Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
The generator does spin all the time but the drag on the accessory drive is proportional to its output. More output = more drag = higher load on engine = more fuel.
The generator / alternator does not provide engine braking per se, we are just talking about the natural effect of coming off throttle or coasting. The engine is still rotating even though it is not gulping fuel; as it is still rotating and driving the generator the regenerative action takes some of this energy, converts it into electrical power and dumps it into the AGM battery.
There is precious little on Topix about it but there is a very good document in the JLR technical library. In its current guise the regenerative system was introduced for MY12:
Member Since: 12 Dec 2005
Location: The Gaff
Posts: 50936
I have seen that little ditty but I suspect it is a bit misleading to use the words "Smart regeneration" as it implies that the system is similar to those used commonly on electric vehicles where it uses electric motor drag or the brakes to help out....or indeed Fords Econetic which also uses the brakes.
Ford wrote:
Smart Regenerative Charging
Smart Regenerative Charging captures ‘free’ electrical energy
when drivers brake, which is then fed back into the vehicle battery.
This maintains efficient battery charge levels which reduces
overall fuel use. An advanced battery management system
continually monitors the charging status so regenerative charging
adds to the battery in the most optimal way.
The Disco obviously doesn't have this yet.
The way I see it Disco doesn't use the drag of the engine when braking ...the generator module just says "hello... now is a good time to draw what I need" ...the test for this would be if you coasted in Neutral ...and I suspect the module would do the same thing.
I could be wrong of course 21 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021
24th Jul 2015 10:04 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
It is energy recovered by the rotation of the wheels delivered through the gearbox to the engine. The 'engine braking' effect is the sum of all the mechanical drag on the engine (further moderated by the 8-speed box logic too as it is all linked). If you put it into Neutral the energy recovery mode would cease.
The terms are misleading and I am sure JLR just added 'Smart' just to look good.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi DG and sorry mate but there is far more to the reasons why the D4’s alternator operates in the way it does to be able to post it here. But here is a bit of a breakdown that may explain the basics.
The optimum voltage of any fully charged battery is 12.7v.
If the cranking battery is in a fully charged state state then the alternator can run at lower voyages than was the standard, just a few years ago.
Now there is a subject that needs to be covered first and it will then help to give you an answer to your questions.
In any DC circuit ( 12 volt in this case ) any current load connected to that circuit will draw more current as the voltage goes up.
For example, a 100w driving light globe will draw 8.3 amps at 12v and 9.7 amps at 14v.
And obviously the reverse is the case, and thats what Land Rover ( and many other vehicle manufacturers ) are exploiting when the lower the operating voltage of the alternators.
Next, if an alternator’s voltage regulator is set to run at constant voltage, say 14v, then all the devices connected to the alternator will all continue to draw the same level of current, except any lead acid batteries in the system.
But if something extra is added to the system, like turning on a set of 100w driving lights, then the additional 20 amp current draw will cause a slight voltage drop at the alternator.
This is where the alternators voltage regulator does it’s job and adjusts the voltage the alternator is operating at till it is again operating at 14v. This compensated increase in voltage allows the alternator to produce the extra 20 amps needed to power the two 100w driving lights.
If you turn the driving lights off, there will be a reduction in the current being drawn by the system and this will cause the alternator’s output voltage to rise, and again, the voltage regulator will now compensate by decreasing the voltage the alternator is to run at.
This is all fine except that in a constant alternator voltage setup, there is no way to control the amount of current an alternator is producing. The amount of current being produce is simply based on system current demand, not on any form of actual current control.
This may come as a surprise to most but the energy produced by an alternator is NOT free. I costs fuel to produce the current output of the alternator.
This is a theoretical exaggeration of what happens, but say you are driving at a constant 100 KPH and its a nice day so no headlights on and you have the sound system off.
After a 100 km drive you find you have used 10 lts of fuel.
Now do the same drive at night with a few driving lights being used and your sound system cranking up. You now find you have used 11 lts of fuel for the same drive time and distance.
the energy used by the alternator to produce current, comes from the alternator pulling on the motor, via the pulleys and belts and the more current the alternator needs to produce, the higher the pull of the belts on the engine, and the engine will burn more fuel to accommodate the higher current draw, while maintaining the same KPH.
Now to the reason behind the variable alternator voltages.
The manufacturers of new vehicles are having a hard time keeping cranking batteries charged and the primary reason for this is because most people these days use their vehicles as shopping trolleys, doing lots of short trips, which means they rarely drive long enough to fully charge their vehicle’s cranking battery.
So first off, the manufacturers are doing everything they can to put as much charge back into the cranking battery in the short time that is available.
With lead acid batteries, the fastest way to charge them is to apply the highest voltage the battery can safely tolerate.
The they program the BMS to operate the alternator at the maximum safe voltage for the type of cranking battery installed.
For simplicity sake, I’ll stick to the 14.7v used in new D4s.
So the voltage is raised to 14.7v to charge the cranking battery with the maximum current the battery will draw.
Problem is that every other electrical device connected to the system is also now drawing more current, even though they don’t need to operate at the higher current, and this unrequired high current being draw by all the electrical devices will cause a high fuel usage.
Once the battery is deemed by the BMS, to be fully charged, there is now no reason to maintain the higher operating voltage, as power is now being wasted for for no gain.
So the BMS is programmed to lower the voltage of the alternator and this lowers the current draw across the whole system.
This lower current draw means less energy being pulled from the motor by the alternator, which lower fuel consumption and ultimately lower exhaust emissions.
The average operating voltage of a D4 is about mid 13v but when you accelerate, to reduce energy being pulled from the motor at the very time it needs all it can produce to move the D4, the alternator will drop even lower, mid to high 12v.
If the battery is still not quite fully charged, then any time you apply the brakes, as the vehicle itself is not needing and energy from the motor, the BMS increases the voltage of the alternator and as the voltage goes up, so does the amount of current the battery will draw.
This is what regenerative brake charging is about.
DG, sorry this is so long winded but it’s pretty hard to cover all the different factors behind the reason for the D4’s variable alternator voltage operation.2008 TDV8 RR Lux + 2009 D4 2.7
24th Jul 2015 11:25 am
Dudleydisco
Member Since: 20 Jun 2014
Location: York
Posts: 853
DG wrote:
You are both well respected on technical views but it would be nice if you could give up the squabbling ......lets have constructive rather than destructive debate please chaps.
I'm sorry if I sparked this off, but I've certainly learnt a lot more about how the D4 system works and why they've designed it like they have
As Tim said, a lot of us only do short journeys, so can sometimes fall foul of the BMS charging strategy. Regular use of my CTEK has meant that I've not suffered from any battery related problems . . . so far!
I can see why JLR want to improve fuel economy and emissions. My only observation would be that, if this forum is anything to go by, there are a lot of problems relating to battery issues, but nobody really complaining about fuel economy D4 MY14 XXV - RLD/IID BT
D4 MY13 HSE Lux - RLD/IID BT
P38 RR - Sad parting
110 - Even sadder parting
S3 88" - Still going strong after 23 years of ownership
24th Jul 2015 11:48 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
The emissions are the real target for the regenerative systems and if you are doing short journeys the system will be doing its best to recover the state of charge, even if it means backing off the eco-friendly stuff.
As for me, I'm sticking with the laws of physics as they appear to work!
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 12 Dec 2005
Location: The Gaff
Posts: 50936
So from various posts here am I right in thinking that there is no physical system of regeneration "added" to the vehicle...capturing energy ...save only the control module deciding when to increased draw to based upon when there is excess available energy.
This sounds like what I thought i was previously describing anyway ....if not then I think I need someone to draw me a picture
...please include a cat 21 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021
24th Jul 2015 1:16 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
Correct, it is just using the vehicle systems to harvest kinetic energy, but it only does this when the battery is ok and the conditions are right.
The cleverness is the coordination between the different systems and the ability for the system to 'learn'.
I know some may not be at the age of believing but the D4 can go above 14.7v at warmish temperatures if the battery is cool. It is not untypical to see around 15v at the early part of a journey before the system throttles back to normal schedules voltages to prevent overheating.
For a given wattage the current does not increase when voltage increases, it goes down. This is why you can have thinner wires at high voltages and big fat cables at lower voltages for a given amount of power. Power (Watts) = Volts x Amps.
The D4 controls the output of the alternator and the available current. For a given voltage it can produce more or less current. If it produces only enough current to keep the systems happy and only has 2 amps available for the battery then that is all the battery will get, even if the voltage remains the same and even if the battery is capable of taking a higher charging current. It can, of course, increase the current available to the maximum that the battery can accept.
What picture would you like?
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Robbie wrote:
Correct, it is just using the vehicle systems to harvest kinetic energy, but it only does this when the battery is ok and the conditions are right.
The cleverness is the coordination between the different systems and the ability for the system to 'learn'.
I know some may not be at the age of believing but the D4 can go above 14.7v at warmish temperatures if the battery is cool. It is not untypical to see around 15v at the early part of a journey before the system throttles back to normal schedules voltages to prevent overheating.
For a given wattage the current does not increase when voltage increases, it goes down. This is why you can have thinner wires at high voltages and big fat cables at lower voltages for a given amount of power. Power (Watts) = Volts x Amps.
Sorry DG for continuing this, but this guy belongs back in kindergarden and is simply making it up as he goes along.
Robbie, you haven’t got the slightest idea what you are going on about, your version of the “Laws of Physics†is nothing short of fairytales.
Both Watts ( P ) and Volts ( E ) are variables and you need a constant to be able to calculate the current ( I ) in a circuit and current is another variable.
The constant in any circuit is it’s RESISTANCE ( R )
So the correct calculation to find the current ( I ) in a circuit is I=E/R
Using the 100w light globe, where the resistance remains constant at any voltage.
So with a voltage of 12v and a resistance of 1.44 ohms, you have a current draw of 8.3 amps
And with a voltage of 14v and a resistance of 1.44 ohms, you have a current draw of 9.7 amps.
This is, for instance, why cable has a resistance value not a wattage value, because the resistance is the only known constant.2008 TDV8 RR Lux + 2009 D4 2.7
24th Jul 2015 3:16 pm
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Folks, for Robbie’s benefit, if someone out there has access to a variable power supply can you carry out a test for Robbie.
Get a small light globe, you do not need a 100w globe.
Place an amp meter in the circuit in series with the globe and measure the current at 12v and then again at 14v.
The current will be higher, not lower, but higher at 14v.2008 TDV8 RR Lux + 2009 D4 2.7
24th Jul 2015 3:50 pm
Dudleydisco
Member Since: 20 Jun 2014
Location: York
Posts: 853
Sounds like Ohms Law to me V=IR, or as we're looking at it here I=V/R. I is current, V is voltage and R is resistance D4 MY14 XXV - RLD/IID BT
D4 MY13 HSE Lux - RLD/IID BT
P38 RR - Sad parting
110 - Even sadder parting
S3 88" - Still going strong after 23 years of ownership
24th Jul 2015 4:01 pm
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Yep, same calculation.
I=V/R or I=E/R2008 TDV8 RR Lux + 2009 D4 2.7
24th Jul 2015 4:05 pm
Dudleydisco
Member Since: 20 Jun 2014
Location: York
Posts: 853
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum
....if not then I think I need someone to draw me a picture 
