How much power does it take to stop w/o brakes?

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israndy
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To those of you who have added an ammeter to your bikes display I am curious about using regen to stop the bike. I can see it adds power to the battery as the kinetic motion is drained away, but at SOME point it must actually TAKE power to cause the bike to come to a stop. I have asked this years ago, before we knew so much about the bike and I think people thought the bike was regen all the way to zero mph, but it cannot be. It should have difficulty doing regen on a full battery for example, but my bike stops fine on a full batt.

Now that I am months away from buying a Tesla Model 3 I am seeing all sorts of interesting posts on the Tesla forums and they are asking the same question there. Someone here must know where the transition between regenerating power and stopping the bike is.

-Randy

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MEroller
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Re: How much power does it take to stop w/o brakes?

As long as the motor-turned-generator creates a higher internal voltage than the controller lets through from the battery even just coasting with the "throttle" only marginally open will create a current flow into the battery. My old-school Kelly controller actually allows this to happen, without active regen taking place. The curret turns negative on my Cycle Analyst display, and I can feel the decceleration kicking in with a slight jerk. As soon as things get too slow and internal generator voltage drops below what the controller lets through from the battery (via PWM) the current turns positive again, letting the motor creep forward. This I like to call "passive regeneration" and is fairly easy to grasp.
During "active" regen however the controller tries to power the respective motor coils in reverse polarity, which opens the floodgates for the much higher generator voltage to drive current back into the battery. This creates much more substantial negative current than the passive variant I described above and thus also causes considerable decceleration. With careful phase voltage modulation the controller can turn down the applied reverse voltage proportional to the ever smaller generator voltage to keep actual negative regen current flowing into the battery right down to standstill. But this also reduces decceleration to virtually zero apart from rolling resistance. My other scooter with Lingbo VEC controller shows this active regen behaviour and really keeps the current negative on the Cycle Analyst down to standstill, ending in just -1A or so. The Kelly cuts active regen at approx. 10km/h and calls it an anti-lock feature :-) And the Lingbo cuts out the passive regen and the associated jerking by applying a minimum current proportional to motor rpm.

The aggressive BMW i3 one-pedal-driving is different as it actively electrically brakes the car to a standstill - no real tapering down of regen at slower speeds, and no friction brakes needed. That I also do not fully understand...

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antiscab
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Re: How much power does it take to stop w/o brakes?

israndy wrote:

To those of you who have added an ammeter to your bikes display I am curious about using regen to stop the bike. I can see it adds power to the battery as the kinetic motion is drained away, but at SOME point it must actually TAKE power to cause the bike to come to a stop. I have asked this years ago, before we knew so much about the bike and I think people thought the bike was regen all the way to zero mph, but it cannot be.

Hi Randy,

On my Vectrix, full regen down to zero:
Speed: battery amps:
100kmh -75A
70kmh -60A
45kmh -30A
10kmh 0A
5kmh 2A

to go to 0, it does mean putting a little bit of power into the motor

I must admit, with electric cars, I absolutely detest single pedal regen - it makes it impossible to coast easily

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R
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Re: How much power does it take to stop w/o brakes?

All vectrix have an ammeter. kill swich off, then pull left brake, kill swith on, enable go. Yo get a permanent C on the display ( current) and voltage.
You need MC 2xxx or newer, mc1xxx (nimh and the laird) does not have this feature.

israndy
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Re: How much power does it take to stop w/o brakes?

antiscab wrote:

I must admit, with electric cars, I absolutely detest single pedal regen - it makes it impossible to coast easily

Thanks for that info AntiScab,

Yeah, that's why I like the Vectrix, just roll the throttle backward and pick your amount of regen, almost to the level of emergency braking.

My Honda Insight has more regen as you press on the brake pedal, but you start to feel the actual brakes catching as you continue to press (at least you do on a 17 year old car, don't remember feeling it when the car was new).

I was shocked at the regen by releasing the accelerator on my Mitsubishi iMiev, at least it is just a gear position, and not the default. I like the economy position, one down from drive. Barely lets you accelerate when you stop the accelerator and coasts well when you release. But then I only have 16 kWh, so I can eat thru the battery pretty fast if they let me gun it the way I was able to gun the Vectrix on the first version of the software.

-Randy

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Also a new 2013 Volvo C70 hardtop convertible, a 2000 Honda Hybrid Insight, and a 1999 Jeep Grand Cherokee
RVs: a 40' Airstream Sky Deck, a 23' LTV Serenity RV
EVs: a 2012 Mitsubishi i-Miev and two 2007 Vectrix VX1 motorcycles, and in line for the new Tesla Model 3

LeftieBiker
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Re: How much power does it take to stop w/o brakes?

The 2018 Leaf has "e-Pedal" braking, which means strong regen to a very low speed, then the friction brakes are applied as needed to a complete stop, when your foot is off the accelerator in that mode. They did this so the car will hold still on an uphill position without the brake pedal, but I wonder if they also found it easier and less stressful on the drive system than using full regen to stop the car.

israndy
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Re: How much power does it take to stop w/o brakes?

I wouldn't call it using Full Regen to stop the car, I'd call it using the battery to stop the car, full regen implies it's converting motion into energy, what the Vectrix does at the end to stop is use the battery to power the motor backwards to quench the kinetic energy.

-Randy

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Also a new 2013 Volvo C70 hardtop convertible, a 2000 Honda Hybrid Insight, and a 1999 Jeep Grand Cherokee
RVs: a 40' Airstream Sky Deck, a 23' LTV Serenity RV
EVs: a 2012 Mitsubishi i-Miev and two 2007 Vectrix VX1 motorcycles, and in line for the new Tesla Model 3

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