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Published on June 16th, 2019 | by Steve Bakker

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For Tesla End-To-End Charging, There’s Supercharging & Destination Charging. For Everything Else, There’s The Mobile Connector — Part II

June 16th, 2019 by  


We learned in Part I of this series that Tesla upped the ante when it introduced the Gen 2 Mobile Connector at the same time as the release of the Model 3. We also learned that the Gen 1 Universal Mobile Connector (UMC) has been deprecated, and that since January 2018, all Tesla cars now come equipped with the Gen 2 Mobile Connector (MC).

And we learned that the Gen 2 charge cord is rated for less maximum current than its predecessor (32 amps vs 40 amps), but is a safer solution, especially because the newly designed Gen 2 cord has a facility for lowering the charging current if the plug or outlet overheats. We also discovered that the circuit board embedded in the Gen 2 adapters signals the Mobile Connector as to the outlet’s capacity, along with employing a unique identifier which could allow Tesla to backtrack to the source supplier if any issues arise with the adapter.

A New Adapter, A New Challenge

Because of the change to the new technology Gen 1 UMC adapters no longer fit the Gen 2 Mobile Connector. Tesla only supplies adapters for 120V/15A and 240V/50A outlets (NEMA 5-15 and 14-50, respectively) with the Gen 2 MC included in most cars (some Model 3 owners report that the 14-50 adapter is no longer included). If an owner needs an adapter that is not included, the first place to look is the online Tesla store. The Gen 2 adapters listed there all employ the new Gen 2 electronics.

Note: The Tesla Model 3 Home Charging Guide can be used by any Tesla owner to learn of the locations where each plug type is commonly found. For example, I like the NEMA 6-20 adapter, as the matching outlets are often used for plug-in motel air conditioners. Don’t forget the old proverb:

“You can never be too rich, too thin, or have too many charging locations.”

But wait. What if you need an adapter that Tesla doesn’t offer? Tesla has never marketed adapters for every outlet type and the Gen 2 adapter offerings are no exception. This is where third-party suppliers come in. Several companies produce aftermarket adapters for the Gen 1 UMC, but it’s a whole new ballgame with the Gen 2 adapters. If a third-party company wants to supply adapters that utilize the safety features of the Gen 2 MC, the aftermarket companies need to come up with an adapter that is capable of detecting the correct charging amperage. It must also have an integrated temperature sensor, a way of signaling the MC if the plug overheats, and the adapter even needs to present the expected unique ID to the Mobile Connector that all bonafide Tesla adapters are coded with.

In other words the third-party boys need to come up with a circuit board and firmware very much like the one Tesla uses. As it happens, that’s exactly what the folks over at EVSEadapters did. It took awhile, but the company was able to locate a source for the circuit board and reverse engineer the signaling process used to talk to the Gen 2 MC. The Gen 2 adapters sold by EVSEadapters even emulate the firmware used to communicate with the MC, and each adapter is programmed with the requisite unique ID. As a result, the company is now offering Gen 2 adapters not available in Tesla’s line up.

I’m not going to put you to sleep by listing every Gen 2 adapter in the EVSEadapters lineup, but let’s use the NEMA TT-30 outlet as an example of a somewhat common outlet that Tesla has never gotten around to producing an adapter for. TT-30 is a NEMA standard for Travel Trailers (center adapter in above photo). It’s a 120V/30A circuit found in RV campgrounds. Many RV campgrounds are equipped with the higher amperage NEMA 14-50 (220V/50A) outlets, but many other other parks only offer TT-30 outlets. Therefore some travelers like to carry one of these adapters just in case a supercharger isn’t handy. This EVSEadapters offering properly signals the Mobile Connector to inform the car to draw no more than 24 amps, as well as monitor the adapter’s temperature. Why 24A instead of 30A? Don’t forget that all-important 80% rule!

Note: The circuit board in the Gen 2 adapter adds 60% to its cost.

By the way, have you been wondering how your author came across all the details of the Gen 2 adapter innards? I promise you I didn’t get them from Elon. He and I exchange cupcake recipes, but that’s about it. Actually, the owner of EVSEadapters was kind enough to share that very-hard-to-come-by information. So big kudos to EVSEadapters. If you like this article, they deserve the credit.

Adapters to Avoid

To wrap this discussion up, I want to mention a class of outlet adapters on the market that you want to be cautious about using. These adapters work with both Gen 1 and Gen 2 charging cables and are notable in that they contain neither resistors nor the requisite embedded circuit boards. I refer to them as Tomcat Tesla adapters. They physically adapt the MC to the matching outlet, but they don’t follow Tesla’s protocols for safe charging. This class of charging accessories can be dangerous to use because they don’t properly inform the car to set the charge rate correctly.

Such adapters are easy to identify. Here is a simple trick to spot them:

Instead of plugging into the Tesla charging cable directly, such adapters plug into one of the Tesla supplied adapters such as the 14-50.

That is the tell. I’m going to pick on the popular TT-30 Tomcat adapter available from several online outlets as an example. Let’s pretend that Barbie and Ken are going camping at River City RV Park and they buy such an adapter for the trip (Dick and Jane would never do this). Note how the adapter is configured to receive a 14-50 plug, not the end of the Mobile Connector. This adapter requires that you first fit the Tesla 14-50 adapter to the Gen 1 or Gen 2 Mobile Connector and then plug the Tomcat adapter into that adapter. If you’ve made it this far in the article you understand why this approach is problematic. Think for a second as to why this is solution must be used with caution. The answer is in next paragraph.

Right. The adapter that’s plugged directly into the Tesla charging cord is what the car goes by when setting the charge rate. The 14-50 adapter signals the car (via the MC) to charge at 40 amps. The car thinks it’s plugged into a 50A outlet, but in fact is plugged into a 30A outlet and should be drawing no more than 24A. When the car tries to draw 40 amps from the 30A outlet there’s gonna be trouble in River City. At best, the circuit breaker on the outlet is going to pop. That’s if things go well. Even then, what if the breaker is in a locked electrical box? Of course at worse Barbie and Ken might suffer a major meltdown, and the River City RV Park could turn into the biggest weenie roast this side of Hades.

There is a workaround when using this kind of setup. You can manually turn down the charge rate from the touchscreen of the vehicle. Many owners who have purchased such adapters use this strategy. In some circumstances, this approach was the only way to plug a Tesla into certain outlets because nobody made a proper adapter for it. It’s just that you have to remember to change the charge rate from the display, and although the setting is persistent, you never know when a software update may reset it. Most importantly, Tomcat adapters defeat the very strategy that Tesla has designed into the Gen 2 MC because they isolate the Gen 2 adapter from the outlet.

OK. That’s everything I’ve been able to learn about this topic. Hopefully this treatment has been instructive and worth your time.


Non-technical Executive Summary

  • All Teslas now come with an improved charging cord named the Gen 2 Mobile Connector.
  • For safety reasons, the maximum current for the Gen 2 MC was reduced from 40 amps to 32 amps.
  • To further enhance safety, the Gen 2 outlet adapters can sense when an outlet overheats and reduce the charging current to safer levels.
  • Avoid the use of any third party adapter that requires plugging into a Tesla adapter rather than directly to the Mobile Connector brick.

Epilogue

Some folks were disappointed that the charging cable included with their Tesla was reduced from 40A to 32A. But when you consider the effort that Tesla went to in order to spot, and compensate for, overheating issues at the outlet, my bet would be that going to a 32A system was primarily a safety play. When the Mobile Connector first appeared on just the Model 3s, of which the onboard charger of the standard range model coincidentally draws a maximum of 32A, it seemed as though the 32A charging cable was included with all variants of the Model 3 simply for cost reasons.

And that may be true. But rather than starting at the car and solving for a proper charging cable for the 32A onboard charger, Tesla instead may have started at the wall outlet. The company may have first determined a reasonable maximum current for safe outlet charging, with a fairly flexible cord, from receptacles of an unknown condition, and then designed the new Mobile Connector and the onboard charger to follow that number. That’s speculation, but the notion is further underscored by the fact that all Tesla cars now ship with the 32A cable. 32 amps at 240 volts charges the car at a reasonable speed (28-30 miles per hour), and if you need to charge as fast as the onboard charger of the long-range Model 3 or the S/X can handle, the Tesla Wall Connector with its fatter, fixed charging cord is designed for that job. 
 





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About the Author

is a semi-retired teacher, writer, and technologist who is currently passing time by attempting to cure his ignorance as to how electric cars work.



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