Ever noticed how some people gulp down ten cups of tea in an hour, while others sip one all afternoon? It depends on where they’re from, what their body can handle, and even how they’re feeling that day.
And strangely enough, it’s the same with EVs. They don’t all charge the same, and your home charging setup can make a big difference.
That can be surprising for new EV owners. It’s not a one-size-fits-all when it comes to charging speed. This blog explains why that’s the case, so you know how to get the most out of your EV home charger.
Onboard charger limits are – well, the limit
Your home supplies electricity as alternating current (AC), but your EV’s battery stores power as direct current (DC). Inside the car, there’s a built-in device called the onboard charger that converts the AC from your home into DC for the battery. This onboard charger controls the maximum amount of power your car can accept when charging at home, so it limits how fast your EV charges, regardless of how powerful your wall charger is.
Most UK EVs have a 7.4 kW onboard charger. That means even if you’re lucky enough to be able to install a 22 kW wall charger, your car still only charges at 7.4 kW. Some newer or premium models support higher AC rates, but they’re in the minority. It’s worth checking your EV’s tech specs before investing in faster hardware. If your onboard charger only supports 3.6 kW or 7.4 kW, upgrading your wall charger won’t improve the speed. It’s not worth the money. You’d see the difference only if your vehicle allows for it.
Level 3 fast chargers supply direct current straight to your EV’s battery, bypassing the onboard charger. However, these chargers aren’t available for home installation.
Your home’s electrical supply may cap the output
The second factor is what your home can supply. Most houses in the UK have a single-phase supply. That supports chargers up to 7.4 kW.
To achieve speeds of up to 22 kW, you would need a three-phase supply. This is more common in commercial properties and newer homes, but rare in most homes. If you feel the need to upgrade, this involves coordination with your distribution network operator (DNO) and a significant investment.
Even if your home’s supply allows higher loads, your existing fuse board might not be able to handle them. A full load assessment from a qualified electrician is the only way to be sure. Keep in mind that faster charging puts extra strain on your electrical system. This could cause issues, such as circuit breakers tripping when using high-power appliances like kettles or ovens.
And with all that said, remember what we said earlier. If your car can’t charge faster than 7.4 kW, there’s no point in upgrading.
Cable and connector specs affect real-world speed
Charging cables matter more than people think. A lower-rated cable limits the current, even if the car and charger are both capable of more.
For example, a 16-amp cable delivers approximately 3.6 kW. If your charger is set to 7.4 kW but you’re using that cable, you’ll never charge your EV at full speed. That also applies to connectors and sockets. A loose or partially plugged-in connection can slow things down or cut power entirely.
So, always match your cable to the system. Use the right mode (usually Mode 3 for home wall-mounted EV chargepoint boxes), check the amp rating, and inspect for wear. If something feels off, swap the cable first, as this is often the quickest fix.
Battery temperature and charge level influence the curve
Charging isn’t linear. Your battery charge levels don’t increase at a regular rate. EVs draw power more quickly at lower battery levels and slow down near full charge. This helps protect the battery from stress and overheating. It’s all controlled by the car’s built-in battery management system (BMS). It’s why charging from 20% to 80% often takes as long as 80% to 100%.
The same system (the BMS) responds to external temperature. Charging slows down when the battery is cold because the chemical reactions inside don’t happen as quickly. Lithium ions move more slowly in low temperatures, so the battery can only accept power at a reduced rate. Some EVs have systems that warm the battery before or during charging to improve speed, but not all models include this feature. That means cold weather often means slower charging. The best way to avoid this is to schedule your charge after your drive, when the battery is still warm.
Household loads and smart scheduling reduce peak speeds
Your EV isn’t the only thing pulling power. If your heating’s on, the oven’s running and someone’s making toast, your charger might throttle its output to avoid blowing a fuse.
This is where load balancing comes in. Most smart chargers now include it. They temporarily reduce the current to keep your system safe. While it may seem annoying at times, it’s actually an inherent sign that your charger is working properly. And it’s much better than having your circuit breakers trip regularly.
Smart scheduling helps avoid this. Set your charger to run during your household’s quiet hours. For the vast majority of us, that means overnight. Many electricity tariffs are cheaper then, so you’ll save money, too.
How can Electrical Innovations (Derby) Ltd help?
If managing these details feels overwhelming, Electrical Innovations is here to help. We’ll help you find the right charger for your home and EV. Next, we’ll work with you to configure it to meet your household’s needs and ensure everything runs smoothly. Whether you have solar panels, a single EV, or several vehicles, we’ll guide you on what’s worth upgrading and what isn’t. Call us on 01332 498130 or click the button below to book a consultation, and let’s optimise your EV charging setup today.
