Ford BMS Battery Monitoring System: How it Works, How to Properly Charge, How to Power Accessories

[scott011422]

@scott011422

Went to the truck.
"Started it" to get a current reading since the truck was sitting a few hours in the 30'sF

This is where it was when I got home:
(Note that I take a screenshot just as I shutdown because I'm looking for a random severe parasitic draw. Hasn't happened in several days now)

Notice the SOC for both batteries.

12V = 91%
300V = 64% (top of the range with Ford's Hybrid strategy)

So a few minutes ago after about 4.5 hours of truck parked, as I said I started it. Keep in mind almost NOTHING happens when you start a Powerboost, it's in Park, and the HV Battery is at 6X%.

In fact if you turn off Climate and lights and heated seats/wheel, the truck is not going to make a peep, but it's definitely ON because the "Alternator" (DC/DC converter) is doing what an alternator does.

The screenshot above is a couple of minutes after the truck was "running" because the SOC was 87%, not 88%, when I first started it. Also the battery voltage was 13.1, not 14.4. So in the couple of minutes that I took to raise the hood and get a meter on the battery while the truck was on, both the 12V battery voltage and the SOC had increased marginally. Notice the Alternator is providing 47 Amps. (headlights off, climate off)
And whatever 12V Battery Current (the pid) actually is, it's reading 21Amps. Is this amps the battery is supplying? Or is 21 of the 47 amps from the alternator going to recharging the battery? (This is what I REALLY want to know)

So I shut the truck down. Hit the key Fob lock button. Floorboards tucked. Then I realized I left the phone in the truck. Unlocked doors. Zone lighting came on. Floorboards deployed.
I locked it up again. Floorboards tucked. Walked to the front of the truck to put a meter on the battery for you. The truck sensed me again and deployed the floorboards and zone lighting! Dang it. Lol
One more key Fob command and lights out, floorboards tucked.

I PUT THE KEYS in the RV.

Walked to the truck and put the meter on the posts.

12.57V

Why the BMS says it is at 88%?
I don't know.
And I bet if I started the truck it would be 87 or 86 after all my fumbling with lights and floorboards.

Snakebitten
At face value those numbers look good. 90% for an AGM is roughly 12.62. So high 12.5's and high 80's SOC is at least in the ballpark. Your voltage might be a tad high since you "Started" the truck. After any charge is put into a battery its best to let the battery sit to fall down to rest or "Standing" voltage. Rule of thumb for 12v is an hour. Depends how long you charged it. May be worth redoing if you feel like it.

- Pop the hood when you get home so you don't have to wake the truck up more than necessary.
- Let the truck sit for at least an hour. Anything more makes no difference.
- Take battery voltage.
- Now you can use Forscan to check your SOC .

**EDIT**
Snakebitten, looking again at your pictures, It interesting that your first picture shows battery voltage at 12.4v Puts you about 70% SOC
**EDIT**

In looking at other forums and what Pavementends above is showing, 12.3ish volts seem to be where these 2021 and up fords like to sit for full charged. That's far from the 12.73v AGM would like to be at. Its very possible that Ford has at least an "OK" battery, there just abusing it by undercharging. AGM batteries are like the NI-CAD batteries of old power tools. They tend to form memory if not kept fully charged.

In the off chance Ford uses the BMS Reset as a "Tare" or "Zero" for the battery, I fully charged mine last night. Took 4 hours to charge and most of the night to condition, This was after the truck was showing 98% SOC and 12.3v at the battery. This morning I removed the charger and did the manual BMS Reset. When I got to work, (20ish min) Forscan was putting the battery at 100% SOC, 1 Amp of charging and 12.7v on shutdown. I'll keep an eye on it through the weekend.

Its obvious at this point that Ford isn't using the voltage to run the SOC. Maybe initially when the BMS is first initiated at the factory? There has to be something else since alot of us are seeing low voltage at high SOC. And since the charge level drops off, Ford isn't looking at the battery voltage, just the SOC.

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[pavementends]

I fully charged mine last night. Took 4 hours to charge and most of the night to condition,

Curious if you disconnected the battery from the truck first?

I'm finding that if I leave the battery in and connected to the truck and charge overnight ~10 hours my Noco Genius 10 (on AGM setting) still only charges the battery to 12.3-12.4 volts. Would this in itself mean the battery is bad or failing?

 

[scott011422]

Curious if you disconnected the battery from the truck first?

I'm finding that if I leave the battery in and connected to the truck and charge overnight ~10 hours my Noco Genius 10 (on AGM setting) still only charges the battery to 12.3-12.4 volts. Would this in itself mean the battery is bad or failing?

Its hard to say. Did the charge complete? I'm not sure yet how the AUX battery effects the smart chargers. I did leave everything connected because I wanted the BMS to see the charge. Also, the Ford document on charging doesn't say anything about the AUX battery either.

But I'll go on to say its not impossible that the charger didn't see the AUX battery and shut down. I'm not sure if the NoCo will turn itself back on if the voltage drops. Pushing 10 amps the 8AH AUX battery would absolutely charge faster than the 80AH main battery. Charger sees the high voltage and shuts down. Then the voltage leaks back into the lower charged main battery until they stabilize. Only way to be sure would be to pull the battery and charge at room temp.

Really, Ford should be isolating and maintaining that AUX battery until needed. Could be why Ford is charging with Figuring out SOC rather than voltage.

 

[pavementends]

Its hard to say. Did the charge complete? I'm not sure yet how the AUX battery effects the smart chargers. I did leave everything connected because I wanted the BMS to see the charge. Also, the Ford document on charging doesn't say anything about the AUX battery either.

But I'll go on to say its not impossible that the charger didn't see the AUX battery and shut down. I'm not sure if the NoCo will turn itself back on if the voltage drops. Pushing 10 amps the 8AH AUX battery would absolutely charge faster than the 80AH main battery. Charger sees the high voltage and shuts down. Then the voltage leaks back into the lower charged main battery until they stabilize. Only way to be sure would be to pull the battery and charge at room temp.

Really, Ford should be isolating and maintaining that AUX battery until needed. Could be why Ford is charging with Figuring out SOC rather than voltage.

I have a 3.5EB - does my truck have an Aux battery not immediately evident under the hood?

 

[scott011422]

I have a 3.5EB - does my truck have an Aux battery not immediately evident under the hood?

I dont believe so. There should be a battery somewhere if you have propower, But i don't believe thats tied into the main battery.

 

[JCM]

Curious if you disconnected the battery from the truck first?

I'm finding that if I leave the battery in and connected to the truck and charge overnight ~10 hours my Noco Genius 10 (on AGM setting) still only charges the battery to 12.3-12.4 volts. Would this in itself mean the battery is bad or failing?

Follow up to my previous post, I did exchange my Genius 2 for a Genius 5 which should be able to charge up to a 120 Ah battery. It also has a repair mode.

Upon connecting it and setting it on AGM mode it started with the first flashing light indicating 25%. Coming back within an hour it had progressed to green (100%) which the Genius 2 never did. Consistent with pavementends, that was still only 12.3-12.4 V.

I then initiated the Repair mode which forces a higher voltage charge and attempts to repair sulfation, etc. After running the repair mode I set it back on AGM which started again at 25% and when I checked at around 4 hours it was still showing 25% (and less than 12.3 V measured at the battery). After letting it run another 12h overnight the charger was still indicating 25% and my multimeter showed 11.95 V at the battery. Truck started, but not the quickest crank it's done...

I'm sure my battery is in less than great health considering it can't maintain 12V during a cold overnight with a 5A trickle charger attached. That said I think the BMS charging strategy is limiting things (perhaps to ~12.3V in normal charging) which may be damaging or otherwise reducing the battery's ability to maintain a higher level of charge.

 

[pavementends]

I dropped by Les Schwab Tires on the way home just now and they used their battery tester which showed it as a good battery, just like O'Reilly's. Also, and more importantly, theirs read my battery at 12.61 volts, which, in our trucks, sounds to be a healthy/normal charge (albeit lower than the ~13 volts in other vehicle batteries in my experience) and measured 95% of the advertised CCA. I'm considering mine a good battery and moving on from the theory that an undiagnosed failing battery was the cause of my OTA 3.5.3 failing this week. Also also, the Les Schwab guys did say, "yeah, we've definitely replaced batteries in new F-150s recently".

Thanks for your guidance, folks!

 

[Snakebitten]

I've been keeping an EAGLE EYE on the new PID-Package it's starting to become familiar enough that I can at least notice what is noteworthy and reach up for a quick screenshot. Which allows me to capture a screen full of data that I can analyze later when I'm not preoccupied driving.

Anyways, lo and behold I DID catch the "Vehicle Battery Current" (Ford's nomenclature) pid value go negative! -1 Amp, in fact.

It's only momentarily. A few seconds. And then returns to a positive integer, usually in low single digits, but occasionally a short burst of double digits, say 11 amps.

 

[scott011422]

I've been keeping an EAGLE EYE on the new PID-Package it's starting to become familiar enough that I can at least notice what is noteworthy and reach up for a quick screenshot. Which allows me to capture a screen full of data that I can analyze later when I'm not preoccupied driving.

Anyways, lo and behold I DID catch the "Vehicle Battery Current" (Ford's nomenclature) pid value go negative! -1 Amp, in fact.

It's only momentarily. A few seconds. And then returns to a positive integer, usually in low single digits, but occasionally a short burst of double digits, say 11 amps.

SnakeBitten, What was your SOC when that happened?

 

[Snakebitten]

Also I noted that the Battery voltage drops from 14.X as soon as I put the truck in Park. I suspect that the voltage is regulated similar to a traditional Alternator? And so the Battery Charging Strategy in Park is altered.

 

[Snakebitten]

SnakeBitten, What was your SOC when that happened?

I added the screenshot above for clarity

 

[scott011422]

I just went out to check voltages. 12.35 at the battery. "Started" the truck, opened forscan, 98% SOC with no current on the battery at all. Actually went to -1 amp a min before I turned the truck off. So even at 12.35v the truck was very happy with that. Was actually pulling more power out of it.

I also checked at 9:30 and was at 12.49, 100% SOC and no current to the battery.

Truck is going to keep this battery at 12.3ish Volts.

Also, If 12.7 is 100 SOC, How is 12.35 98%???

 

[scott011422]

I added the screenshot above for clarity

My battery voltage just now, running, but in park was also right at 12.7v. Although it was 12.6 in this picture, must not of been that low long, I don't remember seeing it.

 

[Snakebitten]

Correct me if I am wrong, but I think the 2 Battery Current Pids are the reverse of each other.

I know for a fact that the "Hybrid Battery Current (amps)" pid is -integer for charging current, resulting in increased SOC. Regenerative braking can hit as many as -62 Amps and the SOC increases dramatically fast simultaneously.
As soon as you request Torque with the throttle the Amps are a +integer and the SOC is drained from the Hybrid battery.

Because the 12V battery SOC is so much slower to increase/decrease, it's not as easy to perceive the correlation of + or - Battery Current values. But the SOC is increasing while the current is a +integer. So it MUST be the reverse of the High Voltage sister pid.

And that would explain why when you first start the truck, the Battery Current can be 6,8,14 Amps, but just a few minutes later it's 1Amp and stays at 1Amp for substantial amounts of time.
Just like on the ICE trucks discussed here, a 1Amp charge rate is common.

Anyways, I THINK I'm starting to make some sense of things. And if these deductions are true, it's the DC/DC converter (Alternator) running the 12V show once the ignition is enabled.

In the screenshot above, it's 51 Amps.
I can literally increase it by 10 Amps by turning on the seat heater. And another ~10 by turning on the heated steering wheel.
Yet the Battery Current can be completely unaffected.
Again, the +integer is the amps being "absorbed" or "charging" the 12V battery?

 

[scott011422]

SnakeBitten, Yes, The DC/DC converter runs the truck completely. Now it will pull large amps from the battery for a few seconds sometimes. I havent figured out what thats for. But you see it across all the 12v systems. Something big happens once in awhile and the battery has to fill in. I've seen it take 107 amps on one occasion.

I don't know about the HV battery. I apparently dont have that pid open. I would assume + is charging and - is a load but i dont know.

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