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Please refresh me as to why YOU started worrying about your battery in the first place.

I don't think there is anything wrong with the 12 V battery. I am only posting my observations in the hopes that they may provide some insight into how the car maintains the 12 V battery. My typical week consists of a 60 mile round trip plus 15 minute commutes one-way to and from work. Since I have the Fusion Energi, the car also has the opportunity to charge the 12 V battery overnight while charging the HVB. Prior to applying the TSB, the SOC of the 12 V battery averaged 69% over two months. I check the SOC each morning. It ranged from 55% to 84%. I think it needs to get below 50% for battery saver mode. So even with the opportunity to charge each night, the car was unable to maintain full charge to the 12 V battery.

 

Now after applying the TSB, the car is much more aggressive in charging the HVB. It has spent many hours drawing power from my 240 V charger to charge the 12 V battery, at least 24 hours, and has only managed to get the SOC up to 91% (I'm not sure that the SOC measurement is accurate. I think the typical accuracy of most battery management systems in measuring SOC is about 5% to 10%). I will have to see in the coming weeks how effective the new programming will be in maintaining the 12 V battery. If the Fusion Energi has so much difficulty in maintaining 100% SOC, the Fusion Hybrid will have a much more difficult time since there is no opportunity to charge the Hybrid overnight by plugging the car into a 240 V charger. Since I don't experience the battery saver message, it would be informative to compare my observations with a Hybrid that does experience the problem.

Edited by larryh

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When I look at the 60 mile commutes, the SOC of the 12 V battery generally increases by 2-3%. For the 15 minute commutes to and from work, it increases by 1-2%. Overnight and during the day the SOC decreases by at least 2-3%, probably more. So once the charge on the 12 V battery starts getting low, I don't see how the car can keep up if the only opportunity to charge is when the car is on while driving to and from work or during the 60 mile commutes. The only way my car keeps up is by charging the 12 V battery when it is plugged in overnight to charge the HVB. The question is should the car be able to keep up to maintain 100% SOC, and if so, why isn't it doing so?

Edited by larryh

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It would be nice to know how they are determining the 12 V battery SOC and how accurate it is. I suspect they keep track of the amount of current flowing into and out of the battery. Obviously, the car tracks the 12 V battery current and voltage, or I wouldn't be reporting it. It also tracks the 12 V battery estimated temperature, age, and type. Finally, it has several counts that it maintains: Cumulative Battery Charge When Ignition Is On, Cumulative Discharge From Battery When Engine Is Off, Cumulative Discharge From Battery When Engine Is On, and Cumulative Discharge From Battery in Sleep Mode.

 

The following link provides some details about the BMS for the Ford F150, which is probably similar to the Ford Fusion Hybrid BMS: http://www.f150forum.com/f38/battery-management-system-reset-109656/.

 

The post talks about the BMS using a Hall Effect Sensor near the negative battery terminal, which implies that the BMS is measuring current flow. It also refers to SOC drain timers and load shed. I assume load shed refers to shutting down non-essential functions to conserve 12 V battery charge when SOC is low, i.e. battery saver mode. The BMS SOC can be reset to a default of 85% (FORScan offers that option) along with the SOC drain timers. This stops load shedding, and probably battery saver mode (at least until the car learns the actual SOC). It takes approximately 8 hours for the BCM to learn the correct battery SOC, when the car is left undisturbed.

 

 

Edited by larryh

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Last week, the SOC of the 12 V battery ranged from 84% to 93% Prior to applying TSB 14-0020, the SOC ranged from 55% to 84%. The car has spent a significant amount of time charging the 12 V battery when plugged into the 240 V charger.

 

When I look at a 15 minute commute home three weeks ago prior to applying the TSB, the amount of current supplied to the battery was 0.53 Ah. Today, the car supplied 1.08 Ah, or 2.04 times as much. So the battery appears to be accepting charge faster than before. My guess is that all that charging has made the 12 V battery more active.

 

The maximum SOC I have observed so far is 93%. But if I look at the SOC a little later, it quickly drops back to 90% and stays there. The SOC generally falls about 2-3% during the nine hours I park at work. But today, for some reason, the charge was 91% when I parked at work and was only 67% nine hours later when I left. I don't know what happened to the 24% SOC. This was the first time I have observed such a large drop. The trip home only charged it back to 70%. I'll have to see how much additional charging occurs tonight when it charges the HVB and if the car is able to keep up with the amount of charge that was consumed. Hopefully it doesn't use that much charge very often.

Edited by larryh

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The reason for the 24% drop in SOC yesterday appears that the BCM does not always compute SOC accurately. This morning, when I started to work the SOC was 73% and was still 73% when I arrived. When I left work for home, the SOC had jumped to 91% and rose to 93% by the time I arrived home. I don't think the 12 V battery charges itself. The BCM must not have computed SOC accurately.

Edited by larryh

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You're right but it depends if there is load on it... Its kind of hard to measure SOC with load as the voltage drops immediately.

 

 

The BCM tracks the current flow into and out of the 12 V battery. The SOC should be maintained regardless of the load on the battery.

 

When there is no load on the battery, it recalculates SOC. The car must be left undisturbed for 8 hours. The jump from 91% to 67% the first day, and the jump from 73% to 91% the next day occurred while the car was left undisturbed for 9 hours at work. The car does not seem to recalculate SOC consistently--there can be significant error.

Edited by larryh

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It has now been a month since TSB 14-0020 was applied. This past week, the SOC of the 12 V battery, as reported by the BCM, has been between 89 and 91% when I check in the morning. After resting for about three hours, I measure the voltage to be around 12.85 V. Prior to the TSB, the SOC averaged around 70% and the resting voltage was more like 12.55 V. So the TSB definitely changed how the battery is charged and maintained, and probably also strengthened the battery. Over the month, the charging voltage has gradually reduced from 14.7 V to about 14.3 V now. The charging algorithm and battery are both adapting--I am not sure what is happening. Hopefully it is for the better.

 

I'm not sure how this TSB would apply to the Fusion Hybrid though. I have the Fusion Energi, so when I leave the car plugged into the charger, the car can charge the 12 V battery anytime it wants and it seems to want to do it a lot this past month.

Edited by larryh

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