Brake energy recovery - How does it work?

[Bap33]

Hi guys,

 

When I bought my MY2017 Mk3 (TDI190 4x4 DSG6), I had been told by the dealer that it was equipped with a brake energy recovery system? 

Does anyone know how it technically works?

Just curious to know.

Thanks.  

[Kenny R]

Charge Management & Regenerative Braking (Micro hybrid 2)

Charge Management

• It is likely that vehicle owners would not be aware of the installation of this technology as its operation is seamless, unlike Stop/Start which is clearly detectable as the engine stops if all system operating conditions are fulfilled when the vehicle comes to rest
• When the alternator is running it can typically consume up to 10% of the power produced by the engine. The charge management system effectively switches off the charging system by disconnecting the alternators drive from the engine. This increases the loads placed on the battery but significantly improves the fuel economy of the vehicle
  • The major fuel economy benefits of a charge management system are achieved on longer distance journeys. The use of this system shows that one technology alone is not the solution to every drive cycle but is important as part of an overall package of emission reduction and economy initiatives
  • The life expectations of the battery are greatly increased as it is supporting all of the electrical loads on the vehicle when the charge management system is operating
  • The introduction of charge management systems has resulted in the development of new battery technologies and designs with increased performance. These include EFB and AGM battery types which have a significantly better cyclic life and improved operation in low states of charge

 

Regenerative Braking

• Regenerative Braking systems recover the energy normally converted into and lost as heat during vehicle braking. When available the recovered energy is fed back into the charging system to recharge the battery
• A conventional technology battery is very inefficient when utilized in in a regenerative braking system. This type of battery is only able to reuse approximately 5 to 15% of the recovered energy due to its relatively high internal resistance. New battery technology developments such as EFB and AGM with reduced internal resistances provide more efficient use of the recovered energy.

[john999boy]

13 minutes ago, Bap33 said:

When I bought my MY2017 Mk3 (TDI190 4x4 DSG6), I had been told by the dealer that it was equipped with a brake energy recovery system? 

Does anyone know how it technically works?

I’m gobsmacked to find this out!

 

Old dogs & new tricks spring to mind.

Edited 20 December, 2020 by john999boy
Eating humble pie.

[Breezy_Pete]

The theory is that when braking, the alternator is electronically adjusted to give a higher than usual output voltage that can supposedly dump a lot of charge relatively quickly into the battery.  This puts more mechanical load on the alternator, so helping to slow the vehicle.

 

I've always had the gut feeling that the amount of time I have the brakes on during any of my normal journeys would make this energy recovery miniscule, if I had a car with such system.

 

 

 

[Warrior193]

Although not mentioned in the section posted by Kenny, my understanding is that the regen also adjusts the alternator charge-rate to charge the battery during periods of 'coasting in gear' - can anyone confirm?

[shyVRS245]

28 minutes ago, Warrior193 said:

Although not mentioned in the section posted by Kenny, my understanding is that the regen also adjusts the alternator charge-rate to charge the battery during periods of 'coasting in gear' - can anyone confirm?

Yes just like an F1 car using KERS which can harvest energy for the alternator to charge the battery the recovery of energy is gained by either pressing the brake pedal or lifting off the brake pedal (coasting in a DSG car in Eco mode) which is why even F1 drivers sometimes coast on the straight to recover electrical energy which results in the red flashing light on the back of the back to warn other drivers they are slowing down but importantly not actually physically pressing the brake pedal. Even an F1 car can save quite a bit of fuel by doing this and not losing much lap time in the process as the recovered energy can be used by the driver by pressing a button on the steering wheel for improved performance exiting slow corners. The 3.0litre V10 engine produced 900bhp, the 2.4litre V8 produced 780bhp and the latest 1.6litre V6 Turbo with KERS produces 950bhp. Lessons learned in F1 have been gradually introduced into road cars.

[SuperbTWM]

Its just another addition to make a small impact on emissions more than anything else.

 

For arguments sake the alternator will charge the battery to 80% and then the voltage will drop to the point where it runs all the consumers and maintain the state of charge. You then have  a long period of braking like getting off the motorway or an extended period of engine braking and the battery now has 100% charge.

 

The car then drops the alternator voltage below the battery voltage and lets the battery drain from 100% back to 80%, during which time the engine is basically just free-wheeling the alternator saving a few polar bears.

 

 

[Andysuew]

Brake Energy Recovery in detail. 3 seperate recordings of voltage and current on the VAG “Smart” alternator. Very interesting the wide scope of both voltage and current across the 3 seperate runs. Equipment used to takes recordings was Fluke AC/DC Volt meter and Fluke DC current meter. Both meters able to record live data. 
 

Voltage data recorded directly from battery positive terminal and negative earth connection on the firewall. Current recorded directly from main positive cable 100mm from positive battery terminal.
 

All three runs were over a total of 100+km distance incorporating Urban, highway, and back street roads. 

SKODA RUN 1.pdf SKODA RUN 2.pdf SKODA RUN 3.pdf

[Breezy_Pete]

Nice work!

Will be interesting to look at those in detail later.

 

[SuperbTWM]

Good data, thanks for sharing 

[J.R.]

"When the alternator is running it can typically consume up to 10% of the power produced by the engine"................

 

Ah that wonderful old phrase "up to" once again!

 

My mental calculation tells me that a 120 amp alternator at maximum output would only equate to just under 2 hp, I doubt that they ever run at maximum output but I suppose after a cold engine start with all the accessories switched on, heated screens, heated seats, post heating glow plugs etc it could be 2hp.

 

Maybe with the lowest powered engine at tickover it might just equate to 10% but the alternator could never give maximum output at such low RPM.

 

Who writes this twaddle & why is it not proof read?

[Q102]

I suppose you never really notice a Skoda doing it.

My Porsche 718 has a charge management system. The first time I saw it, I thought the alternator was broken as the battery voltage just kept dropping while I was cruising down a motorway. It then started to rain, so lights & wipers on, battery voltage shot back up to 14ish

[Breezy_Pete]

The magnitude of the voltage peaks is interesting to me, minimally higher than a conventional alternator (at cold temps anyway). I have a feeling if I fire up my car shortly, at frosty degrees C I'll see similar initially.

Seems to contradict the notion that start-stop batteries need a higher charging voltage than regular batts. In fact, almost all the time, they have a much lower one.

 

@Andysuew Is your battery AGM or EFB? presumably still the original?

 

Could you estimate the ambient temperature in which these logs were taken? Pretty warm in your location I guess, 30C+? 

The peaks don't seem to reduce noticeably during the course of each drive, so engine bay temperature doesn't seem to modulate the peaks down.

Have you considered doing a comparative log with LIN connection to alternator unplugged?

 

A UK winter-time data set (or just peak voltage numbers) might be interesting, anyone over here doing some monitoring on one of these new-fangled systems?

 

Here's my 'voltage across battery posts' at first start at around 0°C, conventional alt, and battery.  It reduces as the engine bay warms down to around 14.3V.

 

Edited 30 December, 2020 by Wino

[xman]

5 hours ago, Wino said:

The magnitude of the voltage peaks is interesting to me, minimally higher than a conventional alternator (at cold temps anyway). I have a feeling if I fire up my car shortly, at frosty degrees C I'll see similar initially.

Seems to contradict the notion that start-stop batteries need a higher charging voltage than regular batts. In fact, almost all the time, they have a much lower one.

 

 

I think the charging system is probably based mainly on controlling current going into and out of the battery using feedback from the current sensor mounted on the negative terminal. It can track charge (coulomb counting) and so be able to maintain/increase/decrease the batteries SOC, whatever the battery management system demands at any moment

 

EFB and AGM batteries have considerably greater charge acceptance ability than old conventional lead acid batteries so you won't necessarily see large increases in voltages with charge current although its likely the alternator can allow the voltage to rise higher if demanded by the battery management to maintain current flow e.g. when the battery is older and/or knackered

 

 

 

 

Edited 30 December, 2020 by xman

[Breezy_Pete]

9 minutes ago, xman said:

controlling current going into and out of the battery

Only way to do that is varying the voltage at the alternator output, no?

[xman]

Just now, Wino said:

Only way to do that is varying the voltage at the alternator output, no?

 

Using the current sensor in a negative feedback loop to control current and yes the voltage will vary, but because of good charge acceptance at the battery, it only takes a little extra voltage to increase current into the battery significantly. Most of the time e.g. when cruising at constant speed, if the the SOC is on target (say 80%) the battery will not be charging and the voltage will fall back to a level where only the active current consumers are being supplied.

 

I have not looked at the alternators on these cars, but the inbuilt regulators must be completely different allowing the voltage and current to be controlled externally, maybe even via a digital channel.

[xman]

14 hours ago, J.R. said:

"When the alternator is running it can typically consume up to 10% of the power produced by the engine"................

 

Ah that wonderful old phrase "up to" once again!

 

My mental calculation tells me that a 120 amp alternator at maximum output would only equate to just under 2 hp, I doubt that they ever run at maximum output but I suppose after a cold engine start with all the accessories switched on, heated screens, heated seats, post heating glow plugs etc it could be 2hp.

 

Maybe with the lowest powered engine at tickover it might just equate to 10% but the alternator could never give maximum output at such low RPM.

 

Who writes this twaddle & why is it not proof read?

Lets check then.....

 

EV's often quoted as achieving 3 to 4 miles per kWh (includes ancillaries/battery/convertor/motor losses)

 

Lets assume 4 miles achieved for 1 kWh of output power at the motor, that's probably on the low side.

 

40 mph average for a hour therfore requires 10kWh

 

120A 14.3v alternator is 1.7kW

 

Up to 10% requirement (1kW) therefore 70A from the alternator

 

[Breezy_Pete]

As I understand it, a LIN data stream tells the alt to change it's voltage setpoint up/down as reqd. Current flows as a consequence according to Ohm's law, into connected loads, including the battery.

[xman]

6 minutes ago, Wino said:

As I understand it, a LIN data stream tells the alt to change it's voltage setpoint up/down as reqd. Current flows as a consequence according to Ohm's law, into connected loads, including the battery.

 

A battery is not a resistive load (neither are many of the other current consumers) so Ohm's law is of no use, The main controlling sensor (used in a negative feedback control loop configuration) is the current sensor on the battery, and if that fails (or someone disconnects it), the system will revert to an old fashioned fixed voltage (temperature compensated) charge system.

Edited 30 December, 2020 by xman

[Breezy_Pete]

4 minutes ago, xman said:

A battery is not a resistive load (neither are many of the other current consumers) so Ohm's law is of no use

[J.R.]

1 hour ago, xman said:

Lets check then.....

 

EV's often quoted as achieving 3 to 4 miles per kWh (includes ancillaries/battery/convertor/motor losses)

 

Lets assume 4 miles achieved for 1 kWh of output power at the motor, that's probably on the low side.

 

40 mph average for a hour therfore requires 10kWh

 

120A 14.3v alternator is 1.7kW

 

Up to 10% requirement (1kW) therefore 70A from the alternator

 

 

The quote was speaking of an infernal combustion engine and was complete b******s.

 

I bet the number of forum members whose cars have less than 100 hp could be counted on one hand, 10% is laughable even with the "up to".

Edited 30 December, 2020 by J.R.

[xman]

51 minutes ago, J.R. said:

 

The quote was speaking of an infernal combustion engine and was complete b******s.

 

I bet the number of forum members whose cars have less than 100 hp could be counted on one hand, 10% is laughable even with the "up to".

 

Usual robust but somewhat misguided reply from Monsieur jr.

Quote

When the alternator is running it can typically consume up to 10% of the power produced by the engine. 

Most car engines of any type when cruising produce very little power, just enough to overcome rolling resistance and aerodynamics.

 

Many many, members have 3 pot non turbo fabias, I have one for example, it is rated at 70ps at 5500 rpm, never ever been anywhere near full output level even at 70 mph (3500rpm)

 

1 litre of petrol contains 9.1kWh of energy.

 

At 40mph, lots of petrol engined cars will do 50 mpg i.e. in one hour use 3.64 litres or 33 kWh of energy, petrol engines are around 30% efficient at best so thats 10kWh power developed, tying up with what EV's are reporting as typical energy useage.

 

Soon be new year, and I will be leaving Briskoda, so no need to reply.

[J.R.]

I thank you for your calculations of fuel consumption & energy, its a good way of looking at it, I would be very surprised if during the one hour and 40 miles the alternator would have drawn 1kwh of the 10kwh developed.

 

I wish you a happy & contented 2021, if you can get bent out of shape by a cordial technical discussion about how much power is consumed by the alternator on an internal combustion engine then you are wise to take a break.

 

Editted, I have just read your reasons for withdrawing, I agree with you and completely understand.

 

On my part, I have, as my New Year's resolution, decided to leave this site again as the constant resident left wing socialist claptrap on Briskoda is getting me seriously down. Hopefully I will only return if I require help to resolve a technical issue with one of our Skodas, which with a little luck might be never.

 

 

Edited 30 December, 2020 by J.R.

[xman]

Thanks for the cordial reply, the bending out of shape comes from the political socialist EU claptrap and constant insulting language being posted elsewhere by less than half a dozen members, going on now for years. I think you probably know who I mean.

 

Have a happy and prosperous new year @J.R. and everyone else. 

[J.R.]

Yes I just read it and editted my posting which overlapped with yours.

 

I am in complete agreement, however on the French forum I belong to its many times worse, I come here for a break!

 

They are reacting very badly because the joy they were hoping to feel at the downfall of the UK has been denied them.