There is spare charging capacity at home in the evening – just not always at the same time

Your charger runs at lower power in the evening so there is enough electricity for the rest of the home. That makes sense while you are cooking. But once the kitchen has quietened down, the car may continue charging for hours at the same limit even though more capacity has become available.

This is where dynamic load balancing helps: charging can follow the home's changing electricity use. A straightforward comparison can show whether that flexibility is simply convenient in your case, or whether it makes the difference between having enough energy and falling short before you leave in the morning.

Start with what you need by morning

Suppose you want to put 36 kWh into the car after a longer day, measured at the charger. You have seven hours. The car can accept up to 11 kW of alternating-current (AC) charging, and during quieter periods the home's electrical supply can provide that power.

We chose 36 kWh deliberately for this example. The aim is not to fill an entire battery, but to see whether the energy needed for the next journey fits into the time the car spends at home. The battery may store less energy than the charger delivers because the car also uses energy during charging.

You can run the same calculation for your own car. An ordinary commuting day calls for a different amount of energy from a long trip. A well-planned charging system should also cope with the larger, predictable top-ups.

Your home's electricity use determines what remains for charging

The home and the car share the same grid connection. When the household needs more power, less is available for charging. As household demand falls, more can be made available to the charger again.

Zaptec Sense adjusts the charging allowance to the home's measured consumption. The right Sense metering variant depends on the local electricity meter and electrical installation. You can find an overview of the variants on the manufacturer's Zaptec Sense page.

In other words, the device helps you make use of spare capacity that already exists. It does not change the rated limit of the grid connection; it changes how much of that limit the home is using at any given time.

The same seven hours, two different outcomes

In our example, the power available for charging changes over three periods. These are assumed values that remain constant within each period, not real measurements.

After four hours, 22.08 kWh has passed through the charger. Another 13.92 kWh is needed to reach the target, which can be delivered at 11 kW in about 1 hour 16 minutes. At the assumed power levels, the full 36 kWh could therefore be delivered in roughly 5 hours 16 minutes.

If the limit stayed at 4.14 kW throughout, seven hours would deliver 28.98 kWh. That would leave a shortfall of 7.02 kWh. Varying the charging power can therefore make the planned morning energy available from the same grid connection.

When does this affect what you buy?

If your charging window is regularly this tight, it is worth asking for a control system that follows household demand when you request a charger quote. You can only benefit from the higher late-evening power if the car is still plugged in then and still needs the energy.

The picture is different for an everyday requirement of 18 kWh: even the fixed 4.14 kW used in the example would cover it within seven hours. In that case, automatic control may mainly provide a faster top-up and more headroom, for example before an unexpected evening trip.

With a suitable grid connection and car, Zaptec Go can provide home charging at up to 22 kW. A car that accepts no more than 11 kW AC will still be limited by the vehicle and the available supply capacity. The Zaptec Go product page also states the maximum power.

There must be capacity on each phase

In a three-phase home, spare capacity needs to be checked phase by phase. A household appliance drawing heavily on one phase can restrict charging even when the total figures still suggest that plenty of power is free.

The example above already uses power that the car can actually accept. Before installation, a qualified professional must also inspect the protective devices, cables, electrical protection and phase loading. Being able to select a higher current in an app does not mean the electrical installation can safely supply it.

Three details will show you the next step

Write down the rating of the main fuse on each phase, the car's AC charging capability and the time between arrival and departure. Then choose one typical day and one higher-demand day and note how many kWh need to pass through the charger.

With those details, you can assess when the required amount could be delivered through your connection. If the available time is still not enough, a site assessment can identify where the electrical installation may need upgrading.