Chargepoint over charging A LOT

[thardie]

Used my CHAdeMO adapter for the first time today at a ChargePoint station. ChargePoint says this:

Energy
11m 48s 11:37 AM-11:49 AM
7.401 kWh @ $0.12/kWh$0.89

Tesla Fi says this:
11:37 AM - 11:49 AM
12 Minutes Start - 74 %
End - 82 % Used - 6.2 kWh
Added - 6.39 kWh 103.1 % Avg Voltage - 394.64V
Max Voltage - 397V Avg Amps - 85.7A
Max Amps - 86.96A

That's a huge error - 1kWh difference in 12 minutes?!

This also showed up during charging where the Tesla reported a charge rate of 34kW and the station said I was charging at 40 kW.

 

[Tz00]

I believe that TeslaFi only grabs instantaneous values once per minute (by default), so 12 data points while the charging ramps up/down/starts/stops isn't going to be very accurate. I've charged for less than a minute and TeslaFi missed the entire charging session.

 

[Tz00]

Also, the ChargePoint station could be measuring the AC input power, which would include AC-DC conversion losses. They would be billed by the utility based on AC input, so may as well show that (and bill the end user if applicable).

 

[davewill]

There's another thread around that shows a big discrepancy between the displayed kW rate on the charger and the one in the car. There were examples from multiple charging networks. I'm wondering whether the CHAdeMO integration has an issue in this regard.

 

[edigest]

What "Charge Efficiency" does TeslaFi indicate? I bet it is about 86-87% which would be normal for a 8kW station.

Some of the energy coming in is used by the converter. If the charging efficiency is 86%, 6.36 kW is received by the battery of the 7.4 kW sent by the charging station.

 

[dsgerbc]

Sounds like a normal outlet to battery charging loss.

 

[camalaio]

Does the data TeslaFi pulls show "pulled in power", or "net power gain"? That is, does it account for something like having the AC or heat going? (In which case the amount delivered to your vehicle would be higher than the amount charged, as some of it was used for HVAC)

 

[darth_vad3r]

What "Charge Efficiency" does TeslaFi indicate? I bet it is about 86-87% which would be normal for a 8kW station.

Some of the energy coming in is used by the converter. If the charging efficiency is 86%, 6.36 kW is received by the battery of the 7.4 kW sent by the charging station.

8kW station? It’s probably a 50 kW DCFC station since OP said the station was reporting 40 kW.

 

[darth_vad3r]

I believe that TeslaFi only grabs instantaneous values once per minute (by default), so 12 data points while the charging ramps up/down/starts/stops isn't going to be very accurate. I've charged for less than a minute and TeslaFi missed the entire charging session.

This may be true, but if Teslafi is looking at the API values available it reports energy added from the charge session. You could poll the car once after the session and get the energy number.

86% does seem low for DCFC though. I like the idea above about the station showing you AC power input to the station. This would explain large DCFC power losses from station to car, because the loss isn’t actually there, it’s “before” the station delivers the DC to you.

API reference: State And Settings
See: charge_state.charge_energy_added

This used to stay the same after charge session ended so you could check it after the charge was complete, but actually it seems that 2019.24.x just changed this to reset it back to 0 after the charge is complete. So in that case we are back to TeslaFi polling frequency missing up to 60s of charge energy added at the end of the charge.

 

[darth_vad3r]

ChargePoint says this: 7.401 kWh @ $0.12/kWh$0.89

Tesla Fi says this: Added - 6.39 kWh

That's a huge error - 1kWh difference in 12 minutes?!

This also showed up during charging where the Tesla reported a charge rate of 34kW and the station said I was charging at 40 kW.

40 - 34 = 6 kW discrepancy evident right from your 2 screens.
6 kW * 12 / 60th of an hour = 1.2 kWh difference.

So, there’s your difference right there. The station may be reporting AC power “cost” before delivering DC to your car.

 

[wwu123]

Everyone's asking all the wrong questions - the real question is, where in northern CA can you find a public ChargePoint station that only charges $0.12 per kwh? Or is this a workplace-subsidized one that is only authorized for employees?

j/k..

But Teslafi can show errors even on long-ish sessions, such as the fact it's claiming >100% efficiency on your session based on the API data. I've seen that many times charging at home. It does look like the main issue here is the 34kw vs 40kw reporting discrepancy though.

 

[darth_vad3r]

Everyone's asking all the wrong questions - the real question is, where in northern CA can you find a public ChargePoint station that only charges $0.12 per kwh? Or is this a workplace-subsidized one that is only authorized for employees?

I totally asked (myself) that exact question!