current output available from a given solar panel is limited by the size of panel. This means that the solar panels which would be sized and selected to meet the current requirements of the pump at normal operating load are not going to be able to start the pump in normal or traditional manner. Some kind of soft start approach is needed.
Also based on sunlight available over the day time, the output voltage, current and power from solar panels is going to vary, this needs to be maximized by making the pump run at various voltage and/or AC frequency. The standard AC motor which is expected to operate at 50 Hz power supply, can actually be made to run over a range of supply frequency (35 to 55 Hz) without any significant side effects. In this range of frequency, the output power of the motor varies almost linearly and this inherent feature can be used to match the solar panel output with the pump-motor power requirements.
All the above leads to a solution which has to be based on some sort of electronics to support following features.
DC to AC conversion
Soft start or gradually increasing voltage during startup
Output voltage and frequency modulation to optimize the power generation from the solar panels.
For 1 and 2 above there already exists a robust industrial device called Variable Frequency Drive (VFD). VFDs are often used in various industries to control the load and/or speed of standard AC motors which drive the heavy plant and machinery.
Most VFDs allow AC (single or three phase) or DC power supply as input and generate three phase AC power as output.
VFD – Variable Frequency Drive
Internally the input AC power supply is first rectified to DC, that is what makes VFD suitable to run with Solar Panels. Then a microcontroller based circuitry drives a set of power transistors (IGBT or MOSFETs) to achieve DC to AC conversion with a SPWM (sinusoidal pulse width modulation) technique.
The output power is a sine wave with a configurable mains frequency (10 to 60 Hz as an example) but laden with spikes or chopped waveform with a carrier frequency of a few kilo-Hz. This is acceptable for standard AC motors, or rather the carrier frequency used in commercially available VFDs is optimized to keep the motors healthy and not to generate any ill-effects, especially high frequency harmonics.
Output Wavefrom from a VFD
The same waveform as explained and shown above, is generated in all the three phases of the output, but appropriately phase shifted by 120 degrees from each other. That makes a nice power source for a three phase AC motor.
During startup the VFD outputs a lower frequency of say 10 Hz and correspondingly lower pulse width (effectively a reduced AC voltage at the output). It is then gradually increased over a period of 5 to 15 seconds to normal operating frequency of 50 Hz. That is how a soft start is implemented.
VFDs have a simple and basic keypad with start, stop, menu buttons. Keypad permits setting of various configurable parameters, and also displays the operating status/errors if any.
Connectivity with external controlls is also provided, which allows dynamically setting the output frequency and voltage, external start and stop commands etc.
A fewer brands of VFDs have started manufacturing VFDs with additional features as below.
Customized phaseshift of 90/110 degrees (instead of 120) between the three output phases, to emulate the 3 wire power supply of a single phase capacitor run motor.
Changes to output frequency at runtime based on an inbuilt MPPT (maximum power point tracking) algorithm, essential for solar panels.
Test Results
With the concept explained so far as above, we have carried out a few real life tests using a VFD and borewell submersible pump.
Equipment used is listed below
FRECON Make Solar VFD, model number FR150T – 2S – 2.2B -H, this accepts single phase AC input or DC input and gives out 3 phase 220 VAC. Has configuration settings to connect a single phase motor across the three U V W output terminals, and also has a MPPT algorithm in-built into it. It is not a Make In India brand but has ample presence of local dealer network in India. Build wise seems a good robust build.
Kirloskar make borewell submersible pump model Jalaraj KP4-1009 with 10 stages impeller, single phase 1 HP, 220VAC oil filled motor.
An unbranded borewell submersible pump, 10 stages, 0.5 HP 220VAC water filled motor, purchased from local market.
Energy Meter Secure Make, single phase 220VAC 30 Amps, 3200 pulses for 1 KWH unit consumption.
Power was taken from normal household AC supply
Water flow and pressure measurement was carried out using conventional simple techniques.
Normal AC power supply was connected to the input of VFD
Output terminals of the VFD were connected to the pump as given in the user guide of the VFD, i.e. U>>Y, V>>R, W>>B
Two different voltage settings were used for testing at 100% and 80% of normal using F00.16 configuration of VFD.
Valve in the delivery line was kept open in such a way as to be near the operating point to get 2.5 to 3.5 bar pressure and around 1800 LPH flow.
Below are few images and videos related to the tests carried out.
Short Video of the Trial Run, shows the simple setup, pump, energymeter and VFDFrecon VFDconnection diagramPressure GaugeUnbranded 0.5 HP pump, This turned out to be actually a 1 HP pump with much less efficiency than the Kirloskar PumpOutput from VFD visually seen using light bulbs. VFD was configured for a single Phase Motor. This is typical to the FRECON Solar VFD model that they have provided a configuration setting. F08.00 = 2
Important observations
The VFD was tried in two different wiring arrangements. Two wire output mode: This is as per connection F08.00 = 1, whereby the run capacitor of the motor would be kept in circuit and only two wires of the VFD output were connected to the motor starter. In this case it was seen that the motor draws relatively more current untill it starts rotating and there after settles down to normal operating current. The starting current in this case is not as high as it would be otherwise on normal AC power supply, but still higher than running current. This is expected to be so and likely due to the inadequate capacitance at lower starting frequency. Three wire output mode: This is as per connection F08.00 = 2, as shown in figure 2.11 In this case the motor draws steadily and gradually increasing current until it stabilizes to the normal running current. This is a very important and useful aspect of the connection arrangement supported by this VFD since it will help deployment of optimum capacity of solar panels.
Further Work
It is essential to carry out similar tests with input power taken from suitably selected solar panels at various time of the day.
An online calculator for panel capacity is presented here at the below link. This will be useful to select the panel ratings for a given pump capacity.
On 30-March-2022 this VFD and 1HP single phase pump was installed at a farm site in Murbad.
Total of 1600 Watt Solar Panels are used to drive the VFD which is a mixed set as below. 8 x 100 Watt 18 V in series with ( ( 4 x 100 Watt 46 V in series ) x 2 such strings in parallel )
It was seen that pump delivers 3000 to 3600 LPH water at about 30 feet total head, panel side voltage found to be in the order of 300 to 330 VDC, the VFD appropriately keeps regulating the output frequency from 35 to 50 Hz in order to maximize the solar energy generation from the panels and the VFD output voltage was seen to be in range of 160 to 220 VAC.
Long term trial run is planned and results will be published.
Video of the VFD in operation and solar panels used.Water flow from the pump
For irrigation of small farms where water source is available nearby (either an open well, pond, lake or any such water body) it is possible to use small pumps and operate them on solar panels.
छोटे खेतों की सिंचाई के लिए जहां पानी का स्रोत पास में उपलब्ध है (या तो एक खुला कुआं, तालाब, झील या ऐसा कोई जल निकाय) छोटे पंपों का उपयोग करना और उन्हें सौर पैनलों पर संचालित करना संभव है।
These pumps are easily available at reasonable prices online as well as in local market in most of the cities and small towns accessible to farmers. They are used very commonly in battery operated backpack sprayers used for pesticides.
ये पंप अधिकांश शहरों और छोटे शहरों में ऑनलाइन और साथ ही स्थानीय बाजार में उचित मूल्य पर आसानी से उपलब्ध हैं। वे आमतौर पर कीटनाशकों के लिए उपयोग किए जाने वाले बैटरी चालित बैकपैक स्प्रेयर में उपयोग किए जाते हैं।
This post explains some important aspects of this type of pumps for use at small irrigation sites.
यह पोस्ट छोटे सिंचाई स्थलों पर उपयोग के लिए इस प्रकार के पंपों के कुछ महत्वपूर्ण पहलुओं की व्याख्या करता है।
Such a pump is run by a DC motor and has a PVC block head where positive displacement of water is achieved by action of miniaturized pistons inside the block.
ऐसा पंप डीसी मोटर द्वारा चलाया जाता है और इसमें पीवीसी ब्लॉक हेड होता है जहां ब्लॉक के अंदर छोटे पिस्टन की क्रिया द्वारा पानी का दबाव बढाया जाता है।
A pump having single motor is often priced at 550 to 650 INR and delivers upto 3 LPM water and claims to generate pressure of 70 PSI or 5 Bar i.e. upto 50 meters of height.
सिंगल मोटर वाले एक पंप की कीमत अक्सर 550 से 650 रुपये होती है और यह 3 लिटर प्रति मिनिट तक पानी दे सकता है और 70 पीएसआई या 5 बार यानी 50 मीटर ऊंचाई तक का दबाव उत्पन्न करने का दावा करता है।
Pump with twin motor is also available and priced at 1000 INR, delivers 5 to 6 LPM of water at similar pressure.
दो मोटर वाला पंप भी उपलब्ध है और इसकी कीमत लगभग 1000 रुपये है, समान दबाव पर 5 से 6 लीटर पानी की आपूर्ति करता है।
Next two images show a single motor and dual or twin motor pump.
अगली दो छवियां एकल मोटर और दोहरी या जुड़वां मोटर पंप दिखाती हैं।
The DC Motor used is a DC motor with brushes and follows a standard specification named as 775 motor, some details can be found here.
The motor can be operated over a wide range of DC supply voltage (6 to 36VDC) but the pump manufacturers normally mark the pump for operation in range of 12 to 14.5 VDC only.
We have installed such pumps at a couple of sites and safely connected to solar panels of 12VDC nominal (or 18VDC MPPT voltage). The motor of the pump nicely works with the electricity generated by solar panel during the daytime. As the intensity of sunlight changes throughout the day, the output flow of water varies and is acceptable for the irrigation purposes.
Inlet and outlet of the pump is however a non-standard (or at least not easily available) tubing size. Most suppliers provide a PVC/HDPE tube with threaded PVC nut to attach to the pump outlet nozzle, but the connectors with standard pipe sizes (say 0.5 or 1 inch nominal bore pipe) are difficult to find.
We have used a typical nozzle connection seen in pictures and created a simple skid mounted assembly of this type of pumps, eiether one pump on the skid or 2 on the skid as per the requirements.
With 2 pumps on the skid it is seen that 150 to 200 watt panels are adequate for operation throughout the day. For single pump a panel of 75 to 100 watt is appropriate.
Next few images explain the mounting approach we have used and is only a suggestion. Any suitable alternative can be followed that meets the needs and materials availability at the installation site.
Single Pump Skid
Dual Pump Skid
Front view of the pump skid with inlet and outlet pipes on left side.
Seen from top at an angle / 3-D view.
Left Side View
Rear View
Right Side View
Top View
Important Instructions
Pump and motor must never be submerged in water and water must not get into the motor.
DC power supply polarity needs to be correctly followed. Green wires to be connected to negative terminal of the battery or solar panels, and red wire to positive terminal.
DC supply voltage must never exceed 18 volts.
In no case, AC supply / mains supply shall be applied to the motor, it is hazardous besides the fact that it will permanently damage the motor.
Testing of pump without water by supplying DC power for a second or say two seconds is ok, but must not run the motor for longer duration without water.
At the inlet pipe a suitable filter in form of nylon mesh is highly recommended. The internal piston mechanism of the pump is too small to get clogged by smallest of the particles.
This type of pump can generally start from dry run and can self prime in a few seconds, but if it does not do so, please do not run it dry for long time. Instead open the nozzles and check if any clogging or blockages. Try to pull water from outlet nozzle or pipe by sucking the air.
The pump can lift water from upto 5-6 feet on the suction side, however it is better to keep the suction pipe length as small as possible.
It is recommended to install a footvalve at end of the suction pipe submerged inside the water, it is best to attach a filter mesh around the footvalve.
Make sure that the pump skid is mounted on a sturdy platform or base. Alternatively pump can be suspeneded firmly inside an openwell clearly above the water level.
Use solar panels of 12VDC nominal voltage only, any higher voltage panels if connected to the pump will damage the same. It is better to first check the nameplate on the backside of the solar panel before connecting for the first time. The nameplate should read 12VDC nominal and/or 17-18 VDC MPPT or maximum power voltage.
Single pump skid is suitable to operate with 75 to 100 Watt panel and dual pump skid with 150 to 200 Watts. Excessively higher wattage of the solar panels must be avoided.
This type of pump is supposed to be used for intermittent duty only however through our experimentation in actual sites, we find that using the pump every day for 3 to 5 hours is fine.
Connect the outlet pipe with suitable coupling or union with the delivery pipe to be arranged at the site to suit the distance of the final delivery location away from the water source.
Ensure that the inlet and outlet pipe connections do not lead to forces on the pipes or the skid.
If in doubt please reach out to us through email or phone.
Demonstration of 3 pumps at a site in murbad
Update on 21-Sep-2022
We have taken measurements of the pressure and flow generated from this type of mini pump and the videos below are useful to understand the performance.
It was seen that when operating with a 16VDC power adapter one twin pump could produce 2 Bar pressure (20 mtr water column equivalent).
At 1.5 bar the pump delivered 180 LPH and at 1.0 bar the pump could deliver 300 LPH of water flow.
Internet of Things (IoT) is about connecting various devices (sensors, controllers, display units, alarms and any such instrument/equipment) with each other using public internet and may partly run through private network of the end user.
With this primary capabaility, IoT opens out many opportunities for systems control, remote data monitoring and to execute commands that carry out various operations based on desired conditions.
With improved data connectivity and availability + the reducing prices of electronic devices, IoT is picking up fast and more importantly it is also getting easier for hobbyists and individuals to deploy IoT projects all by themselves.
Besides the hardware and software to implement any IoT project, what is equally important is a consistent and fairly reliable mechanism to receive and store the data points in a (near) real time manner.
Setting up such a data store can turn out costly, but there are many such online services available. For industry grade volumes and quality of service/reliability, such data logging services providers offer various plans with different charge structures.
For hobbyist and DIY users, most if not all these online services offer a free option but obviously with limited resources granted to the user.
A few of the popular service providers are listed below, this is just a very small list.
Let us see how to open an account and create a data logging channel with one of the service providers, namely thingspeak.com
Create an account with ThingSpeak
From your computer or mobile phone connected to internet, open the web browser and go to the URL link ThingSpeak SignUp
Enter your email address and Country and First Name, Last Name on the sign-in page, then click Proceed / Next / Continue button. We recommend using the same personal Google email id as you use on your mobile phone google account.
It will warn you about your email address being personal email id. Refer the image below. Please Tick / Select the check box near Use this email… and click Continue button. After this it will display a message mentioning about having sent a link to your email address.
Open your e-mail box and find the mail received from ThingSpeak, check if the email has gone into spam folder. Please ask for resending the mail again, if required, by clicking the Send Me the Mail Again link.
Locate the URL link available in the email that you received and click the link or button or copy paste that URL link in a new browser tab/window. Please keep the previous tab/window of ThingSpeak still open for further use.
This new tab/window (not shown here) which you opened from your email by clicking the verification link / button – will show some message like your account/email after successful verification. This is actually a mathworks account which is another website like ThingSpeak, both of which share common authentication and some other such few features.
After this verification is successful, resume in the previous ThingSpeak tab/window, by clicking the Continue button.
It will take you to sing-up page where you will be asked to specify your user id and password for ThingSpeak login. Please set a valid user id and password for your ThingSpeak account, this is entirely different and not connected with your email address. Remember and/or note down the user id and password for future use.
Then proceed to login to ThingSpeak web site or you will be automatically logged into ThingSpeak.
At the first login it may ask for some additional information like – what purpose you plan to use ThingSpeak for, (refer next image). Please specify non-commercial/ personal use and click ok.
Create Channel
A channel is one identifiable register/data store to capture data.
For example let us say – a user has 2 different locations where he /she wants to monitor the ambient temperature and humidity at every 5 minutes continuously.
To be able to do this the user will setup the needed sensors at the respective locations and data acquired by the sensors will have to be posted to some internet based URL. This URL will receive the data values and store them for later use and analysis.
For this example, the user needs to have two different registers or data stores one per location and each register needs to support at least three fields (namely timestamp, Temperature in deg C., Humidity in %).
So it is like two readings one each for the two locations, comprising of 3 field values each will be received and saved every 5 minutes. That is 576 readings per day and over 2 years it will be around 0.42 million or 420000 readings. Each reading is about 40 bytes say, so just 16 MB of data over 2 years. The data volume for these two datastores is not really that high, but it is important that the datastore has to provide a reliable and continously available mechanism of data logging.
When translated in the terminology of ThingSpeak, this means two channels one each with 3 fields of data are necessary to be created.
Thingspeak allows upto 4 channels to be created by every user having a free account.
So let us see how to create a channel.
After the ThingSpeak login account has been created and successfully logged in, it is required that a new channel be created in the page shown below.
Click the New Channel button, the website will take you to next page.
On this page specify a channel name and select / tick against all the 8 fields shown in the page. Then click Save Channel button. There are other two buttons provided as below
Clear Channel – This clears the old data that may have been captured so far in this channel. It is recommended to not clear the channel unless you are sure that you want to lose the data forever.
Delete Channel – This deletes the channel altogether. It is strongly recommend to not click this ever, especially after any of the field device is using the channel.
Important Parameters of the Channel
Please note down the Channel Id, Name and Read and Write API Keys, as it shows in the web page in the API Keys tab. Once the channel is created the Keys and Channel Id can be used by any device/software so that the data to be collected by any field sensor or device can be posted to the channel. These values can be altered any-time by the the user login who created the channel, but if the channel keys are setup in any IoT device as a part of one time configuration then the altered values (especially the Read and Write API keys) need to be updated in all the devices and programs where the old keys were used.
Verifying the channel
Once the channel is created it can be tested by executing below commands in browser address bar.
Write to Channel https://api.thingspeak.com/update?api_key=WRITE_KEY&field1=123456&field2=0.56
The above comamnd submits and saves one data point with values of two fields to the respective thingspeak channel with matching WRITE_KEY.
This comamnd retrieves 20 data point from the thingspeak channel specified by the CHANNEL_ID
View the data graphically
Thingspeak provides a nice and simple way to view the datapoints. It would be a good activity to explore this part in details to understand what options it gives to view the data, i.e. various types of graph, number of datapoints to be viewed etc. https://thingspeak.com/channels/CHANNEL_ID/private_show
