Explained: Why the 2016 Toyota Mirai, Honda FCV Concept, Have CHAdeMO Sockets on Them

Yesterday, Japanese automakers Toyota and Honda both unveiled their latest hydrogen fuel cell sedans, with the official pre-LA Auto Show press events for the production-ready 2016 Toyota Mirai fuel cell sedan and the 2014 Honda FCV Concept car.

Behind the small panel in the upper-left corner of the Toyota Mirai's trunk is a CHAdeMO DC connector. But what is it for?

Behind the small panel in the upper-left corner of the Toyota Mirai’s trunk is a CHAdeMO DC connector. But what is it for?

On paper, the two cars serve a similar function in the automotive world. Both offer seating for four, a range of around 300 miles per fill of their hydrogen tanks, feature the latest high-pressure, energy dense hydrogen fuel cell stack technology and have similar performance figures.

They also both come with something that has many plug-in car fans scratching their heads in disbelief: built-in CHAdeMO DC sockets.

Usually found on cars like the 2015 Nissan LEAF electric car and 2015 Kia Soul EV, CHAdeMO sockets have traditionally been used to connect fully electric or plug-in hybrid cars to CHAdeMO DC quick charge stations. Designed to refill the car’s battery packs from empty to 80 percent full in around 30 minutes, CHAdeMO DC sockets bypass a car’s on-board charger and pump high current, high voltage power direct into a car’s battery pack.

But while both the Toyota Mirai and the Honda FCV Concept have small on-board traction battery packs to store energy recaptured during regenerative braking and excess power generated by the on-board fuel cell stack, neither battery pack is big enough to make use of the high-power charging current normally used in DC quick charging stations.

The Toyota Mirai Fuel Cell Sedan can use this CHAdeMO socket to provide emergency power when required.

The Toyota Mirai Fuel Cell Sedan can use this CHAdeMO socket to provide emergency power when required.

So if the sockets aren’t use for charging, what are they used for?

The answer is plain and simple: emergency power generation.

In both cases, the Toyota Mirai and Honda FCV concept can be used as emergency power generators, combining the compressed hydrogen in their fuel tanks with oxygen in the air in their hydrogen fuel cell stacks to produce water and electricity at a rate of up to 100 kilowatts of instantaneous power.

During normal operation, that energy is fed directly to the car’s electric motor to provide motive power. But when stationary, both cars can be put into a special emergency power mode, feeding any power generated at the fuel cells directly to an external power inverter connected to the CHAdeMO DC socket.

Like a DC quick charger in reverse — or Nissan’s LEAF-to-Home two-way charging station and emergency back-up generator — the DC power flows from the CHAdeMO socket onto the car into the emergency backup generator, where it is converted back into alternating current at the correct mains voltage for the country the car is in.

Unlike the Nissan LEAF, whose on-board battery pack can be used to power a backup generator for the length of time it takes for its 24 kilowatt-hour battery pack to be depleted, the 5 kilograms worth of compressed hydrogen found in the Toyota Mirai and Honda FCV Concept equate to around 200 60 kilowatt-hours worth of electricity.

Honda's FCV Concept -- also debuted yesterday -- features a CHAdeMO socket for the same purpose.

Honda’s FCV Concept — also debuted yesterday — features a CHAdeMO socket for the same purpose.

That means either car could theoretically power an average home for up to seven days using an appropriate equipped backup power-station, provided of course they had a full tank of compressed hydrogen to start with.

The presence of CHAdeMO sockets on both cars also explains why Honda’s Power Generator Concept — a small external inverter unveiled yesterday which is about the same size as a small internal combustion generator — also has a CHAdeMO connector on it. Small and portable, it can draw up to 9 kilowatts form the Honda FCV concept via its CHAdeMO socket to provide emergency power when and wherever it’s needed.

Sadly however, the feature is one-way only: you can’t use the CHAdeMO socket to recharge either vehicle’s tiny on-board traction battery pack, and you can’t use it to re-electrolyse water back into oxygen and hydrogen.

The Honda Power Exporter Concept features a CHAdeMO plug, which draws power from the Honda FCV Concept and turns it into mains electricity.

The Honda Power Exporter Concept features a CHAdeMO plug, which draws power from the Honda FCV Concept and turns it into mains electricity.

This feature, while unlikely to be of much use in certain future Hydrogen fuel cell markets, is a unique added bonus feature for those who live in areas where earthquakes and other natural disasters are common, like remote parts of Japan or more rural areas of the U.S.

Of course, that particular feature is only possible in more remote areas if there’s somewhere to refill the hydrogen fuel cell vehicle in the first place, something that’s a completely different type of challenge.

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