Onboard Charger Efficiency Measured

[UVCatastrophe]

Hi Everyone,
I have seen a lot of suggestions that the optimal EVSE current to charge at is the lowest possible current. Based on the reasoning that minimizing the I^2R losses minimizes overall loss. However this seems to ignore the efficiency of the AC to DC conversion equipment. Given the fact that no data on the operating characteristics of the onboard charger are available from Ford...

I went through the process of measuring the actual current draw from the car for each current set point from the EVSE and also measured the AC voltage at the car for each current set point to obtain the AC power delivered to the vehicle. I then compared that to the energy output from the onboard charger based on data from the Car Scanner OBDII reader to come up with an efficiency as a function of EVSE current set point for my Wallbox Pulsar Plus.

Based on the data it is outrageously inefficient to operate at very low AC wall current at 240Vac! There is a linear increase in efficiency with wall current from about 70% at 6A (lowest i can run) up to a maximum of almost 96% efficient at 18A. At that point there is a slight decrease for a reason I don't understand ( any guesses are welcome) and then a very broad plateau at ~94% all the way out to 40A (the highest I can run). I really wish this data were available from Ford so that we could make informed decsions on how to operate our vehicles. I know it might seem like that low current effecienty is bad but I think that the engineering team should be commended for how flat and efficent their power coverter is from 20A to 40A, I just really wish the data was availbile. Please let me know if this information is usefull or if you have any questions.

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[GatorGrowl]

The difference between what my ChargePoint Flex at 48A reports sent versus the amount the car reports receiving is a little less than 7%.
I’ve not measured it for lower amperages.

 

[Mach-Lee]

Interesting, good work. I would expect some efficiency differences at different amperages, but did not expect the cliff at the bottom end. Are you sure the battery heating wasn't running during the test? You could cycle back through the lower amperages after charging a while to make sure.

I might take a look at this as well.

 

[UVCatastrophe]

Yeah, I thought of that, so I jumped around while taking the data. You can see the structure at 5A increments at the higher current, those were the first data points I took. I did my best to randomize the order in which the data was collected. I did notice a trend that the efficiency was higher towards the end of the test, but that was a 1-2% kind of effect.

 

[SpaceEVDriver]

This is great. How many data points have you collected for each amperage? Do you also have the various vehicle component temperature data as well? What were the environmental conditions (exterior temperature? Garaged? Etc)?

 

[Maquis]

Excellent work. This is pretty much what I expected.
The drop in efficiency at the low end is likely due (for the most part) the fixed overhead from the systems that run during charging. People want to talk about I^2R losses, but most of the voltage drop here occurs at semiconductor junctions which is pretty fixed.

There was a thread a year or so ago when a guy insisted he charged as slow as possible to minimize losses. I tried to counter his argument, but he wouldn’t hear it. I hope he’s still around.

Another thing to consider is that even though it appears that the efficiency is slightly lower at 40A vs say 20A, you are charging for only half the time to achieve the same SoC at 40, so the total energy “lost” is actually less at 40A.

 

[ocdxfv]

The 120v charging rate for the Ford cable is 12 amps, which appears to be around 85% efficiency. Not too bad for occasional use. Thanks for this info.

 

[ChasingCoral]

This is awesome work!

The Lightning charges at up to 80A and the Ford Charge Station Pro is an 80A charger. I would guess that curve continues flat all the way to 80A.

Of course, your work would have to be replicated with a Lightning and FCSP to know for sure.

 

[Maquis]

The 120v charging rate for the Ford cable is 12 amps, which appears to be around 85% efficiency. Not too bad for occasional use. Thanks for this info.

The data above is at 240V. The efficiency will be lower at 120V.

 

[kltye]

This looks an awful lot like computer power supplies. Typically the power supply is most efficient around 30-80% of its rated maximum power, so the poor showing at 6A makes sense, and the dropoff at the end also makes sense. Thank you for your work!

 

[dbsb3233]

Hi Everyone,
I have seen a lot of suggestions that the optimal EVSE current to charge at is the lowest possible current. Based on the reasoning that minimizing the I^2R losses minimizes overall loss. However this seems to ignore the efficiency of the AC to DC conversion equipment. Given the fact that no data on the operating characteristics of the onboard charger are available from Ford...

I went through the process of measuring the actual current draw from the car for each current set point from the EVSE and also measured the AC voltage at the car for each current set point to obtain the AC power delivered to the vehicle. I then compared that to the energy output from the onboard charger based on data from the Car Scanner OBDII reader to come up with an efficiency as a function of EVSE current set point for my Wallbox Pulsar Plus.

Based on the data it is outrageously inefficient to operate at very low AC wall current at 240Vac! There is a linear increase in efficiency with wall current from about 70% at 6A (lowest i can run) up to a maximum of almost 96% efficient at 18A. At that point there is a slight decrease for a reason I don't understand ( any guesses are welcome) and then a very broad plateau at ~94% all the way out to 40A (the highest I can run). I really wish this data were available from Ford so that we could make informed decsions on how to operate our vehicles. I know it might seem like that low current effecienty is bad but I think that the engineering team should be commended for how flat and efficent their power coverter is from 20A to 40A, I just really wish the data was availbile. Please let me know if this information is usefull or if you have any questions.

That's generally about what I would have expected. I assume there's some fixed overhead that comes off the top no matter what the power level, that would take up a larger share of a low rate. I probably would have expected a more gradual decline though.

Since most EVSE's don't go below 16A on 240V, means it really doesn't matter much. 5-7% loss is pretty consistent with what we've heard. But good to see confirmation that it's the same basic loss% anywhere from 16A to 40A.

 

[Hammered]

How exactly was the method for calculation done?
For instance, were you using a current transformer monitoring AC amps ahead of the EVSE? Were you looking at actual power in the battery? For lower charging rates, given that the DC/DC comes on as do pumps, it's a given that there will be more losses given that the vehicle's LV side is using about 500 watts depending on variables.

The only logical way to gauge the efficiency is to compare the watts that came out of the wall vs the watts that are in the battery.

 

[voxel]

The 120v charging rate for the Ford cable is 12 amps, which appears to be around 85% efficiency. Not too bad for occasional use. Thanks for this info.

My guess at 120V (the data above is for 240V) is your efficiency will be sub-70%

I started charging my RAV4 Prime and my first Tesla at 120V and saw 60-70% efficiency (via TeslaFi logging)

 

[Fixbear]

The difference may be the DC-DC charging the LVB. At the lower amperage a higher percentage will try to top the low voltage.

 

[Shayne]

This looks an awful lot like computer power supplies. Typically the power supply is most efficient around 30-80% of its rated maximum power, so the poor showing at 6A makes sense, and the dropoff at the end also makes sense. Thank you for your work!

Max power needs to be above rated?

Good info ?The EPA testing calculated to 13% lose 87% efficient which seems to be in line. I have been using 85% in estimate cals (appears conservative). This data looks really flat after it ramps up. Good job.

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