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Public Electric Car Charging: Our First Attempt

Thanks to the loan of a 2010 Tesla Roadster and a welcome coincidence, took its first crack at charging an electric car using a public charging station — with mixed results.

If range anxiety is the No. 1 concern among potential electric-car buyers, the second, and related, one is where they can expect to plug in and recharge once they venture out into the world. Talk of public charging stations has been minimal and vague, especially in's hometown of Chicago. Imagine our surprise when two such stations appeared in the parking structure we use for our test vehicles.

The operator, InterPark, plans to install chargers at 12 of its Chicago locations, the first of which was ours. A look at the ChargePoint station finder shows only a few installations in the Loop, Chicago's business district, and one of them is a literal stone's throw from our offices.

Chicago's Tesla dealership kindly lent us a Roadster 2.5 for an upcoming review, and we eagerly parked it at one of the charging posts. We had opened a ChargePoint account online and received a ChargePass, which is a bar-coded key tag. Holding the tag in front of the box, a unit built by Coulomb Technologies, signed us in and unlocked the thing.

Then the obstacles began.

The station supports 240- (level two) and 120-volt (level one) charging. Although electric cars charge faster at 240 volts, the unit's pistol-grip connector is incompatible with the Tesla, a surprise for two reasons: One, the auto industry chose this connector, called SAE J1772, as a standard for the U.S.; two, Tesla has converter cables to accommodate almost a dozen different outlets with varying ampere ratings, from the RV park standard to a generator cable, but it doesn't have one for SAE J1772.

In Tesla's defense, the Roadster has been the only electric car on the U.S. market longer than a year, and that arguably makes Tesla’s connector the de facto standard, but it doesn't change the inconvenient truth. Tesla is working on a converter, but it's not ready yet. General Motors suffered a similar setback with the EV-1.

So we resorted to the level-one option, but we soon found that the Tesla 120-volt cable's plug has a ground-fault-circuit interrupter built in (you know, one of those test/reset safety devices) that makes it too tall to fit into the charger's recessed outlet. Strike two. The sole electric car and the most common charging station on the market simply don't like each other.

We produced a 9-inch-long extension cord, which allowed us to make the connection and lock the charger's door. Success. But when we connected the other end to the Roadster, we got nothing. The charger's display reported a ground fault and said it would try again in 15 minutes. Unfortunately, the retry didn't work, and neither did later attempts using the second Coulomb unit. Strike three; we were out.

The car charged fine at 120 volts at my house, and there's a converted Volkswagen Beetle that has been charging successfully for more than a week at our office location, so where was the problem? With the car? With the charging unit? Possibly both.

The next morning, I drove the Tesla to the only other parking facility downtown, where I found exactly the same kind of Coulomb stations. I followed all the steps, and voila! We were charging. The same type of hardware and the same car got along fine. Tesla has suggested there might be a wiring error at our stations, and the operator will be looking into that. However, the homemade electric Beetle charges without incident, and some Tesla owners have described the car's onboard charging electronics as finicky. (We'll address that in our upcoming Roaster review.) It's possible both parties share some responsibility. We'll try and get to the bottom of it and report back. In our next post, I'll detail how we set up our ChargePoint account and how consumers will be billed.