Variable Voltage System Stuff

[RangerBill]

Clearly you are the one in the wrong here. The Amp Meter detects Amp Draw from any Loads that are being Drawn. Not hard to understand right? With that being said, that gets sent to the next Controller which most likely is the ECM. After that it gets sent to the BCM VIA CAN. The BCM processes that information and sees the the Load through that Amp Meter. If the Amp Meter wasn't there, then the BCM would not have any idea of the exact Load Value. Part of why you need to keep any added Grounds from Aftermarket Equipment on the Body or Chassis. Once that load is processed, a signal is sent to the Alternator to increase the Amps as needed to maintain the Target Voltage.

Why this is hard for you to understand is beyond me.

Also the Battery is a crucial part of the circuit. Without it in place, things will not operate correctly if at all.

The BMS sensor on the battery negative terminal will only detect current going into the battery or exiting the battery. It doesn't measure all load currents unless the engine is not running (alternator not charging the battery). Alternator charging current is supplied directly to the load and only excess current needed to charge the battery is measured by the BMS sensor (if the alternator output can keep up with the applied load and battery charging current needed). If the alternator cannot keep up with the applied load, then the excess current needed will be supplied by the battery, and the BMS sensor will measure this battery supplied current only. In this state, the alternator supplies current and the battery supplies the excess current needed that the alternator cannot supply (if it cannot meet the load). This is why it is called a Battery Monitoring Sensor because it only monitors the battery current (whether supplying battery current to the load or receiving charging current from the alternator).

In the old cars with no electronics (as long as you kept the radio off) you could start the car and disconnect the battery and run the engine, lights and heater without the battery connected. The alternator was supplying the power to the load. If there was a BMS sensor on the battery, it would not be measuring any current flow with the battery disconnected.

Another point, the BMS sensor also measures battery voltage as it has a wire to the positive battery terminal for this purpose (and supply operating voltage to the sensor).

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[Frenchy]

The BMS sensor on the battery negative terminal will only detect current going into the battery or exiting the battery. It doesn't measure all load currents unless the engine is not running (alternator not charging the battery). Alternator charging current is supplied directly to the load and only excess current needed to charge the battery is measured by the BMS sensor (if the alternator output can keep up with the applied load and battery charging current needed). If the alternator cannot keep up with the applied load, then the excess current needed will be supplied by the battery, and the BMS sensor will measure this battery supplied current only. In this state, the alternator supplies current and the battery supplies the excess current needed that the alternator cannot supply (if it cannot meet the load). This is why it is called a Battery Monitoring Sensor because it only monitors the battery current (whether supply battery current to the load or receiving charging current from the alternator).

In the old cars with no electronics (as long as you kept the radio off) you could start the car and disconnect the battery and run the engine, lights and heater without the battery connected. The alternator was supplying the power to the load. If there was a BMS sensor on the battery, it would not be measuring any current flow with the battery disconnected.

Another point, the BMS sensor also measures battery voltage as it has a wire to the positive battery terminal for this purpose (and supply operating voltage to the sensor).

And yet with Variable Voltage Systems we are instructed by Vehicle Manufacturers to have any Electrical Accessory Grounds Connected to the Body or Chassis. If it was ok to put it directly on the Battery, the. It would not matter if there was a little Amp Meter or not.

Remember that with Modern Vehicles, the Battery is a crucial part of any Electrical System. If the Battery is bad(and I mean Real Bad like won't hold a thing), the vehicle won't be able to run. I have seen this on a few vehicles including Ford Vehicles. That Sensor gets used as it helps the Battery complete its Circuit with every electrical load.

In reality it is very simple. It's just taking the time to understand it

 

[RangerBill]

Another way to think of this is the battery and alternator are parallel circuits with the BMS sensor in series with the battery only and can only measure battery currents. The alternator supplies most or all of the load currents (with the engine running) and is not measured by the BMS sensor (only battery charging or discharge current is measured). With the engine not running, the battery will supply all load current and then the BMS will measure all load currents. This is true only when the alternator is not rotating.

 

[RangerBill]

If you would connect a DC amp clamp meter to the battery negative cable (the cable that goes from the battery to the fender), you would be measuring the same current as the BMS sensor measures.

 

[RangerBill]

And yet with Variable Voltage Systems we are instructed by Vehicle Manufacturers to have any Electrical Accessory Grounds Connected to the Body or Chassis. If it was ok to put it directly on the Battery, the. It would not matter if there was a little Amp Meter or not.

The reason for this is that connecting an accessory ground directly to the negative battery terminal will bypass the BMS sensor and the truck will calculate an incorrect battery state of charge because it will not know what current the accessory is drawing.

 

[Grandaccess]

you can probably add a bluetooth Shunt and track it with your cell phone like we do Solar
our stock batteries are 70ah AGM kind of like a deep cycle

 

[TJC]

In the old cars with no electronics (as long as you kept the radio off) you could start the car and disconnect the battery and run the engine, lights and heater without the battery connected. The alternator was supplying the power to the load. If there was a BMS sensor on the battery, it would not be measuring any current flow with the battery disconnected.

To further clarify, those older cars that could run indefinitely. were equipped with generators, not alternators. Generators had physical magnets in the case supplying the magnetic fields.

As a rule, most alternators have windings electromagnets (instead of physical magnets) that require external power sources to generate the necessary magnetic fields. Turn off the power to the alternator windings and the alternator essentially becomes nothing more than an idler pulley.

The short of it is that as your battery weakens it adversely affects the alternator output capacity. If the battery fully discharges (dies), the alternator stops producing electricity and your engine stops running. Can't fire those spark plugs without juice!

Re: ctechbob's comment on difference of potential, he is absolutely correct. Think of two water tanks connected with a pipe. Now raise one tank higher then the other and watch the water seek equilibrium. It will flow through the pipe until both tanks are at the same level. This is difference of potential.

The water pressure can be considered current. The bigger the diameter of the pipe (or wire in electrical terms), the faster the water (electricity) will transfer until equilibrium is acheived. The pressure (current - measured in Amps) (or size of the pipe) does not enter into the equation unless there is a difference of potential (measured in volts).

 

[RangerBill]

As a rule, most alternators have windings electromagnets (instead of physical magnets) that require external power sources to generate the necessary magnetic fields. Turn off the power to the alternator windings and the alternator essentially becomes nothing more than an idler pulley.

The short of it is that as your battery weakens it adversely affects the alternator output capacity. If the battery fully discharges (dies), the alternator stops producing electricity and your engine stops running. Can't fire those spark plugs without juice!

An alternator in an older car will self-power the field inside (once rotating) and will continue to provide voltage to run the engine with the battery disconnected. The output of the alternator on a modern car with electronics is not pure DC and will damage electronics with the battery disconnected and not filtering the output. Older cars didn't have electronics and would run without the battery once started.

If the alternator is not functioning the battery voltage will drop until the engine will no longer run. If the alternator is working and you disconnect the battery, the engine will run until it runs out of gas as long as the load (accessories) doesn't exceed the output capability of the alternator. Don't try this on a modern vehicle, as it will damage electronic controls.

 

[RangerBill]

The water pressure can be considered current. The bigger the diameter of the pipe (or wire in electrical terms), the faster the water (electricity) will transfer until equilibrium is acheived. The pressure (current - measured in Amps) (or size of the pipe) does not enter into the equation unless there is a difference of potential (measured in volts).

In using this analogy, water pressure is compared to electrical voltage and water flow is compared to electrical current (amps).

 

[TJC]

In using this analogy, water pressure is compared to electrical voltage and water flow is compared to electrical current (amps).

I tried to keep it simple... My focus was on Difference of Potential. Current doesn't matter without a difference of potential. Think birds on a wire. No difference of potential, no cooked birds!

 

[Frenchy]

I think you guys are also missing another point here. With the Vehicle Running at any state(let's say no accessories are on at said time) and you all of a sudden turn on an accessory, the load will pull from the Battery before the Alternator does anything. This is thanks to the Battery having available Amps stored. Of course within the first second or two of the Load being turned on the Alternator will be commanded to apply the needed Amps as the BCM will see that information from the Amp Meter.

 

[TJC]

I would venture to say milliseconds. A millisecond is an extremely long time for a computer. For us humans it is basically instantaneous.

 

[RangerBill]

With the Vehicle Running at any state(let's say no accessories are on at said time) and you all of a sudden turn on an accessory, the load will pull from the Battery before the Alternator does anything.

The alternator only regulates voltage. Since it is regulated at a certain voltage level (commanded by the PCM), the current drawn will increase automatically when an additional load is applied (according to Ohm's Law). The alternator doesn't regulate the current it outputs. The current output (amps) is determined by its voltage output and the load of accessories and the battery state of charge (battery charging current needed). If a sudden additional load is placed on the alternator, the voltage may dip until the alternator voltage regulator reacts to the voltage dip. This dip in voltage should only be momentary.

The only time that the alternator is current regulated is if it is overloaded. The PCM may reduce current by lowering the voltage commanded value. I believe that the alternators are designed to saturate the windings and limit current when overloaded.

The only time that the battery would be supplying current to the load is if the alternator voltage output dips below the battery voltage level and some current would then flow out of the battery for a moment until the alternator voltage regulator reacts, as long as the alternator is rotating and not overloaded or defective. The PCM can increase engine idle speed if necessary to increase alternator output.

 

[awd.nv]

Ok, so what do you guys all set your charging level to in Forscan?

My XLT Tremor was defaulted to 75% I presume because of the accessory switches they added. I wonder if the Lariat Tremor went up from 75 to 80%?

It bugs me that key on, engine off I register about 12.1v, always been that way but now that I have forescan I was thinking about bumping it up

 

[RangerBill]

Ok, so what do you guys all set your charging level to in Forscan?

My XLT Tremor was defaulted to 75% I presume because of the accessory switches they added. I wonder if the Lariat Tremor went up from 75 to 80%?

It bugs me that key on, engine off I register about 12.1v, always been that way but now that I have forescan I was thinking about bumping it up

My 2019 Lariat was set at 75% setpoint. I just recently changed it to 90%.

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