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Regen Braking

11K views 32 replies 20 participants last post by  Landodder 
#1 ·
Does using regenerative braking use up any brake pads or what is the process in which this works?

If I was trying to decrease any chance of problems with the car given the warranty situation, would it be advisable not to use the regen braking?

Also, I have about 1 out of 25 times that I hit the paddle and it shows Hill 1 or 2 , but the car does not slow down or what it seems to do is not engage the regen braking. I assume this is software driven and so it is just failing?
 
#4 ·
You also can't get any regenerative braking below about 10 mph (well, maybe a little at 9 mph :D). The friction brakes start blending in at that point with the brake pedal; but with Hill 1 or Hill 2 and no brake-pedal, you can notice a drop-off in the braking effect around that point. (And you can see it on the generate/accelerate meter.)
 
#7 ·
If you hit the paddle and it does nothing other than changing the graphic, then you have at least 49 battery miles left at that point, and there is no place to store the regen energy.
 
#8 ·
I have the following question - car seems to be able to charge back to batteries up to 15 kW of energy (going downhill), however when charged by cable through charger, it maxes at 3kW. How is it possible to charge battery through regen braking at more than 3 kW? Or does battery only take 3kW and rest dissipates in heat?
 
#10 ·
The first .25G of deceleration is done through regen whether you take your foot off of the accelerator or step on the brake. Once you exceed that decel rate the friction brakes are engaged. I've seen over 90KW of regen while braking. The seamless blending of regen and friction braking is one of the coolest engineering features of the Karma IMHO.
 
#12 ·
The internal power management in the car is designed to carry a huge amount of power (up to 300 KW at full power to the traction motors) and transferring even 150 KW from motors back to the battery during regen braking is nowhere near its maximum capacity. The wiring between the external charger and the on-board charger however is typically limited to 6KW, of which the Karma can only use 3.3KW. This is one reason why it is desirable to be able to use the ICE to charge the battery while driving the car because the generator has a maximum theoretical output of 180KW and would be able to charge the battery much more quickly than the 3.3KW on-board charger from a charging station.
 
#16 ·
That software in its previous state is pretty much unobtainium. Even if we managed to get ahold of it, I doubt it would play very nicely with all the current software. 8AVGMPG may correct me if I'm wrong here, but I also believe that software level was prone to coupler breaking, which none of you want, ever.
 
#17 ·
I don't think anyone wants to regress entirely back to that version. We just want the current software to provide an option for that specific feature. But given all that is going on, it's not really a top-priority item at the moment, at least as far as I am concerned.
 
#23 ·
Back to the original question: will using regenerative braking use up any consumable part - sounds like no as no brake pads.

Is there some moving part engaged however that the more used could break down and so would be safer if you were being the ultimate safety nut for this car not to use it?
 
#27 ·
As I understand it, as you let off the gas pedal there is always some regeneration going on. So, you have 3 levels of this happening: Normal mode (some regen.), Hill 1 (more regen.) and Hill 2 (most regen.). But, assuming you are going 60 and will be slowing to 30, then if you let off the accelerator and use a little regen followed by hitting the brake pedal harder (more regen) or if you use Hill2 which means more regen without pressing the brake pedal and then you will have less momentum and therefore less regen when you hit the brake pedal. Does that make sense? In other words, as I understand it, there really isn't any difference in how much regen you get or how many moving parts are working if you use or don't use Hill modes. You are either achieving regen through Hill mode as you let off the accelerator or you are achieving the same when you slow the car down by using the brake pedal. Both use the same action.
 
#24 ·
That's an interesting question. Back in March of 2011 I read this:
2011-Car Magazine (April)
In Stealth, the engine does not come on unless the batteries are low on juice. When they are fully charged and you are driving down a hill in regen mode, the surplus energy has nowhere to go so it turns the idle engine, albeit at very low rpm.
I interpreted that to mean that they used the excess electricity to turn the generator motor which turns the engine, thus providing engine braking. Not sure if the author was correct or if things had changed since then. But if this is the case, then it would make use of that coupler discussed above.
 
#25 ·
That's an interesting question. Back in March of 2011 I read this:
2011-Car Magazine (April)


I interpreted that to mean that they used the excess electricity to turn the generator motor which turns the engine, thus providing engine braking. Not sure if the author was correct or if things had changed since then. But if this is the case, then it would make use of that coupler discussed above.
I don't understand how that would provide engine braking since the engine is not mechanically connected to the wheels at all. :s

It would however, use up the excess electricity so that regen braking can continue to work even when the battery is full.

I can tell you from personal experience that this feature is not enabled. When I first got my Karma, my route to work went flat for about .8 mile and then down a very steep street for 1.5 mile to the freeway. During my descent, when the battery showed above 48 Miles, the regen would cut out and friction braking would take over. I never heard or felt the ICE being used in this way. Anyone else have a contrary experience?
 
#28 ·
To answer the original question you can use the regen function as much as you want I have yet seen a failure of the traction motors or the RdM caused by using it . It will save you brake wear but I wouldn't my decision if I was to use the regen function to save on brake wear . So far from what I've seen I so no reason why the brake pads won't make it past 30K or better . I've seen very little wear on cars reaching the 15K mark and higher
 
#29 ·
So are you guys saying that you keep your cars in hill mode #2 all the time?? or even hill mode #1? I never know when i should use it. In South Jersey we are not known for our hill because we don't have any :)
 
#30 ·
TL;DR version:
I always drive with Hill mode off.

Long version:
I live in Atlanta which is fairly flat as well. When I first got the car I experimented with Hill mode a lot. Initially I liked the 'one pedal' operation of the car when in Hill 2; using the accelerator pedal to accelerate and letting the heavy regen do all of the deceleration. I would turn it into a bit of a game, seeing how long I could drive even in traffic without touching the brake. Hill 2 was fun because the heavy regen felt like downshifting and engine braking from my previous manual transmission car. I also learned that if you press the accelerator a *little bit* so that the charging/discharging gauge on the right of the cluster was indicating neither of each (straight up) you could effectively coast without spending battery energy or decelerating from regen.

Eventually the constant accelerating-or-decelerating game got a little wearying. I also played with Hill 1, but it was pretty much the same experience damped.

From a range and mileage perspective I ultimately determined that driving with Hill mode off gave me slightly better range. I suppose this is partly due to terrain and partly to driving style. I guess I always 'spent' more battery getting back up to speed after lifting off the pedal than what the regen would add during a normal drive, and since I almost exclusively drive in Stealth there was no ICE adding to the electron bank.

Note that using Hill mode or not entirely preference though; I choose no Hill mode on flat terrain because I'd ultimately rather not have to constantly decelerate in traffic or have to remember to feather the pedal to coast. Also, for me, my goal is to optimize range so as not not need to burn gas. There's no harm, danger or wear to using regen however. You can leave it on Hill 1 or Hill 2 all the time, on flat or hilly terrain. YMMV

Brent
 
#33 ·
Hi, driving now though the second winter with my Karma, generally with no issues and soon reaching 1600 KM. However, on a few occassions, when driving in snow and cold for quite a distance without breaking, once I use the break pedal I feel a "hack" in the regeneration - could it be that some part got frozen during the drive? I have no problems in breaking the car - just feels like the regen feature comes off for a second.
 
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