Calling all electrical experts- strange charging behavior

[SheepDog]

Again, this sounds like normal behavior controlled by the BMS. It's a feature, not a bug. If you were seeing consistently higher readings with your old battery, it might have been due to the deteriorating condition of the battery.

Normal to switch back and forth with throttle input? Maybe a volt or so, but to drop down to 12 volts (which isn't even the voltage of a healthy battery) seems concerning to me. Im wondering if the display voltage is system voltage, and the reason I see 12 volts instead of say, 12.5 or 12.8 ( a healthy battery) is because the car and fuel system etc. are drawing on the battery with no output from the alternator. I'd have to have a multi-meter hooked up to the alternator during this event to confirm.

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[SheepDog]

You could discharge your battery and go drive around to see how it behaves, I will bet money on it staying on higher voltage more often. Maybe constantly, till it’s happy about SOC.

Good idea. Or, as blueflash mentioned, I could disconnect the BMS sensor and see if the alternator just cranks out a consistent 14.5 volts. This would eliminate the alternator being the problem, and tell me that the BMS system is just trying to cut power in the event of full battery (and possibly creating a lean situation at WOT because the pumps are only running on battery voltage, instead of the 13.5 they are designed for)

 

[Mike Pfeifer]

Also, something to consider, these systems don’t just monitor current in and out. They also monitor temperature of the battery (as best as can be determined from the negative post, anyway). This is used to determine state of charge (SOC) and state of health (SOH). And they will use this data to vary the alternator output to most efficiently get the battery back to where it should be (greater or equal to 80% SOC generally). So you will see different results with cold or hot batteries.

 

[Farkel]

It sounds like the only way to answer your concerns would be to check the voltage going to the aftermarket parts. If it's not sufficient, maybe you could adjust it using Forscan. I'm just speculating here...

 

[SheepDog]

Also, something to consider, these systems don’t just monitor current in and out. They also monitor temperature of the battery (as best as can be determined from the negative post, anyway). This is used to determine state of charge (SOC) and state of health (SOH). And they will use this data to vary the alternator output to most efficiently get the battery back to where it should be (greater or equal to 80% SOC generally). So you will see different results with cold or hot batteries.

Thanks. Still though, the direct correlation between manifold vacuum and voltage seems strange. Not to sound like a parrot, but when this 12 volt event occurs and sitting at a stop light, I can rev the motor and the display shows 12 volts no matter the engine speed. Only when the car is moving down the road, in gear, but 0% throttle do I see 14.5 volts. the moment I barely touch the accelerator, drops to 12. I can make it jump back and forth 12 - 14.5 - 12 - 14.5 with just a touch of the accelerator, but only in gear. If the transmission is in neutral, I can rev the motor and it stays at 12 volts

 

[SheepDog]

It sounds like the only way to answer your concerns would be to check the voltage going to the aftermarket parts. If it's not sufficient, maybe you could adjust it using Forscan. I'm just speculating here...

What adjustments are available in Forscan for alternator output? I want the BMS system to function, but dropping to 12 volts would mean to me that the car is pulling from the battery only, and the alternator isn't doing anything during these events.

 

[Farkel]

What adjustments are available in Forscan for alternator output? I want the BMS system to function, but dropping to 12 volts would mean to me that the car is pulling from the battery only, and the alternator isn't doing anything during these events.

I don't know exactly what settings you could change through Forscan, but I do remember reading that the battery is basically only used to start the engine; after that, the alternator is sending the juice to all the electrical components.

 

[SheepDog]

I don't know exactly what settings you could change through Forscan, but I do remember reading that the battery is basically only used to start the engine; after that, the alternator is sending the juice to all the electrical components.

Which is why it's even more strange that the output would drop to 12 volts. Furthermore, I would think that if the system is seeing a higher draw (AC on, seat coolers on, radio on, fuel pumps pulling, high beams on) it would then tell the alternator to increase output, but it doesn't. I can switch every electrical load in the car on, and its still does this.

Only when I let off the throttle, do I see the display showing more than 12 volts. I don't even know if the alternator is actually outputting anything during this event. The display may just be showing 12 volts because the battery is still in the game.

 

[Farkel]

Which is why it's even more strange that the output would drop to 12 volts. Furthermore, I would think that if the system is seeing a higher draw (AC on, seat coolers on, radio on, fuel pumps pulling, high beams on) it would then tell the alternator to increase output, but it doesn't. I can switch every electrical load in the car on, and its still does this.

Only when I let off the throttle, do I see the display showing more than 12 volts. I don't even know if the alternator is actually outputting anything during this event. The display may just be showing 12 volts because the battery is still in the game.

I don't mean to be spliiting hairs, but I believe the voltage shown in the dash display with engine running is only what's going to the battery, not what's being used to power any of the car's components or accessories. The spike when you let off the throttle is normal for the BMS.

 

[Mike Pfeifer]

I think you’re gonna have to get a volt meter connected to see what’s actually happening. But it seems like the alternator is at least capable of full output when commanded to do so. So that leaves the logic on how that’s commanded, which is going to be the biggest mystery of all, unfortunately. It just seems like about once a month there is someone on here replacing batteries and alternators trying to “fix” this problem.

 

[Farkel]

I have nothing else to contribute to this conversation, so I'll leave it with this - if you (Dax) are experiencing issues with fuel delivery or anything else as a result of the voltage fluctuations, they need to be addressed. Otherwise, we're talking about solutions in search of a problem.

 

[SheepDog]

I have nothing else to contribute to this conversation, so I'll leave it with this - if you (Dax) are experiencing issues with fuel delivery or anything else as a result of the voltage fluctuations, they need to be addressed. Otherwise, we're talking about solutions in search of a problem.

Could be, I've just never seen it do this up until about 2 weeks ago. I always had consistent voltage on the display when the engine is running. 13-14.5 volts no matter what.

I will get a log and see if fuel pressure is dropping as a result of this low voltage situation

 

[SheepDog]

Here's a thread with some gents discussing the BMS bullshitz and what it does and doesn't do. Obviously, Ford never intended on me running 2 fuel pumps that each draw 15-20 amps depending on pressure and voltage, so im going to disconnect the BMS sensor and see how things behave.

Starting around post #17

https://www.mustang6g.com/forums/threads/forscan-problem.151686/page-2

@Warpath you still around? Any long term effects of disabling BMS with forscan or disconnecting the BMS sensor?

 

[Skye]

I've been studying several related electrical and charging topics.

I do not think the following will resolve the issue. But it is something worth checking and updating.

Was the original battery a traditional, "flooded" lead acid type? If it was, now that an AGM is installed, there's a setting in FORScan to update that. Also reads like there could be some tailoring.

https://www.focusst.org/threads/setting-battery-type-and-capacity-in-bcm-programming.164969/

https://www.mustang6g.com/forums/threads/using-forscan-to-modify-bms-when-upgrading-to-agm.201195/

 

[SheepDog]

Small update- with the BMS sensor

I've been studying several related electrical and charging topics.

I do not think the following will resolve the issue. But it is something worth checking and updating.

Was the original battery a traditional, "flooded" lead acid type? If it was, now that an AGM is installed, there's a setting in FORScan to update that. Also reads like there could be some tailoring.

https://www.focusst.org/threads/setting-battery-type-and-capacity-in-bcm-programming.164969/

https://www.mustang6g.com/forums/threads/using-forscan-to-modify-bms-when-upgrading-to-agm.201195/

Thanks.

The original battery was the OEM Ford battery. Flooded type. My understanding is that the car will sense the change to AGM on its own, after an 8 hour lockdown. I will hook up Forscan and see if the car has recognized the AGM, or if I need to change the setting.

I did confirm yesterday that when the BMS sensor is unplugged(Inductance ring plug) the alternator delivers a constant 14-14.5 volts. So safe to say that the Alternator is proably fine, and this is some behavior of the BMS system. I believe Forscan can also shut off the BMS system.

The problem with this, is that my fuel system gets reduce voltage during these 12V events which slows down the pumps, and like I mentioned earlier, I never saw the voltage drop this low previously-even with the old battery. I still need to take a log when this happens to see if it is detrimental to fuel pressure.

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