Why won't my plug-in hybrid or older electric vehicle charge at full power – despite an 11 kW or 22 kW wallbox?
Many drivers are surprised when they have a modern 11 kW or 22 kW wallbox, but their car still charges at only 2–4 kW.
It is easy to assume that the wallbox is faulty or incorrectly installed. In reality, however, this is often completely normal and has both technical and regulatory reasons.
Here we explain in simple terms why some vehicles cannot charge any faster and why this is particularly common with plug-in hybrids.
1. The key factor: many vehicles charge on just one phase
Modern wallboxes such as the Compleo SOLO smart can provide 11 kW (3×16 A). That power is technically available – but the vehicle may not be able to use all of it.
Why? Because the vehicle's onboard charger determines how much AC power can actually be accepted.
Many vehicles:
- charge single-phase only,
- are limited to a maximum of 16 A, or
- use smaller, cost-efficient onboard chargers that do not support higher AC charging power.
This applies in particular to:
- many plug-in hybrids (VW, BMW, Mercedes, Volvo, Ford, Toyota, etc.), and
- many older electric cars (e.g. older Nissan Leaf, Hyundai Ioniq and Renault Zoe generations).
2. Austrian requirement: phase imbalance limits single-phase charging
In Austria, the TOR rules (Technical and Organisational Rules) limit phase imbalance. They stipulate that single-phase current may be a maximum of 16 A, corresponding to around 3.7 kW.
The aim is to keep loading across the phases balanced and maintain a stable distribution grid.
For this reason, single-phase charging above 3.7 kW is not permitted, even if the wallbox and vehicle would technically be capable of more.
👉 Result: A vehicle that can only charge on one phase will be limited to around 3.7 kW AC AC – regardless of whether you have an 11 kW or 22 kW wallbox.
3. Example: why an 11 kW wallbox does not always mean 11 kW at the car
Wallbox output and the vehicle's charging power are often confused. Here is a simple overview:
| Device/system | Phases | Current | Max. power |
|---|---|---|---|
| 11 kW wallbox | 3 | 16 A | up to 11 kW |
| 22 kW wallbox | 3 | 32 A | up to 22 kW |
| Single-phase vehicle | 1 | 16 A | 3.7 kW |
| Two-phase vehicle | 2 | 16 A | 7.4 kW |
| Three-phase vehicle | 3 | 16 A | 11 kW |
Conclusion: If your car charges on only one phase, it will remain at around 3.7 kW in this setup, even when connected to a modern premium wallbox.
4. Why do plug-in hybrids often charge more slowly?
Plug-in hybrids have relatively small batteries and are primarily designed to cover shorter everyday journeys electrically. Slow charging overnight or during working hours is therefore usually sufficient. For this reason, many manufacturers fit simple single-phase onboard chargers rated at 10–16 A, giving around 2.0 to 3.7 kW of charging power. This is enough to recharge a PHEV battery within a few hours and is also a cost-efficient solution for the vehicle manufacturer.
5. Why can older electric cars not charge faster?
Three-phase 11 kW AC charging was not always standard equipment. Many older models have:
- 3.3 kW or 6.6 kW onboard chargers,
- often single-phase charging, and
- older charging electronics.
Examples:
- Nissan Leaf (older models) → single-phase, 3.3–6.6 kW
- Hyundai Ioniq (older generation) → single-phase, 6.6 kW
- Renault Zoe (older generations) → charging behaviour depends on grid quality and charger generation
6. Why does my car sometimes show less than 3.7 kW?
Even single-phase charging at 3.7 kW may not remain constant. Possible reasons include:
- cold battery → charging power is limited
- hot battery → thermal protection
- charging power limited by the available connection capacity
- PV surplus mode of the wallbox
- a charging limit configured in the vehicle
This does not necessarily indicate a fault – these are normal control and protection mechanisms.
7. The Compleo SOLO smart: future-proof even when today's car is the limiting factor
Even if your current vehicle only charges on one phase, a modern wallbox such as the Compleo SOLO smart offers many advantages:
✔ Integrated Type A RCD
✔ Integrated surge protection
✔ Optional MID meter for company-car charging records
✔ Direct backend connectivity via OCPP
✔ Ready for future EVs with three-phase 11 kW charging
✔ PV surplus charging possible with an energy manager
A high-quality wallbox is therefore an investment in the future, regardless of the limitations of your current vehicle.
8. Conclusion: slow charging is not necessarily a fault – it can be down to technology and regulations
If your plug-in hybrid or older EV does not charge at the full output of the wallbox, the reason may be:
- the vehicle's single-phase charging capability,
- the applicable Austrian phase-imbalance limit, or
- the technical limits of an older onboard charger.
The wallbox is therefore often not the problem. For most PHEV drivers, the available charging power is entirely sufficient – and when you later switch to a modern EV, you can immediately benefit from the full 11 kW charging capability. Bring the future of charging to your home: discover the Compleo SOLO smart and its smart functions now. Discover the Compleo SOLO smart cable.
