Regenerative Breaking
just saw a an interview with a sales guy on youtube about the vectrix.
Apparently in order to regenerate while slowing down using the vectrix you just put the bike into reverse and it slows down while pushing some of that energy back into the batteries..
My question is.. is it really that simple ?
if you placed a switch on your ebike to put the motor into reverse polarity while going down a hill.. would the energy be fed back into the batteries or would the controller stop it ?
What if you hooked up a bypass circuit that fed directly into the batteries via a voltage regulator whenever you switched the motor into reverse?
ok...
I accept that it might be potentially hazardous so im not going to try it any time soon..
one thing I have noticed however with a crystalyte 408/4012 motor is that if you roll the bike with the throttle on faster than then the actual speed of the motor then it creates some drag.. I assume that this resistance is being created by the current flowing into the motor. with all that power going nowhere I assume this is what your referring to when you say the motor will overheat and then potentially fry.
anybody who did electronics 101 knows that any electric motor can also be used as a generator.
so what if (in the case of the vectrix) the reverse throttle did two things..
Firstly it cuts off the power to the motor using a relay.
and secondly it reverses the polarity of the motor onto a different circuit where the power coming from the motor was stored not in the battery pack.. but in a high voltage rather large capacitor.. (I don't even think you would need to reverse the polarity on the motor.. you could simply hook the capacitor up in reverse.)
then the next time the throttle is engaged the alternate circuit is broken and motor is driven not from the battery pack but firstly from the capacitor, once the capacitor is fully discharged then power is used from the pack...
by using a buffer you could get the power savings without forcing high amounts of current into the battery pack where it might potentially do some damage.
I acknowledge the point above that on an ebike that has a limited range of say 5-20 miles then 10-15% is hardly worth the effort. but on a long range vehicle which can do 50+ miles then an extra 5 or so miles might make the difference between being stuck out on the highway in the middle of nowhere having to sit in the sun all day trying to trickle charge your ev from a tiny solar panel... or pulling into a town or shopping center that has a power point.
its interesting...
I'm planning on making a long range vehicle as one of my projects after I finish working on my ebike.
Something similar to the solar car in the other forums...
Maybe a four wheel drive or a 2 wheel drive. using hub motors..
I know there will be more than a few problems with calibration etc but still its going to be fun... just imagine how much power 4 hub motors could generate doing down a steep hill...
one thing I have noticed however with a crystalyte 408/4012 motor is that if you roll the bike with the throttle on faster than then the actual speed of the motor then it creates some drag.. I assume that this resistance is being created by the current flowing into the motor. with all that power going nowhere I assume this is what your referring to when you say the motor will overheat and then potentially fry.
no thats not what I'm talking about. What I'm talking about is if you reversed polarity to the motor while riding.
Reversing the polarity will just stop you very fast and potentially fry the motor. The Vectrix does NOT reverse the polarity to the motor or go in reverse or anything like that during regenerative braking. It is just the way the throttle is used to turn on regen, and when the bike is moving forward turning the throttle in reverse tells the controller (or computer or whatever it goes to) to initiate regen. When the bike is stopped doing the same tells the controller to activate reverse and the bike will go in reverse. But the two are completely different!
To recap, the Vectrix does NOT go in reverse mode to regen so please get that out of your mind, lest you do some damage to your bike by trying to switch it in reverse while riding forward.
I don't know what is causing the drag on your bike.
Reversing the polarity of the motor while riding is only going to have an effect if there is still current being drawn from the batteries...
but if you don't need to reverse the polarity to charge a capacitor then thats really a moot point.
I think a better and simpler idea would be to have an extremely sensitive cut off switch attacthed to the rear break handle so that whenever they put their hand on the break handle and squeeze it ever so slightly then it cuts off the juice and goes into regen mode. Rather than current systems which cut off the batteries WHEN the breaks are fully applied.
I don't know of anyone who would ride down a hill without their hand on the break. and that would feel more natural then telling someone to throttle in reverse while going down a hill.
plus has anyone noticed how sore your wrist gets from throttling up and down all the time ?
or maybe thats just me because I have RSI from being at the computer all day.
"10-15% RANGE INCREASE ?
Doubt it, I have seen regen results on electric cars, thats why they scrapped regen, not worth the trouble for what you get out of it."
So really what your saying is I shouldn't bother at all and just spend the money on solar panels to put all over my ev.. lol
"...spend the money on solar panels to put all over my ev.. lol"
Spend them on slightly better(bigger) batteries, charger, BMS, controller, motor or other quality parts of the vehicle and you will more likely gain 10-15% range, than by spending the same amount and effort on regen controller/motor setup, combined with circuits to prevent overvoltage, overcharge (and possibly overcurrent, overheating) of the batteries.
Spend them on slightly better(bigger) batteries, charger, BMS, controller, motor or other quality parts of the vehicle and you will more likely gain 10-15% range, than by spending the same amount and effort on regen controller/motor setup, combined with circuits to prevent overvoltage, overcharge (and possibly overcurrent, overheating) of the batteries.
If this is the case, than regen is superior because it doesn't add any weight, as batteries would. A BMS is essential for taking care of the batteries, but might add some range.
plus has anyone noticed how sore your wrist gets from throttling up and down all the time ?
or maybe thats just me because I have RSI from being at the computer all day.
Mine does when I go on road trips with my bike. You might want to try one of these these. Helps me some.
I was wondering about this issue...I have a 3-phase Mars ("brushless Etek") motor with a Sevcon Millipak SBPM controller that I will be using in my vehicle with a 36V system. Sevcon says the controller has regen, but I can't find much in the controller manual to indicate how this is actually accomplished. The wiring diagram shows how to wire in a forward/reverse switch, and I thought I might as well have a reverse gear on my scooter since it would be so simple.
Given what I've read in the other posts in this thread, I'm reluctant to throw it into reverse while moving forward. I would hate to fry my battery, BMS, or anything else (though I suspect the main fuse might prevent this from happening).
Does anyone know how to enable the regen capabilities of a Millipak controller, or is it just automatic?
Thanks,
Jake
Boy, I can see why new ppl to EV's can get so confused when starting out. There are alot of opinions mixed in before explaining the basic electronic principles behind what happens in regen (power generation) as what the original poster really needed. [Where's Fechter when you need him. He was usually around to straighten out the messes.]
Every motor can be a generator especially PM brushed DC motors. And this goes back to the basic principle of every dynamo - that any time an inductor coil passes through a magnetic field it will create a current and voltage. This current and voltage happens to be in the opposite direction (or negative voltage) from the original motor current direction - i.e. it runs backwards. You can see this very clearly if you have an oscilloscope (aka an o-scope). What as o-scope does is shows voltage performance over a length of time to create a waveform. Luckily with computers this can be done now with a voltmeter hooked in a realtime display program so it does not have to be another piece of equipment to buy. When you do hook one up to an o-scope and run a PMDC motor as a generator, you will find that a saw tooth pattern will be created not a true DC straight-line. In fact this line pattern will be dependant upon the RPM of the generator and the timing of the brushes on the commutator.
CONTINUED>>>
What does all this mean for an application in the EV world? This means even when coasting a back voltage will be created to the controller. A GOOD controller will be able to handle this back voltage (negative voltage). This can be done several ways. Usually, a good controller has the mosfets that have a high enough resistance to counter this voltage (like a diode) and it dissipates as heat. OR, A controller with regen will take this opposite voltage and feed it back to the batteries. OR a separate DC regulator (sometimes variable) is switched via relay to the batteries which involves disconnecting the controller and running the circuit "backwards" or "reverse" to the original motor direction. (GEE didnt you just say that?)
The problem you will encounter with regen (besides the proper way to charge the batts) is determining how much braking force is needed. Hopefully it is adjustable like in the Vectrix.
NOW for the other arguments whether the validity of regen - that topic will be for each operator to decide per the driving situation, but hopefully it is at least available to everyone. It is the old argument of coasting vs. regen. My stance on this - Everyone in the EV world argues about % in some form and this one topic ppl will spit out % from thin air both for and against regen. Its pretty simple to me...at least have REGEN available for the rider/driver because not every driving situation is the same and there are different driving needs. Can you travel a good distance without using power from the batteries and treat the vehicle like a rollercoaster or soapbox derby car? - YES. Can you add energy and life to batteries when you do have to stop? - YES. But at least have it available.
I was wondering about this issue...I have a 3-phase Mars ("brushless Etek") motor with a Sevcon Millipak SBPM controller that I will be using in my vehicle with a 36V system. Sevcon says the controller has regen, but I can't find much in the controller manual to indicate how this is actually accomplished. The wiring diagram shows how to wire in a forward/reverse switch, and I thought I might as well have a reverse gear on my scooter since it would be so simple.
Given what I've read in the other posts in this thread, I'm reluctant to throw it into reverse while moving forward. I would hate to fry my battery, BMS, or anything else (though I suspect the main fuse might prevent this from happening).
Does anyone know how to enable the regen capabilities of a Millipak controller, or is it just automatic?
Thanks,
Jake
I have not used that controller and motor combination yet so I could be wrong. According to the pdf on the electricross site. http://electricross.com/Downloads/Millipak%20PMAC%20User%20Manual%20April%202006.pdf
pg 19 shows the various settings and pins of your controller. does it come with an interface cable and program so that you can select the setting from your comp? normally, an ac controller has so many different combos that it becomes necessary to allow the user to decide it from preset programs. once you decide that then go to the section in the manual for regen.
EVEN after my long discertation even I screwed that up...Now I am gonna have to add disinformation BAD INFO to my rep. I forgot that power generation will still follow the original path of rotation. But switching the output will allow it to back to the batts....SORRY ABOUT THAT.
From the manual that goodnslo references - the MilliPak appears to do four different types of regen braking - I believe you want the Footbraking option (a potentiometer tied to either the front or rear brake):
Footbraking can be initiated in one of two ways:
- Via an analogue input configured as a Footbrake Pot. Using a potentiometer allows the
operator to vary the amount of braking they want. See below.
- Via a digital input configured as a Footbrake switch. When the switch is active, the system
will brake at the footbrake level
What I don't know is what the voltage and current levels output by the controller are. So, you may need control circuitry between the MilliPak output and the batteries to prevent attempting to overcharge the batteries. Also, if you want to get maximum benefit from regen AND you find that the controller outputs more than you need THEN you need to capture that extra power (e.g. in a supercapacitor). To me that's why regen is not worth it - even if the smarts are in the controller then there are likely still extra components needed to implement it effectively. From what I've read, and I take goodnslo's point that the % are really rather arbitrary, I can't see the amount of energy recovered being worth that extra cost and complexity (this is all from the POV of a motorcycle - a city bus has a lot more potential for effective gains through regen).
So, think carefully about how to implement the complete regen system and what costs vs. what benefits you will get - like most things "the less you know the simpler it seems".
BTW, does anyone know why implementing regen for a series wound motor is more difficult than from a PM motor? If you look at kellycontrollers.com you will see that they offer regen on some controllers - but not the ones for series motors. Any idea why? Not that it matters much because I don't want regen anyway... ;-)
with the rotor and stator in series, the magnetic field of the stator collapses right when the rotor passes or builds up an inductive field. Its easier to have the stator and rotor parallel.
Let me try and clarify. I hope this can help.
If you are traveling forward and you switch the motor wires to make the EV go reverse than current will still flow in the same direction out of the batteries. As long as the current is flowing from + to - than the battery will be discharged.
You can do a bench test to prove what I'm saying. Take any small motor (a little hobby motor from radio shack for example) an amp meter, and a small battery. Run the motor. As you slow it down it will draw more and more current. When hold it stopped it will draw even more current. And when you rotate the motor in reverse you will actually be able to draw even more current than when the motor was stalled. This will result in a lot of heat and the battery being discharged really fast.
So how do you use the motor on the bench to charge the battery? The way to do this is to rotate the motor fast enough in the same direction that it would run when you connect it to the battery. Faster than it would run no-load, so that it generates a higher potential than the battery. If you do this you will see the amp meter go negative because now current is flowing in the opposite direction.
I know it's kind of confusing. But think of it this way. What happens when you connect two batteries like this:
+ => -
- => +
Can you see that both batteries will have current flowing in the direction of + to - ? You may know from experience that you'll get a big spark and both batteries will get hot and discharge quickly. Please DON'T do this, it's dangerous. Its just like connecting two batteries in series than shorting them out.
Now what happens when you connect two batteries of different potential like this:
+ => +
- => -
Can you see that the battery with the lower potential will have current flowing from - to + and will actually be charged?
Isn't it obvious that a motor rotating in the opposite direction to that which it would run when connected to the batteries will have a potential opposite that of the batteries? This is not what you want. You want a potential greater than that of the batteries.
That helps, and yes, it seems obvious now. So here's what I've learned:
1) Don't switch into reverse while moving forward.
2) I'll have to assume that the regen abilities of the Millipak controller are automatic, but even if there aren't any,
3) Regen for a motorcycle isn't worth much anyway.
Thanks!
Jake
Thank you Andrew that was far more accurate than anything that I attempted to explain.
10% range increase, maybe at ideal condition without electric/magnetc losses.
I doubt they did away with regen on electric car, can`t imagine Tesla doesn`t have regen, Phonex - no regen????
It depends how is implemented. It is only natural to use propety of DC motor to reduce friction breaking.
I cannot imagine NOT to have regen on heavy TF , I can imagine wear on shoes if TF didn`t have regen, it is far, far from any gadget - serves very useful purpose.
Beauty of regen is that the fastest you go the bigger electromagnetc drag is as a principle.
It is common knowledge that regen does not increase range even by 10 %.
Miroslaw
Awhile ago( witnin the past 6 months ) read about a new all electric car develop by Audi using 4 motors one in each wheel , and NO BRAKES whatsoever , the article claim that brakes will no longer be required with well designed regeneration . the system would bring the car to safe and complete stop .
There was a mechanical parking brake on the car .
Like to believe that Audi is well along the technology knowledge curve so as not to go chase a worthless concept case like regeneration .
The limiting factor in regen and charging efficiency and/or current is again Impedance ( the much hated word that everyone know about and do not want to face ) if the thermal characteristic of the batteries is addressed then amazing thing can be done with charging and of course discharging .IT all started with .....IMPEDANCE .....HOW LOW IS IT ?
Yeah I saw the same with wheel motor car...I think something I linked to from here that was a mini cooper converted. The description stated that with the regenerative braking regular brakes were eliminated.
Now, perhaps USATracy, Andrew or somebody else can tell me their guess about this. I've asked before somewhere on the forum but no particular specific responses as I recall. You guys know from my posts that I have the XB600. It was very soon after I began riding it that I realized when I put on the front drum brake...something was happening to provide braking to the rear wheel....but then the rear wheel drum brake is the other brake lever than the front of course. So I knew the rear drum brake wasn't being actuated as well by pulling the front one. And just to be sure I watched when I applied the brake. To find out what was sort of happening I put the bike on centerstand,key switch on,I kneeled down by the rear wheel and reached up and pulled the front brake...then tried to turn the rear wheel. Sure enough it was very hard to turn. I could move it but only with alot of force. Release the brake and of course the wheel was free. So apparently when I actuate that front brake lever it is not only using the front drum brake to mechanically stop the front wheel but it is doing something to hold the back wheel from easily turning. My question...anybody have a guess or answer to what it's doing? I'd really like to understand how it works this way. It really makes for a good braking system. I use the back brake most of the time but when I really need a quick stop I use both the back AND the front and I'm getting single braking on the front and a "double" braking (mechanical drum, something electrical to the motor) on the back.
Not that any of you guys would think this....but let me clarify I do know that when one applies the brakes it cuts power to the motor...on any scooter I've had. THis is more than cutting power as I've described above.
Thanks to any of you guys who can help me understand how this is working.
Gushar
I'm new and I've been looking at which controler to buy. Some of them have a lot of wires, and when looking at the wiring diagram, I noticed that some brake levers have a switch to cut power as soon as you begin applying the brakes. This would prevent you from accidentally applying the brake and power to the motor at the same time. Perhaps it cogging or its aligned for regen mode?
http://www.popularmechanics.com/blogs/technology_news/4223118.html
I just read the recent Popular Science, and theres a $30 gadget hack where you open up a discarded electric screwdriver and replace the battery with capacitors from a camera flash unit. When I Googled it, I found Coleman is making a factory capacitor screwdriver for $99. Here's my thoughts and questions:
Lead/Acid batteries last longest when only drained 50%, and re-charged 10% of amps (yes?, a 10 AH battery should be charged at 1 amp? perhaps 2 amps for short periods?) So, it seems they can only absorb a small portion of the regen amps available on a downhill.
The capacitor screwdriver recharges in 90 seconds (could capacitors absorb ALL the regen amps produced?)
With the same volume of capacitor bank as the original NiCD battery, the screwdriver performed only half the number of "screw-drives", so, a chemical battery is still better volume-wise for the majority of power storage.
From this I have speculated that:
2 AH of capacitor storage can replace 1 AH of battery range, but you should only have as much capacitor as you could fill during an average downhill in your e-bike usage profile. It's my understanding that capacitors can be charged/drained ten-thousands of times.
This shouldn't be hard to verify or refute, but whats the best way to attach capacitors so they "charge first/drain first" to save on range and battery life?
Hi,
people interested in regenerative braking might be able to make some use of this video, so I put it here as well:
The video was recorded a while before my Vectrix died.
It shows the instruments of my Vectrix accelerating from zero to 100km/h, then decelerating with full regenerative throttle applied.
It's done with 111kg ballast on board, including the lot.
Add in the published weight of a Vectrix, use a stop-watch and you might be able to calculate a few things (if your physics and maths are less rusty than mine).
Interestingly, if you look at 0 - 80km/h, it appears to decelerate quicker than it accelerates!
From 0 - 100km/h and back this effect is even more pronounced.
It can sometimes be difficult to be sure if it is really completely flat, but it was close to flat.
The acceleration time I measured using this video lies smack-bang in the middle between the measurements obtained from other videos, which were done on a piece of road with a slight slope; and done in each direction. I believe that means that the road this video here was made on is very close to flat.
There was very little wind.
My Vectrix is currently still out of order, waiting for a thorough service and repair; the acceleration may be different for other bikes.
Mr. Mik, ............. Toyota Camry :(
Hi,
I've put some more info about real world regen braking effect here: http://visforvoltage.org/forum/2547-vectrix-reports
Mr. Mik
With all that said, pretty sure most good AGM's can take the short bursts of high amp charge from regen with no problem, that is going straight into the interface charge of the battery and is going to be sucked right out when you open the throttle and never even become part of the absorbed charge of the battery.
Yep, they can take very high short bursts of high-amp charge. I'm almost 100% sure that the amount of power from regen would be no problem for most AGMs, but maybe for flooded lead-acid. However, this might heat them up some. While this is not a problem directly, after you are done riding and you put them on the charger than there may be a considerable risk for thermal runaway unless allowed to cool, or using a charger with thermal compensation.
Also, does the Vectrix even HAVE AGM, I thought they were some other chemistry ?
NiMH
For Mik's video, I get 10.5 sec deceleration.
Kinetic Energy E = (1/2)mv^2
m = mass in kilograms
v = velocity in meters per second
E = energy in joules
The mass of the vectrix is 210 kg, plus 111 kg = 321 kg.
The amount of kinetic energy when moving 27.78 meters per second (100 km/hr) = (1/2) * 321 * 27.78^2 = 123,842.6 joules. That much energy dissipated over 10.5 seconds (assuming constant dissipation) equals 11,794.5 watts in power to dissipate during the 10.5 seconds to stop from 100 km/h.
Assuming the motor is 85% efficient in regen average through the speed range, and the controller that is needed to increase the voltage is 90% efficient. That's 76.5% efficiency of the regen system, which would result in 9022.8 watts being put into the batteries.
The batteries are rated 125v and 30 ah. I don't know what the DC resistance of the batteries will be to a charge current. This will change with SOC. I also can't seem to find the potential of the NiMH chemistry. It appears to be somewhere between 1.3v and 1.4v, anything above which will charge a NiMH battery. Assuming the voltage rises to 1.4v per cell at this charge rate than the voltage would be about 145v and the current would be about 62 amps, or just over 2C during maximum regen.
Assuming the voltage rises to 1.4v per cell at this charge rate than the voltage would be about 145v and the current would be about 62 amps, or just over 2C during maximum regen.
Thanks for the maths, Andrew!
Does "just over 2C" mean that it is reasonable to believe that the Vectrix battery would be able to absorb the lot of the energy during 100% regen braking?
Here is another report about my Vectrix' regen braking, on the longest steepest hill I know of:
http://visforvoltage.org/forum/2547-vectrix-reports
Mr. Mik
I don't have any more information other than what is available from this page: http://www.vectrix.com/Portal/1/Language/47/Page/63/Battery_Pack.aspx hence, I don't have nearly enough information to say for sure.
But it certainly is reasonable to assume that it can. R/C car enthusiasts charge NiMH batteries at well over 2C, and this is for the entire charge cycle. They do get hot, though.
I'm not sure about the efficiency of the NiMH pack under these high charge rates. From this page: http://www.powerstream.com/NiMH.htm
The coulometric charging efficiency of nickel metal hydride batteries is typically 66%, meaning that you must put 150 amp hours into the battery for every 100 amp hours you get out. The faster you charge the worse this gets.
It may be that the efficiency varies a lot during the charge cycle, and the batteries may be more efficient at taking charge initially. Assuming 66% efficiency (again, it may be considerably higher than this), than in additional to the inefficiencies already calculated the overall regen efficiency would be about 50%.
That means of the 123,842.6 joules in energy for traveling 100 km/h if you put in full regen, than you could only get 61,921.3 joules back out of the batteries. This is equal to 17.2 whrs. Also of note is that when you start again and engage the motor power the inefficiencies of the motor and controller come into play and reduce the amount of recoverable energy further.
All things considered though, I think this is very significant. Based on your report the vectrix range is anywhere from 26.35 to 41.6 miles. And the total energy available from the batteries to do this I calculate could be about 3,450 whrs (92% of nominal energy 3,750 whrs). This means 83 to 131 whrs/mile in energy consumption depending on speed and other factors. So 17.2 whrs could add .13 to .2 miles or 693 to 1056 feet in range, and this is only using regen to stop once from 100 km/h.
I realized I'm slightly off in the charge efficiency calculations. The 66% quoted is the coulometric charge efficiency. That is, the amphour charge efficiency which is only one component of power. The voltage charge efficiency may be somewhere around 58.7% (1.2v (nominal voltage)/1.4V (charge voltage minimum) = .857). So the overall energy efficiency could be somewhere around 56.6%, but again this is just a rough calculation. And I don't know how efficiency varies during the charge cycle, and if the batteries are much more efficient initially.
This would reduce the overall regen efficiency to 43.2%, and the resulting recoverable energy in the instance of applying full regen from 100 km/h to 0 km/h with 111 kg payload is 14.9 whrs. This could result in an additional .11 to .18 miles range. Still very significant IMO especially if you vectrix battery runs flat and you have to push.
It is important to note that I applied a lot of assumptions in this calculation. I didn't just guess, but tried to come up with reasonable estimates like the efficiency of the motor and controller during regen, or the available energy from the battery pack.
Vectrix Real Word Regenerative Breaking Report Part 2
Thanks for your calculations Andrew, most interesting!
Tracy: The acceleration/regen deceleration video still works as far as I know...
I'm partially replicating this regen braking Vectrix test here because of it's relevance to this forum.
.
This test also starts at the top of a steep downhill test run:
3.9 km downhill, 350m height difference.
Motor used gently for about 1km to get bike to 80km/h on the last, less steep part.
Photo 1:
51km Est Range ;
15.8km Trip A ;
400m elevation.
.
.
..........................................................................................
Photo 2:
54km Est Range ;
19.7km Trip A ;
50m elevation.
.
.
.
What I think it means is:
A 3.9km downhill run with an average 11% slope adds 3km to the range rather than dropping the range.
My estimate is that the range would have dropped by between 1 and 3 km without regenerative braking, but this needs to be tested by using the disk brakes only on this trip once my Vectrix is running again (or has been replaced).
Only a minority of commuters will have this sort of steep climb or descent included in their regular route, and usually they will drive down the mountain to get to work while the battery is full anyway.
But I arrived home on that day with Est Range 21km left, which usually meant pretty much empty for my Vectrix, and so the regen braking saved me from having to push several km!
.
Mr. Mik
The vectrix has a special throttle that you roll in reverse to put in the regenerative breaking, but you are not actually "putting the bike in reverse".
If you do actually put the motor in reverse polarity while riding at full speed to regen than you are probably going to fry the motor in like 2 seconds. The current will still be flowing the same way out of the batteries this way, so you'll also discharge your batteries really fast.
To regen you need a way to increase the voltage being generated by the motor so that it will charge the batteries and the direction of current flow will be opposite that of discharge. This can be done somehow by using a controller, though I'm not sure exactly how. It can also be done with a shunt motor by varying the field strength.
There are some controllers on the market that can do regen such as this.
2- Cant dump as much back in the batteries as you can pull out in the same time frame (not SLA) so will never be efficient recovery with SLA unless some complex capacitor engineering is implemented.
There's been fast charging testing done charging SLAs in 15 min to 80% DOD. They can be charged very quickly for a short period without heating up too much, so they could likely take the regen energy just fine. Additionally SLA are a very efficient battery type (you got most of the energy out that you put in). I think they are an ideal battery for a system with regen.
regen braking is not going to add much in the manner of range, thats one reason no one bothers to do it. When you weigh the benefits vs the costs, complexities and return on investment it is a loser option.
It might add 10-15% depending from what I hear. Its not amazing, but its certainly significant. Additionally it helps make your vehicle more efficient and use less energy, which could be a big deal if you are using solar or wind energy. It helps reduce brake wear a lot, to where you might never have to service the brakes. Also it will help reduce how much you discharge your batteries each trip which might add some battery life.
I think most EVs in the future will use regen braking.
KZ750 Motorcycle Conversion
900 watt scooter
Pic from http://www.electricmotorbike.org/