Level 1 Living at 16 Amps

[eNate]

The EVSE only limits current to what it is set to or limited to, once it confirms that it is plugged into the EV, power can be turned on and the EV can start a charging session.

I would only point out that the EVSE has no internal means to LIMIT current. It's a safety pass-thru, and communicates to the car the maximum current that's available, as you wrote. However, if the car goes haywire and pulls more current than it is supposed to, the EVSE isn't required to have a means to monitor this, so won't open the contactor (unless it senses a ground fault or voltage irregularity).

In that instance, the breaker in the panel and proper gauge wiring in the walls are protecting the home.

 

[alohart]

I would only point out that the EVSE has no internal means to LIMIT current.

I guess that depends on the meaning of "limit". An EVSE probably can't limit its output current except to turn it off completely if the output current exceeds the maximum current specified by the pilot signal.

I also found this in an OpenEVSE source code header file:

// if OVERCURRENT_THRESHOLD is defined, then EVSE will hard fault in
// the event that the EV is pulling more current than it's allowed to
// declare overcurrent when charging amps > pilot amps + OVERCURRENT_THRESHOLD
#define OVERCURRENT_THRESHOLD 5 // A
// go to error state overcurrent by OVERCURRENT_THRESHOLD amps

I couldn't find in the source code for our JuiceBox where charging would be stopped if the output current exceeds the current corresponding to the pilot signal, so it appears that a JuiceBox would depend on the charging circuit's circuit breaker to protect against a runaway EV onboard charger.

 

[eNate]

I'm betting that's a feature of the Open EV, and I can't argue against including it, although it is one more thing to malfunction and prevent charging.

I was nosing around inside a Clipper Creek 40A unit I have and the input and output wires are directly connected at a contactor with no apparent means of current sensing.

There's a CT coil around the pair of output wires, and I emailed CC to ask about them, whether they "were for current sensing." The response was "this is used to sense current through the hot lines for imbalance. It is part of our CCID circuit in layman’s terms it is the GFCI." That's exactly how a GFCI works, so unless it's dual function and we were talking past each other, I don't think this EVSE would know it the car was pulling above 40 Amps.

Edit: I just sent of another email to my contact at CC, describing this scenario. If I get a reply I'll share it.

 

[alohart]

I'm betting that's a feature of the Open EV, and I can't argue against including it, although it is one more thing to malfunction and prevent charging.

The header information I posted is in a conditional compilation section that suggests that it would be included only when an OpenEVSE has an optional ammeter. Our JuiceBox has an optional CT coil that is used to measure current for output energy calculations but apparently not to stop charging if the charging current exceeds that expected by the EVSE. It appears that output current measurement to stop charging should an on-board charger misbehave isn't part of the J1772 protocol.

 

[eNate]

It's seems like a belt-and-suspenders approach, but I can understand arguments for and against.

As for Clipper Creek, I received a reply from my contact this morning : "This is a very good question, the answer is that the HCS-50 will try to supply the 48 Amps if the car goes haywire but the breaker is there to stop current flow when it goes over the 50 amp it is rated for."

So again, at least the house won't burn down!

BTW I'm still mostly "living life at Level 1" as described at the top of this thread, but recently added the HCS-50 for my wife's ID.4. I've doubled down and added a 20A, 240V receptacle outside the garage so I can use my Duosida EVSE at Level 2 if I need to charge at home while she's plugged in. I've only plugged the new 40a unit into the i3 once.

 

[gt1]

I'm not surprised that a 16A EVSE makes a big difference. A car draws a couple of amps of a parasitic load to service its internal circuitry, battery cooling, conversion losses, etc... You're probably doubling your effective charge rate. A long time ago I had an idea to try to draw more than 12A from a 5-15 circuit, but after some problems with heat and tripping the breakers even at 12A I realized that the 5-15s have no power reserves to accommodate such shenanigans.

 

[agzand]

Many chargers have overcurrent protection. If the car draws more than the rated current they will throw a fault and disconnect. If the voltage in the circuit drop due to a poor connection and the car tries to draw the same power it could result in an overcurrent fault.

 

[eNate]

<span>I'm not surprised that a 16A <a href="http://www.myelectriccarforums.com/electric-vehicle-charger/" class="interlinkr" target="_blank">EVSE<span class="tip">Compare EVSE equipment</span></a> makes a big difference. A car draws a couple of amps of a parasitic load to service its internal circuitry, battery cooling, conversion losses, etc... You're probably doubling your effective charge rate. A long time ago I had an idea to try to draw more than 12A from a 5-15 circuit, but after some problems with heat and tripping the breakers even at 12A I realized that the 5-15s have no power reserves to accommodate such shenanigans.</span>

You might be right.

12 Amps was getting me 25% SOC increase over 8 hours of charge.

16 Amps gains me 40% over 8 hours.

16 Amps represents a 33% power increase over 12 Amps...

however

25% per charge x 1.33 = is only 33% (that's 33% gain in SOC), and I'm gaining 40%. That's a SOC gain of 60% at 16A compared to charging at 12A.

The one caveat is that I always have a departure time set with battery preconditioning on, and I was using the stock 12A BMW EVSE in the late fall and winter, prior to upgrading to the 16A unit. So it's possible my 25% gains were affected by electricity consumption of the onboard heater (potentially up to 3 kWh on colder nights, about 10% of my 28kWh battery). Though my 16A EVSE pretty consistently gains me 40%, with no notable deviations due to extreme temps.

 

[bwilson4web]

I drove 800 mi home, a 2017 BMW i3-REx. On the last leg, I drove on battery until the REx took us home. My plan was to put it on an L2 to measure the charge energy in a mostly depleted battery and took a nap:

• 7 hrs later - 29.5 kWh (higher than estimated 25 kWh at dealer)
• 12 hours later - 40 kWh (hummm)
• 15 hours later - 40 kWh

So my first hypothesis was cooling the car down from the long drive was the primary driver. We've also had 85-89 F (~30 C) temperatures suggesting there may have been a battery protection mode. The dealer claimed to have charged the car overnight but when I picked it up a 2:00 PM, it did not show 100% SOC so I suspect some parasitic load drained part of the battery. Regardless, I will setup a time recording video recorder to gather more data.

Tonight, I will take it on a battery exhaustion drive with a reset trip meter. I'll top off the tank and on the way back, stop at an Electrify America fast DC charger to see if I can record the charging curve. My goal is to find the maximum range at ~65 mph (~100 kph.)

Questions? Concerns? Requests?

UPDATE

I drove until the REx came on and the 5-6 miles to reach the EA station:

• 106 mi EV @65 mph until REx kicked in on Standard Day temps and no wind, flat section.
• 30 kWh to 99% at EA CCS-1, 150 kW charger.
• 28.4 kWh - trip meter 105 mi, 3.7 mi/kWh, 59.9 mph

Battery, REx, and A/C good. Local BMW doing wheel alignment and general mechanic’s inspection.

Bob Wilson