regen capability

Discussion in 'Clarity' started by victor_2019, Jul 29, 2019.

  1. victor_2019

    victor_2019 Active Member

    I noticed, at least compared to my kona EV, that the regen capability of the clarity is not that great.

    the kona in the highest regen setting can really slow down the car quite fast and in the dashboard display you can see it adding a lot of distance worth of energy back in the battery (I've seen it add several kilometers worth when slowing down from highway speeds).

    but the clarity EV range barely moves by a few hundred meters when doing regen and even on the highest setting, the car doesn't slow down that fast. in the kona I can rely on the regen only to slow the car down and stop it without the brake, but when I try the same thing in the clarity it usually ends up with a hard panicked braking halfway through when I realize it won't slow down fast enough on regen only.

    also, one thing I've seen and I always found it funny, is that when I select the 4 levels of regen, sometimes the 4th chevron will blink then disappear. then I select level 4 again, and again it blinks and disappears. finally I can select 4 levels.

    almost as if the car can't handle too much regen...

    then on my last trip it suddenly clicked that this always happens when I select level 4 regen at high speed and that is when the most power can be generated, so it really must mean that the car can't absorb all that energy.

    and I realized the difference between the clarity and the kona.

    the kona has a 150 kw motor and the battery can handle outputting 150 kw of power to the motor, and also to accept this kind of power back from it (or at least most of it, since it can charge in theory at 100 kw from a fast charger). so it can use a lot of regen.

    the clarity power train on the other hand has a 135 kW motor however the motor can't produce that power from battery alone, on;y when the combustion engine is also providing power via the generator, because the battery doesn't have enough capacity.
    so that must also mean the battery doesn't have enough regen capacity...

    but if the car in EV mode can produce decent acceleration, why can't it produce similar regen deceleration? is the battery power capacity smaller in charging than in discharging modes? (can discharge faster than it charges?)

    perhaps someone can clear some of my confusions...
  2. Sandroad

    Sandroad Well-Known Member

    Interesting questions. I doubt there’s any vehicle with electric drive that can produce decel as fast as accel without friction brake use. I can’t imagine how hard it would be to drive the Clarity if it could full stop in around 10 seconds from 60 mph using only regen. The Kona is a full electric car with almost 4 times the battery capacity of the Clarity PHEV. Perhaps a better comparison is to the Clarity BEV?
  3. Mowcowbell

    Mowcowbell Active Member

    Victor, was your Clarity battery nearly full when you tried full regen? It will back off regen or even start up the ICE if the battery is nearly full and you attempt to regen more power than it can hold.
  4. victor_2019

    victor_2019 Active Member

    why? is the battery not capable of accepting the energy?

    every other part of the powertrain (motor, gears, inverters) is perfectly able to put in the same amount of energy in acceleration or braking.
  5. victor_2019

    victor_2019 Active Member

    no, the same thing happens even if battery is at 50% capacity. last time I noticed this was below 50%. but the common thing is speed, at high speeds it will not accept the 4th level but then as the car has slowed down a bit then it will accept it.
  6. craze1cars

    craze1cars Well-Known Member

    Long mountain descents result in the same thing. I believe it charges too fast and heat builds up too fast risking battery damage. So Honda programming kicks in and eventually on general long downhills you can only get 2 chevrons where earlier in the descent or would give you 4 chevrons. At this point it is relying more on friction braking and no longer able to capture all that energy. I’ve seen this many times. Coming off 80 mph interstate runs same thing it simply won’t allow 4 chevrons until the car is slowed down to 50ish. I think the regen is capable of putting so much energy into the battery so fast it could cause damage, so it’s programmed to not allow it in certain circumstances. It’ll do this even with a near empty battery well below 50%
  7. Chuck

    Chuck Member

    If you notice the dash display you will see that 'full' 4 chevron regen will only go down about 1/2 way to max. As you press the brake pedal it will drop down the other 50%. If you keep pressing it will use the all the regen and it will start using the friction brakes. I find it easy to drive an avoid friction brakes but I agree the regen is not that strong, maybe 20-25kw as a wild guess. In my wife's Bolt has have seen 70kw during deceleration using the max regen paddle, we can go the whole day with touching the brake pedal. There is no technical reason why the Clarity could not have a stronger regen, it was a conscious decision by Honda to make it this way, perhaps to make it more 'normal' feeling????
  8. stacey burke

    stacey burke Active Member

    The Clarity manual is your friend.... from the manual
    In the following situations, the stage may not change
    and the stage number will blink even if you pull back
    the selector. The deceleration stage may decrease or
    cancel automatically:
    • The high voltage battery is fully charged or its
    temperature is too cold or too hot.
    • The speed of the vehicle is beyond the deceleration
    range with SPORT mode off.
    • Hybrid system protection is needed.
    • The paddle selector is operated while your vehicle is
    stopped automatically by ACC with LSF.
    fotomoto likes this.
  9. victor_2019

    victor_2019 Active Member

  10. Ray B

    Ray B Active Member

    Just a few comments; sorry if they are a repeat of what I've mentioned in the past.

    I believe (but do not know for sure) that SPORT mode in the Clarity PHEV not only allows for the car to remember your regen paddle level, but also unlocks a little more aggressive regen energy capture. I haven't road tested it (not sure there is an easy way), but I found this chart somewhere in one of Honda's R&D tech papers discussing the Clarity Fuel Cell car and they showed how SPORT allows for more aggressive deceleration and energy recovery:

    Also, it is worth mentioning the obvious fact(s) that the car can be decelerated in several ways.
    1. Coasting (equivalent to one chevron of paddle activated regen); going uphill or facing a stiff headwind will also decelerate obviously but this does not allow for as much regen.
    2. Regen paddle - note that all the braking with the paddles is done through the front wheels only. I will come back to this in a minute.
    3. Brake pedal - not rocket science, but it is important to remember that although the brake pedal does incorporate regen energy recovery, it (in my opinion) does engage the rear brakes concurrently. I have no proof, but it only seems logical that the brake pedal does have a set brake bias programmed in which is different than 100% front : 0% rear (which would be the case if the brakes only engaged the front wheels' regen unit during mild/moderate deceleration).
    4. Cruise control deceleration - if the car suddenly goes down a steep hill or if you just manually drop the set speed quickly (hold the 'Set -' button for 5 mph drops) you can get pretty intense regen which exceeds the paddle regen.
    5. ACC - if the car encounters a slower vehicle ahead and ACC is on and working the same situation as #4 will happen and the car will decelerate commensurate with the needs of the situation. Presumably this may involve the friction brakes if the need arises.
    6. Emergency stopping - similar to the extreme case in #5 but does not need to have ACC engaged to make it work. Presumably this emergency case is mainly/only using friction anti-lock brakes.
    Anyway, I only wanted to spell all these scenarios out to make the point that the car has a very complex braking system. The engineers desire was to recapture as much regen energy as possible, but the only thing that takes priority over that is the stability of the car. You will take more and more risk of vehicle instability if you bias the high speed braking only through the front wheels. I believe this is the ONLY reason it downgrades the paddle braking during high speed paddle engaged slow-downs (like off-ramps). It is not to protect the battery, but only to protect the occupants from losing control. This is especially dangerous in cases where the car encounters sudden loss of grip in rainy or snowy conditions, but also on dry pavement if you make an abrupt steering correction while using aggressive regen through only the front wheels, which will set up a big oversteer condition and potential disaster.

    I cannot guarantee all these statements are true - we'd have to bribe a Honda engineer to subscribe to the forum and contribute some truths.
  11. Sandroad

    Sandroad Well-Known Member

    Because of the 3rd sentence in my post above. I think it would very difficult and dangerous to drive a vehicle that would decelerate that fast using only its front tires, at least here in a Michigan winter. And it would very hard to modulate the accelerator pedal to drive smoothly. And the brake light would need to come on every time the driver lifted off the accelerator. So I think it’s not practical to have the car capable of decel as fast as accel using only the in/out current to/from the battery.
  12. victor_2019

    victor_2019 Active Member

    OK, but then what about all the BEVs that have one pedal driving? How do they overcome these challenges?
  13. ab13

    ab13 Active Member

    The issue is battery durability. The large battery will take a smaller "load" during regeneration since the power is split over the whole battery. The Kona battery is almost 4x bigger so the cells see almost 1/4 the power than the smaller pack in the Clarity. So the Clarity pack would actually work harder to charge and discharge at high rates continuously. So apparently they limit the regen rate to limit the stress on the battery. The battery needs to last for 10+ years. They may be being conservative, but only time will tell.
    David Towle and fotomoto like this.
  14. Clarity Dave

    Clarity Dave Member

    A rule of thumb I've found in places is that if you keep the ratio of charge rate (in kilowatts) to battery capacity (in kilowatt-hours) below 1:1, battery life is not significantly compromised. This is expressed as "1C" though I've been unable to find a formal definition of the "C" unit.

    A citation of 1C can be found in

    For the Clarity, this says the charge rate should not exceed 17 kW (note that maximum level 2 charging is no more than 240V*30A=7.2 kW). Charging via regenerative braking would be limited so as not to decrease battery life as well.
    Last edited: Jul 30, 2019
    fotomoto and KentuckyKen like this.
  15. Chuck

    Chuck Member

    With the Bolt in winter the traction control works if you try to apply to much regen(almost always only with the 'max' paddle'), I assume other full EV's with strong regen are similar. Not sure if you can see in other cars the kW's being generating during regen, I really like how the Bolt show the electrical load, really shows the impact of the heater and the relative lack of impact of AC.
    KentuckyKen likes this.
  16. DucRider

    DucRider Active Member

    Any EV that can fully stop using "regen" is required to use battery power to do so. At very slow speeds electric motors regeneration capability drops off and must be supplemented by energy from the battery (essentially running the motor in "reverse")
    KentuckyKen likes this.
  17. insightman

    insightman Well-Known Member

    I didn't realize EV traction motors could do that. Why doesn't the Clarity do that when the battery is fully charged instead of running the ICE?
  18. fotomoto

    fotomoto Active Member

    AFAIK no hybrid does this and instead spins the ICE as a compression airbrake (similar to a J-brake on a diesel truck) and when that meets its limits, then friction braking. My guess is heat/durability concerns of both the traction motor, inverter, and battery. These items in BEV's are larger to take the load because they can't rely on an ICE but even they too as noted above by the Bolt owner have their limits and eventually revert to hydraulic friction braking. The Bolt also has a "hill reserve" setting that drivers can activate that keeps the battery from wall charging to full. The reserve is then used for regen. Great for owners who live/charge at high elevation.
  19. 2002

    2002 Well-Known Member

    I would think it wastes a huge amount of electricity, especially at higher speeds and braking levels. Probably generates a lot of heat also.

    Except maybe for Clarity as there are anectodal reports here that ICE is actually burning gasoline. I would think one evidence for that is that it is remaining on for the duration of the warmup cycle, which it wouldn't need to do if it was just spinning.

    Wouldn't that be nice. Or at least be able to specify charge to SOC percent.
  20. fotomoto

    fotomoto Active Member

    Yeah, my C-Max does the same thing. I have a scangauge on it and it does burn fuel on that first activation. I have zero hills here yet this happens at the end of my street block when at least one or a combination of the following occurs: A) the battery is full, B) driving in Low gear (max regen), C) I hit the brakes too hard, D) the battery is hot, or E) just finished level 2 charging (see D).

    This same scenario doesn't happen in my Clarity (sport/4 chevrons regen). I suspect the cooled and much larger pack is enough to handle my scenario.

    Last edited: Jul 31, 2019
    2002 likes this.

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