Bad, Better, Best: Battery-Inverter Communications & Compatibility

As discussed in the previous article, “closed-loop communication” is a buzzphrase that vaguely describes "communicating batteries." In this article, we will compare basic and advanced battery communication, discuss the challenge of 'good' inverter-battery communication, and what happens when it's absent, incomplete, or working like a dream. 

Battery communication is more complicated (and more critical) than most brands care to delve into - and this is understandable; too much information can overwhelm, and no battery manufacturer wants to discourage a potential customer who already owns a Schnider, Solark, or any other brand from using their battery.

A battery bank is the cornerstone of any power system. Whether storing solar energy for later use or actively powering AC loads in a home, the battery is always operating and is therefore the logical choice for the main system controller. It sets voltage and current parameters for all other system components. If a communicating lithium battery is going to be connected to my inverter or a larger solar system, it's wise to ask: what data can I access from the BMS (battery management system), and how is that data going to be shared (or not shared) with the rest of my system?

Who's running the show?

In a power system with closed-loop communication, the inverter, solar charge controllers, and other components do not control the battery. Instead, the battery informs the decisions made by everything else in the system. The performance of any battery-inverter combination depends on how effectively the battery can fulfill this role. For the battery to receive what it needs and for the system to operate at peak performance, these control messages must be accurate and well-understood by the rest of the system. As you will see, this is not always a given.

Basic communication

In a basic battery communication system, the main information shared is the battery telling the inverter whether or not it will accept or give a current at this moment. A system with basic communication offers reliability and noticeable performance advantages over non-communicating lithium batteries. For example, the batteries will shut off the inverter before reaching a critically low state of charge and will accept a full charge until they reach their capacity limit.  This level of communication provides a nuanced step above protection-centric BMSs such as the ability to continue discharging in circumstances where the batteries are too cold to accept a charge. This simple step up can enable a lot more system functionality and is worth consideration. The current generation of Victron Smart Lithium batteries feature this type of communicating BMS and are sufficient for many applications.

Advanced communication

Advanced communication requires a good BMS, capable of monitoring more than just cell voltages. If your BMS gathers extensive information and can actively manage that information, it opens up a world of possibilities for your system, such as remote starts, relay control for heaters, and generator auto-starts. A great example of this is Pylontech’s communicating LiFePO4 batteries.  

In addition to reporting the state of charge, Pylontech batteries also provide information about high and low cell voltage, high and low cell temperature, and even the battery's ideal charge current. With this information, the Victron inverter can optimize the charging process and maximize the battery's capacity, allowing it to be discharged down to 95% DOD (Depth of Discharge), also known as 5% SOC. This communication occurs seamlessly and does not require complex programming during commissioning. Simply connect the batteries using a specific Victron-manufactured cable, and the system is good to go. Victron's DVCC function takes over from there.

The Challenge of Battery-Inverter Compatibility

While an advanced lithium battery can share a lot of detailed information, the rest of the system must be able to speak the same language. If the inverter cannot receive and interpret this information correctly, diagnosing and resolving issues appropriately becomes much more challenging. 

Seamless communication doesn't just fall in our laps; it's something that's battled out in the trenches by engineering teams and software developers. The historical relationship between manufacturers plays a significant role as well. Getting the communications right requires substantial effort and financial investment, and many battery manufacturers don't have the means or the opportunity to collaborate with a major inverter manufacturer. 

How does this play out? While many customers are excited to get their hands on the latest and greatest battery, they find themselves on hold, waiting to report an error code the development team did not foresee. Why? Because power systems don't operate in a lab. In the real world, people install things wrong, put wires in the wrong places, run their systems in adverse temperature conditions, and connect batteries to loads that were not anticipated. When the power system receives incorrect or unexpected data, it may trigger alarms or shut itself off entirely. For example, if a battery samples a temperature or voltage that is wildly high, it may shut down the entire inverter system, even if the issue lies in erroneous data rather than a faulty battery cell. 

What you don't know can't hurt you…

Ah, not so with lithium batteries. For example, most communicating lithium batteries report average temperature, but this level of information is not adequate for systems in environments where high or low temperatures are a concern. It's like saying, "Your fingers are frozen, but your core is warm, so you're OK, right?" What is truly needed is the maximum and minimum battery temperature to understand the full temperature range. Data that doesn't provide the complete picture gives a false sense of security. This is a major reason why some manufacturers have yet to transition from lead acid to lithium, despite the benefits of lithium batteries, such as lower weight and higher energy density. There are lithium battery brands that take pride in not having any communication capabilities at all. Sometimes, it is easier not to be aware of a problem rather than be responsible for fielding calls about an error code that no one can interpret or resolve. If the issue can’t be pinned on the battery, it must be the fault of some other component…right?

Given the challenges of software compatibility, many companies have developed their own all-in-one solutions, ensuring communication compatibility but limiting flexibility. If you're reading this, you're likely a fan of the modular, open-source approach to power system design offered by Victron Energy. If you're looking for a system tailored to your needs, there are many options for components made by many different companies. However, the success or failure of such a system depends on how well the components ‘talk’ with each other as a unified system.

The advanced product integration we currently enjoy between Victron and Pylontech was expensive, time-consuming, and necessitated ongoing maintenance from both companies through continuous learning and firmware updates. Look out for an upcoming article about what you can see and troubleshoot in a Victron-Pylontech system (it’s impressive). With this inverter-battery combination, system owners can quickly check the overall status of the battery bank, including voltage, state of charge, temperature, etc, and should a specific problem arise, it can be viewed and confirmed because Pylontech batteries communicate internal error codes to your display monitor, whether it be a touch screen display or Victron's VRM portal. This level of integration builds trust in the system's performance; we can see that the system is working as it should and the batteries fade into the background because they know what to do, and they are actively managing the rest of the Victron system.

In summary, incomplete or inconsistent battery-inverter communication can: 

• Confuse and frustrate the end user and installer providing tech support.

• Obscure the true point of failure, delaying resolution. 

• Reduce the battery's life if unknown or poorly understood issues are allowed to persist. 

• Damage confidence in the system and the brand.

• Affect the morale of your technical teams and end users. 

You can see why Intelligent Controls only works with a limited number of proven lithium brands that are known to work well with Victron gear and with which Victron affirms compatibility.

Bad, Better, Best

To illustrate our point, here are some recent real-world examples of closed-loop battery systems encountered by our team that either fell short of or exceeded expectations:

Bad: A new lithium battery bank in an industrial application suddenly goes offline.

Why? Well, the batteries didn't provide an exact reason for the system going offline. When we isolated the communication cable from the BMS, the system returned to operation. It happened again when the battery SOC was at 34%. We don't know why; months later, we still don't. It happened again recently, and we can't do anything about it. We documented the issue and talked to the battery manufacturer, which is very large, and was able to fly someone across the country to look at the system. They couldn't repeat the issue, so they replaced the network cable with their external BMS. Nothing happened at that moment so they assumed the problem was fixed…was it? No, it happened again within a week. The company isn't going to take the batteries back. Is there hope of a resolution? Not really. Is the issue related to their software's compatibility with Victron equipment? For sure. What is the company going to do, hire a lawyer? That's not a path anyone wants to embark on. 

Better: The coms might work, but the customer needs help to figure it out.

This is a common scenario, and it's a mess to figure out. A customer had their own batteries from a well-known budget brand that they wanted to pair with their new Victron system. He brought the batteries in for our team to help pair them with his inverter. It took us two days to figure it out. After being passed around to multiple tech support personnel, we finally found someone who could talk to the engineering team. We soon learned that the communication pathway we needed was outlined in an older manual for a battery which we did not have (different voltage, different product). Did this battery company really not anticipate customers using the battery with a Victron inverter, despite touting Victron compatibility as a selling point? If you need to be a computer wizard or have a few free days to spend on the phone, is the battery really compatible? 

Buyer Beware

Most budget battery companies don’t have support from the inverter companies they claim compatibility with. Rather, they reverse-engineer communication protocols established by officially supported brands or simply buy and incorporate their BMS boards. This works to varying degrees of effect, but at the end of the day, they don’t benefit from hotfixes or the firmware updates one would expect when two companies are hip-to-hip in supporting each other’s products. Every few months Victron releases new firmware for the Cerbo GX. If they wanted to fix something, they would. Find the short list batteries that Victron confirms compatibility with here.

Best: A boring install with no issues, maintenance, or need for ongoing support

A customer with an ambitious amount of PV power put in a large Pylontech battery bank that he wanted to have in a single communication string with the rest of his system. All it took was a one-hour visit from a member of our team to install a communication hub combiner, and now there are 24 batteries in full communication. The system has purred along efficiently and without issue ever since. When communication works well, it becomes uneventful. You install a system, and you never hear from the customer again. If there is a need for further assistance, all the necessary information is available to you thanks to continuous system data-logging and easy-to-visualize dashboards populated on VRM. 

>>> Related Reading: Active Management: Expect More From Your BMS

Conclusion

If a communicating battery does not absolutely nail closed-loop coms with the inverter it's paired with, it can create a real box of worms for everyone involved. This is, unfortunately, very hard to avoid without both manufacturers coming together to confirm compatibility and good communication between their products. 

At best, poor battery communications creates a frustrating system to live with. At worst, it creates a hazardous system lacking necessary safeguards. Unfortunately, most battery companies live somewhere in the middle, and customers get suboptimal performance, limited perspective or control, and a sprinkle of anxiety to flavor their big investment.

In the next article, we will discuss a battery-inverter combination that excels in communication and explain why Pylontech and Victron Energy provide a complete solution that simplifies complex capabilities for end users. 

Have a question about your application? Send us a message here or reach out directly to mike@icmontana.com.