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Battery saver message

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When I connected a charger to my 12 V battery this weekend, within a minute the green light indicating the 12 V battery was full came on. The car reported that the SOC was 72% before connecting the charger. Just like when I turn the car on, the current started out at about 20 amps and then dropped to about 2 amps within four minutes. So I believe the 12 V battery is just fine. I'm not sure charging it with an external charger is going to do anything useful.

Edited by larryh

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After my drive this morning, I am now charging the HVB. Initially, the DC to DC converter was not even enabled--the car was not charging the 12 V battery at all while charging the HVB. About half an hour later, it enabled the DC to DC converter and is now charging the 12 V battery at the lower voltage level of about 13.3 V.

Edited by larryh

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Low Voltage Battery Charging System - Overview

GrySql, where do you dig up this fascinating information? Do you have moles deeps inside of Ford engineering? ;)

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When looking through the logs I have made while driving and charging the car, I observe the DC to DC converter voltage applied to to the 12 V battery as follows:

 

Percentage of Time Voltage

44% 14.3

50% 13.3

5% Off

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Guys, I posted a Forum rules sticky at the top of the Welcome thread. Please adhere to them. Thanks. Occasional Banter is OK, but criticizing each other is not accepted.

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I had some TSBs applied yesterday to the car. TSB 14-0020, to fix the issue I was having with the Service Engine Soon light coming on when using the Engine Block Heater, seems to have changed the car's behavior with respect to charging the 12 V battery. It appears the technicians reflashed the SOBDMC, BECM, SOBDM, and PCM. For the past three trips, the DC to DC converter voltage setpoint has been 14.7 Volts the entire time. Before, it initially started at 14.3 Volts and later dropped to 13.3 Volts. I will have to monitor to see if the behavior has also changed while charging the HVB. At the end of the third trip, the SOC was 84%.

Edited by larryh

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I was reading a Ford broadcast message, something the dealers get every day. There is supposed to be a fix for the battery saver message in the 3rd quarter of 2014. Possibly due to the electric water pump...

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I tried a simple experiment to verify what SOC is measuring. I plugged the car into the 240 V charger with the charger turned off and turned on the car. When I do this, the DC to DC converter is disabled and the entire 12 V power supply to run the car comes from the 12 V battery. The lights, radio, and other accessories in the car consumed 23 amps of power for about 25 minutes. The SOC dropped linearly from 81% to 51% (R^2 = 0.9976, where 1 is perfectly linear). The equation for SOC vs. time was:

 

y = -0.0211x + 80.695,

 

where y is SOC in percent and x is time in seconds. Interpolating (which probably is not accurate), if the SOC were 100%, it would take 100/.0211 = 4739 seconds or 1.32 hours to discharge the battery drawing a current of 23 amps. That means the capacity of the battery is 23*1.32 = 30.2 Ah. The rated battery capacity is 43 Ah. I don't know the actual procedure used to compute battery capacity.

 

At 51% SOC, the car no longer powers the power points after turning off the car. So it definitely recognizes that the 12 V battery is low and is trying to conserve energy.

 

I previously did this unintentionally. The car stopped working after 45 minutes. So extrapolating, the car is completely dead when the SOC is about 25%. I don't intend to repeat this experiment again to determine the actual value.

From what I have read, the Ah capacity of a car battery is usually measured using a discharge rate that results in a full discharge over 20 hours. The rated capacity of the battery is 43 Ah, so a discharge current of about 43 / 20 = 2.15 amps should be used to measure the battery capacity. I was using 23 amps. The observed battery capacity decreases with increasing current draw according to Peukert's law: the capacity of the battery in Ah at a one-amp draw rate is 9daf5525d40e98044b159be81976b957.png where I is the actual draw rate, k is the Peukert constant which ranges between 1.1 and 1.3 for a lead acid car battery, and t is the time to discharge the battery.

 

Going through the math, it should take between 0.92 to 1.48 hours to fully discharge the battery at 23 amps assuming a capacity of 43 Ah (for k ranging from 1.1 to 1.3). I estimated 1.32 hours if the battery were fully charged. But I doubt the current flow would remain 23 amps as the SOC reaches 0%. There are too many unknowns and assumptions to draw any firm conclusions regarding if the SOC is being measured correctly or the capacity of the 12 V battery is actual 43 Ah.

Edited by larryh

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Hey Larry, you should edit your profile so that is say resident Braniac under your interests! :) A+b-d/w*q=z went way over my head. LOL My math consists of 0+7=8. No that isnt wrong either, it just happens to be how my math works for the job I do.

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My college degrees are in Physics/Math/Computer Engineering, so I should be able to figure these things out.

 

After the upgrade to the SOBDMC, SOBDM, PCM, and BECM, the car is now very persistent in charging the 12 V battery when the charger is plugged in. Prior to the upgrade, the only time it charged the 12 V battery was when the HVB battery needed charging. Now, it charges the 12 V battery if the car is plugged in and the HVB is fully charged. It charged the battery for four hours this morning until the timer shut off the charger. The SOC has gone from 86% to 88%.

Edited by larryh

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Do you want to hear what I think about this or not ?

 

If all of your readings are assumed to be accurate AND that behavior continues.........

that is, charging near full blast all the time AND the SOC never going above 85%......

your battery is weak.

 

AND the behavior you noticed before, with the charging voltage dropping off after a while,

is more like what a conventional charging system would do.

One that never falls below 14.7 would be considered to be overcharging......and that is hard on a battery too.

The dealer was supposed to check the 12 V battery during the inspection. I let the service manager know. He claims everything was fine. But, I didn't talk to the technician servicing the car, so I can't verify that they actually tested it. The service manager just seems to say yes to all your requests, but I have a suspicion they don't actually make it to the technician servicing the car and they don't actually ask the technician if your requests checked out OK.

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Now I am confused what the car is doing. If I turn the car on and off when it is plugged into the charger, it will start charging the 12 V battery for up to four hours at about 14.5 V. It did not do that prior to applying TSB 14-0020. It currently claims the SOC is 91%. When I measure the voltage of the 12 V battery with no load after sitting for 20 minutes, it reads 12.99 V. That seems rather high. I wonder if it is underestimating SOC and now overcharging the 12 V battery. I notice that the count of start/stop events recorded by the BCM was zeroed out when they reflashed by the modules. I wonder if there are parameters associated with the 12 V battery that are incorrectly set. It reports the correct age for the 12 V battery, 444 days.

Edited by larryh

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