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evnow
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Re: Why the heck don't any Hybrids / EVs use Ultra-Capacitors?

Fri Jun 25, 2010 8:16 am

What is the max regenerative power that can be captured - considering typical stopping deceleration, 3000 lb car and initial 50 mph speed ?
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Re: Why the heck don't any Hybrids / EVs use Ultra-Capacitors?

Fri Jun 25, 2010 8:43 am

A Tesla Roadster will generate 80-90amps (DC) back into the battery pack during full regen. I believe this amount could be higher, but is limited because it would otherwise cause trouble with the Traction Control (imagine doing this on a slippery uneven surface). I have heard of current in the triple digits (low 100's) in the case of Toyota RAV4EV, but can't confirm. (Under full acceleration the Tesla will easily pull 600-700amps (DC) out of the battery (which is discussed as being 375V nominal, but that of course varies with SOC).)

And the Roadster will slow from 55 to 15 in about 700 feet (2,735 lbs curb weight) under full regen (that 80amp number).

Hope these data points help you.
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Re: Why the heck don't any Hybrids / EVs use Ultra-Capacitors?

Fri Jun 25, 2010 9:40 am

It appears that the Ranger EV can move 200A into and out of the pack. That's well within the range of lead acid and NiMh - and certainly within the range of lithium.

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garygid
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Re: Why the heck don't any Hybrids / EVs use Ultra-Capacitors?

Fri Jun 25, 2010 11:23 am

80kW is 80,000 watts, a lot over "90W".

80kW is moving about 240 amps out of (or into) a 333v battery, ignoring losses.

The 240 amps in would be essentially a full charge (20kWh) in 15 minutes.

But, likely the regen rate is limited to some fraction of that. A 20kW (1C = one hour) regen recharge rate would be reasonable, but Nissan could have chosen to use a much smaller maximum regen rate.
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Re: Why the heck don't any Hybrids / EVs use Ultra-Capacitors?

Fri Jun 25, 2010 11:30 am

LEAFer wrote:A Tesla Roadster will generate 80-90amps (DC) back into the battery pack during full regen. I believe this amount could be higher, but is limited because it would otherwise cause trouble with the Traction Control (imagine doing this on a slippery uneven surface). I have heard of current in the triple digits (low 100's) in the case of Toyota RAV4EV, but can't confirm. (Under full acceleration the Tesla will easily pull 600-700amps (DC) out of the battery (which is discussed as being 375V nominal, but that of course varies with SOC).)

And the Roadster will slow from 55 to 15 in about 700 feet (2,735 lbs curb weight) under full regen (that 80amp number).

Hope these data points help you.

I have seen at least 300 amps on the ACP drive with full off-pedal regen (set on high). I was going down a large hill with 3 passengers and came to a stop on a dry surface as fast as traditional brakes could. The regen released at about 3 mph and the then I hit the brake pedal. I never touched the brake pedal until the last second or two. This was FWD so there was plenty of traction for the regen.

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Re: Why the heck don't any Hybrids / EVs use Ultra-Capacitors?

Fri Jun 25, 2010 11:37 am

Wow, Thanks!
That is an example of really useful, usable amount of Regen.

There is no good reason that this amount of Regen could not exist (gradually increasing through the first half-inch of the brake pedal travel) before the mechanical brakes engage.
See SOC/GID-Meter and CAN-Do Info
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Re: Why the heck don't any Hybrids / EVs use Ultra-Capacitors?

Fri Jun 25, 2010 11:42 am

EVDRIVER wrote:This was FWD so there was plenty of traction for the regen.
That's probably a key difference. I think the Tesla could do even more regen, but I think Tesla has decided that it's "strong enough" compared to conventional cars, and being RWD with Traction Control they are also being conservative about it. The fact that 2/3 of weight is in the rear may also be a factor arguing for less regen than what the drive train is capable of (basically a "reworked" ACP version).

(Keep in mind, Tesla's regen works purely off the "go pedal". The brake pedal -- if and when you need it rarely -- is completely friction brakes.)
2011 Silver SL+QC [Mfg: 11/2010] 36mo/15k LEASE
06Jun2013 Status [28.5 months][34,173 miles][11 bars]
Lost CapacityBar 6/6/13 @34,173 miles while in LEAF Battery Monitor: 83.41%, 71.4F (avg); cool overnight;

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Re: Why the heck don't any Hybrids / EVs use Ultra-Capacitors?

Sat Mar 26, 2011 5:28 pm

I thought the issue with Ultracaps was that they have high power density (charge/discharge rate) but low energy density (storage). Wouldn't UltraCaps be the perfect instant power boost in an electric sports car?!? ;) What would today be like Nitrous for sports cars and sport bikes? Ya know, little red button on the steering wheel called "boost"? Hint, hint Nissan...? For a sports car...! HINT!!!
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Re: Why the heck don't any Hybrids / EVs use Ultra-Capacitors?

Sun Mar 27, 2011 12:05 am

TimeHorse wrote:Of course, I will admit that if the LEAF has a 80kW motor and I assume for the LEAF the regenerative component would simply be turning the electric motor into a generator, I guess there's no way to recover more energy anyway, at least here.
Leaf regen is limited to 30 kW max (about 1C) - presumably to preserve battery life. And as documented the amount of regen when the SOC is above 80% starts tapering off until there is none at 100% charge. So presumably, a series super-cap should allow one to increase regen up to 80 kW (max of the motor). If the super-cap had a capacity of 0.5 kWh, that would take about 20 seconds to charge to full from empty - more than enough to capture all the energy required to stop from any reasonable speed at a regen rate of 80 kW.
TimeHorse wrote:As someone said, this may be a better issue for the hybrids, depending on how their configured. It's really a question of how the Regenerative Breaking is configured.
Definitely - combined with the typically low capacity of the hybrid pack (a couple kWh at most) which also limits max charge/discharge rates, even a small super-cap of a couple hundred Wh should significantly improve efficiency.

The big question is: at what cost/weight/complexity penalty? I suspect that in most cases it's more cost effective to simply increase the size of the pack a bit which will allow you to increase the power rating of the pack itself while not increasing the load on individual cells.

BTW - a lot of the previous discussion of maximum regen amps is not too informative unless we also know the voltage and capacity of the cells in question...

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