# anyone know what ithe largest storage supercapacitor available for sale??



## electro37 (May 18, 2008)

I have a need for a supercap. with enough power storage to power a 500watt motor for approx. 30 minutes. The motor would have a 36 Volt power need.


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## major (Apr 4, 2008)

electro37 said:


> I have a need for a supercap. with enough power storage to power a 500watt motor for approx. 30 minutes. The motor would have a 36 Volt power need.


Hi electro37,

Those numbers show about one megajoule. You will need multiple cells for an ultracapacitor system for that voltage and energy. Also some type of voltage controller, for a 36 volt constant discharge and recharging from what ever source you have. Such ultracap systems can be made from available cells or modules. Cost would be like $10,000 or higher.

Batteries might be a better choice. 30 minute time constants are better suited for batteries. Ultracaps are better suited for applications in the 5 to 50 second range. Of course other considerations enter into it.

Hope that helps,

major


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## ClintK (Apr 27, 2008)

electro37 said:


> I have a need for a supercap. with enough power storage to power a 500watt motor for approx. 30 minutes. The motor would have a 36 Volt power need.


The largest ultracap I found during my search (that showed a price) was Maxwell. http://www.tecategroup.com/ultracapacitors/maxwellboostcaps.php

I go into a bit of the costs and calculations on post #3 and #9 of this thread: http://www.diyelectriccar.com/forums/showthread.php?t=16785

Your biggest hurdles are finding DC to DC converters to maintain 36 Volts and then the costs associated with such a large capacitor.


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## ClintK (Apr 27, 2008)

major said:


> Those numbers show about one megajoule. You will need multiple cells for an ultracapacitor system for that voltage and energy. Also some type of voltage controller, for a 36 volt constant discharge and recharging from what ever source you have. Such ultracap systems can be made from available cells or modules. Cost would be like $10,000 or higher.


Assuming prices haven't changed, I figured $11,250 for .97 MJ a couple months ago. If you've got the cash though I'd love to see your setup!


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## major (Apr 4, 2008)

ClintK said:


> Assuming prices haven't changed, I figured $11,250 for .97 MJ a couple months ago. If you've got the cash though I'd love to see your setup!


Hey Clint,

Here's a 1 MJ cap set I did a few years back. And no, I don't have that much cash.

Regards,

major


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## ClintK (Apr 27, 2008)

major said:


> Hey Clint,
> 
> Here's a 1 MJ cap set I did a few years back. And no, I don't have that much cash.
> 
> ...


I'm officially impressed. What capacitors did you use (C & V rating)? Why did you do it ("just because" is an acceptable answer)? And how much did it cost (do you still have both arms)?


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## major (Apr 4, 2008)

ClintK said:


> I'm officially impressed. What capacitors did you use (C & V rating)? Why did you do it ("just because" is an acceptable answer)? And how much did it cost (do you still have both arms)?


Hi ClintK,

156 Maxwell 2600 Farad cells in series. 2.5 V/cell. 400 V max for the set. Was for a commerical truck. Had funding, so I still have both arms and legs.

Regards,

major


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## Jacob Riskin (Jun 10, 2008)

As far as I know Maxwell makes the biggest Ultracaps on the market, at least until EEStor brings a product to market.

If anyone knows anything else I'm curious as well.


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## Nielmo (Oct 13, 2008)

electro37 said:


> I have a need for a supercap. with enough power storage to power a 500watt motor for approx. 30 minutes. The motor would have a 36 Volt power need.


Capacitors store energy as charge which makes them a bad choice for fuelcells.
The reason is that voltage drop is proportional to the discharge. This means at halftime your voltage will be half of what you started with.
Assuming you have a constant current discharge your voltage will look something like this.
0 min = 36V
10min = 24V
20min = 12V
30min = 0V

If you want to make sure you have at least 24V from your cells after 30min you must load them up to 60V at start (assuming the same discharge rate).


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## Nielmo (Oct 13, 2008)

Nielmo said:


> If you want to make sure you have at least 24V from your cells after 30min you must load them up to 60V at start (assuming the same discharge rate).


You could also *tripple* your capacitors and charge them to 36V. That would also guarantee 24V after 30min at the same load.


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## Tesseract (Sep 27, 2008)

electro37 said:


> I have a need for a supercap. with enough power storage to power a 500watt motor for approx. 30 minutes. The motor would have a 36 Volt power need.


Familiar with this equation? 

E = ½CV²

Where E is in Joules, C is in farads and V is in volts).

1 Whr = 3600J. Thus, a typical 12V/100Ahr battery is the "equivalent" of a 4.32MJ capacitor. Unlike the capacitor, though, most batteries maintain a constant voltage during discharge. Unlike most batteries, capacitors can usually accept huge pulses of current without complaint. Hence, they are best employed as a buffer when, for example, a motor controller goes into regen when the batteries are still fully charged.


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