Myenergi Zappi EV Charge Point Notes

Introduction

The Zappi EVSE units from myenergi are generally regarded as a good option for domestic EV charging in the UK. They’ve been around for a while and they’re well supported in terms of integration with energy company systems (e.g. for Intelligent Octopus Go).

Following some consolidation of the variants they manufacture, there’s now just a ‘multiphase’ Zappi unit which accommodates a 3-phase supply but can also be connected to just one phase. The model number is 2H22UW-G (U for ‘untethered’; W for ‘white’) and it’s the V2.1 hardware. The trailing -G on the model number signifies that it’s the UK (GB, presumably?) variant with extra compliance features required to satisfy the Smart Charge Point Regulations.

Operation & Installation Manuals

One frustration is that the latest documentation for the Zappi devices isn’t as easy to find as it should be:

  • There’s no paper installation manual supplied with the unit – which is increasingly common when firmware updates change the look and feel of the setup screens. However, the QR code on the supplied quick-start guide, for “Installation and User Manuals” sends you to https://support.myenergi.com/hc/en-gb which is just a generic guidance page with various hints and tips – not the PDF of the latest version of the manual.
  • An Internet search turns up multiple variants of the Installation and Operation manuals on the myenergi website, most of which appear to be older versions of the documents though they still specify they apply to the right model and hardware version
    • This is how the electricians installing the Zappi charge points found the manuals they consulted
  • The ‘official’ place to obtain the latest manuals from appears to be the Downloads page for the Zappi Multiphase which currently lists:

One important change included in v2.4 Operation & Installation manual is this part of the Wiring section:

9.2.2 Supply

The single phase zappi should be connected to a 230V nominal AC supply.

The supply final circuit should be protected by an overcurrent device sized to 120% of the Design Current and accordance in accordance with local regulation requirements.

zappi incorporates 6mA DC residual circuit protection (RDC-DD) in accordance with EN 62955. Local

regulations may require 30mA Type-A RCD protection to be installed upstream.

There’s a footnote which clarifies the 120% of the Design Current requirement, which reads:

For a 32A zappi this would require an overcurrent protective device of the next nominal size (e.g. 40A).

I’ve come across this recommendation previously, for different 32A charge points, and the one that I had installed as part of a research project in 2017 also had a 40A MCB fitted. The explanation for that was that EVSEs typically pull their full rated current for hours on end, and that’s an unusual load profile for a circuit breaker to cope with.

(Earlier versions of this same Zappi manual specified a 32A circuit breaker instead.)

CT Clamp Connections

In the absence of any specific guidance, I connected the Grid CT cable to the CT1 input and the CT cable for the Tesla PowerWall 3 (a hybrid solar inverter with DC-connected battery) to the CT2 input. I was then puzzled as to why the CT CONFIG menu for CT2 only offered the options of:

  • Generation Only
    • With the power flow in the App appearing correct – as if the system was generating from solar PV (even when it was discharging the battery)
  • Storage Only
    • With the power flow in the App appearing reversed

Neither of those options seems appropriate for a combined Generation and Storage device.

Then I came across this zappi 2.1 Multiphase Technical Bulletin which explains that CT2 can only be used for “Uni-directional readings (typically used for generation or solar monitoring).” whereas CT1 and CT3 are for Bi-directional readings.

The CT cable for a combined inverter and battery system needs to be connected to the CT3 input instead of CT2, so that the additional CT Type options become available and it can be set to Gen & Battery.

Device Pairing via Ethernet

These newer Zappi models (the ones with serial numbers starting with a ‘2H’) include a built-in ‘vHub’ (virtual Hub, presumably) so the separate hardware Hub device required for earlier models is not required in order to connect to the Internet. My installation is slightly unusual in consisting of two Zappi chargers (for convenience when charging EVs parked in different locations, both inside and outside the Garages) and no other myenergi devices. In terms of expected usage, one of the Zappis is firmly the ‘Primary’ one and the other is ‘Secondary’.

It’s therefore clear that the ‘Primary’ device should be assigned the role of “Load Controller” – which might as well be the one that also has the hard-wired CT clamp connections. For convenience, this is also the one that is assigned the role of “Gateway Device” (i.e. running the vHub). The other one is the “Secondary Device” and needs to be ‘paired’ with the primary one to gain visibility of the CT readings etc. and to appear in the myenergi App and Account web page.

Some of the documentation on the myenergi website – notably How to use Ethernet to pair with zappi v2 – says that Ethernet (or WiFi) pairing will be used in preference to (868MHz) RF pairing:

An Ethernet connection will be used in preference to a wireless link provided both devices have Ethernet connections and are on the same network (LAN)

The Operation & Installation Manual also says (near the bottom of Page 7) that:

When pairing devices, they will automatically use the Ethernet link if available.

However, that wasn’t happening automatically and initially I was only able to get the devices paired by selecting ‘Legacy’ mode for the RF communications, which doesn’t seem ideal. They have clear line-of-sight to each other and they’re only about 10 metres apart but – given that both devices are connected back to the same Ethernet switch, it seems best to use Ethernet for pairing, if at all possible.

The Myenergi documentation and posts on the Community Forum suggest things like ensuring the Radio is Disabled in the Bootloader menu, and turning Ethernet Off and On again there too, but none of that had any effect. There’s an entry in one of the Info screens which says the Ethernet Frame Type is 88b5h, hinting at the use of raw Ethernet frames for inter-device communication. While researching more detail about what those frames might look like I came across this post on the Myenergi Community Forum which noted some issues with Ubiquiti UniFi network equipment and a solution of disabling IGMP Snooping on the Network (Subnet) the devices are connected to – which, sure enough, did fix the issue.

Digging a bit deeper and using tcpdump to print out the Ethernet traffic showed Ethernet frames like the following:

# tcpdump -e -p -i vlan01.0056 ether host 28:97:b8:09:e9:f1
...
08:51:47.511209 28:97:b8:09:e9:f1 (oui Unknown) > 71:b3:d5:3a:6f:00 (oui Unknown), ethertype Unknown (0x88b5), length 70: 
	0x0000:  cbda e9f8 0000 0000 0000 0000 0000 0000  ................
	0x0010:  0000 0000 0100 0000 20e8 1035 d1ff a086  ...........5....
	0x0020:  9301 7d13 a060 0000 0000 1406 0000 3203  ..}..`........2.
	0x0030:  0811 0500 0000 0000                      ........
08:51:47.911668 28:97:b8:09:e9:f1 (oui Unknown) > 71:b3:d5:3a:6f:00 (oui Unknown), ethertype Unknown (0x88b5), length 90: 
	0x0000:  cbda e9f8 0000 0000 0000 0000 0000 0000  ................
	0x0010:  0000 0000 0100 0000 34e8 7a7a d101 a086  ........4.zz....
	0x0020:  9301 ea0d 4d00 0000 7816 0000 3001 0000  ....M...x...0...
	0x0030:  ff08 0000 0000 0000 0000 0000 0000 0000  ................
	0x0040:  0000 0000 0000 0000 0000 0000

My hypothesis is that since the Destination address for those Ethernet Frames is an odd number, they’re regarded as Multicast Ethernet Frames and with IGMP Snooping turned On the UniFi switch attempts to map them to IP-level Multicast addresses – but there aren’t any of those since this is purely Ethernet traffic with nothing to make sense of at the IP level.

As vindication for my approach of putting devices like these on a dedicated Network Subnet (VLAN) it was straightforward to turn off IGMP Snooping just for that one Subnet, via the UniFi Controller. In my case there are just two devices within my Myenergi ecosystem – and they’re connected to two (adjacent) Wired Ethernet ports on the same UniFi Layer 2 network switch – but with additional devices and perhaps a more complex network topology it would be even more beneficial to have them segregated from other network traffic.

Solar PV Usage Priorities

With multiple devices from different manufacturers, all of which try to make efficient use of excess solar generation, there’s lots of scope for unintended interactions between the competing algorithms. The most common of these is when the Myenergi ecosystem thinks there’s excess solar generation available (because it can see energy coming from the PowerWall – which it thinks is Solar PV generation) and it charges the car battery by depleting the house battery. While the Zappi has configuration settings like “Avoid Drain” these only work when there’s a separate battery, monitored via a separate CT clamp.

Currently, the priority order for using solar PV generation is:

  1. Export it to the Grid, up to the 5.5 kW DNO-imposed Export limit
    • This is financially beneficial since any export is paid at a flat rate of £0.15 per kWh
    • However, this means exporting at the same time as all the other solar PV in the vicinity is exporting, which isn’t necessarily the most effective way to use the energy
      • It could be stored in the house battery then exported later in the day, when there’s more demand but less generation – but that’s much more complex to manage
  2. Use it to power the House loads
    • These would otherwise be supplied by discharging the PowerWall, using energy imported at the off-peak tariff rate of £0.07 per kWh
  3. Use it to charge the PowerWall, reducing the amount of import required to re-charge the PowerWall overnight
    • This is fine but on a sunny day the PowerWall will be full by mid-morning – meaning solar generation needs to be ‘curtailed’ (i.e. thrown away) later in the day
  4. When the PowerWall is fully charged, use any further generation wherever it can sensibly be used – since otherwise it will be wasted
    • Charging an electric car – by asking for a ‘boost’ charge on the Zappi
    • Heating the hot water storage tank using its immersion heater – by asking for a ‘boost’ on the immerSUN

Setting an Export Limit on the Zappi of less than 5.5 kW risks having it start charging the car battery when it would be better to charge the house battery instead – so the Export Limit needs to be set to a higher figure. For now, it’s set to 6 kW.

General Guidance Notes

While there’s good information on the myenergi website, a lot of it seems to be scattered about in technical articles and bulletins (like the limitations of CT2, which you’d think would be mentioned in the installation manual which covers the wiring of the CT connections). Here are some guidance notes I found useful:

  • Compatibility Mode
    • This refers to compatibility with certain models of car and the characteristics of their built-in chargers
    • I’m almost certain this defaulted to ‘On’ for my newly-installed Zappi v2.1 but the guidance notes here say it should be ‘Off’ unless told otherwise by myenergi technical support
  • Zappi & Intelligent Octopus Go
    • The Zappi must be in Eco+ mode – and Octopus will force it to that mode if it isn’t
    • This means it will still divert excess solar generation if that appears to be available
      • But it’s only able to (automatically) judge that from the Grid CT clamp – and it can’t differentiate solar generation from PowerWall battery discharge – so the Export Margin needs to be set to avoid the Zappi draining the house battery to charge the car battery
  • How to stop myenergi products diverting exported power
    • Basically: by setting the Export Margin on the Load Controller device

CC BY-SA 4.0 Myenergi Zappi EV Charge Point Notes by Marsh Flatts Farm Self Build Diary is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.