panamamike
Posts: 121
Joined: Sat Jan 25, 2020 10:21 am

6.6 Kwh chargepoint delivers 6.1 Kwh?

Sat Mar 14, 2020 10:09 am

Wondering if this is normal, to only pull 6.0 to 6.1 Kwh vs. the 6.6 Kwh available.

alohart
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Location: Honolulu, HI

Re: 6.6 Kwh chargepoint delivers 6.1 Kwh?

Sat Mar 14, 2020 11:26 am

I assume you meant to write "6.6 kW chargepoint delivers 6.1 kW" because I'm not aware of any EVSE that limits the energy delivered to an amount like 6.6 kWh.

The power of EVSE (kW) is determined by the voltage and amperage. If either is lower than expected, the power would be lower than expected. The voltage is outside the control of an EV's charger and depends on the load on the charging circuit or in the local area and the electrical resistance of the power wires.

An EV's charger does control the current by telling the EVSE what current to deliver. As a battery pack nears a full charge, the charger will tell the EVSE to reduce the current and thus the charging power.

So it's normal for an EVSE to deliver less than its rated power as charging approaches full, if the supply voltage is lower than the rated voltage (likely 208 V for a 6.6 kW EVSE), or if the electrical resistance of the power wires results in a voltage drop when delivering the relatively high charging current (e.g., 30 A).
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

PBNB
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Location: Vancouver, BC

Re: 6.6 Kwh chargepoint delivers 6.1 Kwh?

Sat Mar 14, 2020 3:28 pm

My Chargepoint runs on a 240v 40amp circuit and consistently provides 7.2 kWh of charge to the i3.

When my buddy came over and plugged in his Volt, we saw the kWh drop to 3.6 and tried to adjust his car settings to accept more but that was all the car would take.

This appears to be determined by the car. I am not too sure if there is a charger (or even mine) that will exceed that output and allow the car to draw more kWh.

I don't know what the top end kWh is for a Level 2 charger. Or what the Level 2 max is for the car.
2015 i3 REX

eNate
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Re: 6.6 Kwh chargepoint delivers 6.1 Kwh?

Sat Mar 14, 2020 4:34 pm

An EV's charger does control the current by telling the EVSE what current to deliver. As a battery pack nears a full charge, the charger will tell the EVSE to reduce the current and thus the charging power.

Just a nit to pick...

The car doesn't (can't) tell the EVSE what current to deliver, and the EVSE doesn't have the ability to regulate current.

The communication on the J-1772 protocol is the EVSE indicates the available current to the vehicle. It is then up to the car (charger) to use up to that amount of current, and if the charge conditions call for less than what's available, the car doesn't communicate this to the EVSE, it just uses less.
Last edited by eNate on Sun Mar 15, 2020 12:25 am, edited 1 time in total.
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jadnashuanh
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Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: 6.6 Kwh chargepoint delivers 6.1 Kwh?

Sat Mar 14, 2020 7:01 pm

Power is the product of the volts (think pressure) and the volume (think amps). If either is lower than the design, the amount of power delivered will be less. My guess, the supply voltage was low. The pilot signal announcing how much current is available should remain constant. It's up to the car to not exceed that. If the car was not that discharged, it will naturally slow down the charging rate, thus delivering less power. An EVSE is just a smart power switch.
Jim DeBruycker
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)

panamamike
Posts: 121
Joined: Sat Jan 25, 2020 10:21 am

Re: 6.6 Kwh chargepoint delivers 6.1 Kwh?

Sat Mar 14, 2020 7:28 pm

Thanks for all the input. Yes I'm aware that the car is technically the charger and controls the amount of charge it pulls. That said, I typically charge from near empty and the charge maxes out at 6.1kW where the Chargepoint EVSE indicates it's capable of doing 6.6kW. Was wondering why this discrepancy existed, I know that different cars can accept different amounts of charge and the i3 can do 7,7kW. I figured if the BMW can do 7.7 it should be able to take advantage of the maximum 6.6kW, but maybe due to other factors the real current is 6.1kW?

Wanted to know what other folks got for a charge value at a 6.6kW station. I've been using the same set of charges, 3 at one location and a 4th at a second location, they all perform at this level. Was wondering if this was an issue with the car.

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MKH
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Re: 6.6 Kwh chargepoint delivers 6.1 Kwh?

Sun Mar 15, 2020 6:40 am

I typically charge from near empty and the charge maxes out at 6.1kW where the Chargepoint EVSE indicates it's capable of doing 6.6kW. Was wondering why this discrepancy existed,
Kilowatt hours is calculated by taking the 'appliance' wattage, multiplying it by the number of hours of 'run-time', then dividing by 1000. A guess would be that the car, in controlling the 'draw' is not pulling full 'watts' initially until the battery temp raises to optimum charging temp, and/or reduces the 'draw' toward the end of the charge cycle to prevent over-charging/overheating the battery.

Would also depend on the algorithm the Chargepont software is using to extrapolate/calculate (guesstimate) the kwh.
Mark H.
2015 i3 Rex, Capparis White, Tera World, Technology & Driving Assistant, Parking Assistant, Harman Kardon Audio System, 19 inch 427 wheels, EVoInnovate EVSE

alohart
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Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 6.6 Kwh chargepoint delivers 6.1 Kwh?

Sun Mar 15, 2020 1:40 pm

eNate wrote:
Sat Mar 14, 2020 4:34 pm
The car doesn't (can't) tell the EVSE what current to deliver, and the EVSE doesn't have the ability to regulate current.

The communication on the J-1772 protocol is the EVSE indicates the available current to the vehicle. It is then up to the car (charger) to use up to that amount of current, and if the charge conditions call for less than what's available, the car doesn't communicate this to the EVSE, it just uses less.
I was careless and incorrect with my description. Thanks for this clarification!
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

jadnashuanh
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Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: 6.6 Kwh chargepoint delivers 6.1 Kwh?

Sun Mar 15, 2020 3:54 pm

Does the Chargepoint unit show average charge rate, or instantaneous?
Jim DeBruycker
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)

panamamike
Posts: 121
Joined: Sat Jan 25, 2020 10:21 am

Re: 6.6 Kwh chargepoint delivers 6.1 Kwh?

Sun Mar 15, 2020 9:50 pm

jadnashuanh wrote:
Sun Mar 15, 2020 3:54 pm
Does the Chargepoint unit show average charge rate, or instantaneous?
It shows the actual/instantaneous. I can monitor the charge session with the app.

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