Is regenerative braking really worth anything?

[E-HP]

I'm just sayin'. Both my e-bikes have DD hubs, but they don't coast like regular bikes at all.

So until someone makes a declutching DD hub, you either get regen or a bike that coasts freely, but not both.

Ya, not the best for coasting. I have a poor man's freewheeling button that applies about 50 watts, so if I'm going 20 mph, it will coast a block or so on flat ground. Going downhill, it will go negative above 25 mph, but I'm usually regenning by then anyway.

 

[LeftieBiker]

I have a poor man's freewheeling button that applies about 50 watts, so if I'm going 20 mph, it will coast a block or so on flat ground.

Wouldn't that be a "Rich man's freewheeling button"? The poor just stop pedaling.

 

[ZeroEm]

Wow did not realize that this was such a touchy topic. Fairness, mines better than yours, if I don't like it you should not use it, Ride on big soft tires and it does not coast. Well one of these days i'm going to connect my reverse how do you like that.

 

[99t4]

trackebike, your description of your local topography is a utopia of non-braking cycling bliss. Not everyone is as fortunate.

I don't think so. I think it is more about riding style/technique. You're going to have to explain to me these long descents you make where you are able to re-coup significant energy.

Not going to explain because I did not claim my use of regen braking re-couped significant energy. My cycling environment forces me to use the brakes, evidently more than yours, and my use of regen braking saves me the cost and time of having to replace brake pads as often. So that answers your question: "Is regenerative braking really worth anything?" Yes, approx. $100/ year for me. Worth it.

"I think it is more about riding style/technique."
Maybe. I'm always open to ways to improve my skills. Do you have any tips for me?

 

[trackebike]

Maybe. I'm always open to ways to improve my skills. Do you have any tips for me?

I don't know if I can help someone who is burning through $100 /year in brake pads. But I know that it is not the norm. Heck, I don't spend that much in pads on my truck!

Were you burning through $100 a year on brakes pads prior to having an e-bike?

 

[trackebike]

i like rswannabe thread
https://endless-sphere.com/forums/viewtopic.php?f=6&t=103634&p=1526300&hilit=rswannabe#p1525987

Yeah - his claims are so believable...quoting him..

"I've read that you only get about 5% back at best, but I'm seeing far more than that <snip> That's a regen recapture rate of 17.7% and is way higher than I have seen any other reports of, but I believe it."

Sorry - I don't believe it. I don't believe it because I can't envision a bike ride where I am hitting the brakes enough to recover 17%.
If somehow I were to find myself in such a ride it would be something that is so non-typical, off the edge of the bell curve, and a super outlier epic event. I would be talking about it for years.

 

[donn]

I don't believe it because I can't envision a bike ride where I am hitting the brakes enough to recover 17%

Suit yourself. I've never seen 17%, so maybe I shouldn't believe it either. Lies! How can he think he will get away with it!? [ for the humor impaired, that was written in jest. ]

So, actually it probably is slightly off - given the usual source of these numbers, it's probably a bit short of 16%. That's really quite possible, though unusual. I don't remember seeing that ever, but occasionally get 12% of forward Wh. I will just assume that you don't believe this either. Suit yourself. I think you're making a fool of yourself here, but you do what you have to do.

One factor in this that I think is hard for some people is that riding at high speed will eat into this figure, significantly. Wind resistance losses can't be recovered at all, and that goes up dramatically. When you're burning twice as much power to get there in a hurry - twice as much per unit distance - your regen is going to tend to be half as much, when expressed a percentage of forward watt-hours. For example, 15mph vs 25mph - the latter will use twice as much battery to get there (and that's without any leg input.)

 

[caseylain]

The regen brake on my ebike was more then capable of bringing me to a stop if I applied it early enough. I had a programmabIe controller so I set the regen current up to 50 amps, which is higher then most setups. I also gave it its own button so I could regen brake without using mechanical brakes. I don't actually know how much energy I got back but just the thought I was at least stealing back some of my momentum from the damn red lights felt good.

Also so you know I do bicycle delivery downtown so I do a LOT of braking. I've developed a serious hatred for all the red lights robbing me of energy.

Unfortunately I was regening so much I burnt out the controller.

 

[john61ct]

Again, I do **not** think the recaptured energy justifies spending more on regen braking for many use cases.

Same with pad wear & tear, although I believe those cases to be more common.

But there are situations where the added braking effectiveness and capacity is a huge advantage, in fact for some cases **absolutely essential** to basic safety.

Those cases are less common to be sure, but they do exist.

Notice the OP was careful to eliminate those factors from their polemic.

 

[fechter]

Actual number from a hilly 46 mile trip

 

[99t4]

Were you burning through $100 a year on brakes pads prior to having an e-bike?

No. Previous (non e-)bike was much lighter, and I didn't ride it as much, or as fast. ALSO, I didn't say I spent $100 on pads. I considered downtime and labor costs, etc.

I got the e-bike because of local road infrastructure failures because the car is not effective transportation ATM so I rely on the e-bike for ~90% of my transportation needs now. Must say it has been much more pleasurable and enjoyable. Repurposed a kiddie trailer to haul the necessary items around for work and shopping, which increases the demands on the braking system.

Remember: My cycling environment is much different than yours. Please try to understand that before telling me I'm mistaken, or lacking skills, or doing it wrong. Just stop it, as it doesn't contribute to a constructive discussion.

 

[Balmorhea]

I don't know how much did you haul in your trailer. But you, your bike, and everything you could possibly put in there and carry on your person don't amount to as much mass as me on my bike, empty. Almost nobody does. My city isn't flat but isn't especially hilly either. I have lived and ridden in cities that were hilly by anybody's standards, though.

My rim brake pads (Kool Stop) last me for many years. Long enough that I can only say "many". Disc brake pads, on the other hand, have had sometimes shockingly short wear life. I have only my bikes for transportation. I don't use regen braking, because I value a reliable bike that doesn't unscrew its axle nuts and destroy itself.

 

[Steph]

This is the part of my commute for which I’m considering regen. You can see the descent and the speed profile.


First slowdown is at a sharp turn before the real descent starts. I usually don’t slow that much but cars really slow down, visibility is bad and ice sheets tend to form in winter.
Second one is a T junction with a stop for me, a very justified one because I cannot see the right incoming lane and I take the left one.
Third one is a bumper after a sharp turn (I don’t see what’s ahead but there are often pedestrians walking their dog...). Then, it’s getting into a long descent on cobble stones; I freewheel or even pedal unless wet or iced.
Fourth is a big junction with a traffic light with a quite short green window so I nearly always have to stop. From this point on, traffic is heavy and commuters are not not most careful/patient kind of drivers so it’s not smart to be on the edge of controllability.
Fifth is a traffic light for a school. Just then is a big descent. It’s not uncommon to keep the brake half squeezed because traffic limit my speed.
Sixth stop is a junction, where I need to wait for a gap in facing traffic to take a left turn. Then the steepest part (it has a 30kmh limit which drivers tend to follow or go even slower because the way is very narrow); there’s also a stop at the bottom that tends to accumulate cars. Here again I have to brake a lot.
Last stop is the stop I mentioned, plus I’m taking a very sharp right turn.

To sum up, I have at least two sections where I regularly squeeze a bit the brakes for a long time (40m descent total so roughly 35kJ of gravity energy considering my weight) and a few hard stop (that I can either address aggressively of anticipate smoothly).

Not to generalize, but I’m quite confident that my commute will benefit from regen.

(For the curious people, this trip corresponds to the Meudon ascent of Paris Versailles running race, except for the lowest section, which takes a steeper variation).

 

[qwerkus]

You guys forget the main advantage of dd hubs: no internal moving parts. Running a dd hub in true FOC (no sensors) is the sturdiest setup any ebike can have. This means a working motor AND a working brake in any conditions. Imo this is why I moved to dd hubs. That and silence.
Regen is negligible and I would trade it any time for a freewheel ...

 

[trackebike]

This is the part of my commute for which I’m considering regen.

Part of your commute. You need to be specific here. How far and what is the rest of commute like?

Not to generalize, but I’m quite confident that my commute will benefit from regen.

I'm glad you did not generalize. For if it is the case where one commutes down a long hill then it is most certainly not typical.
In any case I don't think you will get from regen what you conjecture.

(For the curious people, this trip corresponds to the Meudon ascent of Paris Versailles running race, except for the lowest section, which takes a steeper variation).

OK, so it looks like you are talking about the image below...what is this about 1.6km of 7% descent? It is nothing much, and you are expecting too much from regen.



Let's look at it another way. Your motor in the bike is something like 80-85% efficient. I presume it is that or even less so when regenerating. Assuming you braked the whole way down (which you did not, you braked in little bits) you would only recouped probably 1/2 of that hill back on regen. But since you braked in small bits going down that decent you will get even less.

I climbed 3/4 mile 7% on my e-bike last night without applying power (I was staying with other non-ebike riders), If you got half of that back through regen in your situation, then you got a hill of beans.

 

[E-HP]

This is my regen from last week. 5 days, maybe 10 miles per day. No hills, totally flat bike path. I was mainly playing around testing my throttle technique, and battery pack performance, so I probably only hit my actual brake lever 3 or 4 times per ride, mainly braking with throttle. On two days, I rode in a direction that had almost zero braking. The other three days, I went the other direction, so slowing for cross streets every 3 blocks or so, all using throttle, then accelerating to about 28mph before slowing for the next cross street. Not a lot of regen, but you can still go pretty far on 1Ah at 66V, so can't complain about free energy, especially from riding on the flats.



I see something more like 14% (whichever way the CA calculates it) on normal rides around my neighborhood.

 

[john61ct]

Do not trust CA calculations.

Use precise A/B testing discharge to compare the remaining Ah after the ride with regen vs without

 

[Steph]

This is the part of my commute for which I’m considering regen.

Part of your commute. You need to be specific here. How far and what is the rest of commute like?

Actually I don’t need to be specific (even this part of my trip is not fully relevant, I mostly wanted to present the braking profile in sync with the slope) and that’s a big part of my equation:
As mentioned in a previous post, my plan (yes, my bike is not converted yet) is to go for a clutched motorisation, so I can de/activate it for both driving and regen situations.
For the rest of my commute, I plan to keep the bike in human power only mode (it’s flat enough for me to pass street legal ebikes so I would only incur motor drag).
Going down, whatever regen I can get is a free gain and a saving on my pad budget. (It won’t get me rich but it’s one maintenance point to do less often, a tiny bit of comfort that I care for).
Going up I don’t even plan to use the assist all the way, but there are a couple of steeper section that really break my rhythm (average slope is at 7% but topping at 12 to 14% in these sections) and this is where I want to use some assist.

Reading all the responses, I get that the typical setup in consideration is for an always engaged motor, and the ”efficiency” relates to the full trip (regen watts/drive watts, with distance of both sections summing as the total trip distance). With a disengaging motor, I could ironically get over 100% (selectively using regen going down and hardly using assist at all); in a sense, using my legs to charge the battery.
Because of this I have a hard time figuring what 7% or 14% regen means for me. I don’t care about extended range, my commute remains the same.

With respect to the initial question, regen‘s, like assist’s, worth depends a lot on your use and what you expect from it. I’m looking for reducing my pads consumption, toying with technology as diy’er and possibly have a near “never plug to a wall” system (in the context of my commute only); the last one being more about curiosity towards its achievability.

Still, something “is worth it” when associated gains exceeds the associated pains. I’ve seen many dissing the gains but I’d be interested in hearing about the pains and as diy community, tackling these pains should be the challenge.

Cheers,
Stephane.

 

[ZeroEm]

by Steph » Sep 25 2020 8:10am

trackebike wrote: ↑Sep 23 2020 7:26pm

Steph wrote: ↑Sep 22 2020 4:52am
This is the part of my commute for which I’m considering regen.

Part of your commute. You need to be specific here. How far and what is the rest of commute like?

Actually I don’t need to be specific (even this part of my trip is not fully relevant, I mostly wanted to present the braking profile in sync with the slope) and that’s a big part of my equation:
As mentioned in a previous post, my plan (yes, my bike is not converted yet) is to go for a clutched motorisation, so I can de/activate it for both driving and regen situations.
For the rest of my commute, I plan to keep the bike in human power only mode (it’s flat enough for me to pass street legal ebikes so I would only incur motor drag).
Going down, whatever regen I can get is a free gain and a saving on my pad budget. (It won’t get me rich but it’s one maintenance point to do less often, a tiny bit of comfort that I care for).
Going up I don’t even plan to use the assist all the way, but there are a couple of steeper section that really break my rhythm (average slope is at 7% but topping at 12 to 14% in these sections) and this is where I want to use some assist.

Reading all the responses, I get that the typical setup in consideration is for an always engaged motor, and the ”efficiency” relates to the full trip (regen watts/drive watts, with distance of both sections summing as the total trip distance). With a disengaging motor, I could ironically get over 100% (selectively using regen going down and hardly using assist at all); in a sense, using my legs to charge the battery.
Because of this I have a hard time figuring what 7% or 14% regen means for me. I don’t care about extended range, my commute remains the same.

Regen does not work with a free wheeling motor. Think of it as a generator if it is not running/spinning your not making electricity.
The % of regen is just the watts recovered from the watts used. What it means for you if you don't care about extended range and just want to save brakes. Set it up with your motor cut out on your brake and tune it where you like and for get about it.

With respect to the initial question, regen‘s, like assist’s, worth depends a lot on your use and what you expect from it. I’m looking for reducing my pads consumption, toying with technology as diy’er and possibly have a near “never plug to a wall” system (in the context of my commute only); the last one being more about curiosity towards its achievability.

Still, something “is worth it” when associated gains exceeds the associated pains. I’ve seen many dissing the gains but I’d be interested in hearing about the pains and as diy community, tackling these pains should be the challenge.

Cheers,
Stephane.

"Worth" why is everyone keep talking about cost and Worth. You have DD motor, average controller and the required motor cut off you are regen capable, no cost. Are you counting how much your time is worth to set it up. If you takes you to long then your time is not worth much.

I have gotten 100% or 100+ regen but don't talk about it. It's all about how you ride. Some times ride with a group that close by and all are non e-bikers and they ride 5-15 mph mostly to the lower end. my level 1 pas is 0w but my system is on so regen works. Figure how much the controller is using being on and me recovering power from my pedaling or human watts. Some times when I ride with this group about 8 mph, I run regen while pedaling to make more work for me. It is easy to see that 100+% is doable but not worth talking about. For me tracking my regen is a waste of time, do look at it and most of the time is around 5%. What I do watch is watts per Km. Have done rides trying to max my regen, many keep your speed down below 20 mph and peddle as much as you can. If I track my regen on a typical ride the watts recovered would be close to the same, the % would change depending on my riding style or how many watts used. I have peddled down hill with regen on to get a few extra watts but we are not good power sources for generators.

 

[E-HP]

I only look at the numbers on the right on my CA display, the Ah. If I have 1.2Ah just riding around on flat ground, and my normal riding style, it's nice. it's usually a lot more since I'm usually riding on hills.

Whether regen is worth something, depends on the person's priorities, but maybe using a different question that might be more universal, using the same 1.2Ah. Let's say you buy a quality battery, for example 48V 16.5Ah Panasonic GA, 40A BMS. So it finally arrives and you eagerly charge it up to test it's capacity.

If it tested at 16.5Ah, you should be satisfied right?; meets expectations.
How would you feel if it tested 15.3Ah?
How would you feel if it tested at 17.7Ah?
When I say regen is nice, I mean it feels like the latter. Sometimes it's really nice.

 

[Balmorhea]

If it tested at 16.5Ah, you should be satisfied right?; meets expectations.
How would you feel if it tested 15.3Ah?
How would you feel if it tested at 17.7Ah?
When I say regen is nice, I mean it feels like the latter. Sometimes it's really nice.

But when you spin the axle and it costs more to fix it than to get another motor, that feels not so good.

Reversing torque does that to pedals, to cranks, and to the axle nuts of hub motors. Using a freewheel rather than a fixed gear prevents it for pedals and cranks, and using forward-only drive prevents it for hub motors.

 

[John in CR]

If it tested at 16.5Ah, you should be satisfied right?; meets expectations.
How would you feel if it tested 15.3Ah?
How would you feel if it tested at 17.7Ah?
When I say regen is nice, I mean it feels like the latter. Sometimes it's really nice.

But when you spin the axle and it costs more to fix it than to get another motor, that feels not so good.

Reversing torque does that to pedals, to cranks, and to the axle nuts of hub motors. Using a freewheel rather than a fixed gear prevents it for pedals and cranks, and using forward-only drive prevents it for hub motors.

If your axle budges at all (loosening axle nuts, clicking when you hit regen, etc.) then you don't have proper torque arms and/or the flat area of the axle isn't of sufficient design. IOW your motor is not properly attached to the bike, which is one place you don't want to take shortcuts. I use clamping dropouts and some of my builds don't even have axle nuts, and none of even need them. The same can be accomplished with clamping torque arms, which are quite easy to make. On/off type regen is nice whether it's tuned soft or strong, the difference is just learning the speed and distances for engagement to use the mechanical brakes little enough that you can go a year or more without fiddling with brake maintenance. Variable regen is several times nicer, plus its gradual engagement causes drastically less stress on the dropouts/torque arms than on/off instant engagement regen, so spinning axles or loose nuts is far less an issue. Once you're sold on ebikes as transportation, then it's time to graduate to a more advanced controller with true control of current with the throttle (torque throttle) and variable regen. The extra cost is well worth the benefits, and with some it actually pays for itself over the long-term through greater efficiency. Proper throttle control and variable regen are things you'll never give up once you experience them regardless of the power and speed of your ride.

 

[serious_sam]

If your axle budges at all (loosening axle nuts, clicking when you hit regen, etc.) then you don't have proper torque arms and/or the flat area of the axle isn't of sufficient design. IOW your motor is not properly attached to the bike,

Agreed.

I don't use regen braking, because I value a reliable bike that doesn't unscrew its axle nuts and destroy itself.

Using the argument that regen will cause the axle to spin is bullshit. The spun axle is not because of regen. It's because of inadequate axle fixing for the purpose. Stop trying to confuse the two things.

You're arguing as if it isn't possible to make dropouts to handle regen. Maybe you can't, but many of us can and have. Happily living with basically more variable regen than the tyre can hold. No problems with the motor, axle, dropouts, or anything else.

It might not be for everyone, but it makes some of us very happy.

 

[donaldallen3797]

I use front hub motors on my drop bar bikes and find the regen feature to be only be outclassed by the cruise control feature. The red button on the left hood is a momentary switch and when I want to slow down it is the first thing I go to. I can fully utilize the front lever while holding it also for full stops. Also works well as a drag brake when I don't want to go too fast downhill and will keep me at around 30 or so nicely while modulating it. As mentioned this is great for saving on pad wear.

thumbnail_IMG_1982.jpg

If you don't think it would work for you then it is easy to leave off the program.

Hi , Can you tell me who's kit your using with cruise control please ? I have the Magic Pie Black Pie 1000 watt and the cruise is a must ...Just wondering who else sells them with cruise control ...

 

[Balmorhea]

But when you spin the axle and it costs more to fix it than to get another motor, that feels not so good.

Reversing torque does that to pedals, to cranks, and to the axle nuts of hub motors. Using a freewheel rather than a fixed gear prevents it for pedals and cranks, and using forward-only drive prevents it for hub motors.

If your axle budges at all (loosening axle nuts, clicking when you hit regen, etc.) then you don't have proper torque arms and/or the flat area of the axle isn't of sufficient design.

You'd think so. But cranks mounted on square tapers don't "budge", and neither do pedals that have been tightened upon mounting. But both can move enough under reversing torque to back the fasteners off, and then everything goes sideways.

The remedy, if you must use fixed gearing, is to check and tighten these things often. I'm willing to bet that not one in ten people running regen braking do that.

You can prevent the problem by using clamping dropouts. I'm willing to bet that not one in a hundred people using regen do that.