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#### sholland

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Can someone please explain how an onboard charger can know that the EVSE is providing 120V or 240V? From everything I've read of the J1772 protocol, it only advertises max allowable current. Is the EVSE hard coded to provide a current level that is appropriate for the level (1 or 2)?

#### rmay635703

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Well a volt meter and switching power supply can handle voltage.

The max current rate is determined by the pilot signal off the EVSE.

The cars software varies from model to model, so while a Leaf will draw 25 amps off 110 vac
My Volt won't top 12 amps

So the answer is "it depends"

#### kennybobby

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The EVSE units come in levels 1,2 or 3. They know what voltage they were designed to operate and that's the designation 1 = 120vac, 2 = 240vac and 3 = DCQC. They also know their max current design point, and that is encoded in the pilot signal sent to the car.

The car charger (level 1 or 2) detects the pilot and knows how much current to expect. The incoming voltage, whether 120 or 240vac, is first rectified to create a DC Buss voltage, which can be read using a resistor divider network. The charger then chops the DC Buss thru some high frequency switching transistors to create a power-factor-corrected AC voltage that is then sent thru a transformer, and then rectified again to create the DC Pack voltage that goes to the battery pack.

#### sholland

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I suppose some background information could help explain why I am asking the question in the OP...

I recently got an Elcon UHF 3.3K charger, which has a CAN interface to control the charger. It requires a CV voltage and charge current command to be sent to it every a couple of seconds or so. It sends the current battery voltage, so just a simple calculation from max level 1/2 power can derive the current the charger should send to the battery. I can also create a circuit [on my CAN board] to read the PWM duty cycle of the pilot signal to ensure the max current available from the EVSE is not surpassed. However, I don't have a way of automatically knowing if I am connected to a level 1 or level 2 EVSE. I didn't want to have to connect the mains to measure the AC input...

For example, I have an OpenEVSE at home that I use for 120V charging. I can set its advertised current at say 10A, 12A or 15A. The car will then read the pilot and know it can't surpass the set current level, but it doesn't know what the power level of the EVSE is. I wish the pilot just advertised available power, which seems like all the charger really needs to know.

#### kennybobby

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The TCCH/Elcon chargers (non-CAN) that i have examined have a circuit to read the input AC voltage and it adjusts the power level accordingly (the power is calculated in the firmware code which has been reversed by user Coulomb). i would think the newer ones would have that feature also.

Of course they don't plug in to an SAE EVSE connector--they are powered directly off the mains outlets.

#### sholland

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The new UHF chargers do come hard coded with an upper limit to the output current, but they do not report the input voltage. They require a CAN command at least every 5 seconds with an output current and target CV. The UHF doesn't directly understand the EVSE signals hence my questions...

#### ga2500ev2017

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Can someone please explain how an onboard charger can know that the EVSE is providing 120V or 240V? From everything I've read of the J1772 protocol, it only advertises max allowable current. Is the EVSE hard coded to provide a current level that is appropriate for the level (1 or 2)?
I'm very late to the party but I believe I can provide some answers. The EVSE provides ground to the vehicle charger. The charger simply has to measure the voltage of both the L1/L2 legs to ground. The EVSE already does this as a part of the ground continuity test requirement.

With 120V the neutral leg is peak 0V with respect to ground. With 240V that same leg has a 120V peak relative to ground. So the onboard charger notes the peak voltage of both legs and essentially adds them up to get the input voltage.

On the EVSE optoisolators with the LED driver between each leg and ground are monitors. A 60 Hz signal indicates 120 volts on that leg...

Hope this helps,

ga2500ev

#### brian_

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... The EVSE provides ground to the vehicle charger. The charger simply has to measure the voltage of both the L1/L2 legs to ground...

With 120V the neutral leg is peak 0V with respect to ground. With 240V that same leg has a 120V peak relative to ground. So the onboard charger notes the peak voltage of both legs and essentially adds them up to get the input voltage.
No, the neutral leg is neutral, meaning that it is at zero volts with respect to ground all of the time. With 240 volt power, both L1 and L2 are 120 V RMS (not peak) from the neutral, but 180 degrees out of phase; L1 and L2 are not 120 V and 240 V from neutral or ground.

This is split-phase or single-phase three-wire power, as is normally provided in North America:

The end result is still that the vehicle's charger only needs to look at the voltage with respect to neutral on both L1 and L2 to know whether it has 120 V or 240 V power available.

#### ga2500ev2017

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I'm very late to the party but I believe I can provide some answers. The EVSE provides ground to the vehicle charger. The charger simply has to measure the voltage of both the L1/L2 legs to ground. The EVSE already does this as a part of the ground continuity test requirement.

With 120V the neutral leg is peak 0V with respect to ground. With 240V that same leg has a 120V peak relative to ground. So the onboard charger notes the peak voltage of both legs and essentially adds them up to get the input voltage.

On the EVSE optoisolators with the LED driver between each leg and ground are monitors. A 60 Hz signal indicates 120 volts on that leg...

Hope this helps,

ga2500ev
No, the neutral leg is neutral, meaning that it is at zero volts with respect to ground all of the time. With 240 volt power, both L1 and L2 are 120 V RMS (not peak) from the neutral, but 180 degrees out of phase; L1 and L2 are not 120 V and 240 V from neutral or ground.

This is split-phase or single-phase three-wire power, as is normally provided in North America:
I'm well aware. However the J1772 connector does not pass neutral to the EV when using 240V. Only L1,L2, and GND are sent over the three power wires of the J1772 connector.

When 120V is used there is only one hot wire, either L1 or L2 from the perspective of the J1772 power wires. The other two are neutral and ground.
The end result is still that the vehicle's charger only needs to look at the voltage with respect to neutral on both L1 and L2 to know whether it has 120 V or 240 V power available.
Not neutral, ground. In short, if neutral is passed as one of L1 or L2, then its voltage with respect to ground is 0V. This means that 120V is sent. However, if neither L1 nor L2 are 0V with respect to ground, then there is no neutral, therefore the power input is 240V. Only ground, the green wire, is sent to the EV in all cases.

This is the reason that a 14-50 receptacal has 4 terminals. They are L1,L2, neutral, and ground. But the 240V EVSE only passes L1, L2, and ground to the vehicle.

ga2500ev

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