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!
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!
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