# Super/Ultra Capacitors



## jlgh (Mar 6, 2010)

robinfryer said:


> Im looking into incorporating super or ultra caps into my design project to deal with the power generated from regen braking.
> 
> Does anyone know what kinds of current/energy transfer rate a lithium ion battery can handle? I dont want to waste time looking at capacitors if the batteries can already take it.
> 
> I heard the specific energy storage of capacitors (Energy storage/mass) is lower than liion batteries as well, so i guess theres no reason to have them unless the energy from regen braking is being transfered at such a short space of time that they become neccesary...?


My two-pennorth:



Many suppliers now seem to offer high power or high energy variants of Li-Ion batteries. The high power ones have high C rating (C rating x amp hours = max current): better acceleration and regenerative braking. The high energy ones have more watt hours per kg: better range. There is little for it but to read about C rating until you understand it, then trudge through the specifications. For good regen you need a higher charge C rating.
Batteries don't do regen power when fully charged. I just do not know whether/how a bank of capacitors would help with this.


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## robinfryer (Mar 31, 2010)

jlgh said:


> My two-pennorth:
> 
> Batteries don't do regen power when fully charged. I just do not know whether/how a bank of capacitors would help with this.


Yes i guess thats a problem with having only liion and regen since the batteries would blow up when forced more charge. Although i cant see why i cant have an ECU that tells the regen to turn off when the batteries are at full charge. 

But again that wastes energy...

I think the cost and mass of the capacitors may be too much anyway.

I want to use the 50Ah batteries on thunderstruck, does anyone have a spec sheet for them, i only have the basic details?


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## dtbaker (Jan 5, 2008)

most Li large format cells 'could' be charged at 1C with a AC motor directly... no ultracap required. For faster or higher amp regen in a hard stop situation a capacitor is a great way to go until you look at realistic limitations.

I found a maxwell ultracap that would hold enough for one 'braking event', and it ends up being 10"x18"30", weighing 150#, and costing about $7k.

For the 20% you MIGHT gain in range with city driving, you are better off buying higher aH batteries to start with.....


If you are building a car, forget anything less than 100ah... you won't get enough acceleration at less than 300amps and 96v to be truely 'roadworthy' even in a small car.


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## jlgh (Mar 6, 2010)

dtbaker said:


> If you are building a car, forget anything less than 100ah... you won't get enough acceleration at less than 300amps and 96v to be truly 'roadworthy' even in a small car.


I guess that is changing/will change as higher and higher C ratings become available?


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## dtbaker (Jan 5, 2008)

jlgh said:


> I guess that is changing/will change as higher and higher C ratings become available?


There are already some with higher C ratings if you have unlimited budget, but with less than 100aH per cell (and less than 10kWhr total) you'll have spent a lot of time and money to have very limited range... Unless you are building a race-only vehicle, it is far more usable and possible to sell to others with a range of 40+ miles and enough power for cabin heat, etc.


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