[tom66]

The GTE has the best, easiest brakes of any car I've driven before. Most cars I've driven have brakes that do very little at the high end, and then become quite sharp over a limited range of motion. Compared to the GTE, which seems to have very progressive brakes. I believe this is a deliberate engineering decision, to allow more of the regen range to map in.

 

[donald]

I appreciate that every time I brake, throttle back (when coasting isn’t deployed) and changing down through the gears using the paddles the battery is charged through recuperation BUT how effective is this recuperation? How much energy is being added to the battery and is it recharging to the same level as a Tesla or any other EV or PHEV? I am very much aware that my GTE will never recharge enough going down a hill to get up the other side - nowhere near. Implying that recuperation is somewhat limited.

It's a very vague question.

I think the answer is 'reasonably effective'.

Please define 'effective' if you are serious about getting a more meaningful answer.

 

[Maturedriver]

It's a very vague question.

I think the answer is 'reasonably effective'.

Please define 'effective' if you are serious about getting a more meaningful answer.

When I referred to being ‘effective’, basically I’m asking if the braking regeneration tops up the battery as effectively as in a car like a Tesla. Just wondered if, being a PHEV, VW installed a half arsed regeneration system.

I thought my question was both reasonable and succinct.

 

[farmergiles]

When I referred to being ‘effective’, basically I’m asking if the braking regeneration tops up the battery as effectively as in a car like a Tesla. Just wondered if, being a PHEV, VW installed a half arsed regeneration system.

I thought my question was both reasonable and succinct.

Do you not think that the Tesla's or other EV's Hv battery can be charged with a much higher current than a PHEV with a 10times smaller battery?
Ergo, they do not produce the same regen charging current. (pity, or the small battery would be charged up in minutes.)

All I can say is that when I was using GTE mode and the battery range was low (below 10) it increased quite quickly both by regening and by using surplus torque whenever possible. Usually when the gom showed 18 or more miles, I'd switch back to E-mode.

 

[tom66]

It will be a little less efficient than a Tesla for two reasons:

* It's limited to 30kW when you lift off, and about 45kW with your foot on the brake. Tesla do 60kW. Polestar is 75kW. Porsche can do up to 250kW when the brake is applied, if the battery is in the right SoC. For the GTE, this means less of the coast down can be recovered before you press the brake pedal.

* It is going into a smaller battery with higher ESR, which will mean greater losses. The motor is also smaller, which will probably result in greater losses.

 

[donald]

When I referred to being ‘effective’, basically I’m asking if the braking regeneration tops up the battery as effectively as in a car like a Tesla. Just wondered if, being a PHEV, VW installed a half arsed regeneration system.

I thought my question was both reasonable and succinct.

I didn't take that meaning from it at all, but the answer is that all electric regeneration should be, in theory, as "efficient" as all the others. The kinetic energy from the car can disappear either by; heating the brakes and tyre, accelerating air it is decelerating down in, or via the transmission system. If the first two are dealt with by a) only using regen, and b) having good aerodynamics, then all such systems will be pretty similar in efficiency.

Meanwhile .... and still way from clear at all ... MoT stations will test brake 'efficiency' meaning their power and rate of deceleration (because friction brakes are 0% "efficient", it can mean nothing else). In terms of 'power', the brakes on a Tesla are pathetically inefficient compared with an electric dumper truck, so depends on your POV. No-one has educated me on 'a Tesla' being the gold standard for all electric vehicles, truly I was not aware of this.

The brakes on a GTE are going to be about a tenth of the power of a Tesla braking, as the battery is a tenth of the size, thus the maximum currents are a tenth. But they are unlikely to be different in terms of the energy they regenerate, the GTE will convert the kinetic energy more slowly.

Whether it will be a factor of 10 in practice I think will more depend on the tyres. Tesla could probably exceed the tyre traction and lock the wheels up if the computer demanded that regen power of the inverter, whereas it is probably not likely for the GTE.

 

[tom66]

Meanwhile .... and still way from clear at all ... MoT stations will test brake 'efficiency' meaning their power and rate of deceleration (because friction brakes are 0% "efficient", it can mean nothing else). In terms of 'power', the brakes on a Tesla are pathetically inefficient compared with an electric dumper truck, so depends on your POV.

Brake efficiency is just there to check if the braking system is compromised, ie bad pads, rusty discs, leaky hydraulics etc. The term 'efficiency' is incorrect, but probably understood well enough. 'Effectiveness' would be better. However, I think it's a mischaracterisation to say that e.g. a Tesla's brakes are inefficient compared to that of a truck. There isn't a car sold today that can't lock its wheels in an emergency, and when it comes to braking in every-day driving, it's entirely down to the tyres. A little Pug 107 - if you could fit Tesla-type-and-size tyres - and put another 1000kg on board as 'equivalent mass' - would stop in the same space as a Model S, within some small margin of error to account for suspension geometry, weight distribution, stability control software and such. But there wouldn't be much in it. Stopping is tyres, and since the invention of ABS, has pretty much only been down to tyres.

The brakes on a GTE are going to be about a tenth of the power of a Tesla braking, as the battery is a tenth of the size, thus the maximum currents are a tenth. But they are unlikely to be different in terms of the energy they regenerate, the GTE will convert the kinetic energy more slowly.

I don't know where you get this from. The GTE can recuperate up to 45kW; this is about 33% less than a Model S/Model 3 can. Not a tenth. Yes, it's about an 8C charge rate, but it's applied for a fraction of time, so well-tolerated by the battery.

Clearly regen power isn't proportional to battery capacity. A Prius Mk1 can regen about 30kW, while it only has a 1kWh NiMH battery, of which about 50% is unusable to extend its lifespan.

Whether it will be a factor of 10 in practice I think will more depend on the tyres. Tesla could probably exceed the tyre traction and lock the wheels up if the computer demanded that regen power of the inverter, whereas it is probably not likely for the GTE.

It's unlikely a Tesla could lock wheels with regen alone.

Let's do some simple maths, a modern car can go from 60mph to 0mph in about 3 seconds. If it weighs 1500kg, it has about 540kJ of potential energy. So, it dissipates in its brakes about 150Wh in 3 seconds, or a peak power of 180kW dissipated in the brakes.

It is true that the regen is only on one axle, so we could assume a peak regen power of 90kW on just the rear wheels might get you to the point where the maximum traction of the tyre is exceeded. At which point, the ABS might kick in. The regen braking system does interact with the ABS on every EV I'm aware of, though in many cases it simply acts to disable regen during an ABS event (it doesn't 'pulse' on the Golf, from what data I've gathered.)

It looks like a Taycan might manage it in fact - which is quite impressive. It probably means that, barring some other factors relating to battery cooling, they can likely reduce the heating of the brake discs on sustained sporty driving. But, metal - even ceramic brake discs - are comparably cheap to batteries capable of dumping 4C continuously, so I wonder if it has any significant cost-benefit in the real world.

 

[donald]

Brake efficiency is just there to check if the braking system is compromised, ie bad pads, rusty discs, leaky hydraulics etc. The term 'efficiency' is incorrect, but probably understood well enough. 'Effectiveness' would be better. However, I think it's a mischaracterisation to say that e.g. a Tesla's brakes are inefficient compared to that of a truck. There isn't a car sold today that can't lock its wheels in an emergency, and when it comes to braking in every-day driving, it's entirely down to the tyres. A little Pug 107 - if you could fit Tesla-type-and-size tyres - and put another 1000kg on board as 'equivalent mass' - would stop in the same space as a Model S, within some small margin of error to account for suspension geometry, weight distribution, stability control software and such. But there wouldn't be much in it. Stopping is tyres, and since the invention of ABS, has pretty much only been down to tyres.



I don't know where you get this from. The GTE can recuperate up to 45kW; this is about 33% less than a Model S/Model 3 can. Not a tenth. Yes, it's about an 8C charge rate, but it's applied for a fraction of time, so well-tolerated by the battery.

Clearly regen power isn't proportional to battery capacity. A Prius Mk1 can regen about 30kW, while it only has a 1kWh NiMH battery, of which about 50% is unusable to extend its lifespan.



It's unlikely a Tesla could lock wheels with regen alone.

Let's do some simple maths, a modern car can go from 60mph to 0mph in about 3 seconds. If it weighs 1500kg, it has about 540kJ of potential energy. So, it dissipates in its brakes about 150Wh in 3 seconds, or a peak power of 180kW dissipated in the brakes.

It is true that the regen is only on one axle, so we could assume a peak regen power of 90kW on just the rear wheels might get you to the point where the maximum traction of the tyre is exceeded. At which point, the ABS might kick in. The regen braking system does interact with the ABS on every EV I'm aware of, though in many cases it simply acts to disable regen during an ABS event (it doesn't 'pulse' on the Golf, from what data I've gathered.)

It looks like a Taycan might manage it in fact - which is quite impressive. It probably means that, barring some other factors relating to battery cooling, they can likely reduce the heating of the brake discs on sustained sporty driving. But, metal - even ceramic brake discs - are comparably cheap to batteries capable of dumping 4C continuously, so I wonder if it has any significant cost-benefit in the real world.

I don't think you actually read my post.

Such is the issue when someone bandies around loosely defined terms and thinks they have asked a precise question.

.. and here we go again "Oh, donald said 'this' which I think means 'that' so donald is wrong and a troll", "I didn't mean "that" ', "Oh you DID mean "that", I know you did" .. etc....

"Regen effectiveness" ... could mean aaaaaabsolutely anything.

If someone has a question regarding regen effectiveness, please define it, and then we can have a proper conversation about it.

 

[tom66]

Donald, I was just correcting obvious errors in the post you made, nothing more.

I agree with the broad statement that EVs will have similar regen efficiency, although there are lot of variables to muddy the water, there's no reason in principle it should vary all that much.

 

[donald]

Donald, I was just correcting obvious errors in the post you made, nothing more.

I agree with the broad statement that EVs will have similar regen efficiency, although there are lot of variables to muddy the water, there's no reason in principle it should vary all that much.

There were not any errors, you misread it.

The braking power of the recuperation possible in Tesla is going to be 10 times the GTE. While the GTE can do 45kW a Tesla can do 450kW. But 450kW would lock the wheels, so actually it is unlikely to recuperate that much because of the tyres. That is what I said, and I stand by that as correct.

Was there anything else you felt were 'obvious errors' or was [your misunderstanding on] that it?

 

[tom66]

The braking power of the recuperation possible in Tesla is going to be 10 times the GTE. While the GTE can do 45kW a Tesla can do 450kW. But 450kW would lock the wheels, so actually it is unlikely to recuperate that much because of the tyres. That is what I said, and I stand by that as correct.

I don't agree with this statement. For one, we know the supercharging limit of a Tesla is about 120 - 250kW depending on the model. Not only that, this peak power is only available at a very limited SoC range. So I am not sure you can just go "10x the battery capacity therefore 10x the regen"; the cells in a Tesla (18650, NCA Li-Ion in Model S, some proprietary chemistry in the 3) are distinct from that of the e-Golf/GTE cells used in these VW vehicles, which appear to be much more tolerant of high C discharge/charge, probably at the expense of density. (The GTE's battery is huge being a 7.6kWh unit. It takes up the entire rear bench seat area.)

And, I gave a pretty good example of a wide disparity in battery-capacity-to-regen: the Mk1 Prius at 1-to-30 (and a Prius battery is also pretty big.)

 

[donald]

I don't agree with this statement. For one, we know the supercharging limit of a Tesla is about 120 - 250kW depending on the model. Not only that, this peak power is only available at a very limited SoC range. So I am not sure you can just go "10x the battery capacity therefore 10x the regen";

45kW is only available on the GTE under specific SOC, too. Why do you say that of Tesla but not GTE?

It is a transient charging load, just a few seconds at a time. 4 to 5C is fine, lots of cars do that for regen.

Prius battery is not Li-ion. I don't know what its typical charge/discharge rates are.

 

[tom66]

45kW is only available on the GTE under specific SOC, too. Why do you say that of Tesla but not GTE?

It is a transient charging load, just a few seconds at a time. 4 to 5C is fine, lots of cars do that for regen.

Prius battery is not Li-ion. I don't know what its typical charge/discharge rates are.

45kW is available from 0% to 90% SoC. It's pretty close to available all the time. The only time I've had "Regen fade" was coming down a steep hill with the battery at 85%+ SoC. Otherwise, I've managed 2 minutes of continuous regen at 30kW+ down steep grades.

New Prius is Li-Ion (a mere 750Wh!), and it has the same high charge rates.

If "lots of cars" do 4-5C, why are Tesla and many other EVs capping out around 60kW? Why are PSA not doing 100kW on e-CMP, VW not doing 120kW on ID 58kWh, etc.?

 

[donald]

If "lots of cars" do 4-5C, why are Tesla and many other EVs capping out around 60kW?

Tyre grip That is PRECISELY why I mentioned it and is PRECISELY the thing you chose to ignore, which lead to it being completely confudibubbled. Like I said, I don't think you read what I wrote.

Whether it will be a factor of 10 in practice I think will more depend on the tyres. Tesla could probably exceed the tyre traction and lock the wheels up if the computer demanded that regen power of the inverter, whereas it is probably not likely for the GTE.

On this point,

New Prius is Li-Ion (a mere 750Wh!), and it has the same high charge rates.

If you are saying Prius has a Li-ion capable of recharging at 60C, then it is not any conventional battery that goes in any other EV available here. Li-titanate might be able to take that, maybe that is what is in there? I have no idea. I like LTO, hat tip to them if they have done that, but Toyota did not see fit to bother letting me know.

 

[donald]

The braking power of the recuperation possible in Tesla is going to be 10 times the GTE. While the GTE can do 45kW a Tesla can do 450kW. But 450kW would lock the wheels, so actually it is unlikely to recuperate that much because of the tyres. That is what I said, and I stand by that as correct.

I don't agree with this statement.

Incidentally, it occurred to me I really shouldn't have to argue this exceptionally obvious point. In fact, it is so obviously true it didn't even occur to explain why.

So there is nothing for you to 'agree' or not to, it is not an opinion;

If you have one GTE battery, we're saying it can absorb 45kW. Right?

Put two in parallel, double the capacity, each absorbing 45kW, total = ?

Now puy 10 in parallel, how many could 10 lots of GTE batteries absorb?

Bolt 10 GTEs end to end at their bumpers to make a long car 10 times as long and 10 times the battery capacity. What is its regeneration power now?

Why that point even came up, I don't really understand. But maybe my mechanical intuition is not just one page ahead, it is a whole chapter, and I unwittingly and unintentionally leave people behind in what is trivially obvious to me but may be less obvious to others. For this, I apologise and plead guilty.

 

[tom66]

Dude, YOU are the one who claimed that a Tesla would have 10x the braking capacity of a GTE - even though that is clearly not the case in reality. I showed with some simple maths that you could lock the wheels on about 90kW/axle.

I don't know for sure how Toyota are able to charge their battery with such high currents for a small capacity, or even how VW manage it, but they clearly can do so without worrying the battery too much.

I absolutely agree that tyres are the limiting factor in braking! I literally gave you an example of this concept. On this, we do not disagree.

We're done here - I wonder why I even bother engaging with you. Maybe there's something in the back of my mind that thinks you'll change, but you have to always have the last laugh. Ten pages ahead my arse. 😁

 

[Maturedriver]

Gordon Bennett 😳! When I started this thread I thought my question was relatively simple and uncontroversial? The responses have proved to be interesting, entertaining and informative.

I think I can conclude that the regeneration on the GTE is somewhere between 30kW and 45kW. Nothing special, but reasonable.

 

[donald]

Dude, YOU are the one who claimed that a Tesla would have 10x the braking capacity of a GTE

.... just like I said in post #28, here we go.

"donald said", "it wasn't what I meant", "Yes you did, because I know what you meant" ....


etc......

- even though that is clearly not the case in reality.

Like I said, I still don't think you read what I wrote...

Whether it will be a factor of 10 in practice I think will more depend on the tyres. Tesla could probably exceed the tyre

I showed with some simple maths that you could lock the wheels on about 90kW/axle.

Proving exactly what I said in the first place Like I said, you didn't seem to have read what I put in the first post.

Why are you trying to 're-prove' something I already wrote, if you actually read it?

I recommend you just go back and re-read my original post. If I have left anything unclear, fine, just ask for clarification that diving straight into your aggressive and rude argument.

I don't know for sure how Toyota are able to charge their battery with such high currents for a small capacity, or even how VW manage it, but they clearly can do so without worrying the battery too much.

I absolutely agree that tyres are the limiting factor in braking! I literally gave you an example of this concept. On this, we do not disagree.

We're done here - I wonder why I even bother engaging with you.

You have this the wrong way around.

 

[donald]

Gordon Bennett 😳! When I started this thread I thought my question was relatively simple and uncontroversial? The responses have proved to be interesting, entertaining and informative.

I think I can conclude that the regeneration on the GTE is somewhere between 30kW and 45kW. Nothing special, but reasonable.

If 'regeneration power' was the question, then yes that has a much more objective answer. I assumed you were trying to ask some question 'combined with' efficiency.

As mentioned, it is possible to calculate the regeneration power from tyre traction, but note that there is a difference between front wheel and rear wheel drive. A rear wheel drive will be able to regen much less power than it can accelerate, and a FWD can regen much more power than it can accelerate, these being large body forces.

The ideal is therefore a 4WD arrangement, which Teslas have, and they will have the capability to regenerate the same amount of power as they can accelerate with. As the Plaid X has 700kW of acceleration power through 4WD, so there is no theoretical restriction on it being able to regenerate 700kW. It's just 'that' backwards. Whether Tesla set a limit on regen power, I don't know but it is not an engineering constraint. I guess the front motors might be lower power than the rear, so the actual max power will not be fully reversible in that way. Won't be far off... I'll make a guess .. 450kW.