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

[KTM753]

Every time I think I understand something on this truck, the rabbit hole gets deeper. Thanks!

Always!

Windows built in calculator has a programming option that converts integers (whole numbers) into hex if you want to see different values for SOC options.

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[HammaMan]

I have changed mine to the hex for 94%. My 12v SOC is always 100%(or hits it within a few minutes of starting, the underhood batt is 100%, the aux batt is not, throwing off the 12v's SOC as it's a combination of both batts in the PB).
My voltage with the fan 5 trick (hybrid/EV only) is 14.3v (+/- .3/1.1, measured at 10ms intervals, no smoothing)

 

[KW58]

I have changed mine to the hex for 94%. My 12v SOC is always 100%(or hits it within a few minutes of starting, the underhood batt is 100%, the aux batt is not, throwing off the 12v's SOC as it's a combination of both batts in the PB).
My voltage with the fan 5 trick (hybrid/EV only) is 14.3v (+/- .3/1.1, measured at 10ms intervals, no smoothing)

I’ve seen where you were experimenting with a lithium aux battery, you still running that setup or back to AGM? I’ve wondered about the parallel setup throwing off SOC values, I may have to isolate the two LV batteries from eachother to get resting voltages and see if it’s my under hood or under seat battery that’s actually the weak one.
The other day when I got to 85% for the first time I’ve noticed and the DC/DC voltage dropped down in the 13s I tried your fan trick…what an oddity but pretty cool.

 

[HammaMan]

I’ve seen where you were experimenting with a lithium aux battery, you still running that setup or back to AGM? I’ve wondered about the parallel setup throwing off SOC values, I may have to isolate the two LV batteries from eachother to get resting voltages and see if it’s my under hood or under seat battery that’s actually the weak one.
The other day when I got to 85% for the first time I’ve noticed and the DC/DC voltage dropped down in the 13s I tried your fan trick…what an oddity but pretty cool.

Yes, I still have the LFP in the truck. The SOC value is a combination of all batteries in the truck if wired to where the CT/shunt can see them. With the LFP in place the SOC value is moot as the truck gets back to 100% very quickly as the LFP eats current as it's being monitored from the current transformer the aux batt's negative cable. The AGM batteries are always at 100%. The SOC value only sees the missing energy from the LFP, which replenishes quite quickly. Truck has been sitting for about 37 hours now and the batt voltage is pretty much 13.3

 

[KW58]

@KW58 Take a look at this post. The hex value for 22' & 23' might be different than 21'.

https://www.f150gen14.com/forum/threads/new-battery-h7-or-h8.21266/post-424022

Text I was referring to:

"Changes made. While updating the SOC at 726-08-02 I had a thought. Stock value was 05 00, which in hex is 1280. The spreadsheet shows that this value is divided by 16 to give you 80. 05 A0 is 1440, divided by 16 is 90. Are we sure this is a percentage, rather than target voltage to the hundredths place? ie 1280 = 12.80V, 1440 = 14.40V. Not that this change has seemed to do anything, but where is the division by 16 coming from?"

I went back and looked at some asbuilt data that I saved a couple months ago and I had the same 0500 in those bits. Will take a look to make sure it hasn't changed with some update the truck has received since then next time I have the truck hooked up to forscan.

 

[Hyins]

There are three BMS config in BCM, I recommend setting to

TargetSOC_Cfg: 726-08-02 xxxx xx07 80--
0780=120%, the value from 2020+ Police Interceptor Utility with AGM H8 and 2021+ F-150 Police

RegenFunctionActive_Cfg: 726-07-02 xxxx x0xx xx--
RegenFunctionActive means Ford Smart Regenerative Charging, in PIU it was 0=disabled

RefreshFunctionActive_Cfg: 726-07-01 xxxx x1xx xx--
RefreshFunctionActive means SRC battery refresh phase, it was 1=enabled by default

Edit:
about SRC
https://www.motor-talk.de/forum/aktion/Attachment.html?attachmentId=749293

and see attached .pdf from Ford

 

[MLCRNMedicTX]

Howdy, All! I wanted to give an update after changing the Forscan values to the ones mentioned by Hyins. I have been running this way for one week and am happy with the results. I, too, was disappointed with the factory BMS strategy and wanted to maintain my battery in a fully charged state. Therefore, I bought a new EverStart AGM Platinum H8 and changed the Forscan settings to conventional charging and a SOC at 120%, followed by a BMS reset. I also rebooted the BCM. I did get the low SOC and brake error warnings due to low voltage even after the reboots and clearing the DTCs; however, after setting overnight, all was back to normal with no errors upon starting the next morning. Since then, I have had no issues, and the truck charges all the way back to a SOC of 100% while running and then trickles at around 1-2 amps to maintain full charge. The resting voltages are right around 12.7 volts after sitting overnight. Thanks again, Hyins, for the recommendation. Try it out and let us know your results. I will post back here if any issues pop up.

 

[scott011422]

Anyone do this to a PowerBoost yet?

 

[Calson]

Going above 95% SOC is going to shorten the battery life. The problem is that Ford needs to use two batteries and a higher output alternator to meet the electrical demands of the truck. I had this with my diesel powered pickup and it worked.

FLAT and AGM batteries should not be discharged below a 50% SOC. They are not designed to be deep cycle batteries but the poor Ford BMS treats them as such.

My truck battery was at 4% SOC when the BMS kicked in and started limited functions. I bought an Optima H7 battery that is more like a marine battery that can do light discharges as well as function as a starter battery.

My XLT trim level truck came with the smaller H6 battery for god knows what reason. $65,000 for a truck and it has the lower capacity battery. Greed knows no limits.

 

[PaulGrun]

Just to repeat myself a bit - especially for those who are tweaking the Target SOC value using Forscan, be aware of the Law of Unintended Consequences.
As an engineer myself, I can safely say that virtually every design parameter represents a trade-off of some sort. In this case, it is unlikely that the stock Target SOC value of 80% was chosen at random. Without a doubt it represents a tradeoff of some sort. The problem is that none of us knows what those tradeoffs might have been. However the link posted just a few comments above hints at some possibilities - one is a requirement to provide excess charge capacity and another is to account for the need for refresh cycles to avoid excess sulfation of the plates.
I really don’t know the reasoning behind either one, but then again none of us do.
I am NOT saying that the engineers got it just exactly perfect when designing the system and we already know that Ford has released at least one OTA update to tweak the system. I wouldn’t discourage anyone from monkeying around with his/her truck; just pointing out that none of us are playing with a full deck, hence the point about unintended consequences.

 

[Snakebitten]

Just to repeat myself a bit - especially for those who are tweaking the Target SOC value using Forscan, be aware of the Law of Unintended Consequences.
As an engineer myself, I can safely say that virtually every design parameter represents a trade-off of some sort. In this case, it is unlikely that the stock Target SOC value of 80% was chosen at random. Without a doubt it represents a tradeoff of some sort. The problem is that none of us knows what those tradeoffs might have been. However the link posted just a few comments above hints at some possibilities - one is a requirement to provide excess charge capacity and another is to account for the need for refresh cycles to avoid excess sulfation of the plates.
I really don’t know the reasoning behind either one, but then again none of us do.
I am NOT saying that the engineers got it just exactly perfect when designing the system and we already know that Ford has released at least one OTA update to tweak the system. I wouldn’t discourage anyone from monkeying around with his/her truck; just pointing out that none of us are playing with a full deck, hence the point about unintended consequences.

I have great respect for this point of view.
But I also believe that the OEM has no choice but to set parameters and strategies for a hypothetical use case. Or put another way, they had to choose some estimated range of hours running per day/week, for example.
I do think the original charging strategy was sufficient for a constantly driven truck, but was way too conservative for those on the other end of the spectrum. And I think the forum has well documented the impact and shortcomings.

Having said that, the new charging strategy, at least on my Powerboost, is a fairly dramatic shift. I wouldn't call it a tweak by any means. It's fairly aggressive by comparison.

Which brings up my final point. I agree with you that someone should use some degree of caution if all they are going to do is edit Asbuilt values without monitoring the necessary PIDs to witness the affects of any changes made. I personally do not want 100% SOC, nor would I do anything to assist my truck in aiming for that.

 

[Henfield]

Not knowing how long Ford Factory batteries last I took a look at the H7 and H8 AGM batteries from Walmart. There is a 50 cca (850-900) difference between the two. That seems minimal to me......
Is that worth it?

 

[PaulGrun]

I have great respect for this point of view.
But I also believe that the OEM has no choice but to set parameters and strategies for a hypothetical use case. Or put another way, they had to choose some estimated range of hours running per day/week, for example.
I do think the original charging strategy was sufficient for a constantly driven truck, but was way too conservative for those on the other end of the spectrum. And I think the forum has well documented the impact and shortcomings.

Having said that, the new charging strategy, at least on my Powerboost, is a fairly dramatic shift. I wouldn't call it a tweak by any means. It's fairly aggressive by comparison.

Which brings up my final point. I agree with you that someone should use some degree of caution if all they are going to do is edit Asbuilt values without monitoring the necessary PIDs to witness the affects of any changes made. I personally do not want 100% SOC, nor would I do anything to assist my truck in aiming for that.

I agree in all respects, particularly that Ford was/is compelled to find a happy medium which in all likelihood satisfies no one. The corollary is that it’s almost certainly true that there is a set of parameters which would be “more optimal” for any particular given owner.
Unfortunately, however, it’s nearly impossible for us to know what that set of parameters is, nor what other unseen side effects may be impacted by tuning the charging strategy. For example, we can certainly observe the difference in e.g. resting voltage or resting SOC. But what we can’t see, for example, is any possible impact on e.g. battery longevity.
Truth in advertising - I’m one of the lucky ones who hadn’t had any significant battery/electrical problems, despite the fact that my driving profile is probably as hard on a battery as it’s possible to be (80% of my trips are less than 5 miles).
Given the lack of issues I’ve faced seems to lend credence to the ‘bad batch of batteries’ theory. Which is the only thing I can think of as to why some folks have significant problems and others don’t.
Still, I strongly agree with your points.

 

[bhamilton]

Hey Everyone,

Hoping y'all can help me figure out what I need to do here.

I started getting the 12v state of charge low errors a couple weeks ago. I work from home, so most weekdays, my only driving is to and from Starbucks in the morning. Tossed my battery charger on (which is also a maintainer) per the recommendation in the youtube video, but fairly quickly it reported the battery was charged and switched over to maintainer mode and stopped charging. Checked my SOC using OBDII and it only reported ~48%. Performed a BMS reset and now it reports in the 70s but I can't get past 78%. Drove the truck almost all day today and it still only got to 78%. I had hit 80% a few days ago but it quickly went back down and hasn't gotten back since.

Do I need to disconnect the in-cab battery and then charge the under-hood one?
Do I need to do the opposite of above?
Do I need a new battery?
Do I need to get a manual battery charger where I tell it when to stop charging?

I've got an OTA update that won't load because of this (23-PU1009-SS-NS)

Thanks for your advice!

 

[Kodiak]

I agree in all respects, particularly that Ford was/is compelled to find a happy medium which in all likelihood satisfies no one. The corollary is that it’s almost certainly true that there is a set of parameters which would be “more optimal” for any particular given owner.
Unfortunately, however, it’s nearly impossible for us to know what that set of parameters is, nor what other unseen side effects may be impacted by tuning the charging strategy. For example, we can certainly observe the difference in e.g. resting voltage or resting SOC. But what we can’t see, for example, is any possible impact on e.g. battery longevity.
Truth in advertising - I’m one of the lucky ones who hadn’t had any significant battery/electrical problems, despite the fact that my driving profile is probably as hard on a battery as it’s possible to be (80% of my trips are less than 5 miles).
Given the lack of issues I’ve faced seems to lend credence to the ‘bad batch of batteries’ theory. Which is the only thing I can think of as to why some folks have significant problems and others don’t.
Still, I strongly agree with your points.

Sadly I think there were a bad batch of batteries that was added to the variables just to mess up everyone's analysis.

My truck was built the end of August 2022 and did not ship to Granger until the middle of December 2022. I picked it up the end of December 2022 so I have had this truck 17 months and have only driven it 4300 miles. 1150 miles was getting home to VA from Granger. This truck can easily sit for over a week without being driven. When I do drive it is usually under 15 miles and is often stop and start most of the way. I have only had 1 instance of the OTA update failing and after charging the battery the OTA went through the next night. I know I am one of the lucky ones that just must have gotten a good battery.

With that said I do wish Ford would add "built in" tools to monitor the PID's on the main screen so people with the knowledge could make tweaks and understand what affects those tweaks are having. An engineer's "happy medium" may work for most but having a tech wonderland on wheels lets people do so much more. I understand why they do not want Gobber to have the incentive and the tools to muck up the system and then blame the truck, but that could be covered in warranty language. A lot of knowledgeable people could really do a lot of good.

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