For example, a customer charges his/her Electric Vehicle (EV) overnight (from home) and is charged by the energy company for the relevant number of kWh consumed.
The formula for kWh can be broken down as follows:
Power (kW) = Volts (V) x Amps (A)
Energy (kWh) = Power (kW) x Time
So how does this translate to EV battery charging and PicoScope?
The capture to follow is the first experiment looking at EV charging over a 6-hour period with PicoScope
The instrument panel indicated approx. ¼ charge remaining with a range of 11 miles prior to charging and 55 miles ¾ charge thereafter
The scope used was the PicoScope 4823 and the connections are as follows:
Channel A 12 V battery voltage
Channel B 12 V battery current
Channel C HV battery voltage (using x200 differential probe)
Channel D HV battery current
Channel E Type 2 Mode 2 (Main’s charger) AC voltage (using x100 differential probe)
Channel F Type 2 Mode 2 (Main’s charger) AC current
Channel G Proximity Pilot (PP)
Channel H Control Pilot (CP)
The test above captures the connection of the Mains Type 2 (Mode2) charger into a domestic 3 pin power outlet (Max 10 A) at 2 m 53s and disconnection at 6 h 11 m (Total charge time approx. 6 h 8 m)
I have included the desired measurements (between the time rulers) for each channel and will summarize below:
Channel A 12 V average battery voltage 13.55 V during charging
Channel B 12 V average battery current 1.974 A during charging
Channel C HV maximum battery voltage 342.5 V during charging
Channel D HV average battery current 4.762 A during charging
Channel E Type 2 Mode 2 (Main’s charger) AC RMS voltage 239.3 V during charging
Channel F Type 2 Mode 2 (Main’s charger) AC RMS current 7.882 A during charging
Channel G Proximity Pilot (PP) average voltage 1.522 V during charging
Channel H Control Pilot (CP) Positive duty 28.57% during charging (measurement error)
The support question was; exactly how much energy is consumed by the vehicle against how much is charged by the energy company?
Let’s take a look at current
As we can see from the results above, the mains charging current (RMS 7.882 A) is split between the 12 V and HV batteries. If we add these together 1.974 + 4.762 = 6.736 A total DC charge current
Looking at these values as a percentage of DC current against AC RMS current we have:
6.736 A (DC) / 7.882 A (RMS AC) = 0.85 x 100 = 85 %
Approx. 85% of the RMS current applied by the mains charger is converted to DC and then split between the 12 V and HV batteries (Which equates to a 15% loss of total mains current)
For further information regarding the above, PicoScope 7 Automotive looks at HV charging current split using 3 x BNC+ current clamps within the EV Guided Tests along with a supporting video.
Click on Guided Tests > Electric Vehicles > Charger vehicle tests > Charging current split
Looking now at power loss
Main’s power utilized = 239.3 RMS V x 7.882 A RMS = 1,886.16 W (1.886 kW)
Power utilized by 12 V battery = 13.55 V x 1.974 A = 26.75 W (divide by 1000 for kW) = 0.027 kW
Power utilized by HV battery = 327.7 V (Average) x 4.762 A = 1,560.51 W (1.561 kW)
Total power utilized by these batteries = 1.561 kW + 0.027 kW = 1.588 kW
Power loss = 1.886 – 1.588 = 0.298 kW
Efficiency = Total power utilized by batteries / Total power delivered from mains
1.588 kW / 1.886 kW = 0.842 x 100 = 84.2% efficient
Power loss = 100 – 84.2 = 15.8%
Of course, 100 % of the RMS current, power and energy applied by the mains cannot be used for DC charging as numerous components will “consume” during the AC to DC conversion process along with coolant pumps, fans, AC compressors, relays, networks and ECU’s (Not to mention natural losses such as heat, cables and connections)
The thermal image below reveals the varying heat losses about the charging system
If we are to now look at the energy consumed from the mains supply (energy company) using RMS values the customer charge should equate to:
Power (kW) = Volts (V) x Amps (A)
239.3 RMS V x 7.882 RMS A = 1.886 kW
Energy (kWh) = Power (kW) x Time
1.886 kW x 6-hour charge time = 11.316 kWh consumed from the mains supply
Estimated cost at 14 p per kWh is £1.58 which is not bad for the estimated range of 55 miles
Let’s take a look at Energy loss (which should be the same as power loss)
Main’s power consumed = 239.3 RMS V x 7.882 A RMS x 6-hours = 11.316 kWh
Power consumed by 12 V battery = 13.55 V x 1.974 A x 6-hours = 0.162 kWh
Power consumed by HV battery = 327.7 V (Average) x 4.762 A x 6-hours = 9.366 kWh
Total power consumed by these batteries = 9.366 kWh + 0.162 kWh = 9.528 kWh
Energy loss = 11.316 – 9.528 = 1.788 kWh
Efficiency = Total energy consumed by batteries / Total power consumed from mains
9.528 kWh / 11.316 kWh = 0.842 x 100 = 84.2% efficient
Energy loss = 100 – 84.2 = 15.8%
Here is where I need to repeat the above tests whilst also monitoring workshop mains consumption as I don’t have this data at present. Theoretically the energy charge should be £1.58 and I do wonder if this will be the case!
I will repeat this test over a longer time period using both PicoScope & PicoLog looking at the pros and cons of both. I hope to capture a charge cycle beyond 12 hours to a point where charging is halted by the vehicle rather than disconnection by the owner
I hope the above gives some insight into mains charging of EV’s and I will report back with more data ASAP
Here is to looking to the future case studies. Get those folks to get you an ID.3 or ID.4 soon too.
The Flir camera I went for after many weeks deliberating was the Flir C5
Good performance, nice screen size, compact, neat features & stand alone /independent of a mobile phone
Another piece of kit to carry but it never ceases to amaze me how thermal image contributes to diagnosis, even if reinforcing what you already know from the scope captures (or what you may not know)
We have discussed PicoLog software previously in this forum post viewtopic.php?p=100425#p100425 and recently in this YouTube video here https://www.youtube.com/watch?v=20hByAi ... Automotive looking at parasitic drain
Thanks again to the efforts of our software teams, PicoLog now supports our Automotive range of scopes which includes the 4225A & 4425A and associated BNC+ probes
PicoLog 6.2.6 can now be downloaded from https://www.picoauto.com/downloads (see below)
So where does PicoLog fit with regards to automotive?
Think about applications where “Time or Trends” are more relevant than sample rate (Hi-Resolution)
“Temperature” is a typical example where we may have minimal activity over short time periods and therefore it is not necessary to plot the change in temperature at 1 million samples per second (1 MS/s) only to discover there was no change! (1 MS/s is over-kill)
Consider PicoLog as a graphing multimeter (but with benefits)
Parasitic drain is another example or, electric vehicle charging as we will discuss below.
Before I go on, PicoLog can record for days months & years using 1 sample every millisecond, second, minute or hour and it is worth holding this thought as typically (with PicoScope 7) we are all about micro & milliseconds at high resolution where a “minute” is a lifetime!
The fastest sample rate of PicoLog is 1000 samples per second (1 kS/s) but please bear in mind file sizes when logging for long periods of time at this rate
In the example below, PicoLog is recording for approximately 24 hours capturing our e-Golf charging from discharged (4-mile range remaining) to fully charged at a sample rate of 1 kS/s
The saved file size above = 428.079 kB; to put this into perspective, a 2-minute video shot in Hi-Resolution is approx. 300 kB.
Why is this important?
Managing files is one thing (i.e., transferring, sharing, and storing) but more importantly, when you come to export data from PicoLog (e.g., in csv format) and attempt to load into Excel for further analysis or conversion, you simply end up with “over-load” (Excel would “suffer”, but other software is available that is capable of handling high volumes of data)
With that said, if you are purely looking at “trends” why sample at 1 kS/s?
Referring to the captures below (Images 2 & 3) notice how channels A and B are measuring mains voltage and current at 50 Hz. To faithfully capture and display mains frequency at 50 Hz we need a higher sample rate; refer to image 3 where we have used the PicoLog zoom feature to reveal the 50 Hz sine wave thanks to sampling at 1 kS/s
Image 3 below demonstrates the benefits of using the high 1 kS/s sample rate of PicoLog
As you can see from the image above, there is a compromise to consider which is predominantly governed by what you wish to achieve. If you need to log mains AC, then a 1 kS/s sample rate is required at the expense of file size but with the benefits of seamless logging for as long as you like.
Returning now to the task at hand (EV charging exercise carried out in a controlled environment) let’s look at the DC current delivered to the 12 V and HV batteries respectively.
Note: These “slow changing” DC signals could have been logged comfortably at 1 sample per second so reducing file size yet still returning valid results
Note above the charge duration (10 h 36 m) and how the current delivered from the Mode 2 (10 A) charger is divided throughout the vehicle with approx. 643 mA supplied to the 12 battery and approx. 4.868 A to the HV battery (N.B., these are not true average values, they are values acquired by placing the signal ruler through the majority of the plotted waveform)
We have covered charge distribution and power losses in the forum post here viewtopic.php?p=101926#p101926 using PicoScope but I thought it would be a good exercise to compare these calculations using PicoLog measurements as we have captured a full charge cycle from start to finish as controlled by the vehicle On Board Charger (OBC)
Here is where things get a little clunky with PicoLog as we do not have the full range of measurement and math channel features of PicoScope. This will change and here is another example of the relentless development work carried out by our software teams https://www.picotech.com/library/picolog/picolog-6.2.6
In order to determine the RMS value of our mains voltage and current (Channels A & B) we take the peak values of each channel and multiply by 0.7071 (See below)
Below are the calculations derived from our PicoLog capture above
Main’s power utilized = 234.74 RMS V x 7.30 A RMS = 1,713.602 W (1.714 kW)
Calculating power utilization of the 12 V and HV batteries requires voltage values as well as current. (Watts = V x A)
In our experiment above we only have mains voltage and current, not DC voltages
With that said, let us look at the total amount of current consumed by the batteries (12 V & HV) against the RMS current delivered to the vehicle from our Mode 2 charger
Approx. average 12 V battery current throughout charging 0.643 A
Approx. average HV battery current throughout charging 4.868 A
Total DC current (consumed by batteries) = 4.868 + 0.643 = 5.511 A
Mains RMS current 7.30 A – Total DC current (consumed by batteries) 5.511 A = 1.789 A
We therefore have an alleged current loss of 1.789 A! (Or do we?)
Efficiency = Total current consumed by batteries / Total current delivered from mains
5.511 / 7.30 A = 0.755 x 100 = 75.5 % efficient
Power loss = 100 – 75.5 = 24.5 %
“Of course, 100 % of the RMS current applied by the mains cannot be used for DC charging as numerous components will “consume” during the AC to DC conversion process along with coolant pumps, fans, AC compressors, relays, networks, and ECU’s (Not to mention natural losses such as heat, cables, and connections)”
If we once again refer to our original post viewtopic.php?p=101926#p101926, the calculated “current” losses differ somewhat using the 4823 with PicoScope 7 (15 % instead of 24.5 %)!
We must bear in mind the variables between these tests which are not the same!
With our PicoScope 7 experiment we were charging for 6 h 8 min (PicoLog was 10 h 36 m)
PicoScope 7 calculates the “Mean” and “RMS” values accurately during the entire charge time (between the time rulers) whereas with PicoLog, I have simply positioned a ruler over the majority of the signal to derive an average.
Our PicoLog RMS values were obtained by zooming into a tiny section only of our 10 H + capture to derive peak AC current and Voltage where math’s was applied (Peak x 0.7071)
Add into the mix battery consumption characteristics (dependent on SOC) and the inherent properties of current clamp “drift” over time and temperature, we must concede allowances have to be made.
As you can see, these variables will introduce differences that we need to be aware of and accommodate accordingly.
To summarize the above let us look at the pros and cons of PicoLog
I guess the takeaway from all the above is that PicoScope 7 is not PicoLog but does have logging capability. Likewise, PicoLog is certainly not PicoScope 7 but does have some neat features and several applications within our industry. To quote James Dillon “Right tool, at the right time for the right job”
As food for thought………
The original EV charging post above (30-04-21) also looked at the costs involved when charging over a 6-hour period @14p kWh (£1.58)
Roll onto today (20 months later) with domestic electricity costs running at approx. 34 p kWh, our PicoLog experiment above would cost:
Energy (kWh) = Power (kW) x Charge time
1.714 kW x 10.5 hours = 17.997 kWh
17.997 x 0.34 = £6.12!
To put this into perspective, if we used the values and charge time (approx. 6 hours) from our original post (30-04-21)
The cost to charge today would be:
11.316 kWh x 0.34 = £3.85, an increase of £2.27 (approx. 144%)
Food for thought indeed but still cheaper than petrol/diesel for a typical range of 100 miles in our e-Golf
A final word to the wise about logging
Given your laptop may be recording for prolonged periods when using PicoLog, ensure power and screen saver settings are set accordingly, power supplies are uninterrupted and suspend “Windows Updates.” I was not aware (until learning the hard way) that Windows Updates can halt active applications and update as and when required! (Do not forget good batteries for probes requiring power)
If you are taking advantage of Pico Cloud for logging https://www.picotech.com/library/picolo ... loud-6.2.0 then ensure a stable internet connection throughout the logging period
I hope this helps, take care…..Steve
Unfortunately we cannot use the attenuators (10:1 or 20:1) for mains voltage measurements
Only the signal path is attenuated with 10:1 or 20:1 attenuators which therefore commands a differential probe must be used
Could you take a look at this forum post which will help clarify the above?
I hop[e this helps, take care......Steve