ForScan HVB Data Analysis, SOC, Estimated SOC, SOC Range

[plus 3 golfer]

Recently there seems to be members that question whether their HVB is "OK" as they watch the battery symbol and believe that the HBV isn't performing as it should.   I have suggested many times to get ForScan and record data.  Then, after the fact one can look at the data and assess how their HBV is performing.  I understand that everyone may not have the knowledge or excel skills to do the analysis but IMO, this is the only way one can determine how their car is performing.  The dealer will be no help.

 

One simply needs to record three PIDs with ForScan:  

 

BATT_CHAR [sOC] (%)

BAT_PACK_VOLT(Volt)

BATCURBECM(Amper)

 

One then computes the energy going into and out of the HVB.  The BECM also does this ("columb counting").  Once the ForScan data is uploaded into Excel, the volts are multiplied by the Amps and multiplied by the change in time between time stamps.  Typically with my ELM327 I will see about 25+ scans per second which would be 25 rows of excel data per second of recording.  So, if the volts are 250 V and the current is 100 A and the difference in time stamps on two successive rows is 40 msec (1/25), then the energy out of the HVB would be 1000 Wsec.  If the next 39 time stamp intervals were the same volts and current, then the total energy out of the HVB would be 40,000 Wsec.  So, one simply acciumulates the energy flow for each time stamp period.  The cumulative energy in the HVB will decrease (SOC decreases) for positive Amps out of the HVB and increases (SOC increases) for power flow into the HVB (PID shows negative current).  

 

The first chart shows the SOC and accumulted energy flow (kWh) over about 150000 scans, about 6000 plus seconds (over 1 hour and 40 minutes) of driving 75-78 mph on I17 between Flagstaff and Phoenix - downhill about 6000 ft.  So, the largest change is kWh is 0.514 kWh between about 1291 and 2916 seconds.  The SOC went from 34.2% to 70.7%.  A change of 36.5% in SOC represents 0.514 kWh.  0.514 kWh divided by 36.5% = 1.397 kWh -- the energy capacity of the HVB. Pretty close to 1.4 kWh. :)   You can pick other points on the graph and do the same calculations. 

 

The second chart shows the error in the estimated SOC of the HVB based on the "columb counting" and the PID SOC.  As one can see assuming 1.4 kWh HVB capacity, the estimated SOC never exceeds 0.35% difference.  Over the total time period the difference (error) is virtually zero from start to finish.

 

I don't know how much HVB capacity I have lost but the Ford algorithms continue to allow full use of around a 30% to 70% range of the initial 1.4 kWh of range.  Idaho National Lab shows their test vehicles lost around 6% of capacity at about 105,000 miles (my current mileage).  I'm going to continue to analyze the data I collected and will post voltage vs SOC curves trying to see where the knee of the HVB discharge curve might be.  With 150,000 data point, I can segregate the data based on discharge rate and develop a series of curves and compare against INL test data. 

 

I still believe that we have little to worry about with respect to HBV longevity in our C-Max Hybrid.  To this date I know of no one that has had a HVB capacity issue.  In fact, several members have over 200k miles and still get great FE.  Paul (ptjones) you need to keep that baby going so we can see how far the HVB will go.  ICE may need major work before the HVB. 

 

BTW, I need a faster PC.  I have my sons 6 year old gaming desktop.  It's still fast but running spreadsheets with 150,000 rows and 10 columns takes several seconds to complete.  But the graphs are the real time consumming functions - minutes sometimes especially curve fits.

 

Edited November 29, 2018 by Plus 3 Golfer

[plus 3 golfer]

Attached are voltage vs SOC discharge curves for the HVB from the data recorded in the first post.  Four ranges of discharge current were graphed with natural log curve fits. I can run charging curves also but it's moot as the curves would be higher than the discharge curves.

 

Typically, battery capacity in Ah is estimated by fully charging a battery and then applying a discharge current that will fully discharge the battery in one hour. The C-Max design capacity is 5 Ah.  So, it will take a current of 5 A one hour to fully discharge the battery.   The 5 A  is referred to as the 1C discharge rate for the HVB.  For our lithium ion HVB, one stops discharging at the minimum HVB voltage of 209 V (2.75 V per cell X 76 cells).  This results in a rated capacity of 5 Ah.  Multipling the 5 Ah by the nominal HVB voltage of 281.2 V (3.75 V per cell X 76 cells) yields the 1.4 kWh HVB rating.

 

Since I can't apply a 5 A continuous load to the HVB nor charge the HVB to it full capacity (100%SOC), I segregated the data into four ranges: a 1C range (0-10 Amps), a 3C range (10-20 Amps, a 15C range (60 - 70 Amps) and about a 24C range (100 - 135 Amps).  The SOC of the data ranged from about 35% to 70%. I also put two large yellow circles on the graph indicating the approx. data points from INL battery tests at 1C discharge rate.

 

 

Bottom line:  I believe these tests indicate that my HVB is performing very well.  There is likely some capacity loss in my HVB similar to what INL Ah tests show but it doesn't affect performace as it does in the Energi where usable kWh of EV range can be substantially reduced.  Based on my curves, I would expect the 30% - 70% SOC range to be available for the life of my car (several hundred thousand miles). 

 

 

[SnowStorm]

Which OBDII adapter are you using?  Mine is a cheap one that frequently stops working and you have to restart data acquisition.

[plus 3 golfer]

Which OBDII adapter are you using?  Mine is a cheap one that frequently stops working and you have to restart data acquisition.

My old adapters did the same - a bluetooth and a wifi which I paid less than $20 for.  I decided to get the OBDLink MX for $80 so that I could scan PIDs on both HS and MS CAN automatically,  The only issue is that if the software is updated, it "forgets" the settings and according to ForScan, one has to uninstall ForScan, reinstall and set it up again to scan both CANs before initiating the first scan  It defaults to HS CAN and can't be changed after the first scan.   

 

Looks like its on sale for $60.  It virtually work all the time.

 

OBDLink MX Bluetooth OBD-II Scan Tool for Android & Windows

[plus 3 golfer]

I note that the "PID rate" max spec. for the OBDlink MX is:

 

MAXIMUM PARAMETER ID (PID) RATE

~100 PIDs/second for PC & Android

 

I was scanning 14 PIDs from four modules: BECM, BdyCM, SOBDCM (TCM) and PCM all on the HighSpeed CAN.  I just spot checked and the worst rate that I found was 14 PIDs at 18 times per second. The best rate I found was 14 PIDs at 27 times per second. The average scan rate for the 14 PIDs was 42.1 msec based on 6,347,605 msec / 150,674 scans which would be 14 PIDs at 23.75 times per second. I wondered why it would take about 3X longer to scan 100 PIDs per second than the same 14 PIDs about seven+ times per second?  The MX module should simply be a passthrough interface of the PID to the modules on the CAN as it clearly passed about 330 PIDs per second on average. 

 

But the MS CAN is slower than the HS CAN. My guess is that the MX Max rating of 100 PIDs / sec is based on the MS CAN baud rate.  A quick search indicates that HS CAN can have a baud rate of up to 1 Mbits/sec depending on cable length and MS CAN has a max baud rate of 125 kbits/sec.

 

Now when comparing the MX module scan rate with my older ELM327 modules, I looked at some older data and could only get about 120 PIDs per second on the old ELM327 compared to 330 on the MX module which is over 2.5 times faster.  In addition, the MX module specs show a curent draw of <2 mA when in battery saver mode. I'm fairly sure that one of my other ELM327s had a "sleep mode" that was more like 10 mA. So, leaving the MX plugged in all the time is no issue.

 

For $70 one can get the OBDLink MX and the ForScan APP. and then one can have fun "playing" with the data  Also, this is probably $30 less than a trip to a dealer for a "diagnostic scan" only to be told there's nothing wrong with your car.  :)

 

 

[plus 3 golfer]

I note that the "PID rate" max spec. for the OBDlink MX is:

 

MAXIMUM PARAMETER ID (PID) RATE

~100 PIDs/second for PC & Android

 

I was scanning 14 PIDs from four modules: BECM, BdyCM, SOBDCM (TCM) and PCM all on the HighSpeed CAN.  I just spot checked and the worst rate that I found was 14 PIDs at 18 times per second. The best rate I found was 14 PIDs at 27 times per second. The average scan rate for the 14 PIDs was 42.1 msec based on 6,347,605 msec / 150,674 scans which would be 14 PIDs at 23.75 times per second. I wondered why it would take about 3X longer to scan 100 PIDs per second than the same 14 PIDs about seven+ times per second?  The MX module should simply be a passthrough interface of the PID to the modules on the CAN as it clearly passed about 330 PIDs per second on average. 

 

But the MS CAN is slower than the HS CAN. My guess is that the MX Max rating of 100 PIDs / sec is based on the MS CAN baud rate.  A quick search indicates that HS CAN can have a baud rate of up to 1 Mbits/sec depending on cable length and MS CAN has a max baud rate of 125 kbits/sec.

 

Now when comparing the MX module scan rate with my older ELM327 modules, I looked at some older data and could only get about 120 PIDs per second on the old ELM327 compared to 330 on the MX module which is over 2.5 times faster.  In addition, the MX module specs show a curent draw of <2 mA when in battery saver mode. I'm fairly sure that one of my other ELM327s had a "sleep mode" that was more like 10 mA. So, leaving the MX plugged in all the time is no issue.

 

For $70 one can get the OBDLink MX and the ForScan APP. and then one can have fun "playing" with the data  Also, this is probably $30 less than a trip to a dealer for a "diagnostic scan" only to be told there's nothing wrong with your car.  :)

 

 

[jdbob]

In section "418-00 Module Communications Network Description and Operation" of the service manual it says that the max speed of the HS-CAN bus is 500 kbps. Might be different on different car models. You are right about the 125 kbps MS-CAN.

[plus 3 golfer]

Whoa, looks like the Obdlink MX is no longer on sale at $59.95 as price now shows $79.95.  Might have been a Black Friday or Cyber Monday week sale.

[plus 3 golfer]

In section "418-00 Module Communications Network Description and Operation" of the service manual it says that the max speed of the HS-CAN bus is 500 kbps. Might be different on different car models. You are right about the 125 kbps MS-CAN.

Thanks, didn't think of looking in the Service Manual.  So, there is likley a 4:1 ratio of max. number of PIDs that can be scanned in one second on the HS CAN compared to the MS CAN.