We have solar panels, and a Zappi charger that we use regularly for our Hyundai Kona EV. My wife now wants to buy a Hyundai Inster EV. Can we mount another Zappi on our house for her car? – Christopher E from Co Clare
The short answer is yes, you can (although I’m not speaking authoritatively for the Zappi charger brand in this instance), but it might not be as much help as you think and here we must delve into the messy world of maths. Please bear in mind that I flunked honours maths in my pre-Leaving Cert, and had to drop down to pass maths for the actual exam ...
So, let’s start with a single charger, which is generally rated to provide 7.4kW of charging power. Now, that is based on a huge number of assumptions, which include the power that actually reaches your house (which may depend on your physical distance from the nearest transformer) and the standard of the wiring that runs through your house.
Let’s assume for the moment that you’re getting a decent power supply to the house, and that the wiring is fairly good, which presumably it is if you’ve already got a charger running. Now, your electricity connection can generally provide up to 10-14kW of steady power output, assuming it’s a 12kVa (kilo-volt-amps) connection, which is the standard for domestic power supply.
RM Block
[ Self-charging: Using solar panels to provide your car’s chargeOpens in new window ]
Now 14kW is a lot of power, on single-phase AC electricity at any rate, and that seems like a lot more than the 7.4kW your car needs to charge. Ah, but there are other items in your house drawing power. An electric oven draws 2.2kW.
A kettle draws a surprising 2.7kW. A tumble dryer is running on about 2.5kW, and a power shower needs a massive 10kW. So you can see how this is starting to add up, and also why the recommendation is to charge your EV at night, when there’s less demand on the system, when electricity is cheaper, and when there’s lots of spare capacity from wind generation.
So, you already have one charger that’s drawing 7.4kW. Now you want to add another charger that’s drawing the same 7.4kW, and suddenly you’re drawing 14.8kW, and you don’t have much headroom left in the electricity supply if you want to make a cup of tea. A smart charger will automatically balance the load it’s creating, and slow down the charging process if it needs to, but you’re definitely flirting with a trip-switch moment here.
There are a couple of options, though. You can replace your current charger with a two-socket charger, which will split the load between the two cars when they’re charging at the same time, meaning each will get 3.2kW of charging power, which will help reduce the overall demand on your electricity supply.
Or, you could get your house upgraded to 16kVa 70-amp power, but that’s not a domestic supply, that’s more like a commercial supply and you’re looking at a big cost to convert. Probably the best solution is the two-socket smart charger which will balance the load and just charge that bit slower if both cars are connected at the same time. Or maybe you and your wife just need to come up with some sort of charging rota?
