How To Monitor A Powerwall & Solar Array

If you have recently purchased or built a DIY powerwall or other large format home backup battery then you are probably wondering how to monitor a powerwall. Powerwall monitoring devices range from as simple as a voltage display all the way up to a complete monitoring solution that tracks current, volts, and watt hours over time. 

The easiest and lowest-cost way to monitor a powerwall is with a simple voltage display. The next step up would be to use a display that reads both current and voltage to monitor your powerwall. This way you can know the amount of power that is actually flowing through your powerwall battery. The ideal powerwall monitoring setup would include both a current and voltage display and also connect via wifi or Bluetooth to enable the powerwall to be remotely monitored. The problem is that despite the demands, general-purpose powerwall monitoring devices that support wifi are few and far between. The good news is that with a little time and effort, you can make a DIY WiFi-enabled powerwall monitoring system. 

In this article, we will explain several different ways that you can monitor a power wall. We will cover voltage displays, watt meters, and energy monitors. We will also discuss the difference between each type of powerwall monitoring technique.

What Is Powerall Monitor

A powerwall monitor is a device that is mounted on or near a battery and measures how much current goes in and out of the battery. A powerwall monitor can also tell you the estimated state of charge of a battery. These devices range in cost and feature set but are generally inexpensive. In this section, we will go over some of the different types of powerwall monitors. 

What Type Of Powerwall Monitor Do I Need?

Usually, the answer to that question would begin with ‘It depends on your application’, but the fact that it's a powerwall battery implies that it is a large, high-capacity battery or bank of batteries that is more than likely running a load of a non-insignificant size.

For this reason, it's best to get a powerwall monitoring device that can read both voltage and current. If you know the current and voltage, it's easy to find out exactly how much power your powerwall battery is providing. 

This is because total power, or watts, is the voltage multiplied by the current. Because it's such a simple calculation and requires just two inputs, most powerwall monitors that can read current and voltage also display the result of that multiplication on the screen in watts.

How To Monitor Powerwall Voltage

There are several battery meters on the market that can be useful for general voltage and current level assessment. It's important to keep in mind, however, that these consider the fact that these are not precision devices.

Basic voltage monitors are just that- basic. They can help you estimate the capacity of your battery bank but it's important to note that these are known to be pretty inaccurate. So if it says 42.5 volts, your battery might really be at 41.6 volts or 43.1 volts. 

[[ aff type=aff ~ link=https://amzn.to/3kzBadO ~ title=`Supnova Voltage Monitor` ~ image=https://admin.cellsaviors.com/storage/supnova-voltage-monitor.jpg ~ description=`Monitors 8 to 100V, can set high and low voltage alarms, and estimates the state of charge.` ~ height=small ~ buttonText=`Check Price`  ]]

Because of their dirt-cheap pricing and extreme ease of installation, these basic powerwall voltage monitors are worth buying if all you need is a simple solution. All you really have to do is get used to its inaccuracy offset and then you can use one of these things to get a general idea of your battery capacity. 

NOTE: These things are NOT accurate enough to be used for battery charging. If the meter says 4.2 volts, the voltage level could really be at 4.4 volts and you could overcharge a cell.

Even at higher voltage batteries where a volt or so or more off is not a safety issue, it's still a performance issue. If you are setting your charging voltages and currents based on the readings of super inaccurate meters like these devices, then you are either going to not be getting the most of your battery or will be asking a little more of it than you think you are.

For this reason, it's much better to spend a few extra dollars to get a more accurate piece of equipment. The good news is that in spending those few dollars for more accuracy, you also get more features and generally a higher current carrying capacity. 

Hall Effect Sensor Capacity Meter/Battery Tester

This powerwall monitoring device is neat because they don't require the current to be directly sent through them to be measured. Even without directly measuring the current, these devices are very accurate. Because of the type of sensor it is, you have to make sure that you have it in the correct orientation. 

[[ aff type=aff ~ link=https://amzn.to/3m8gh9R ~ title=`DROK Charge and Discharge Monitor` ~ image=https://admin.cellsaviors.com/storage/DROK-voltage-current-monitor.jpg ~ description=`Offers 7 functions, voltage from 0-90V, current from 0-100A, real-time power, battery capacity, amp-hour, watt-hour, and time.` ~ height=small ~ buttonText=`Check Price`  ]]

This powerwall monitor is a little more sophisticated than the devices above. It can also even store the capacity and load tests over time. This can be useful in assessing the health of your off-grid system.

This powerwall monitor has no remote monitoring capability, so that means in order to use it you will have to walk right up to it and read what it says. This is enough for most people, as unlike generators and solar panels, power wall batteries are generally installed in normal parts of the house. 

This makes sense because powerwall batteries are sensitive to the elements and need to be operated in a climate-controlled environment unless extra special care is taken to make the battery suitable for an untraditional environment. 

Powerwall Amp Meters and Voltage Monitor

This is one of the most direct and accurate ways to measure battery capacity. A battery shunt tells you exactly how much electricity is running through it. This particular powerwall energy monitoring solution only allows you to monitor the flow of energy in one direction, but that is a limitation of this particular device and not a current shunt limitation as they are bidirectional devices.

[[ aff type=aff ~ link=https://amzn.to/3SvJNCH ~ title=`DROK DC Power Meter Monitor` ~ image=https://admin.cellsaviors.com/storage/DROK-DC-Power-Meter.jpg ~ description=`Shunt based: voltage range DC 6.5~100V; current range 0~100A; power test range 0~10kw; battery level test range 0~9999kwh.` ~ height=small ~ buttonText=`Check Price`  ]]

The one drawback of a shunt-based current sensor is that in order to sense how much current is running through it, a current shunt produces a small voltage drop. The thing is, the voltage drops that are produced by these devices are just so small that almost no power is lost in the process.

How To Monitor A Powerwall’s Temperature

Most people that are concerned with how to monitor a powerwall will also be concerned with how to monitor powerwall temperature. It’s important to consider that not all powerwall monitoring solutions will include temperature monitoring.  In fact, almost none of them do. 

For safety, performance, and the highest-possible lifespan, a battery should be placed in an area where the ambient temperature will be acceptable for its operation. It’s equally as important for a battery to be able to shed heat generated internally. Heat building up inside a battery is often worse for the battery than heat creeping in from the outside. Just as important as shedding heat is making sure that your battery pack is kept warm during the colder months of the year. 

Heat can build up in a battery as a result of many factors, and not all of them involve failures. Batteries will, to a degree, heat up during normal operation. It’s up to the designer of the battery and how the user uses the battery in its implementation which determines how much heat is internally generated by the battery. 

The general rule of thumb is that if you have a battery that has more than 50 cells or gets regularly used on a daily basis or gets used under high current circumstances (50 amps or more) should to be temperature monitored.

Can Powerwalls Be Monitored Remotely?

Yes, but remote powerwall monitoring devices are kind of hard to find. There are very few commercially available remote powerwall monitoring solutions. This Goupchn 400A remote battery monitor, however, is a good example of a decently priced remote battery monitor with modern connectivity features. 

[[ aff type=aff ~ link=https://amzn.to/3Zrt2dR ~ title=`Goupchn 400A Monitor With Wireless` ~ image=https://admin.cellsaviors.com/storage/Groupchn-400A-Battery-Monitor.jpg ~ description=`Shunt based so highly accurate. Wireless monitoring so you can check on it through the app. ` ~ height=small ~ buttonText=`Check Price`  ]]

This device is a coulomb meter that is able to measure voltage, current, power, charge, and discharge capacity,  and watt-hours over time. The user interface keys are used to change the settings to adjust things like the over-voltage protection level, the under-voltage protection level, battery chemistry, and more. 

Unlike many other current meters, this one makes use of the fact that a differential reading is required to read current. Differential readings work regardless of the polarity, so this meter can read current flow in both directions. 

It's got a bright, easy-to-read 2.4-inch color LCD, and the buttons are made of silicone, so they have a high-quality feel to them. 

This monitor can be used with a variety of battery chemistries including but not limited to lithium-ion batteries, ternary lithium batteries, lead-acid batteries, and lithium phosphate batteries. This meter even offers an RS485 communication port so that it can be adjusted by a third-party microcontroller or computer system. 

This powerwall battery monitor includes an app that lets you view all of your powerwall stats and change settings on your smartphone.

One of the cool things about this powerwall monitor is that it has a control output that can be triggered any time there is an over current, over-voltage, or other faults. This signal can then be sent to a relay or bank of MOSFETs to be able to control the flow of power. 

The problem is that there are simply not many devices like this. Wireless powerwall monitors are a relatively new market segment, so it's just a matter of time before there is a large variety of devices to choose from. 

How To Build A DIY Remote Powerwall Monitoring Device

This won't be a programming tutorial, but in this section, I will explain the general layout and system topology for wirelessly monitoring a powerwall battery using Wi-Fi. A remote powerwall monitoring device has some basic criteria and requirements that need to be met.

Parts Required 

• Microcontroller
  Any basic microcontroller will be fast enough to carry out this task. The problem is that not all microcontrollers have wireless built-in. If you are using a microcontroller without wireless, then you will need to pick up a dedicated WiFi module to interface your system with the internet.
  
  Instead of doing all of that, I recommend using an ESP8266 or ESP32 microcontroller as either of them has more than enough power for the task at hand, plus they have built-in WiFi. 

[[ aff type=aff ~ link=https://amzn.to/3Ye0Ni8 ~ title=`ESP8266 NodeMCU` ~ image=https://admin.cellsaviors.com/storage/ESP8266-NodeMCU-CP2102-ESP-12E.jpg ~ description=`ESP8266 NodeMCU microcontroller with WIFI Serial Wireless Module, easy to program!!` ~ height=small ~ buttonText=`Check Price`  ]]

• Analog to Digital Converter
  While it’s true that just about all microcontrollers have a built-in analog-to-digital converter, an external ADC will be required to accurately read the current and voltage from your powerwall.
  
  For a project like this, I recommend using the Texas Instruments ADS1115 analog-to-digital converter. It has 4 channels and supports differential measurements, which is the type of measurement that needs to be performed when reading a current shunt. 

[[ aff type=aff ~ link=https://amzn.to/3KI36Xt ~ title=`ADS1115 16 Bit 4 Channel` ~ image=https://admin.cellsaviors.com/storage/ADS1115-16-Bit.jpg ~ description=`High precision 4 Channel Analog-to-Digital ADC Converter.` ~ height=small ~ buttonText=`Check Price`  ]]

• Current Shunt
  A current shunt is a device that produces a tiny but consistent voltage drop that is proportional to the amount of current that’s flowing through it. 
• Voltage Divider
  These chips and modules pretty much max out at 5 volts. This means in order to read a voltage higher than that, you must first divide the voltage down to a lower level that is safe for the chips to read.
  
  Depending on the voltage of the powerwall you are trying to monitor, you will have to build a different kind of voltage divider. This page has an excellent voltage divider calculator that can be used to find the exact resistor values needed to make your voltage divider. 
• Voltage Sensing
  In this example, we will explain how to monitor a 7S or 24V powerwall battery. A 7S lithium-ion battery has a full charge voltage of 29.4 volts, but our analog-to-digital converter can only read a maximum of 5 volts.

  

As you can see from the image above, a 10k and a 2k resistor is all that is needed to scale a maximum of 29.4 volts down to a maximum of 4.9 volts. 

This simple device makes it so that a microcontroller and its peripherals can safely read higher voltage levels. As you would expect, some math has to be done in the microcontroller to scale that figure back up to the real voltage level.

• Current Sensing
  Current sensing requires taking a differential measurement. Normal analog to digital conversion measures one voltage level with respect to ground. In contrast, different sensing measures one voltage with respect to another voltage.
  
  When sensing current through a current shunt, one of the differential measurement pins is attached to one side of the shunt and the other pin is attached to the other side of the shunt. This allows the analog-to-digital converter to be able to precisely measure the voltage drop across the current shunt.
  
  As you would expect, the voltage across the voltage shunt will be very small. Luckily the ADS1115 has a programmable gain amplifier. Turning the gain amplifier to 16x makes it so that you can easily read small signals such as those produced by a current shunt with extreme accuracy and stability. 
  
  The ADS1115 analog-to-digital converter comes with an extremely easy-to-use API that several Arduino libraries have already been built around. If you would like to learn more about how to use this analog-to-digital converter, check out this tutorial on how to use the ADS 1115 with arduino. 
  
  
• Wireless Connectivity
  Chips like the ESP8266 and ESP32 have built-in Wi-Fi. The ESP32 even has built-in Bluetooth. With either chip, a WebSocket server that continually updates a webpage with new data can easily be created.  
  
  The tutorial in the link is everything you need to know to build a device that can generate a web page that can be used for reading and or controlling the microcontroller and whatever it's connected to.

How To Monitor A Powerwall Over WiFi

Using the above information and with some time and effort, it's possible to create a simple program that reads the current and voltage of a powerwall and then broadcasts that information to a web page via web sockets.

You can even make it so that when you click certain buttons on the web page, it changes settings and does other tasks on the microcontroller. There are a ton of tutorials online that clearly explain each aspect of this system's requirements. To actually make it happen it just takes time and patience.  

Once you get it up and running to the point where you can read the current and voltage, it's just a matter of doing the math and operating on those variables over time to calculate watt hours, battery capacity, and more.

You can even attach a relay to it and use that to connect or disconnect your charger remotely. Once you get into the realm of working with electronics on this level, the possibilities really are endless. 

Remember, the ADS1115 has 4 inputs, and 2 inputs are used to take a differential measurement. The current sensor requires a differential reading and the voltage can be read with just one input. This leaves one more input that can be used for whatever you want, such as a temperature sensor so that you can remotely monitor your powerwall’s temperature. 

Is It Worth It To Build A DIY Powerwall Monitor?

Absolutely. Sure it takes a lot more work, research, and effort, but it ultimately costs a lot less money. The best part is that the ADS1115 is a precision instrument with a built-in voltage reference. This means that you can really trust that its readings will not only be accurate but consistent. The ADS1115 far surpasses the quality of the analog-to-digital converter reading the current and voltage in just about any powerwall monitor on the market. 

Another important thing to consider is that pre-build powerwall monitors use weak CPUs that can’t provide quick update rates. This manifests itself in a sluggish or laggy user interface and update rate, hurting the overall experience. 

The ESP32 and other cheap, off-the-shelf microcontrollers, however, are extremely capable 32-bit CPUs, and in the case of the ESP32, there are two of them! This means it's possible to achieve a buttery smooth user interface experience and a frame rate that more closely matches what you can get from a full-size computer rather than the cheap, bargain bin microcontrollers that you find in most consumer electronics. 

Conclusion

Knowing how to monitor a powerwall battery is a critical component of making sure your system stays healthy and running at its peak performance. As you have learned, powerwall monitoring devices vary widely in features-set and price. 

Some powerwall monitoring devices are simple voltage meters while others will also tell you the current. More complex powerwall monitoring solutions track these figures and estimate how many watt-hours go in and out of your battery. When it comes to wireless powerwall monitoring, there are a few decent off-the-shelf solutions but don't expect much in the way of accuracy. With a bit of effort and research, however, a really nice quality WiFi-enabled remote powerwall monitor can be built. 

We hope this article helped you learn how to monitor a powerwall, thanks for reading!