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Posted by Jim Wilkins on May 16, 2012, 5:28 pm
 


Look under Disadvantages:
http://en.wikipedia.org/wiki/Electric_double-layer_capacitor

One decent 2500mA-Hr AA NiMH has the same current storage capacity as
9,000 Farads of supercapacitor.

http://en.wikipedia.org/wiki/Capacitance
A 1 Farad supercapacitor discharges by 1 Volt while supplying 1 Amp
for 1 Second. The battery will nominally deliver 1A at 1.2V for 2.5
<HOURS>.

They are valuable only if they can match the size, weight and volume
efficiency of Lithiums at a much lower price.

jsw



Posted by danny burstein on May 16, 2012, 5:34 pm
 


They are right-at-the-edge of being practical for
the "peak shaving", so to speak, uses. For example,
when you're decelerating your car via motor-generator,
you're producing way too much power for transfer
into a battery. But if you could dump that electricity
over to a supercap, and then slowly feed it to
the battery, it almost works.



--
_____________________________________________________
Knowledge may be power, but communications is the key
             dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

Posted by j on May 16, 2012, 8:44 pm
 On 5/16/2012 1:34 PM, danny burstein wrote:

That's my take on it too. I think though, that you don't have to feed it
back, but use it for the next acceleration.

It seems to me that if you can limit the peak current drawn from the
batteries, that you would get a longer life out of them.

Given enough capacitor, peak torque could be impressive. The battery
would limit the horsepower.

  At least, that is roughly how I see this. There seems to be some real
money in sales and investments ($.5B /year). Not all of that can be
small devices...

   Jeff


Posted by Jim Wilkins on May 17, 2012, 12:53 am
 

You really need to assume that the designer knows his job and matches
the battery with the motor. Tire slip limits the maximum starting
torque and braking deceleration.

Perhaps these caps would permit a less expensive battery but their
rapid voltage change complicates the electronics. They store half (or
less) the energy of a battery of the same peak voltage and charge
capacity because their constant-current discharge curve is a triangle
instead of a battery's near rectangle the same height and width.

jsw



Posted by j on May 17, 2012, 11:06 am
 On 5/16/2012 8:53 PM, Jim Wilkins wrote:

That certainly makes sense. But it appears they have solved the complex
electronics (buck boost mostly). Note the number of existing projects:

http://en.wikipedia.org/wiki/Electric_double-layer_capacitor#Automotive

I would think the winning features would be the low internal resistance
and perhaps the low cost.

At any rate, this was all unexpected to me, and shows how much money
there is in the margins of saving energy. At least for large vehicles
where the momentum lost is sizable.  Toyota has a race car project
coming out though (Toyota TS030). And the Chinese have total supercap
buses that get a quick recharge at the stops.

  I take your point that this is not needed for acceleration.

   It's all rather interesting but I don't think it will make it into a
grocery getter anytime soon.

   Jeff


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