Typical regen efficiency?

[Anders]

What is the cost of doing some regen ( >B0) and then increase speed again compared to just let the car roll (B0) using its kinetic energy? Let's assume the car has same initial speed, same distance and same speed at end of distance for both cases.

I can imagine there are some losses in both regen chargers and in electricity engines... Of course "it depends" but what are we talking about roughly? 5% loss? 50% loss?

 

[HHL]

What is the cost of doing some regen ( >B0) and then increase speed again compared to just let the car roll (B0) using its kinetic energy? Let's assume the car has same initial speed, same distance and same speed at end of distance for both cases.

I can imagine there are some losses in both regen chargers and in electricity engines... Of course "it depends" but what are we talking about roughly? 5% loss? 50% loss?

You will find very little difference in the overall range whatever you do. It seems to use the friction brakes a bit more in b0 and b1, so the default b2 is probably the best most of the time.

 

[anko]

TS is not asking about differences between various B settings, but the difference between driving with a constant speed versus driving with a fluctuating speed.

If the efficiency of the e-motors / generators was 100% and that of the battery too and there were no other losses either, it would not make a difference. But clearly this is not the case. So, the question is (IMHO): when you decelerate (without use of friction brakes) and accelerate again, how much energy is lost and how much is recovered?

 

[HHL]

TS is not asking about differences between various B settings, but the difference between driving with a constant speed versus driving with a fluctuating speed.

If the efficiency of the e-motors / generators was 100% and that of the battery too and there were no other losses either, it would not make a difference. But clearly this is not the case. So, the question is (IMHO): when you decelerate (without use of friction brakes) and accelerate again, how much energy is lost and how much is recovered?

Well, I guess it's anyone's guess, however, decelerating and accelerating has to be less efficient than driving at a constant speed. I have read some studies on the benefits of regenerative breaking. Surprisingly, it increases overall efficiency in stop start driving by only about 10% and has only marginal benefit in highway driving.

 

[greendwarf]

TS is not asking about differences between various B settings, but the difference between driving with a constant speed versus driving with a fluctuating speed.

If the efficiency of the e-motors / generators was 100% and that of the battery too and there were no other losses either, it would not make a difference. But clearly this is not the case. So, the question is (IMHO): when you decelerate (without use of friction brakes) and accelerate again, how much energy is lost and how much is recovered?

Well, I guess it's anyone's guess, however, decelerating and accelerating has to be less efficient than driving at a constant speed. I have read some studies on the benefits of regenerative breaking. Surprisingly, it increases overall efficiency in stop start driving by only about 10% and has only marginal benefit in highway driving.

I think you are both wrong (or right :lol: ) - as I read it, the OP wants to know whether coasting in B0 from a fixed speed i.e. gradually slowing down with no Regen before accelerating up to speed again is more efficient than doing the same thing at higher B settings, where you will slow down faster but recover some energy.

Obviously yes, because of energy conversion losses but he/she wants to know how much. In other words, if you are faced with a situation where you have the choice would being in B0 be a significant advantage or only marginal?

For example, where I live in Sarf Lundun most of my journey to work is gently downhill and with a 20 mph speed limit. With no other vehicles and traffic lights, I could probably coast in B0 all the way without exceeding the speed limit :mrgreen: Even with interruptions I find I can use very little battery over say 5 miles, range drops by 2 - matched by battery level.

Before the speed limit came in, i.e. more stop/start driving, having to maintain a 30mph speed with less coasting - still in B0 but more braking Regen, battery level & range dropped faster and further for the same journey. How much of this is due to the drop in average speed as opposed to more coasting is probably impossible to calculate. :?

 

[jaapv]

Especially as traffic conditions have far more impact. I would say that maintaining a constant speed should be more efficient than coasting and picking up speed again.

 

[greendwarf]

Especially as traffic conditions have far more impact. I would say that maintaining a constant speed should be more efficient than coasting and picking up speed again.

Still doesn't answer the OP question :?

 

[anko]

Well, I guess it's anyone's guess, however, decelerating and accelerating has to be less efficient than driving at a constant speed.

Your right. I meant to say: "the difference between actively slowing down (via regen) versus passively slowing down (via coasting)" and failed miserably. Way too early

 

[ian4x4]

Remember the PHEV Outlander Technical Highlights Manual
http://www.myoutlanderphev.com/forum/viewtopic.php?f=9&t=1756&hilit=pdf+owners+manual

If you wade through this you will possibly find the answer to your regen to drive efficiency.

The losses are quite large. Page 19 gives a 15% invertor loss in converting the battery DC back to the Drive motor AC alone.
Add to this the generating losses and losses that the battery gives off as heat.

If the Kinetic energy wasn't free I doubt if it would be worth saving.

Just drive as much as possible without braking, just like any other car. Anticipate!!

 

[greendwarf]

So now we are getting somewhere close to answering the OP question. As he is asking about Regen & then accelerating back up to speed again, it must be twice the 15%, DC to AC to DC again, i.e. at least 30% less, perhaps the 3KW used to spin the motors in B0 - so lets say 20% overall less efficient than just coasting in B0. :mrgreen:

 

[jaapv]

But, in coasting you lose speed as well and must accelerate again, just in a more gently rhythm...

 

[greendwarf]

But, in coasting you lose speed as well and must accelerate again, just in a more gently rhythm...

But, as I keep pointing out, the original question was (as I understood it) regarding a comparison between using higher than B0 to gain regen when slowing down and then using this "extra" energy to get up to speed, against doing the same thing in B0. As the later does not involve energy conversion losses. it must be that coasting in B0 under these circumstances is more energy efficient. :mrgreen:

However, the real question asked was how much more efficient, i.e. what are the net losses in the former - anyone a better idea than my 20% figure :?:

 

[ian4x4]

I really have been trying to get realistic efficiency figures.

From the BMW i3 book
https://issuu.com/brycheinsltd/docs/evs_and_i3

Battery / Motor drive efficiency can get as high as 97% (page 38) but is speed dependant.

Generator / Battery efficiency is about 94% (page 53)

It quotes the internal combustion engine as about 25%, I know this is alarming , and from memory diesels are about 35 to 40% efficient.

The BMW book is full of parameters which alter capacity / efficiency / etc. with temperature, SOC etc., etc.

All energy conversion is costly.