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  • Alan Beard

Zappi Draining home battery

Updated: Jul 12

How to stop a Zappi EV charger from draining your home battery

Are you like many others struggling to get your solar system and Zappi EV charger to work in harmony.

Trying to prioritise which charges first, house battery or car and harder still preventing the EV charger discharging the house battery when charging on Eco or Eco+ mode.

For those that just want the settings without the explanation go to the settings section

Types of System

There are two main types of installations to think about

Zappi with Hybrid Inverter draing house battery

Hybrid Inverter where the solar system and battery share the same inverter, normally used in new installations. The solar industry prefer this solution because it reduces inverter costs and because the link between solar and battery is DC only (green arrows) it's slightly more efficient. But causes the biggest challenges for EV charging systems.

Zappi V charger with separate inverters

Separate inverters, mainly used in slightly older systems or upgrades, this is where the battery and solar system have their own independent inverters.

In each diagram you will see orange CT clamps on red arrows, this is because CT clamps only work on AC power connections and will not work on the DC connections in green.

Advantages with Zappi

The Zappi charger has an advantage over most other chargers because it supports 3 or more CT clamps against the one most other chargers support. This means that it can look at the current flowing to and from the main supply with the grid CT and the battery with battery CT, plus whats flowing from the solar. Most other chargers only have one CT clamp on the grid.

In addition to this it's also possible to set the grid export margin, this is the amount of current that must flow to the grid whilst charging the car in ECO or ECO+ mode, along with a time delay setting. This is very important because a battery will discharge until it starts to see current flowing to the grid.

Settings to stop house battery discharge with Separate Inverters

This should be the easiest system to get working properly.

If the Zappi has a CT clamp on the battery inverter connection and solar inverter connection. With the CT's configured as battery and solar, then set the battery configuration to do not discharge. This is should then stop the house battery being discharged while the car is charging.

If the above doesn't work also try setting grid surplus to 100 or 150w, some may require as much as 200w. Plus a delay of say 30 seconds. Experiment to get the settings as low as possible with the system still working as desired.

Settings to stop house battery discharge with a combined inverter

This is more challenging because the Zappi can only see the one connection to combined solar panel and battery system. This connection will have current out when solar is generating and also when the battery is discharging plus is will see current in when the battery is charging from the grid off peak.

The my energy team have tried to work with the information they have with the CT clamp set as solar/battery but it's a compromise at best. The app shows real time current flow, but doesn't save any statistics and there is no data shown on the charger.

I can understand their argument that accurate data can't be displayed because; for example if they see current out they don''t know if it's solar generated or previously stored from grid.

In this sittuation the main tool we have available on the charger is the export margin setting.

The battery will discharge current until it starts seeing current going to the grid, it will then slow down to stop discharge current. So if we set the EV charger to only charge when its seeing some current going to the grid the house battery should never start to discharge in this sittuation.

On the Zappi this threshold can be set, try settings between say 50w watts and 200 watts, finding the minimum that works. Also set the delay to say 30 seconds so that it rides through short changes without stopping the charge.

Other tools that can be used

Battery systems also have tools that can help, features available change from system to system.

Do not discharge time

Lets use an example sittuation. It's summer time and household use is relatively light, with solar excess from 7.00am to 5.00pm each day.

There is no significant need for the battery to supply power during the day and it's capacity can be saved for evening use. Therefore set the battery to not discharge from 7.00am to 5.00pm. The battery will charge during the day and nothing will discharge it during that time. There may be times when it could be used to fulfil heavy demand during the day but some compromises have to be made.

Controlling if house battery or car charges first

This again is challenging because the house battery and car charger don't have visibility of each other. I haven't seen batteries with settings for export margin, our only tool is export margin setting on the Zappi.

If export margin on the Zappi is set to 0w and the house battery starts charging first, with a standard configuration this can't be stopped. But if the Zappi starts charging first and we want the house to have priority we can increase the export margin on the Zappi until the house battery starts charging first, this will also mean the Zappi won't discharge the house battery.

Configuring export margin on a Zappi charger

This is where to find the full Zappi manual , page 26 onwards has the key information on configuring the grid CT clamp etc. (page number may change in the future)

To set the Export Margin go to

Advanced/Supply Grid/Network/Export Margin

Note this is also the area where Grid limit can be set, do not increase this above 60A, 13.8Kw unless you have permission from your DNO and know your fuse is big enough. The 100A label on the outside of the fuse holder just means the fuse holder can cope with 100Amps, From my experience about 50% of houses will have a 80A or 60A fuse installed.

Changing the wiring to help.

Zappi with separate consumer unit

Install the EV charger on a separate consumer unit, in many cases this will already have been done, if not do not try this yourself and get a qualified electrician to do the work.

Then have the house battery CT clamp on the feed to the main house consumer unit after the split between EV charger consume unit and main consumer unit.

Then the battery will only ever see the household load and never try to discharge to feed the EV charger, it will see any power going to the ev charger as power going to the grid.

As the inverter will see the charger as part of the grid load one down side is that the house battery will always charge from solar before the EV, not a major issue especially if this is what you want.

With EV on main consumer unit

The current draw by the ev charger can still be subtracted from the main load. This is achieved by passing live from the EV charger through the CT clamp along with the supply tails. This can be done inside the CU with a single insulated cable or outside with a double insulated cable, this may require a larger CY clamp, which is available from myenergi.

For this to work, the current flow on the ev charger cable needs to be in reverse to the main supply current so that it's subtracted.

My Energi Libbi Battery and Inverter

My Energi now have the Libbi Inverter battery system which integrates with the my energi app and will allow complete control over prioritisation to overcome these issues. I haven't actually seen a system in action or seen any user feedback so don't know how well it works. But my energi are good at this type of thing so it should be good.

There is now a open control protocol for EV chargers allowing third party systems to integrate with them relatively easy. I have to hope that this is the first step towards a much more open and interactive eco system that will eventually lead to third party systems that create much more integrated overarching household control systems.

If my hope comes true it's going to be a few years away, for now it;s going to come down to using equipment from companies that have the money and scale to build entire solar, battery and car charging eco systems such as myenergi.


This article is intended to provide ideas on how to work around EV charger and battery issues and should not be considered as professional advice. We recommend asking a qualified electrician to make any changes to your system. Any changes you do make are at your own risk, consider impact on warranties etc.

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