Super capacitors anyone?

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retepsnikrep
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Super capacitors anyone?

Postby retepsnikrep » Thu Jan 06, 2011 12:28 pm

Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

ex925
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Location: Plymouth, England

Re: Super capacitors anyone?

Postby ex925 » Fri Jan 07, 2011 9:08 pm

Given my limited understanding, please forgive some very basic questions

Have I read the figures wrong, or are they far bigger and heavier than batteries for comparable energy stored?
Do they quickly self-discharge, or do they store energy for very long in comparison to a battery?
Are these for sale because a newer evolution is about to emerge?
Many thanks for any advice
All the best
Ed

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Jeremy
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Re: Super capacitors anyone?

Postby Jeremy » Fri Jan 07, 2011 9:29 pm

Yes they are far, far, bigger and heavier than batteries of the same energy storage capacity.

Self discharge is comparable to batteries.

They are for sale because they are now readily available, but they aren't a substitute for a battery, by any stretch.

Their advantages are that they have a very high cycle life, many thousands, or tens of thousands, of charge/discharge cycles, they can accept very high charge and discharge rates, into the many hundreds, or even thousands, of amps and they have a fairly low equivalent series resistance, meaning internal losses are fairly low.

The major disadvantage is that, unlike a battery, they are not a near-constant voltage energy storage system like a battery, so the voltage drops all the time that energy is being taken from the capacitor. This creates challenges for the whole system, as it needs to compensate for the wide operating voltage range of the supercapacitor, from zero volts when "empty" to maximum volts when "full".

Their main use in EVs is to act as an energy buffer for regenerative braking, temporarily storing the potentially high regen energy and allowing it to be used more gradually. This sidesteps the problem of limited battery charge rate, by letting the capacitor take the initially high regen current.

Jeremy

ex925
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Location: Plymouth, England

Re: Super capacitors anyone?

Postby ex925 » Fri Jan 07, 2011 10:09 pm

Very grateful, Jeremy, for your patience, and that of so many others on this forum
Takes me a while to get me head round these things, such clear, idiot-proof explanations save me lots of headaches
I do try to make progress and remember things, honest
All the best
Ed

jonathan jewkes
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Location: Bristol

Re: Super capacitors anyone?

Postby jonathan jewkes » Sun Jan 16, 2011 9:10 pm

Jeremy has explained the advantages - can deal with very high current flows in and out.
But as you discharge it, the voltage drops linearly. Most motor controllers can only cope with a certain range of voltages.

But total energy stored is very low. Someone tell me if the following calculation is wrong.
The capacitor is stated to be 83 Farads 48 v
83 farads means that taking a current of 83 amps for 1 second will cause a voltage change of 1 volt.
Then suppose that your motor controller can cope with a maximum voltage of 48v and a minimum of 38v
So the energy you could usefully extract from your capacitor is 83 x 10 amp.seconds, which is 0.23 amp.hours

$895 for a 0.23 Ah "battery" doesn't seem very good value.
Even if you could continue usefully using all the stored energy until it was down to only 1 volt, you would still only have 83 x 48 Amp.seconds (1.1 Ah)

Incidentally, given their very low internal resistance and hence ability to supply very high instantaneous currents, an accidental shorting of the terminals could be dramatic. Hopefully the module contains a fuse!
Jonathan Jewkes
Daily EV user for 10years - an enthusiast and also a realist

tigerbay
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Location: South Wales

Re: Super capacitors anyone? (update)

Postby tigerbay » Sun Feb 02, 2014 1:58 am

Hi, being as it is now 2014, and the cost of such Super Capacitors coming down, with technological development of these, as well as greater capacities of 350F, 400F (and possibly much higher) being commercially available, with only 6x 350F Super Capacitors in series being required to act in place of a regular car battery, as well as the low internal resistance, is it now more possible for these to be used to store alot more energy.
I note the low internal resistance with intrigue. Though I don't know how I can use other capacitors to limit the burst of energy to the output so that it maintains the energy stored for longer periods, especially in the requirement to replicate 4.5Ah (as a minimum) 24 volts for my electric bicycle (details of my project can be found in my introduction here: http://www.batteryvehiclesociety.org.uk/forums/viewtopic.php?f=21&t=3657 ), I would like any advice as to how best to go about experimenting with both mains and portable trickle charging from various sources for my needs when I decide to experiment with Super Capacitor configurations. :)

jumpjack
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Re: Super capacitors anyone?

Postby jumpjack » Fri May 30, 2014 7:48 am

I received 20 supercaps for free from Maxwell some months ago.
They still lay in my drawer, unused. :-(
What I miss/need is a powerful buck/boost DC/DC converter! Without it, SCs have no use on an electric vehicle!
Indeed, a SC can be discharge down to 0V, so you can use almost 100% of its energy... but EV electronics would not tolerate such a wide voltage range.
For example, I have a 60V e-scooter, so rather than using the 20 SCs in series to get 60V, I should build a 10s2p pack: it would be rated 5.4V.
Then I would need a buck/boost converter capable of both converting 5.4V to 60V and 60V to 5.4V, because I also need to repeteadly recharge the SCs pack after each acceleration! (I would use a battery in parallel).

But I can't find around any buck/boost converter more powerful than 150W: I'd need 10 of them in parallel (if such a connection is allowed)... but they cost 100$ each one! :-(

Any suggestion?


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