Using that calculator for a 100W load and 12v = 8.3 amps.
Using it again for a 100W load and 14v = 7.14 amps.
Click image to enlarge
Using a bulb as the example load would add confusion as when supplied with increasing voltage the resistance also increases - they are not a constant resistor. By their very nature filament light bulbs (incandescent) are non-Ohmic conductors. Bulbs are hardly the principal load on a car anyway.
Debate the fact, physics and empirical data only - leave out the aggressive tone and jibe. This is a friendly place.
Land Rover - Turning Drivers into Mechanics Since 1948
Ahh, scratch that, as they would only teach me that filament bulbs are non-Ohmic:
Quote:
An Ohmic device is one which obeys Ohm’s Law, V = IR, where R is constant. A non- Ohmic device is one that does not have a constant resistance. A light bulb is a simple example; the filament undergoes huge changes in temperature when current passes through it. Therefore, the resistance of the filament is not constant, rather, it increases with increased current.
I'll keep looking but it must have lots of girls in the dorms so I don't fancy Kuwait University:
Non-ohmic Devices: If a device behaves in a way that is NOT described by Ohm’s law, (i.e. the resistance is not constant, but changes in a way that depends on the voltage across it.) The device is said to be non-Ohmic. In this case V versus I graph is not a straight line, but has some curvy shape. Such devices do not have a constant value of resistance and the resistance is called dynamic resistance because it is constantly changing. Examples of such devices are tungsten filament (bulb), diode, thermistor etc…
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Again, you still can get it that the current goes up when the voltage goes up, even when using the globe to demonstrate this, the voltage goes up not down, as per your misguided theory.
Why would they lower the voltage in a D4 if the current went up.
This would increase the load on the motor, which would increase fuel consumption and ultimate defeat Land Rovers attempts to reduce exhaust emissions.
It would be pointless.2008 TDV8 RR Lux + 2009 D4 2.7
24th Jul 2015 4:26 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
I've said nothing about reducing the voltage, that came from your good self.
I have explained from my first post on the subject about BMS variable current control, which can be achieved at a fixed voltage if needed.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
So why does the D4 alternator's voltage vary then?
You can not control the current output of an alternator without varying the voltage!2008 TDV8 RR Lux + 2009 D4 2.7
24th Jul 2015 4:47 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
You can, you just vary the output by changing the voltage on the magnets - the drag is proportional to the output. The voltage regulator can maintain the desired voltage strategy and the current that is available is governed by the system.
As the PCM, BCM and BMS know exactly what the draw is and what is going into the battery the total output can be regulated to provide the amperage of your choice at the battery terminals. The current can be set high enough to provide the maximum that the battery can take at its accept rate, or throttled to a minimum (around 2 amps) to provide just a trickle with energy recovery adding more when available. With the alternator working less hard the parasitic drag is reduced and fuel is saved.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
So if as you make out, you can regulate the current coming from the alternator to the battery with out changing the voltage level, as all power going to the vehicle, not just the cranking battery, but to the vehicles electrics, about 40 amps, where does all this come from when the alternator's current it mythically reduced to 2 amps?
Then there are those D4s that have an auxiliary battery or two. Where does all the current come from to charge them.
The only way you could reduce the amount of current going into the cranking battery is to reduce voltage at the cranking battery, by reducing the voltage at the alternator's output. This allows everything else to continue being supplied with what ever current they need but the lower voltage at the craning battery means it will only draw it 2 amps ( if that is what you wanted ).
With your theory, as a battery will draw more current as the voltage goes up, so to stop the battery drawing more than two amps, you would have to starve every other device connected to the cranking battery by turning them off and there is nothing on a D4 to do that.
So again, if, according to your theory, they can control the current without varying the voltage, why does LR waste their time varying the alternator's voltage in the first place?2008 TDV8 RR Lux + 2009 D4 2.7
24th Jul 2015 5:29 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
Voltage and current are both important factors for battery charging but the range of voltages that the battery is happy with is quite limited as it has to be within the band where the battery can accept a charge, but not above a level that would be damaging.
If you provided infinite current to a battery but within the correct voltage band the battery will happily draw what it needs and the current it needs will decay as the SoC increases. If you cap the current it will still charge but at a lower rate - like a low amperage battery charger.
The vehicle systems also need a voltage that they are comfortable with so again this restricts the voltage band that can be used. If you dropped the voltage you could reduce alternator output and stop the battery from charging but some systems would not function.
The JLR charging strategy changes the voltage according to conditions. If it is hot then the voltage is reduced; if it is cold the voltage is increased - but only within the safe band. As said previously, if the D4 knows that the battery is cold and that the delta between ambient and the battery is not too great it knows it can safely provide a higher voltage. That is why you often see voltages around 15v on a D4 just after start as the system knows it can get away with a high voltage and high current without risk of damage.
So for an example at typical UK summer temps a D4 battery with a healthy (greater than 85%) SoC will receive around 15v for the first 25 seconds or so after start. The alternator will be pushing out quite a lot of current to the engine and systems but still providing around 50 to 60 amps to the battery terminals for the first 15 seconds, before tapering off to around 20 amps at 14.8 ~ 14.0v. From there there will be a further decline and within 3 or 4 minutes the battery will be receiving around 4 amps at 14.7v before decaying further to around 2 amps at this same voltage. Effectively constant voltage, variable current, but still with every other option available if required.
Regenerative energy will be on top of this 'trickle' charge of around 2 amps. As the electrical demands of the engine and other systems increase and decrease the alternator output will be adjusted to maintain the 2 amps at the battery terminals. Effectively the battery is now blind to what the rest of the electrical systems are doing - well, within the reaction time of the system.
The other advantage of this methodology is that you do not need to keep excess rpm at idle to cope with sudden demands, so the D4 is allowed to idle at a lower level, which also saves some fuel.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
First off you have not answered the question of how you regulate the alternators current so it only provides 2 amps to the battery while still providing current for everything else in the vehicle.
Again, in your mythical setup, you would have to disconnect everything else from the battery and then you could mythically control a 2 amp supply to the cranking battery.
You really don’t understand how batteries charge.
And once again, how do you power everything else if they are not connected to either the battery and/or the alternator?
QUOTE “The other advantage of this methodology is that you do not need to keep excess rpm at idle to cope with sudden demands, so the D4 is allowed to idle at a lower level, which also saves some fuel.â€
Thats is the other reason the battery in every vehicle, not just Land Rovers, to meet high current demands when the motor is idling or at low RPMs.
So once again, your mythical theories are out the window.2008 TDV8 RR Lux + 2009 D4 2.7
24th Jul 2015 6:22 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
Trust me, I know how batteries charge.
Anyway, I though I had answered the point as to how it can control the amperage at the terminals, but to be clear, the BMS and BCM monitor the current flow at the battery terminal and the PCM will adjust the alternator output to the required level. DG has already quoted how the BMS periodical calibrates its Coulomb Counting for SoC and rate of charge and discharge.
For example, if the alternator is producing 40 amps and the vehicle systems were taking what they needed and 6 amps were flowing into the battery but the BMS wanted 10 amps then the alternator could increase to 44 amps. If the BMS wanted 2 amps at the terminals the alternator could back-off to 36 amps. If you then triggered the heated windows and heated seats the total demand would increase so the alternator output (and drag) would have to increase to maintain 2 amps at the terminals. Current has to have somewhere to go.
None of this is mythical, only empirical and by design. Unfortunately, the BMS did not always get it right. In the early days I saw lots of troubled D4s that I had to datalog all parameters and compare with the published strategy as I had no ability to read the sensed data off the LIN-bus. Forum members were driving around with my USB data-loggers attached to their vehicles to capture data (current, voltage and temperature) over a couple of weeks. Now all I need to do is confirm, or otherwise, the validity of the live BMS data with real-world data. If the data cross-checks I can use the BMS data from the bus for diagnostics. If it does not match then the BMS has a fault.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
In an effort to bring this circle back to the recent beginning (ie yesterday) a new D4 battery requires a reset, a period of learning and a charge to bring it to a full SoC to avoid a lengthy wait from the BMS.
To quote my own example from yesterday where my battery was sipping on its diet of 2 amps at around 87% SoC it has now spent this afternoon gorging itself on just over 8 amps from my battery charger to achieve a bit of a refresh and a full SoC - all under the watchful eye of the BMS that has recorded the quiescent drain being reversed and noted the increased amperage being drawn through the terminals.
As a small trap for new players, when you access the BMS data via the BCM with the vehicle asleep the BCM stays awake. This draws a nice round 2 amps in addition to the normal drain. So your battery will get about 2 amps less than the charger is providing. If the BCM is asleep the battery will take it all, minus the usual drain.
I hope this has been helpful to someone.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Robbie, if your battery charger was providing 10 amps ( 8 for the battery and 2 for sundries ) but only 2 amps from the alternator, then the only reason the alternator was providing just 2 amps is because the output voltage was low.
If the voltage from the alternator was the same as it would have been from your battery charger, then the alternator would have been providing the same or more charge current.
I note how you posted up all the specific details except the most relevant one. You conveniently neglected to mention the voltages at which the battery was taking the different charges.2008 TDV8 RR Lux + 2009 D4 2.7
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