Why Many Home EV Chargers Underperform And How to Make Yours Stop Wasting Time

Many homeowners are surprised when their “7kW charger” seems to charge at only half speed, or when charging sessions cut out unexpectedly. The truth is, an EV charger is only as good as the electrical infrastructure behind it. And if your home setup isn’t optimised, you could be wasting hours and money without realising it.

What Does “Underperforming” Really Mean?

An underperforming EV charger doesn’t necessarily fail — it simply doesn’t deliver the performance it’s capable of. You might notice:

• Your car takes longer to charge than advertised.
• The charging session occasionally stops or resets.
• The charger feels warm or trips the breaker.
• Charging speeds fluctuate throughout the session.

These are common signs that your charger  or your electrical system, isn’t working as efficiently as it should.

The Hidden Causes of Slow or Unstable Charging

Inadequate Supply Cable Size

If the cable supplying power to your charger is too small for the load, it creates resistance and causing voltage drop and slower charging speeds. Professional installers calculate cable size based on load, distance, and installation method to avoid this.

Circuit Overload or Weak Consumer Unit

Your home’s consumer unit (fuse board) may not have been designed with an EV charger in mind. If it’s sharing a circuit with heavy appliances, the charger won’t receive a consistent supply of power.

Charger Placement

Long cable runs from the fuse board to the driveway can lead to energy loss. The closer the charger is to the power source, the more efficient the setup.

Lack of Proper Earthing or RCD Protection

Every charger needs suitable earthing and RCD (Residual Current Device) protection. Without it, not only can your charger underperform — it can also become unsafe.

Wi-Fi or Software Glitches

Smart chargers rely on connectivity to balance load and record energy use. Weak Wi-Fi signals or outdated firmware can cause intermittent charging or loss of functionality.

The Role of Seasonal Demand and Weather

In the UK, cold weather can affect EV battery efficiency and charging performance. However, it can also reveal weaknesses in the installation itself, such as moisture ingress in outdoor units or circuits struggling with temperature changes. A high-quality installation includes weatherproofing and appropriate IP-rated enclosures to handle seasonal shifts.

What You Can Do to Improve Charger Performance

Have an Electrician Evaluate the Supply Setup

A qualified electrician can test for voltage drop, check cable sizing, and confirm that your consumer unit meets the load requirements for EV charging.

Consider Load Management

Smart load management systems automatically balance your home’s electrical demand, so your charger draws power safely without tripping breakers.

Check Firmware Updates Regularly

If your charger connects via Wi-Fi, ensure it’s updated. Manufacturers often release software updates that improve charging performance and reliability.

Get Regular Maintenance Checks

Like any electrical system, your charger benefits from periodic testing. A quick inspection every couple of years ensures it’s safe and performing at its best.

Professional Installation Makes the Difference

A properly installed EV charger should deliver consistent, full-speed charging every time. At JJB Electrical, we don’t just fit chargers and leave. Our team performs complete load assessments, tests voltage stability, checks RCD operation, and ensures the installation complies with BS7671 wiring standards.

Whether you already have a charger that’s not performing as expected or you’re looking to install one properly from the start, we’re here to help.

Optimise your charging experience today!

📞 Call JJB Electrical on 01992 276087
🌐 Visit www.jjb-electrical.com

Your trusted local experts in EV charger installation and testing across Hertfordshire & Essex.