# Regerative braking



## major (Apr 4, 2008)

HDS said:


> It seems that most EV's have regenerative braking that kicks in as soon as the foot is off of the accelerator. Why is that? It seems to me that you would want to glide as freely as possible for as long as poossible and only start the "regen." when the brake pedal pressure is applied.


To mimic the response of the ICE car. It is an entirely programmable feature which the manufacturer chooses to give the public. I think because they feel there is an expectation that the EV will drive/feel like the ICE car. Given a choice I prefer the pure coast mode although it takes some getting used to, but not much.


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## dragonsgate (May 19, 2012)

major said:


> To mimic the response of the ICE car. It is an entirely programmable feature which the manufacture chooses to give the public. I think because they feel there is an expectation that the EV will drive/feel like the ICE car. Given a choice I prefer the pure coast mode although it takes some getting used to, but not much.


There are certain hills around here that I would like to have a bit of regen on but then there are stretches I like to let it coast. If I understand it right with regenerative braking you can feather the peddle while going down hill and cancel out the regen with out using any electricity.


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## Caps18 (Jun 8, 2008)

It is easier, cleaner, and cheaper to implement the instant regen. It doesn't make it right or the best choice though.

I would think that being able to coast and then choose to use regen when you come to a stop sign or red light makes a lot of sense. What I haven't seen is a test that anyone has done that shows how much more energy is saved by being able to coast down a country road or highway, or even in the suburbs at lower speeds. One of the tests I plan to run when I get my truck working is to go to a closed runway (1.25 miles long) and get it up to different speeds and see how far it will go. And then get to the same speed and use 100% regen and see where it stops and if there is someway to tell how much energy was recovered and how far that would get you. Is it 10% more range, 20%, 50%???


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## evmetro (Apr 9, 2012)

Off throttle regen does not make sense unless it is used as Major said above, to make it feel like an ICE. There is a lot of useful energy available to recover, but the only way to recover anything useful is to recover it at the appropriate time, and in the appropriate quantity. Having no regen at all pays off by letting you use kinetic energy that is lost to off throttle regen configurations, but does not allow any waste energy recovery. Having off throttle regen allows recovering of waste energy, but it cancels itself by harvesting useful kinetic energy. The way to get this right is to not have off throttle regen at all, but still collect as much braking energy as possible.

The controller is set up to regen at 10 to 15% of its capabilities on an off throttle regen configuration, so the other 85 to 90% is not used. In my on-demand system that I use, I have no off throttle regen, but I have a thumb button on my shifter knob that is a variable regen button. When I need to slow down, I push the button down as much as I need, and I have access to all of the controller's regen capabilities. The button will slow me down I tiny bit if I need to, and it can bring me to a halt in a heavy emergency stop if needed. The key here, is that this system collects ALL of the braking energy, and it let's me harvest and maintain the ever important kinetic energy that hardly anybody talks about.


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## major (Apr 4, 2008)

evmetro said:


> .... that this system collects ALL of the braking energy, and it let's me harvest and maintain the ever important kinetic energy that hardly anybody talks about.


The braking energy is the kinetic energy, or potential energy if going downhill.


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## evmetro (Apr 9, 2012)

major said:


> The braking energy is the kinetic energy, or potential energy if going downhill.


Thanks. I have been thinking of the braking energy as the heat that is created by the friction brakes that is lost into the air, and the kinetic energy as energy that is lost to cyclic variances of the speed of the vehicle. Either way, I don't see a lot of discussion about how critical this energy is like I see for regen. My road test don't show any significant gains on a flatlands range test at 55mph, but on mountain and foothills country roads, the results are breath taking.


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## kubvan (Dec 9, 2014)

In my on-demand system that I use said:


> I like this idea, I have an old series wound shunt motor and an old curtis controller with no regen. I also at the moment I have no recharge set up for my accessory battery. Not enough sunshine for the solar panel. I am thinking about connecting an alternator to the tail shaft of the motor and indeed having a push button and or brake pedal to engage it. Every little bit helps I think. The other wild idea is to put a rear differential in with some kind of generator to do the same, clearly added weight etc may be counter productive.


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## RIPPERTON (Jan 26, 2010)

*Re: Regenerative braking*

As the self proclaimed King of Regen, I can state through exhaustive test driving that a properly solicited variable regen system can extend range by 27%. This isn't due to gadgetry, its due to driver technique.
There is such an element of fuzzy logic that driving becomes a contest of how well you can read the road and traffic conditions. Looking and thinking ahead to spot red or amber lights and spreading the regen out over the longest interval. In traffic you might use the same coulomb 5 times before its lost in heat and EV's are at their most efficient in traffic jams.
The beauty of regen is that it is proportionate to your driving intensity, ie you don't have to drive aggressively to get the most return. You can use regen exclusively driving from point A to B just by driving sedately and never having to touch the brake pads only to hold the car stationary at the lights.
Like others I also prefer to have no throttle off regen as in 90% of downhill sections arnt steep enough to overcome rolling and wind resistance so its best to let the car roll or use light throttle. Having throttle off regen reduces your control over the vehicle as its a pre-set function that you cant easily over ride without delicate throttle application. In terms of vehicle control, you should never let a machine think for itself. ie no driver input means no machine function. Something Elon should take note of.
Ive measured that for every 1km of vertical descent you can harvest 2kWh of electrical energy but inversely the ascent will cost you 2kWh extra. 
I once did 116km on 8.5kWh driving down the Blue Mountains in Sydney's west where normally I would get 90km on the flat.
KubVan heres an alternator with AC compressor clutch to activate it only during decell.


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## major (Apr 4, 2008)

evmetro said:


> I have been thinking of the braking energy as the heat that is created by the friction brakes that is lost into the air, and the kinetic energy as energy that is lost to cyclic variances of the speed of the vehicle.





major said:


> The braking energy is the kinetic energy, or potential energy if going downhill.


More correctly, I should have said: The braking energy is the change in kinetic energy, or the change in potential energy if going downhill.

The Kinetic Energy (KE) is proportional to the speed squared. So when you brake the difference in KE, start to finish of the braking period, is the energy converted to heat via the brakes, as well as the rolling resistance loss and aero loss during that period.


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## kubvan (Dec 9, 2014)

"KubVan heres an alternator with AC compressor clutch to activate it only during decal."

Perfect !! thanks


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## evmetro (Apr 9, 2012)

*Re: Regenerative braking*



RIPPERTON said:


> driver technique.


Driver technique is huge, but over the long haul, there will be inevitable lapses of this. This is why it pays off to set your EV up in such a way where you don't have to apply technique in order to gain efficiency. Technique AND the right set up will be best, but getting the friction brakes and off throttle regen out of the picture will yield better economy even if you are not applying technique. The key to variable on demand regen is having it easy and convenient to access. I have placed my thumb pot where I like to rest my hand anyway, and I have found that it is much easier to use the thumb pot than it is to use the foot brake. Originally, I was not sure how convenient it would be to add such a control, but I had not taken into consideration how easily humans adapt to the path of less work. As it turns out, the thumb pot makes for a more relaxing way to drive, while it harvests ALL of the braking energy.


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## kennybobby (Aug 10, 2012)

Not sure about the other OEMs, but one thing i appreciate about the mitsu miev is the progressively higher levels of regen available with the shift lever, N-D-E-B, which merely connects to a switch to send a signal to the controller. The regen can be none (coasting), ~10%, ~50%, and 100%, and it can also be modulated in any gear to have none by feathering the throttle position. It would be great to develop this sort of algorithm for the diy controllers.

Ripp and Metro are the undisputed regen masters for sure...not sure why Dan has so much negative rep, lol


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## evmetro (Apr 9, 2012)

kennybobby said:


> Not sure about the other OEMs, but one thing i appreciate about the mitsu miev is the progressively higher levels of regen available with the shift lever, N-D-E-B, which merely connects to a switch to send a signal to the controller. The regen can be none (coasting), ~10%, ~50%, and 100%, and it can also be modulated in any gear to have none by feathering the throttle position. It would be great to develop this sort of algorithm for the diy controllers.
> 
> Ripp is the undisputed regen master for sure...not sure why he has so much negative rep, lol


At this point in the game, I think that the regen features on the 1238 and 1239 exceed what the OEMS have to offer. I don't know everything about all the OEM offerings, but I am not aware of any who capture ALL of the braking energy while also having such a nice relationship with kinetic energy. After all of my testing, I can't imagine why this is not standard equipment on the OEM EVs. An adjustable off throttle setting like the one you describe sounds cool and all, but it is only allowing you to adjust how much energy you would like to waste. I have a DC Metro conversion, an AC off throttle Metro conversion, and my latest Metro AC conversion with the variable on-demand regen system. After driving and testing all three of these conversions on all kinds of roads, I self proclaim myself into Ripperton's master of regen club as well.


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## puddleglum (Oct 22, 2008)

I know I have no experience with this, but it seems to me that a really good setup would be to have no regen on the throttle have the regen connected to a pot on the brake pedal (like evmetro's thumb pot) so the regen simulates the brakes and would do the braking for anything less than a panic stop.


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## evmetro (Apr 9, 2012)

puddleglum said:


> I know I have no experience with this, but it seems to me that a really good setup would be to have no regen on the throttle have the regen connected to a pot on the brake pedal (like evmetro's thumb pot) so the regen simulates the brakes and would do the braking for anything less than a panic stop.


This is actually a reasonable compromise, but inevitably, there would be a blend of regen and friction at some point in order to give the pedal the right feel. A brake pedal pot blend like this would probably need to control a smaller portion of the controller's regen potential than a thumb pot that controls all of it. When you are controlling ALL of the braking action with a pot, there needs to be more travel with a very intuitive feel. In the case of a brake pedal pot, this would mean either a more sudden transition to the friction brakes, or less electronic control range. I leave the factory friction brakes exactly as they were from the factory, ready to function at their best with the factory proportioning valve and all. I have had a few times when I have used the factory friction brakes for sudden stops, so it is nice to have them functioning the way the original engineers intended them to. Most of my sudden stops are handled by my thumb pot, since it is faster and easier than the foot pedal.

I still plan to experiment with the brake pedal pot, since there may be some potential there, but as far as efficiency goes, it still sounds like a blend of friction and regen. Less friction than on an off throttle set up, but any use of the friction brakes at all equals wasted energy.


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## RIPPERTON (Jan 26, 2010)

evmetro said:


> I self proclaim myself into Ripperton's master of regen club as well.


You know there can be only one Master...


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## evmetro (Apr 9, 2012)

RIPPERTON said:


> You know there can be only one Master...


We will have to keep our brains working on how to do better, but at this time, I would allow anybody into the club who has eliminated off-throttle regen and the friction brakes from the equation.


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## kubvan (Dec 9, 2014)

Lots of ideas out there just need to find the right one.

Hydraulic Regenerative Braking.
An alternative regenerative braking system is being developed by the Ford Motor Company and the Eaton Corporation. It's called *Hydraulic Power Assist* or *HPA*. With HPA, when the driver steps on the brake, the vehicle's kinetic energy is used to power a reversible pump, which sends hydraulic fluid from a low pressure accumulator (a kind of storage tank) inside the vehicle into a high pressure accumulator. The pressure is created by nitrogen gas in the accumulator, which is compressed as the fluid is pumped into the space the gas formerly occupied. This slows the vehicle and helps bring it to a stop. The fluid remains under pressure in the accumulator until the driver pushes the accelerator again, at which point the pump is reversed and the pressurized fluid is used to accelerate the vehicle, effectively translating the kinetic energy that the car had before braking into the mechanical energy that helps get the vehicle back up to speed. It's predicted that a system like this could store 80 percent of the momentum lost by a vehicle during deceleration and use it to get the vehicle moving again [source: HybridCars.com].


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## puddleglum (Oct 22, 2008)

evmetro said:


> This is actually a reasonable compromise, but inevitably, there would be a blend of regen and friction at some point in order to give the pedal the right feel. A brake pedal pot blend like this would probably need to control a smaller portion of the controller's regen potential than a thumb pot that controls all of it. When you are controlling ALL of the braking action with a pot, there needs to be more travel with a very intuitive feel. In the case of a brake pedal pot, this would mean either a more sudden transition to the friction brakes, or less electronic control range.
> 
> I still plan to experiment with the brake pedal pot, since there may be some potential there, but as far as efficiency goes, it still sounds like a blend of friction and regen. Less friction than on an off throttle set up, but any use of the friction brakes at all equals wasted energy.


I totally agree that putting the pot on the brake pedal would likely lead to some use of the brakes, but the advantage is that it is much more intuitive for building a car that anyone can drive without the wasted energy from off throttle regen. 
I think that there may be a way to minimize the overlap by simply increasing the freeplay in the brake pedal thereby lowering the applied pedal height. This should give more pedal range to activate the regen. Most cars have a lot of extra pedal travel after the brakes are fully applied anyway. Of course my ideas often function better in my head than in real life and I've never tried it.


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## Moltenmetal (Mar 20, 2014)

That'll be the way I attempt it at first- using the free play in the brake pedal. The pot is fine if nobody else drives your car.

My car is rwd so I will also need a switch to defeat or reduce peak regen current for wet weather driving, otherwise I might lock up the rear wheels. The Curtis econo mode will allow two different regen settings selectable by a switch.


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## evmetro (Apr 9, 2012)

Moltenmetal said:


> That'll be the way I attempt it at first- using the free play in the brake pedal. The pot is fine if nobody else drives your car.
> 
> My car is rwd so I will also need a switch to defeat or reduce peak regen current for wet weather driving, otherwise I might lock up the rear wheels. The Curtis econo mode will allow two different regen settings selectable by a switch.


The rain thing is an important consideration. I took my rig out in the rain when I was setting it up to find out where the regen would become a problem, and kept turning it up further and further until I found the maximum regen setting that I could use without loosing traction in the rain. It has been awhile, but I think it is set for around 68% of maximum. The setting works great in the summer as well, since 68% stops me as well as the tiny little factory brake rotors do. My guess on your rig is that you may have to use a lower setting since you have rear wheel drive. The settings are easy enough to change that you can just change them at the change of the seasons if you end up with two different settings. The economy mode may be a nice way to flip settings with a switch, but I leave the regen settings the same on my economy mode. The economy mode is a fantastic way to improve the range. I use it almost all the time, but it is nice to have the switch ready for when you need to pull out into traffic really fast.


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## Tony Bogs (Apr 12, 2014)

Rain, yes, and also snow, ice, oil. 
So engineers invented the anti-lock braking system. In my case, ABS has prevented several collisions. 
So I'd suggest wheel speed sensor input for regen braking as well.
And a combination of off-throttle regen (with coasting) and the conventional brake pedal action (leaving the existing ABS unchanged).


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## RIPPERTON (Jan 26, 2010)

http://www.ebay.com.au/itm/0-100-PS...825c4d&pid=100009&rk=6&rkt=10&sd=191186493357
Heres a 100psi transducer that has a burst pressure of 20,000psi !
That's a bit better quality than the Chinese ones Im using on my race bike.
What this means is that you could put this in the front brake hydraulic line and it would go through its own pressure range before the pads touch the discs then when you transition from regen to friction by increasing pedal pressure the unit wont blow up because the max line pressure you will generate in the front brakes is about 2000psi.
The only problem with integrating brake and regen controls is making an emergency stop at high speed (100kmh), ie you will generate so much current that the regen function will trip out. Tripping the regen isn't much of a problem, you just reboot to wipe the fault code but the spike of mechanical forces in the motor will eventually wear the windings and or damage magnets. Just say you fine tune the max regen value at 60% so that it works well at low traffic speeds like 60kmh ie it doesn't trip out when you go from regen to friction. That 60% value will trip the system at highway speed.
So.... its better to keep regen and brake controls separate.
Some physics...
http://stoptech.com/technical-support/technical-white-papers/brake-system-and-upgrade-selection


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## major (Apr 4, 2008)

RIPPERTON said:


> The only problem with integrating brake and regen controls is making an emergency stop at high speed (100kmh), ie you will generate so much current that the regen function will trip out. Tripping the regen isn't much of a problem, you just reboot to wipe the fault code but the spike of mechanical forces in the motor will eventually wear the windings and or damage magnets. Just say you fine tune the max regen value at 60% so that it works well at low traffic speeds like 60kmh ie it doesn't trip out when you go from regen to friction. That 60% value will trip the system at highway speed.


Hi Ripper,

This might have been the case with the control system you were using, but the problems you describe are not inherent to regeneration systems. I've done induction motor drives in competition to commercial to personal vehicles and have been able to get full regen braking at any speed, blended with the friction brakes when needed and without any faults or trips. 

Regards,

major


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## RIPPERTON (Jan 26, 2010)

major said:


> Hi Ripper,
> This might have been the case with the control system you were using, but the problems you describe are not inherent to regeneration systems. I've done induction motor drives in competition to commercial to personal vehicles and have been able to get full regen braking at any speed, blended with the friction brakes when needed and without any faults or trips.
> Regards,
> major


 Agreed, this is a Kelly thing. So integrated systems should work in most applications with this transducer.


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## evmetro (Apr 9, 2012)

RIPPERTON said:


> So.... its better to keep regen and brake controls separate.


This is one of many reasons why you are in the masters of regen club. There may be a time and place to blend friction with regen, but ultimate efficiency is not one of them. If one were to have a different goal where a blend is appropriate, it would be very easy to compromise some aspect of the original friction brake system that was most likely very well thought out by engineers who do this kind of thing.

I am with Major on the regen limits, since I run a different controller. I keep my regen set somewhere around 65% range since I need less than 500 amps to handle my braking needs, but I have experimented with full regen as well, until I set it up for wet road safety. I did not experience any problems with the higher current, but my motor mounts did not like it very much.


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## RIPPERTON (Jan 26, 2010)

Mitsubishi for example (IMIEV) probably couldn't expect the majority of their clients to get their heads around a dedicated variable regen control like the Mira had so they had to integrate regen into the existing brake system but in doing so they give up a bit of range ie the EMIEV get 116Wh/km and the Mira often did less than 100Wh/km.
Ideally manufacturers should provide an optional dedicated regen control.


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## ken will (Dec 19, 2009)

_"The Times They Are a-Changin"

I learned to drive in a 1930 Ford where you had to manually adjust the choke, manually adjust the spark advance, pause between gears because they where not synchromeshed, and remember how to get to Grandma's house without GPS,.. and I don't text and drive,.. So I prefer to have control of regen.

Some people prefer not to think while driving,.. so automatic regen. would be better for them.



_


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## major (Apr 4, 2008)

evmetro said:


> There may be a time and place to blend friction with regen, but ultimate efficiency is not one of them. If one were to have a different goal where a blend is appropriate, it would be very easy to compromise some aspect of the original friction brake system that was most likely very well thought out by engineers who do this kind of thing.


A good reason to "blend" or make sure the friction brakes are used regularly is to keep them functional. It isn't good for them to go weeks, months, perhaps years without use because you exclusively use regeneration. That is a recipe for disaster when/if you need those service brakes. I programmed the controllers to fade out the regen (which was on the brake pedal) below 5 or 10mph. That required the driver to push harder on the pedal and transition into the service brakes each time he came to a stop. Also, there is not a lot of kinetic energy at those low speeds to convert to charging current. In fact, some controllers will draw energy from the battery to produce the required braking torque at very low speed. 

I did an industrial EV where the regen was so good that you never had to use the the service brakes. The plant management required me to disable the regen completely before they would consider allowing personnel to use it on the factory floor. All in the name of safety.

major


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## evmetro (Apr 9, 2012)

major said:


> A good reason to "blend" or make sure the friction brakes are used regularly is to keep them functional. It isn't good for them to go weeks, months, perhaps years with use because you exclusively use regeneration. That is a recipe for disaster when/if you need those service brakes. I programmed the controllers to fade out the regen (which was on the brake pedal) below 5 or 10mph. That required the driver to push harder on the pedal and transition into the service brakes each time he came to a stop. Also, there is not a lot of kinetic energy at those low speeds to convert to charging current. In fact, some controllers will draw energy from the battery to produce the required braking torque at very low speed.
> 
> I did an industrial EV where the regen was so good that you never had to use the the service brakes. The plant management required me to disable the regen completely before they would consider allowing personnel to use it on the factory floor. All in the name of safety.
> 
> major


Very true. The 1238 controller that I use for my on demand regen system either cuts the regen or the regen becomes so trivial below 5 mph, that I still use the friction brakes for the last couple of mph before I come to a complete stop. The thumb pot is more intuitive than the brake pedal so using the foot brake feels like a lot more hassle, but if I am chomping on a cheeseburger or doing something with one of my hands, the friction brakes come into play. I like having them in good repair, ready to operate at their best.


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## Duncan (Dec 8, 2008)

I like the idea of using a separate control for re-gen,

When I drive my wife's car I use the cruise control stalk to drive the car in the country,
(Its nearly 20 years old so it does not have any form of "following" cruise control)

I always have the pedals as a back-up and if I want either more power or more brakes than engine braking
(in a high gear there is very little engine braking)

I could envision myself driving an EV with the cruise control allowing say 20% of torque and as much braking (re-gen) as was safe in poor traction conditions

That would work for 95% of my driving - using the pedals when I wanted more power or more brakes

That would give the safety advantage of the big friction brakes and the ABS while recouping most of the available energy


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## sailfish11 (Sep 15, 2007)

Just to through another configuration out there. My regen is off the throttle. I have a manual shift with no clutch. If I was moving, I had to turn off the regen (from a manual switch in my console) in order to shift.
A mechanic helping me with the car suggested putting the clutch pedal back in the car (just the pedal, not the clutch) and moving the switch to the pedal. I did that and it works great!

I live in a hilly area, and I can go up and down hills at a fairly constant speed without ever touching the brakes (the brake lights still come on under regen). If I want to coast, I can feather the throttle or just step on the clutch pedal.

Shifting is also obviously MUCH easier - and more natural feeling (put in clutch, shift, let out clutch).


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## evmetro (Apr 9, 2012)

sailfish11 said:


> Just to through another configuration out there. My regen is off the throttle. I have a manual shift with no clutch. If I was moving, I had to turn off the regen (from a manual switch in my console) in order to shift.
> A mechanic helping me with the car suggested putting the clutch pedal back in the car (just the pedal, not the clutch) and moving the switch to the pedal. I did that and it works great!
> 
> I live in a hilly area, and I can go up and down hills at a fairly constant speed without ever touching the brakes (the brake lights still come on under regen). If I want to coast, I can feather the throttle or just step on the clutch pedal.
> ...


Lol, I tried clutchless with off throttle regen on my first build, and had the same problems. I ended up installing a clutch, but still made the mistake of using the off throttle regen. I could feather the accelerator to over ride the off throttle regen, but did not fully understand yet just how little sense the concept of off throttle regen really makes. Major hit the nail on the head early in this thread that it can make an EV feel like an ICE, but that is about the only thing it does. Off throttle regen does have its place if having your EV feel like an ICE, but if efficiency is the objective, it may not be the wisest choice. From my testing, proper management of kinetic energy outweighs off throttle regen.


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