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car compatibility with dual-plug EVSE

Discussion in 'Technical' started by ChrisC, Nov 2, 2013.

  1. ChrisC

    ChrisC see signature

    Apr 27, 2009
    Atlanta, GA
    #1 ChrisC, Nov 2, 2013
    Last edited: Nov 3, 2013
    Hello all -

    Short version: I think that the new ChargePoint CT4000 "dual" charger may expose a compatibility problem with some cars, and Tesla owners are ideally capable of testing for the problem. Keep an eye out for this new CT4000 in your area, and if you see one, see if you can get another EV owner to come test it with you.

    Long version:

    Earlier this year, Chargepoint announced the CT4000 EVSE, a charger with two J1772 plugs on it. A picture of it is attached to this post. The equipment can be supplied by two separate electrical circuits (e.g. two circuits each with 40 Amps), or it can be configured to be supplied by a single electrical circuit (e.g. one 40 Amp circuit).

    In the latter case, if it's "sharing" a single circuit, then that implies that when two cars are plugged in, it is supplying half the power to each car. Further, it implies that as cars come and go, the amount of available power (actually current draw) that the EVSE advertises to the car should CHANGE. In more technical terms, the J1772 pilot signal's duty cycle should change from indicating one power level to another power level.

    However, ever since this EVSE was announced, I've been itching to do a test. I suspect that this CHANGE in the J1772 pilot, DURING a single charging session, will upset some cars.

    For example, imagine this scenario:
    1. CT4000 dual plug fed by a SINGLE 40 Amp circuit
    2. Car A arrives as the first car and plugs in.
    3. The CT4000 tells Car A (via that J1772 pilot signal) that it can give him 32 Amps (the max allowed, 80% of circuit), and Car A starts drawing 32 Amps.
    4. Car B arrives as the second car and plugs in.
    5. The CT4000 rebalances the load, now telling Car A that he can have only 16 Amps, and tell Car B that he can have 16 Amps.
    6. Car A *should* slow down to 16 Amps, and Car B should start up at 16 Amps.

    My hypothesis is that at step 5, some cars in the Car A position might error out, because the pilot signal is CHANGING while they are charging. Obviously, we should expect the car to adjust its power draw, but this is exactly the kind of thing that I bet some car makers did not implement properly in their car. How the car would react I don't know, but here are some possible ways I imagine the charging will fail:

    - car doesn't like pilot change and stops charging altogether
    - car ignores the changed pilot signal and continues to pull all the power; in this case the EVSE might not ever let Car B start charging
    - similarly, car ignores pilot changes, but EVSE recognizes misbehavior and terminates the Car A session in order to let Car B charge (and thus punishing Car A for being obstinant)

    If you get this far and the power delivered DOES change, then you've got a shared circuit. In that case, do a couple more tests. Continue the sequence above:

    7. Unplug Car B and see if the Car A power ramps back up.
    8. Unplug Car A, and start a new session with Car B.
    9. Start a new session with Car A, and see if the power ramps down on Car B.
    10. With both cars plugged in and charging, on your Tesla ramp the power draw DOWN. See if the power draw then goes up by the same amount on the other car! Note that all Chevy Volts and early Nissan Leafs max out at 15 Amps current draw.

    That's pretty much it. I can't think of anything else to test.

    Tesla Model S owners are ideal for testing this for two reasons:
    - the Model S can draw high power (e.g. the full 32 Amps in the example above)
    - the console display shows you how much current is being drawn that instant
    - you can control how much current to draw, up to the maximum allowed by the EVSE

    So, I did this test last week, after the first CT4000 charger showed up in Atlanta. I got a local Tesla Model S owner to join me (and my Chevy Volt) at the charger site, and we did the test above. THE MODEL S PULLED 32 AMPS AND THE VOLT PULLED 15 AMPS, NO MATTER WHO WAS CONNECTED WHEN. (The Chevy Volt charger maxes out at 15 Amps)

    This tells me that this particular CT4000 was actually connected to two separate circuits! It had a 40 Amp circuit for EACH of the two J1772 plugs. So that wasn't really the test I was looking for.

    The real test will be of a CT4000 station that has a SINGLE circuit supplying it. It's unlikely that you'll be able to tell what kind of installation it is. You'll just have to do the test.

    If you agree that this is an interesting thing to be testing for, keep an eye out for CT4000 stations in your area. If you see one, get another EV owner to join you, test it out per the above sequence, and please report the results here!

  2. Chris1howell

    Chris1howell Member

    Oct 28, 2011
    Los Angeles, California, United States
    J1772 requires that an EV respond to a pilot change within 5 seconds. I would bet the Dual EVSE measures the current to each EV. If a vehicle does not respond the pilot can be turned off and charging can be shut down.

    I built a similar device (4 J1772 connectors on a single circuit) a while back with OpenEVSE. I started a charge session at 6A and ramped up so if the EV failed to respond at least it got the minimum and allowed compliant vehicles to get more...
  3. cwerdna

    cwerdna Active Member

    Jul 11, 2012
    SF Bay Area, CA
    There are a whole ton of the CT4000 series at Google in Mountain View, CA. I know, as charged using one at an event there. As for the issues the OP mentioned, I wonder how their stations and wired and if they'd run into that problem.

    Luckily, Chargepoint's HQ is only a bit over 15 miles away from the Googleplex.
  4. tdiggity

    tdiggity Member

    Oct 3, 2012
    Bay Area, CA
    The data sheet says that you can configure it with two 40A lines, or one per each plug. In your test, I'm guessing that ct4000 had two independent lines running to it.
  5. ChrisC

    ChrisC see signature

    Apr 27, 2009
    Atlanta, GA
    #5 ChrisC, Nov 3, 2013
    Last edited: Nov 15, 2013
    Great information, thanks C1H! That's exactly what I want to test. I just need to find a CT4000 with a shared circuit to do it.

    Is there a public document that describes that pilot / response behavior? Or does it require a purchase from SAE, like IEEE standards documents?

    And thank you for your service to the community with the OpenEVSE project. When I get my next EV early next year, I may do an OpenEVSE build and then repurpose my LCS-25 for portable use.

    If it gives you 20 Amps or more even when another EV is plugged in, and doesn't change that offer when the other car starts or ends charging, then that's good sign that it is NOT a shared circuit.

    Indeed, as I wrote, in bold :)

    If anyone spots one of these chargers, see if you can get another EV to test it for you. See my first post here for test protocol. If it appears to have both plugs on a single shared circuit, I'd be VERY interested in the results.
  6. dtaubert

    dtaubert New Member

    Jan 2, 2014
    San Jose, CA
    My workplace recently ripped out Blink EVSEs and replaced them with CT4000 units. In doing so, there is a single 209V/40A supply for each CT4000.

    When you arrive and plug in to a completely vacant CT4000, 30A is available. When another car (almost always a Nissan Leaf) arrives and plugs in to the other half, it reduces to 16A as one would expect.

    Now, here's the problem. If the other car unplugs, 30A is again available, but the Tesla remembers the 16A "setting" and won't crank back up automatically. It shows on the screen (and on the mobile app) as 16A/30A at that point. I have to walk back to the car and manually adjust the limit on the touch screen from 16A back up to 30A to make it charge at the full rate.

    This appears to be a byproduct of the way Tesla tries to remember configured limits by GPS location. I have tried every permutation that I can think of with limit setting before and after plugging in, but the reduced 16A setting always sticks.
  7. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

    Mar 8, 2012
    Right now you're stuck. My guess would be that in the next release of the App you will be able to change the settings remotely. (This seems an easier to implement fix than having a setting that allows the car to bounce back when more power is seen.)
  8. Cosmacelf

    Cosmacelf Well-Known Member

    Mar 6, 2013
    San Diego
    Send this info to Tesla ownership so that they can write their charging software better.

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