Fast Charging an EV: AC/DC Questions and Renault's Answers

By · November 21, 2012

The Renault Zoe's motor

The Renault Zoe's motor, the "charger" is on top

When it comes to electricity, AC versus DC is an old battle. It dates back to the 19th century with George Westinghouse against Thomas Edison. Nikola Tesla was involved, and alternating current famously won. Nearly everything today is AC—the grid provides AC electricity and all modern electric cars have AC motors.

Even gas cars switched from DC generators to alternators 50 to 60 years ago. The conflict would be over if there wasn't a problem: it's impossible to store AC electricity. A battery can only store DC electricity, so a conversion is needed. AC to DC to charge the battery from the grid; and DC to AC from the battery to the motor to power the car. Fortunately, AC/DC or DC/AC conversion is no big deal. The real issue is how the conversion happens. Let's look at how the world's best selling EV is doing it.

Nissan Leaf

Nissan Leaf

The Nissan LEAF has two charging ports. One is designed for standard AC home electricity, the other one for high voltage DC. But the AC/DC distinction is misleading here because a battery can only accept DC. The difference is that with home charging, the charger and the AC/DC converter are fitted inside the car—whereas with fast charging, the charger and the AC/DC converter are outside, in the charging station. So that makes two charging ports, two chargers and two AC/DC converters. Renault has found a smarter way.

In the Renault Zoe, the French brand introduced a new technology it called the Chameleon Charger. The Zoe has one single port for charging, one single charger and one single AC/DC converter, and it accepts any current from 230V 10A 1-phase up to 400V 63A 3-phase (43 kW). Best of all, it's self adaptive.

The driver only needs to plug in, and the car will charge as fast as it can (actually, it's possible to program the process). The 3.3 or 6.6 kW charging limit between the Nissan LEAF and the Ford Focus is totally irrelevant here. The Renault's way is easier forthe driver, and it's also considerably cheaper on the infrastructure side. EVSE manufacturers who had hoped to sell thousands of expensive DC chargers in every country hate the Chameleon charger because it ruins all their business plans. But it's real. Two other car manufacturers, Smart and Volvo, have already endorsed fast AC charging, and others should follow soon (at least in Europe).

Renault Zoe with fast AC charger

Renault Zoe with fast AC charger

Smart and Volvo are doing it conventionally though, just like the Nissan LEAF, only with a 22-kW charger. Only Renault does it with a system where the charger is integrated, and part of the vehicle drive system. Some say it's not really a charger, and they're not totally wrong, so let's say it's an electronic device doing the charging job. But the more worrying thing is that several electrical engineers are dubious of the technology. American company AC Propulsion looked into it and designed a system called Reductive charger, but Renault's system is different, safer, more robust and better in every way. Most notably, it's much stronger with the ability to sustain 43-kW charging. It's also new technology, fully owned and patented by Renault. And yet, quite surprisingly, I've been told Renault would be very open to the idea of sharing it with other car manufacturers. The Renault-Nissan alliance has invested more than any other brand in EV tech, and they just want the electric car to succeed.

Italy has been convinced, and fast AC chargers are being installed in the country now. It may be too early to dump all the DC chargers we have today, but more and more people are betting that AC will prevail because of its lower cost. An AC fast charging station is only a quarter of the price of a DC one. Few bean counters will hesitate between the two.

Back to the electric car, their specifications sheet used to list many separate elements: a motor, inverter, charger, AC/DC converter, DC/DC converter, etc. If the Renault Zoe shows the way (and I think it does), there will be fewer elements in the future. Things will be more integrated with one component able to have several functions.

New to EVs? Start here

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