Designs for electric vehicle charging stations must take many different factors into account, from the type of vehicles that will be charged, to the interfaces and transactional systems needed, to wireless communications. The methods and protocols used for network communication require special consideration in areas like covered and underground parking.
Watch our recorded webinar to learn from experts at FLO EV Charging and Digi International about the ecosystem of components and protocols that must come together for connectivity to EV charging stations — especially in areas that have limited cellular access.
Digi supports EV charging OEMs like FLO with a range of secure, robust, embedded systems, including Digi XBee® wireless communication modules, Digi gateways, and the Digi ConnectCore ecosystem of SOMs, as well as wireless design and device management services.
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Follow-up Webinar Q&A
Thank you again for attending our session with FLO EV on navigating the design challenges of EV charging station devices and networks. Here are the questions that followed the presentation and their answers. If you have additional questions, be sure to reach out.
Moderator: Chloe Theobald, Events & Content Director, Charged EV Magazine
- Qiyuan Zhou, Application Engineer, FLO EV Charging
- Bob Blumenscheid, Senior Product Marketing Manager, Digi International
How does the load sharing work with the FLO chargers’ communication? Is it with the electrical, or with Cat 5, 6 signal feedback from the chargers?
Qiyuan: The chargers are connected to the gateway through the Zigbee mesh network. And the gateway itself acts as the site controller. So, the chargers would send the commands, or the information, to the gateway over that Zigbee network, and the gateway would then send commands back through that same Zigbee network, about how to share the power.
What happens to the gateway site controller functionalities for PowerSharing and PowerLimiting when it loses connection to either the Internet or the chargers?
Qiyuan: If the gateway loses connection to the Internet, that's not a problem, because all the controls are local to the gateway, so there's no server-side calculations going on. So, if the gateway loses connection to the Internet, the PowerSharing and PowerLimiting functionalities stay intact. And that's one of the advantages of having the programmable gateways at the sites. And if the connection on the Zigbee network is lost, between the chargers and the gateway, then the chargers are programmed to have a default power draw. So, if the connection is lost, then the chargers default to that lower power rating, so that the circuit doesn't trip.
Bob: Adding to that, there are some questions about security. And Digi XBee® modules do implement security. The Zigbee protocol includes encryption of messages. And then, Digi has a TrustFence® security platform, where we leverage features on the XBee module that provide secure boot and authentication and root of trust, which allow you to make sure that a mesh network is completely secure.
Is there a limit for cable run lengths for the hardwired options? And what are some options for scenarios in which the gateway at the parking site is very far from a building router, or a cellular router?
Qiyuan: So, there is a limit, and that's from the Cat 5, Cat 6 standard. That limit is 100 meters, or about 300 feet. If you have a cable run that's longer than that, we recommend using either Ethernet signal boosters throughout your run, or you can buy a fiber optic cable with the transceivers on either end to plug into the gateways.
Who does that site assessment and site survey?
Bob: That’s a good question, Qiyuan. When your EV chargers are installed, are they designed so that they just work, or do you have tools for installers to make sure that the signals are okay and everything's working in the mesh network?
Qiyuan: Usually, we tell our installers it's up to them to evaluate the signal strength on-site. And that can be done using an app on Android phones, and for iPhones, you can enter the field service mode by dialing a code. So, usually, the installer would be the one to handle that. And one thing to note when doing that is you have to make sure that your installer is checking the signal strength on the same network that the gateway will be deployed on. It seems pretty obvious, but sometimes we have run into issues. So, in the U.S., we use AT&T, and in Canada, we use Bell and Telus.
Bob: And Digi's XBee tools include tools installers can use to check the mesh networking and make sure everything's working okay. But I think that's probably part of the design process of antenna placement and other things that are taken care of, so that the FLO products work.
At which level would you limit the power? Would you trip local breakers defined by priority? Or will it trip the main breaker in the main panel?
Qiyuan: So, all of the PowerSharing and the PowerLimiting features are software-based, so they don't actually trip any of the physical breakers. PowerSharing is meant for scenarios where you're over-subscribing a circuit. So, for example, you have two 30-Amp chargers on a single 40-Amp breaker.
So, in that case, PowerSharing is set up so that the total current draw between those two chargers never exceeds, you know, the protection level of that 40-Amp breaker. And for the PowerLimiting, that one is not meant as a circuit protection feature. It's more meant to avoid demand charges. So, the site owner would set a current limit that they don't want the chargers at the site to go over. And then the site controller will make sure that between all of the chargers at that site, that current limit is not exceeded.
Tell us more about LoRaWAN and other mesh technologies that are possible.
Bob: There are a lot of emerging mesh technologies right now. Digi has worked with Zigbee for about 20 years, so it's a very well-known, very understood mesh technology. We are working on LoRaWAN, as a new XBee, and a way to deploy systems as well. So, we'll have some of that later this year. And we're watching some of the other mesh networking technologies that are emerging, things like Matter, that will allow chargers to be put onto a home smart network, and other ones. We will be releasing products as those become viable. It's certainly on our roadmap to track those.
How does FLO allow more than one port on a circuit breaker and still meet the code requirements?
Qiyuan: In the code, there is a provision that if you over-subscribe a circuit, that's okay as long as you have an automatic load management system. So, that automatic load management system is our PowerSharing algorithm, which is hosted on the Digi gateway.
Is the FLO charger designed to receive signal to limit the power output?
Qiyuan: Yes, it is designed to do that over the Zigbee network, and the gateway sends that signal to limit the power output in the case of PowerLimiting or PowerSharing.
This question is about FLO or Digi equipment providing surge protection for spikes or noise on the charging circuits.
Qiyuam: I do believe, for the FLO chargers, there are protections in place. I know for our DC chargers, there's a window in which we can tolerate some, you know, surges or spikes, and also noise. And Bob, maybe you can comment on Digi's side?
Bob: On the Digi side, the power supply would have those protections, and then everything else is connected to the gateway wirelessly. So, I think that's okay. And the Ethernet is protected as well.
This question is about having a mixed gateway deployment with cellular connections on the first level of a parking garage, where there is cell signal, and then hardwired options on the lower levels, where a signal might be weaker.
Qiyuan: So, it is possible, but in practice, we usually don't recommend it because it tends to add confusion for installers. So, yeah, usually... It's possible, but not recommended.