12V battery replacement poll

[RLXXI]

On an associated 12 volt battery topic ... I am curious what others have seen regarding the charging current to their 12 volt battery. Using the Car Scanner app on CarPlay, I recorded 43 amps. On another short trip, which I did not record, I seem to remember 72 amps. Has anyone else recorded or observed their charging 12 volt charging amps?

According the the Ford wsm for 25 ym, " Depending on the vehicle and environmental conditions, the DCDC is capable of outputting as many as 260 amps to the 12-volt battery. "

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[chl]

You're overthinking it... (although I just noticed a unit typo in my original post)

The black thingey hooked up to the multimeter is a current transducer which outputs 10mV / 1 A
https://www.velleman.eu/products/view/ac-dc-current-transducer-appa-32-appa32/?id=374622&lang=en

(and yes, I did zero it before I took the measurement)


If you look at the graph below for example, the chaging current tapers off pretty quickly, after 15min you're down from 52A to 7A, in the same timeframe the SoC have gone from 56% to 79% which is about 8-10Ah, which devided by 0.25 (15min) equates to an average of 30Ah during those 15min, which tracks pretty well with what you're seeing.

Hypothetically, lets say I was off by a factor of 10 and the max I've ever seen (100A) is 10A and the norm which is around 20A or less (see my 90day chart, which would only be 2A then), well, in that case we're talking about 2-3 hours to charge from 40% SoC (when the automatic charging kicks in) and we all know it doesn't take that long... (I attached one of those events as well for s-ts and giggles, as you can see, it takes about 45min to go from 35% to 94% SoC, max charge current that time was 80A)

Oh that's the conversion of the ammeter, I see.

Going down to so low an SOC is another negative for the battery lifespan, assuming the current really goes to 52A.

56% of 35Ah = 21Ah and 79% of 35Ah = 27.65Ah so
56% to 79% in 15 min is: 27.65Ah - 21Ah = 6.65Ah in 15minutes, or
6.65Ah / .25h = 26.6A not 52A

Charging an AGM battery with the DC-DC converter's 300W at 26.5A would mean a voltage of 11.32Volts, but AGMs are typically charged at 14V to 15V during the initial bulk stage.

The Ford spec is that the DC-DC converter uses up to 300W for the AGM battery charging from what I read anyway.

Assuming the 300W and the usual 14V-15V, so assume 14.5V would be a max of 20A during the initial bulk stage.

The rule of thumb for a 35Ah AGM would be at the most 30% of the Ah so 10.5A max current.

I really have a hard time accepting the numbers your seeing, because I assume the Ford engineers would not subject a 35Ah AGM battery to such high currents. But if they did, then it is no wonder these batteries are failing so often.

I had thought the failures were more likely due to letting the batteries get too deeply discharged, not because of over-current charging.

And if the Lightning really charges them at such high currents, then why do we so often have OTA failures due to LOW SOC?

IF the Ford Lightning battery gets deeply discharged which 40% would be, then I would expect the Lightning BMS to start with a low current when recovering them. An SOC of 50% or below is a deeply discharged AGM and is not recommended for AGM batteries to begin with.

A deeply discharged AGM should start with a low current at around 10% of its Ah rating. So for this 35Ah battery, about 3.5A.

The changes to the BMS software has elimintated some of the low SOC OTA problems, but please don't tell me it will lead to overcurrent charging problems!

Not over-thinking it, just using industry standard AGM charging specifications which leads me to question those numbers.

They just don't compute with proper engineering.

 

[chl]

According the the Ford wsm for 25 ym, " Depending on the vehicle and environmental conditions, the DCDC is capable of outputting as many as 260 amps to the 12-volt battery. "

I think it means it is available for the 12v systems (outlets etc. for after market items is limited to continuous 55A) and maybe for the other on-board things like AC etc., not for charging the battery - that number has always been 300W, which at 14-15 volts would be at most 20A.

The dc-dc converter "powers all the standard 12-volt vehicle accessories, such as lights, the audio system, wipers, seat adjusters, window motors, locks, and computers. The 12-volt battery also acts as a temporary backup if the converter's output is exceeded..."

Do you see any 4/0 copper wire going to the 12 battery charger? That's the size needed for 260Amps!

And imagine how fast 260A charger would fill up a 35Ah battery?

35Ah / 260A = 8 minutes!

Yea, I think that's a misleading typo.

 

[mr.Magoo]

56% of 35Ah = 21Ah and 79% of 35Ah = 27.65Ah so
56% to 79% in 15 min is: 27.65Ah - 21Ah = 6.65Ah in 15minutes, or
6.65Ah / .25h = 26.6A not 52A

Well, I did ballpark an average of 30A, so there's that, we're really not that far apart.
The 52A is a snapshot in time, it's whatever the value is at the time the reading is taken, no one ever claimed it was continous, in fact, I even mentioned that it tapers off pretty quickly.

IF the Ford Lightning battery gets deeply discharged which 40% would be, then I would expect the Lightning BMS to start with a low current when recovering them.

Here's a 0% >> 100% cycle from when I learned the hard way that leaving the truck in neutral somehow doesn't shut the truck off and drains your battery. If we focus on the first hour, and add an average calculation, you can see that the average current during that hour is 16.3A and the SoC at the end of it is 55% and while 16.3A isn't 55% of 35Ah I'd personally say it's close enough to where the numbers seem accurate. And in that instance you have a peak current of 35A.

A deeply discharged AGM should start with a low current at around 10% of its Ah rating. So for this 35Ah battery, about 3.5A.

I don't know what to tell you except that it doesn't. (see charts)

The changes to the BMS software has elimintated some of the low SOC OTA problems, but please don't tell me it will lead to overcurrent charging problems!

As stated before,if my data is correct (which I belive it is) they've actually reduced the charge current, so while it still may be (probably is) a contributing factor to the relative short life span, it's actually been improved.

Not over-thinking it, just using industry standard AGM charging specifications which leads me to question those numbers.

They just don't compute with proper engineering.

With proper engineering there would never be any recalls, now would there ? ;-)

While I don't disagree with you, I also have no reason to belive my numbers (well, they're not really mine, they're from the truck) are incorrect, so that can only lead to the conclusion that Ford isn't following charging specifications / reccomendations.

 

[chl]

Well, I did ballpark an average of 30A, so there's that, we're really not that far apart.
The 52A is a snapshot in time, it's whatever the value is at the time the reading is taken, no one ever claimed it was continous, in fact, I even mentioned that it tapers off pretty quickly.



Here's a 0% >> 100% cycle from when I learned the hard way that leaving the truck in neutral somehow doesn't shut the truck off and drains your battery. If we focus on the first hour, and add an average calculation, you can see that the average current during that hour is 16.3A and the SoC at the end of it is 55% and while 16.3A isn't 55% of 35Ah I'd personally say it's close enough to where the numbers seem accurate. And in that instance you have a peak current of 35A.

I don't know what to tell you except that it doesn't. (see charts)




As stated before,if my data is correct (which I belive it is) they've actually reduced the charge current, so while it still may be (probably is) a contributing factor to the relative short life span, it's actually been improved.



With proper engineering there would never be any recalls, now would there ? ;-)

While I don't disagree with you, I also have no reason to belive my numbers (well, they're not really mine, they're from the truck) are incorrect, so that can only lead to the conclusion that Ford isn't following charging specifications / reccomendations.

I think the current that is being measured and reported on the graphs is MORE than just the battery charging current.

If the truck is ON, then there are all kinds of other 12V systems running, battery and converter cooling, the computer, etc. and they are being power through that line you have you ammeter on. Even when the truck is off, some 12v systems are running (computer charge timer for example).

How much of the 12v system's current is being used to charge the battery though?

Well, the BMS is controlling that and it seems that the ammeter is down stream of the BMS in the picture.

The question is how much current is the BMS passing through to the battery though?

One of the functions of the BMS is to control the charging current that gets to the battery. It limits the amount of current getting into the battery from the DC-DC converter so that the battery is not overhcharged.

Some portion of that graph of the current in the 12V system is getting through the BMS to charge the battery, but not 70A, in my opinion.

The specs say the system uses a max of 300W for the 12v battery charger.

----from a search but consistent with what we know----

Functions of the 12V BMS

• Monitors the battery: The BMS continuously tracks the 12V battery's voltage, current, and temperature to ensure safe operation.
• Protects the battery: It prevents overcharging and over-discharging, which can damage the battery and shorten its lifespan.
• Integrates with the high-voltage battery: The BMS can automatically draw power from the high-voltage (HV) battery to recharge the 12V battery when needed. This happens when the 12V battery's state of charge drops below 30% (immediately) or 40% (after a 48-hour delay).
• Manages charging: The BMS controls the DC-DC converter to charge the 12V battery when the truck is running or plugged in.
• Performs load shedding: If the 12V battery's charge is critically low and the truck is off, the BMS may reduce or shed power to non-essential accessories to conserve energy for starting the vehicle.
• Allows for manual reset: After a 12V battery replacement or disconnection, the BMS requires a manual reset to prevent false low-battery warnings

----
Anyway we have gotten a bit off-topic.

Last point: Anybody who wants their 12v AGM battery to last, will get a trickle charger with an AGM mode and keep the AGM battery at 100% when the truck is not being driven.

A $30-$40 trickle charger is a lot less expensive than a new battery out of warranty, not to mention the inconvenience of being stranded somewhere with no juice.

 

[RLXXI]

I think it means it is available for the 12v systems (outlets etc. for after market items is limited to continuous 55A) and maybe for the other on-board things like AC etc., not for charging the battery - that number has always been 300W, which at 14-15 volts would be at most 20A.

The dc-dc converter "powers all the standard 12-volt vehicle accessories, such as lights, the audio system, wipers, seat adjusters, window motors, locks, and computers. The 12-volt battery also acts as a temporary backup if the converter's output is exceeded..."

Do you see any 4/0 copper wire going to the 12 battery charger? That's the size needed for 260Amps!

And imagine how fast 260A charger would fill up a 35Ah battery?

35Ah / 260A = 8 minutes!

Yea, I think that's a misleading typo.

Typo's are a very real possibility but in this case, I think it's just Ford electrical engineers know a little more about it than you think you do.

 

[mr.Magoo]

I think the current that is being measured and reported on the graphs is MORE than just the battery charging current.

How much of the 12v system's current is being used to charge the battery though?

Well, the BMS is controlling that and it seems that the ammeter is down stream of the BMS in the picture.

The question is how much current is the BMS passing through to the battery though?

One of the functions of the BMS is to control the charging current that gets to the battery. It limits the amount of current getting into the battery from the DC-DC converter so that the battery is not overhcharged.

Unlike voltage (that drops with distance and more) current can't just dissapear, or go anywhere else (unless there's a branch downstream of course).

AI in your searches seem to think that you're talking about BMSystem, but the BMSensor on the battery is just that, a sensor, it's not a "valve" that adjusts the flow of current like a faucet, it's just a current sensor, so measuring before or after the sensor makes no difference.

In the case of that cable / sensor, the current either goes TO the battery (i.e. charging, positive value) or it goes FROM the battery TO the vehicle (consumption, a , negative value). Normally the truck (and with that the DC/DC) is ON and in that case the DC/DC charger/power supply takes care of the consumption which is why you rarely see a negative value with the DC/DC / Truck on.

The specs say the system uses a max of 300W for the 12v battery charger.

I'm wondering where you got that information from ? My guess is here.
That's talking about the "emergency" charge and it's 300W - hours - or basically 20Ah (or there abouts) but it doesn't say anything about max charging current/wattage, 100A for 10min and then 3A the remaining 50min will also achive 20Ah or 300 Wh.

If you're interested, the same document talks about how the BMSensor is connected to the BCM and how all that works (component description on page 6)

Anyway we have gotten a bit off-topic.

Agreed, this will be the last from me on the subject in this thread.

 

[NW Ontario Ford Lightning]

Interesting thread:
clearly we hear of problems with the 12v AGM batteries from members, resulting in issues such as the truck missing or not finishing an OTA update, or some operational issue at start up, or in some cases a member reports not being able to operate the door locks/start the truck due to low AGM SOC.

This indicates a problem with the 12v battery management - but what is the problem exactly?:
1) does the system allow the 12v SOC to drop to very low unacceptable values resulting in shortening the battery life;
2) or does the system use excessively high charging current that shorten the AGM battery life.
3) or does it do both.

In practical terms, does it really matter which is the cause? The AGM batteries are "happy" to be left at 100% SOC without life-shortening consequences, why not trickle charge them?

What is the potential harm in adding a 12v AGM trickle charger ?

 

[Lytning]

Hello, Brian, not AI, @Ford Motor Company,

Can you find out and inform us what the maximum charge rate is to the 12 volt battery in our Lightnings?

Thank you,

Steve

 

[EVpower]

I am 28 months into the OEM low voltage battery and have had several battery tests reports recently indicate weak-recharge. What is Fords standard for test results which would call for a warranty replacement of the LV battery?

I'll add that when I have checked the charging current it has been about 40 amps. That does seem high for a 35 AH AGM battery based on the general industry recommendations.

Steve

 

[chl]

Unlike voltage (that drops with distance and more) current can't just dissapear, or go anywhere else (unless there's a branch downstream of course).

AI in your searches seem to think that you're talking about BMSystem, but the BMSensor on the battery is just that, a sensor, it's not a "valve" that adjusts the flow of current like a faucet, it's just a current sensor, so measuring before or after the sensor makes no difference.

In the case of that cable / sensor, the current either goes TO the battery (i.e. charging, positive value) or it goes FROM the battery TO the vehicle (consumption, a , negative value). Normally the truck (and with that the DC/DC) is ON and in that case the DC/DC charger/power supply takes care of the consumption which is why you rarely see a negative value with the DC/DC / Truck on.


I'm wondering where you got that information from ? My guess is here.
That's talking about the "emergency" charge and it's 300W - hours - or basically 20Ah (or there abouts) but it doesn't say anything about max charging current/wattage, 100A for 10min and then 3A the remaining 50min will also achive 20Ah or 300 Wh.

If you're interested, the same document talks about how the BMSensor is connected to the BCM and how all that works (component description on page 6)





Agreed, this will be the last from me on the subject in this thread.

Thanks for the linked document. I had seen the "300Wh" written as 300W in another Ford document or video which seems to have been an error.

Yes, nowhere does that document specify the charging current.

If we assumed the standard max current of 30% of 35Ah, a charging current of 10.5A, and a standard AGM charging voltage of 13-15 volts, say 14V, then that's about a 2 hour charge session to add the 30Wh or energy: 14V x 10.5A = 147W; 300Wh / 147W = 2.04 hours.

That does not seem unreasonably long to me.

Of course, that passage you linked me to is talking about a situation where the battery is at 40% or lower. With that low an SOC, my understanding is one would want to start with a lower current to avoid damaging the battery.

The document you linked to says about the BMS:

The Battery Monitoring is clamped directly to the negative terminal of the battery and grounds to the vehicle at the chassis ground connection point through the negative battery cable and eyelet. It is part of the negative battery cable and cannot be serviced separately....
Should the battery need to be isolated, this should be done by disconnecting the ground
eyelet at the chassis ground.

While that is not particularly clear, I had seen something like that in another Ford document, and it sounded to me like it was saying the BMS is in series between the negative terminal and the truck ground via the ground eyelet. That led to my assumption, which I admit may be wrong, that the BMS did act like a 'valve' as you put it to control the charge current since it seems to connect the battery negative post to the rest of the 12v system via the eyelet, which would include the DC-DC converter.

The BMS is part of a system that regulates the 12v battery charging. That would be done by controlling the charging current and voltage one way or another. It is not unheard of for a sensor to also be a switch ("valve") to control what it is sensing.

Without a wiring diagram or clearer language, I cannot be sure however how that charging control is accomplished.

However it works, it seems to me that those large current levels (70A for example) in the graph would have to be the DC-DC converter current powering the rest of the 12V system (computer, cooling pumps, etc.) which were on at the time the measurement was taken, since it is hard for me to imagine a 70A charging current for the 12v battery.

If we find out from Ford that they are, in fact, using a 70A charging current, then keeping the battery topped off with a more reasonable current level from a trickle charger would be all the more important for long battery life.

 

[mr.Magoo]

Sorry, just one more, since I decided to repeat my "mistake" from earlier this year in the name of science.

If you leave the truck in neutral it'll only partially shut off after the 30min timer, but somehow it remains in neutral and all the electronics is still alive, effectively draining your 12V battery, and fast.

As you can see on the orange line (battery current) it's being "topped off" with 1A, the rest of the vehicle power (12V) consumtion is supplied by the DC/DC converter ~29-30A.

When the vehicle shuts off, around 3.35pm, you see the orange line drop to -31A because power is now drawn from the battery, and similarly you can see the green line drop to 0A because the DC/DC converter is now OFF.

At 4pm SoC have already reached 30% and I rush outside and start the truck back up and set up my multimeter / clamp meter. And as you can see the clamp meter is registering 72A and the Truck is saying it's 69/70A, you can also see the 12V side of the DC/DC converter jump to 100A, 30 for the truck (as per before) and 70A to the battery.

20min later the current is down to a more sensible 9A and SoC is back up to 75%

 

[bmwhitetx]

@chl The BMS (sensor) monitors the current through it and reports that along with temperature and battery age to the BCM via the LIN bus. The BCM then provides the PCM with a SOC and the PCM decides a voltage setpoint for the DC-DC converter (e.g., I've seen 13.7V and 14.4V) which affects how fast or slow the battery will charge (accept current). The SOBDMC also gets involved.

There is not a specific charging current. If Brian says a single number, he's wrong. The current varies and dependent on the voltage the DC-DC has been instructed to provide and other 12V loads. It doesn't provide a constant current. But the BMS tells the system the current flowing in and out of it - and by the PCM adjusting voltage then current can be somewhat regulated in and out of the battery. I see you're also an EE - think KVL, KCL, Ohm's law.

I have taken a BMS apart - it has a microprocessor so its doing some calculations. There is definitely no switch, valve, contactor, etc. It has a current sensor (Hall Effect?) built into the plastic between the input and output lugs.

You might want to spend $29 on a 3-day subscription to PTS. The Service manual has wiring diagrams, system operation description, etc. Much better source than any AI.

PICS: LIN bus and battery positive enter from two pins on upper right. My best guess is current sensor and battery negative are present on the three large pins on the left.

 

[chl]

@chl The BMS (sensor) monitors the current through it and reports that along with temperature and battery age to the BCM via the LIN bus. The BCM then provides the PCM with a SOC and the PCM decides a voltage setpoint for the DC-DC converter (e.g., I've seen 13.7V and 14.4V) which affects how fast or slow the battery will charge (accept current). The SOBDMC also gets involved.

There is not a specific charging current. If Brian says a single number, he's wrong. The current varies and dependent on the voltage the DC-DC has been instructed to provide and other 12V loads. It doesn't provide a constant current. But the BMS tells the system the current flowing in and out of it - and by the PCM adjusting voltage then current can be somewhat regulated in and out of the battery. I see you're also an EE - think KVL, KCL, Ohm's law.

I have taken a BMS apart - it has a microprocessor so its doing some calculations. There is definitely no switch, valve, contactor, etc. It has a current sensor (Hall Effect?) built into the plastic between the input and output lugs.

You might want to spend $29 on a 3-day subscription to PTS. The Service manual has wiring diagrams, system operation description, etc. Much better source than any AI.

PICS: LIN bus and battery positive enter from two pins on upper right. My best guess is current sensor and battery negative are present on the three large pins on the left.

Thanks.

Yea, I dug in to the whole thing a little deeper and see I had assumed a couple things that did not pan out.

The BMS sensor is just a sensor/calculator giving the rest of the battery control system the information needed to control 12v battery charging, so it does not act as a valve/switch,

There are several components involved, and the thingy that charges the 12v battery is the DC-DC Converter Control Module (CCM).

I haven't found a lot of detail about the wiring, but I threw together a block diagram of what I could discern from the Ford docs. I stuck the text into the image (with some corrections for spelling - like battery was spelled 'batter' sometimes):

If the charging voltage is 14.4v and if the measured charging current is really high, that's a sign of a badly depleted battery (the lower the SOC the higher the charging current).

And it is also a sign that Ford did not put any (enough) current limiting circuitry in the charging system, which is...bad. High currents will ruin an AGM over time permanently. Maybe it's an issue with the BMS sensor.

Like I've mentioned before, as I understand it, the maximum recommended charging current for an AGM is generally 30% of the Ah rating. So those currents others are reporting, if really just the charging current, are a bad sign.

I'd like to see a wiring diagram some day - I'm curious about how the DC-DC CCM is wired to charge the battery per the description I read. Is there a separate charge path or does the whole DC-DC converter output voltage rise to charge the battery?

This was the description I used for the block diagram taken from a document that was linked above somewhere:
----

12V Battery Charging System

The 12V battery is charged by the DC-DC converter control module. The Battery Management System (BMS) continuously monitors the battery state of charge condition and provides the BCM with this information. The BCM communicates this information to the PCM over the HS-CAN1. The PCM communicates the battery desire setpoint to the DC-DC converter control module which supplies the necessary charge voltage to the 12V battery....

Battery Monitoring Sensor
The Battery Monitoring Sensor continuously monitors the conditionand state of charge of the 12V battery and provides the Body Control Module (BCM) with this informatinon. The Battery Monitoring Sensor also estimates losses in the battery capacity over time.

The Battery Monitoring Sensor is clamped directly to the negative terminal of the battery and grounds to the vehicle at the chassis ground connection point through the negative battery cable and eyelet. It is part of the negative battery cable and cannot be serviced separately....the battery need to be isolated, this should be done by disconnecting the ground eyelet at the chassis ground.

Body Control Module (BCM)
The Body Control Module (BCM) monitors the Battery Monitoring Sensor and provides the Powertrain Control Module (PCM) with battery state of charge information.

Powertrain Control Module (PCM)
The PCM provides desired voltage set point to the DC-DC converter control module.

Direct Current-Direct Current (DC-DC) Converter Control Module (CCM)
The DC-DC converter control module is responsible for maintaining and charging the 12V battery. It is enabled when the high voltage battery contactors have closed, providing high-voltage power to the DC-DC converter control.

---
Whatever happened to keeping things simple, eh?

 

[mr.Magoo]

Seems to me they'd be much better off going with a 65Ah battery instead and bumping the "emergency" threshhold to, say, 70% SoC. It would achive the same results with less wear and more reserve capacity. I doubt weight savings is a thing on a 7000lbs vehicle and cost difference would be neglible, especially if you account for having to replace a bunch of batteries under warranrty.

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