OBDII data for LVB (12V battery)

Using FORScan I've been able to monitor data and start checking the health of my 12V battery. Quite a few FFE owners have encountered issues with finding their car dead because the 12V SOC got too low.

So far our FFE Body Control Module (BCM) has usually reported the 12V SOC somewhere between 70 & 78%. This doesn't surprise me based on what I have observed. The Fusion Energi quite often shows the "charging" light active on our Clipper Creek EVSE even when the HVB has not yet begun charging or after the HVB is fully charged. Checking what's going on reveals that the Fusion Energi is charging the 12V battery during these periods. The Fusion Energi BCM usually reports the 12V SOC as 95+% when we drive it frequently. If the Fusion sits at home unplugged a lot because we're driving the Focus Electric mostly the 12V SOC will drop to 70-80%. When the 12V SOC is that low in the Fusion Energi the car charges the 12V battery any time it is plugged in to the EVSE. The car also charges the 12V at 4-10 amps when the car is on and being driven. It will usually start charging at around 8-10 amps when the car is first started and then it will drop to about 4 amps for as long as the car is on and the 12V SOC is below about 80%.

The Focus Electric rarely charges the 12V battery other than during the time that the HVB is being charged. The Focus Electric 12V battery SOC is also usually much lower in my observation. The Focus Electric also does not do as much to charge the 12V battery while the car is being driven. Even with the 12V SOC lower than 70% the Focus Electric only charges the 12V battery at 2-4 amps. Once the 12V SOC gets above about 75% the car drops the charging for the 12V battery to less than 2 amps, often less than 1 amp. The Focus Electric does briefly charge the 12V battery at more than 4 amps when the car is first turned on, but this period of charging often lasts less than 1-2 minutes.

The Fusion Energi (and C-Max Energi, C-Max Hybrid & Fusion Hybrid) have had a number of updates issued since the cars were released in late 2012 to change the charging behavior of the BCM to charge the 12V battery more aggressively. Dead 12V batteries have been a common issue for C-Max Hybrid owners and many Fusion Hybrid owners have frequently had their car show them the "BS" (battery saver) message which indicates that the car has gone into a load shedding mode to protect the 12V battery from being discharged because the BCM has detected that it is not sufficiently charged. I believe that these updates explain why the Fusion Energi keeps the 12V battery at a higher average SOC than the Focus Electric. A fellow Fusion Energi owner who has been tracking the 12V SOC in his car for longer than I have has noted the differences in charging behavior after certain updates and has seen a measurable increase in his average 12V SOC after the updated calibration was installed in his car.

In summary, I am going to use an external 12V battery charger to try to get the 12V SOC in our Focus Electric up closer to 100% to see if the car can/will maintain that higher SOC or if it lets it fall back down to the 70-75% range. Other posters who are more versed in lead acid battery chemistry and care methods have indicated that a 70-75% SOC will over time damage the lead acid 12V battery. This may be the cause behind the issues that have caused a number of owners to be plagued with a low 12V battery. Another possible factor is the location of the 12V battery. In the Fusion Energi/Hybrid the 12V battery is in the trunk and thus experiences less temperature swings than a 12V battery that is under the hood. I'm not sure how much heat reduces the life of the 12V battery, but I've found that the 12V in the Focus Electric tends to be much hotter than the 12V in the Fusion Energi since the Focus Electric has the battery under the hood. In this thread I posted about how warm the electric motor & power electronics get which causes the 12V battery to heat up as well.

I'll continue to post more data as I collect it.

Very interesting info - thanks very much!

Its a shame Ford hasn't updated the FFE's 12v battery charging algorithm like the Fusion and c-max.
I have been fully charging my FFE 12v battery once a month with an external 12v charger to be sure.
I do see times with my accesory port plug in voltmeter where after sitting a few days in the garage it can get down to 11.5v, normal level seems to be about 12.3v
Sometims I see the voltage drop for a minute after I open the door and cab light is on to 11.5v but then it quickly goes back up to over 12.0v while in OFF mode, indicating the 12v battery isn't doing great with a temp high load?
Though I might want a new 12v battery soon to compare its response.

I keep a portable small Li-Ion 12v jump starter in my FFE for emergency use just in case, but I've done that in my old Toyota oickup for years too.

I charged the 12V battery with my trickle charger one night that the FFE was left unplugged because the Energi was charging. I followed the instructions in the Workshop Manual to connect the positive cable to the battery terminal and the negative cable to the body ground post. The 12V SOC reported by the BCM didn't increase.

I am contemplating swapping 12V batteries between the Fusion Energi & Focus Electric, provided that it is the exact same battery, but I am concerned about the fact that I cannot reprogram the BCM. The Workshop Manual describes the process the dealer is supposed to use when replacing the 12V battery and it includes programming the BCM with the battery type & resetting the 12V battery age counter.

I charged the 12V battery in the Focus again. It still shows 70% SOC. I wonder if the 12V battery is weak. Next time I am at the dealer I will ask them to check it out.

After the Focus Electric sat unused for 4 days while we were out of town the 12V SOC had dropped to 52% according to the BCM. The car charged the first night we were away and I had a few Go Times with HVAC off set throughout our trip. I think the 12V is weak. It will turn 800 days old tomorrow according to the age tracker in the BCM.

That is interesting. I've left our FFE sit, plugged in, for up to 7 days at a time and the 12V battery still read 12+V when I returned (this was using the cigarette lighter meter; before I got the OBD-II dongle). What was the voltage at 52%? (I'd guess it was in the 11.something range).

jmueller065 said:

That is interesting. I've left our FFE sit, plugged in, for up to 7 days at a time and the 12V battery still read 12+V when I returned (this was using the cigarette lighter meter; before I got the OBD-II dongle). What was the voltage at 52%? (I'd guess it was in the 11.something range).

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I have not checked the voltage. Where do you read it in FORScan? When the car is on won't the voltage read higher because the 12V battery is being charged?

hybridbear said:

I have not checked the voltage. Where do you read it in FORScan? When the car is on won't the voltage read higher because the 12V battery is being charged?

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Many of the Ford modules will report out VBATT (battery voltage), or you could simply measure it (if you have the cigarette lighter meter or just use a meter).

I have seen cases where it doesn't turn on the DC-DC converter and thus you'll just see battery voltage (like when you unlock the door by touching the handle--with the lighter voltmeter plugged in you see it light up at 12V).

jmueller065 said:

hybridbear said:

I have not checked the voltage. Where do you read it in FORScan? When the car is on won't the voltage read higher because the 12V battery is being charged?

Click to expand...

Many of the Ford modules will report out VBATT (battery voltage), or you could simply measure it (if you have the cigarette lighter meter or just use a meter).

I have seen cases where it doesn't turn on the DC-DC converter and thus you'll just see battery voltage (like when you unlock the door by touching the handle--with the lighter voltmeter plugged in you see it light up at 12V).

Click to expand...

Ok, thanks. I don't have another voltmeter. I'll check with FORScan later today. It doesn't seem to work super well if the car isn't off, even if some modules are active such as when opening the driver's door.

12.4-12.5 volts while discharging at 7-10 amps right after I turned the car off. The BCM reports the 12V SOC as 70% again.

The Fusion Energi shows the DCDC converter low voltage setpoint as 14.6 or 14.7 volts. The Focus Electric usually is 13.0-13.6 volts. The Fusion Energi used to use a lower voltage but a software update increased the voltage because of low 12V battery concerns. I wonder if the Focus Electric update to address low 12V battery concerns will increase the DCDC converter low voltage setpoint. The Fusion also keeps a fixed voltage from the DCDC converter. The Focus Electric will vary the DCDC voltage. If you turn on the headlights the DCDC converter low voltage setpoint will increase. If you turn on the HVAC system it will increase.

The car is plugged in and charging now. The DCDC low voltage setpoint is 12.3 V only. The car is not really trying to charge the 12V battery, sending only 0.12 amps of current to it. It currently shows an SOC of 69.

Could just be trickle charging it.

After charging for 1 hr 36 mins the HVB temp had risen to 99 F. At this point I had to leave so I unplugged the car & left. The car had charged from about 40% useable SOC to about 75% useable SOC. I drove a ~6 mile trip and the HVB temp stayed at 99 F. The TMS was not cooling the HVB while charging or while driving. Coming home a few hours later the HVB temp had dropped to 95 F. After arriving home I plugged in the Focus Electric and it is waiting to charge. The car is not cooling the HVB while waiting to charge.

I expected the TMS to kick in when the HVB temp was 99 F, but it didn't.

Resurrecting this 2+ year old thread to provide some more information on how the car handles the 12V system. Correct me if I am wrong but I'm pretty sure the DC-DC converter just puts out a constant voltage and the battery draws whatever current it wants. The DC-DC converter is also supplying power for all the other low voltage electrical systems too. So if the 12v battery is drawing low current when turned on, it's not that the car isn't charging it enough it's that the battery is already nearly full so it won't draw much more current. I have observed a jump started FFE pumping 47A into a 7v dead 12V battery. Supposedly the DC-DC converter is capable of putting out 150A. I know they did a software update in 2015 that was supposed to fix most of the 12V problems. I'm not sure what it changed but when the car is on the DC-DC converter puts out about 14.5ish volts. I have measured when the car is charging the HVB the DC-DC is putting out 13.5V which I assume is to less aggressively charge the 12V and to supply power for the battery TMS. I did not track the whole charging cycle so I do not know at what point the DC-DC converter turns off.

Triangles - I don't know this for sure, but I would suspect all the 12V devices draw from the battery, and the DC-DC converter only charges the battery. If that converter drove all the 12V devices, there wouldn't be a need for a 12V battery ever.

I think the logic is that ICE components all run off the 12V battery (none run directly off the alternator), and they are using all kinds of off the shelf parts for electric cars. Like why, reinvent the windshield wiper if you can just use the same one from an ICE Focus?

Using Forscan and the OBDII reader, there is a value for a set voltage for charging the 12V battery. I've seen it at different values, but I don't know what the intent would be to change it. I think that the DC-DC is there to charge the 12V battery; however, it will supply current for the 12V devices as well. For instance, if you charge your cell-phone while using it, the current needed to run the phone will come from the charger while the phone battery continues to charge.

The amount of current that the DC-DC needs to provide is proportional to the difference between the set voltage of the DC-DC charger and the state of the 12V battery. If the 12V battery is already close to the DC-DC set-voltage, the current will be small. If the 12V battery is low, then higher current will need to be provided. There are limitations to what the DC-DC can provide, so if the current needed to charge is too great, then the voltage at the DC-DC will drop.

If say the charger is set to 14V and the battery is at 12V, and the resistance in the wiring between them is 0.1 Ohm, then the voltage drop will be 2V and the current will be 20A. As the battery recovers back to 13V, the drop is now only 1V, the resistance is the same, and the current provided is 10A. This is just an example, and there are other resistances at play...like internal resistance in the battery and in the DC-DC circuit itself.

But since the current to charge the battery is going into the battery at the same point that current coming out of the battery to run the car, you can say that the DC-DC converter is the current supply for the on-board electrical equipment.

Although the High Voltage battery could power the whole car without a 12V battery, no one is going to do that yet. You hear all those clicks when you plug the FFE in or before you start the car? That's the car controlling the isolation of the high voltage battery. When sitting idle and not charging, the high voltage battery is isolated for safety...so someone doesn't get electricuted. The 12V system runs the car until the car is started and the DC-DC can provide the current the power the car accessories and motor controller after that...so the 12V is essential to run the car's system when the car isn't running. In addition to that, the battery helps regulate the 12V power from the DC-DC. Not sure how essential that is in this application, but it does at least help some.