- DC Fast Chargers can cost a fortune to build.
- About 60% of that cost is a circuit designed to prevent people from getting electrocuted while charging.
- There may be a cheaper, just-as-safe way to accomplish this while also making EV chargers more reliable.
Ever wonder why DC Fast Chargers are so expensive to build? A single 300-kilowatt Level 3 charger—that’s just one stall at a public DC Fast Charger—can run north of $100,000. This cost is just one of the reasons the infrastructure has been slow to build out and has relied heavily on the government cheese, a la federal funding.
Let’s talk about what’s inside of that charger. Crack it open and you’ll find about $90,000 worth of electronics that move electricity from the grid to your car’s battery. Here’s the kicker: an estimated 60% of that cost is for one safety circuit to make sure you don’t accidentally turn into toast if something goes wrong. That means more than half the cost of an EV charger goes into keeping you alive.
Photo by: General Motors
$54,000 In Shock Protection: Why It’s Important
That system is called an isolation link. According to IEEE Spectrum, the actual cost of this protection layer is an estimated $54,000. Scale that up to a full 8-stall charging location and that’s more than $430,000 dedicated to only safety equipment. Here’s how it works:
Gas pumps rely on mechanical flow control to stop fuel from flowing into a car. EV chargers deal with high-voltage electricity, often at 800 volts or more. Electricity is lazy—it’s going to find the shortest path to ground, and if things go sideways at such a high power, it’s enough to fry you instantly. You can see why safety is such a big deal.
An isolation link achieves a safety principle known as galvanic isolation. This means taking two separate circuits in a single electrical system and preventing current from flowing between them. In the world of EV chargers, this means severing the electrical path between the charger’s power source and the car. So on the off chance that a fault does occur, the energy has nowhere to go but back into the grid.
Here’s how IEEE explains it:
Suppose an EV’s battery is leaking. The leaked fluid is conductive, and can therefore produce a current path between the battery circuit and the vehicle chassis. If the ground circuit happens to be broken, then, without isolation, the vehicle’s chassis would be at a high voltage. So a person touching the car while standing on the ground could receive a potentially lethal electric shock. With isolation, there wouldn’t be a shock hazard, because no current path would exist from the electric utility to the car body.
To make isolation happen, every DCFC uses a transformer in its power conversion hardware—that’s the circuit that converts AC to DC power, and vice versa. These high-frequency transformers are capable of moving kilowatts of electricity at high voltages and provide a crucial building block in a circuit without creating a direct path between the grid and your car. It’s a complicated, expensive system, but without it, a charging mishap could turn your Tesla into a Tesla coil.
Cheaper Charging Solutions Aren’t That Simple
Photo by: John Voelcker
Researchers and engineers know that charging infrastructure is too expensive. These experts are looking into ways to cut costs without compromising safety. But some of those ideas come with serious caveats and would mean rewriting how every modern EV charges.
One proposal is to ditch the isolation link in the charger and instead require EVs to have their own isolation system built into the car’s onboard charger. Since OBCs in cars handle power conversion, they are already galvanically isolated. However, most only support power conversion up to Level 2 charging speeds (Tesla, for example, supports up to 48 amps on most models).
This could drastically cut the cost of the chargers, but not every car is built the same.
EVs today have different charging setups and shifting the responsibility to the manufacturer would require a new universal standard that doesn’t yet exist. This means that older EVs could be left out. There’s also the little issue of trusting automakers to adopt a new universal standard and implement it safely. Because if there’s one thing we know, it’s that automakers are 100% reliable at self-regulation (looking at you, Dieselgate, GM ignition switch scandal, and Takata airbags).
Then there’s the massive drawback of cost. Let’s not forget the cost of this circuit doesn’t just disappear. Moving the hardware to the vehicle would simply transfer the cost from the charger to the car. In short, it’s a no-go right from the start.
The Case For Ditching Isolation
Photo by: Electrify America
This brings the problem full circle: safety measures make DCFCs insanely expensive. And with expense comes slower deployments and a potential limit on the number of stalls per site. As for the solution? Some experts are putting it bluntly and recommending ditching isolation links in charging equipment altogether.
On the surface, this might sound dangerous. But IEEE has an idea: what if, instead of isolating the circuits, we added a redundant ground? Think about it: the second ground could mean not only having a redundant failsafe but also detecting a shorted ground and shutting down the charging equipment the instant that it’s detected. This could, in theory, eliminate the need for a costly isolation link. It would also significantly improve charger reliability, as it simplifies the charger’s power electronics by eliminating a major point of failure.
Now comes a second issue that must be accounted for: voltage mismatches.
If the line voltage between the charger exceeds that of the vehicle’s battery, even for an instant, an uncontrolled current could cause component damage to the vehicle. IEEE proposes solving this problem using a buck regulator, a component meant to safely step down the voltage supplied by a power source. The article goes on to suggest that while this does add back a layer of complexity to the charging circuitry, a buck regulator that can handle similar throughput would cost a mere 10% compared to the isolation link.
Will This Actually Happen?
Maybe, but not anytime soon.
The argument for removing galvanic isolation makes sense on paper. The original Tesla Roadster used non-galvanically isolated charging, but it also didn’t have the capability to use DC Fast Charging. Modern DCFCs pumping huge amounts of current into a modern EV’s battery require a bit more safety measures (hence an isolation link). But if—and that’s a big if—the industry can not only develop a reliable and safe way to accomplish this, it could be a game changer for the EV charging game.
Looking from a more realistic lens, the world is already struggling to get public charging right and nobody wants to be the first to take a gamble on safety. Charging companies, automakers, and even regulators would need a rock-solid guarantee that any non-isolated system was just as safe as today’s chargers. Even if that were true, it could take years to roll out any improvements (especially one where safety should be such a major focus).
For now, expect new EV chargers to keep costing a fortune. Because if there’s one thing that the industry just isn’t willing to cut corners on (yet), it’s making sure you don’t get zapped.
