Super caps revisited.

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Super caps revisited.

drdhdmd
Can a super Capacitor in parallel with a lithium ion battery such as a 100ah ThunderSky help increase the maximum 20 second discharge rate past the 3-4C (300-400amps) of the ThunderSky itself to supply at least 1500 amps?

How does one calculate the value of the Capacitor needed.
Thank you,
David Delman
eLectricDeLorean.com
evalbum.com/1482

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Re: Super caps revisited.

Bill Dube
Capacitors don't have the energy content for such sustained
discharges. They are good for only very brief discharges, like a
second or two. folks always talk about using caps in EVs and hybrids,
but you never see them other than in demonstration type research
projects. They have never been used in an OEM EV or hybrid, even
though they have been around for a long time. They just are not practical.

The most practical solution is to use cells with higher discharge
rate capability. This is not what you want to hear, but is really
what a manufacturer of an OEM EV would do.

The next best solution is to parallel each of the low-rate cells with
very high-rate cells of similar chemistry (voltage range), such as
A123ASystems cells. Folks talk about this, seemingly endlessly, but
none ever actually does it.

Bill Dube'

At 09:33 AM 7/16/2010, you wrote:

>Can a super Capacitor in parallel with a lithium ion battery such as
>a 100ah ThunderSky help increase the maximum 20 second discharge
>rate past the 3-4C (300-400amps) of the ThunderSky itself to supply
>at least 1500 amps?
>
>How does one calculate the value of the Capacitor needed.
>Thank you,
>David Delman
>eLectricDeLorean.com
>evalbum.com/1482
>
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Re: Super caps revisited.

Evan Tuer
On Fri, Jul 16, 2010 at 3:10 PM, Bill Dube <[hidden email]> wrote:

> The next best solution is to parallel each of the low-rate cells with
> very high-rate cells of similar chemistry (voltage range), such as
> A123ASystems cells. Folks talk about this, seemingly endlessly, but
> none ever actually does it.

I know someone who has done it (who is/was a member of this list).
What the outcome was, I'm not sure...

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Re: Super caps revisited.

R Willis
In reply to this post by Bill Dube
we have some new maxwell 57 f caps 16.5 volts they look ok but will need to
parallel with a battery if you have to charge from home.

they would be great for regen applications with a fast 1:1 wave

we are still working on how to implement with our units


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Re: Super caps revisited.

Lee Hart
In reply to this post by drdhdmd
On 7/16/2010 8:33 AM, David Delman wrote:
> Can a super Capacitor in parallel with a lithium ion battery such as
> a 100ah ThunderSky help increase the maximum 20 second discharge rate
> past the 3-4C (300-400amps) of the ThunderSky itself to supply at
> least 1500 amps?

Yes, but not enough to be worth the cost. The problem is that the
voltage of the lithium cell doesn't change much with load. With the
capacitor directly in parallel, this means the capacitor's voltage also
does not change much.

The voltage on a capacitor changes drastically (from max to 0 volts) as
you remove energy from it. Not allowing its voltage to change means no
energy can be extracted from it.

> How does one calculate the value of the Capacitor needed.

The internal resistance of the TS 100ah cell is about 0.003 ohms (i.e. a
100a load drops its voltage about 0.2v).

Let's say your supercap has an internal resistance of 0.001 ohm. Then
the instant you apply a 1500 amp load, the current divides in proportion
to the two resistances:

1/4 x 1500a = 375a in the TS cell
3/4 x 1500a = 1125a in the supercap

But, drawing current from the supercap causes its voltage to immediately
drop. Its capacitance and resistance have what is called an RC time
constant. For example, suppose it's a 1000 farad capacitor. Then its
time constant is 1000f x 0.001ohm = 1 second. The current it delivers
will fall to 0.37 of its initial value (1125a x 0.37 = 416a) in 1
second. In another second, it falls to 0.37 again (416a x 0.37 = 154a).

You can see that even a huge 1000f capacitor isn't enough to supply
current for more than a second or two.

The correct way to use supercapacitors is to keep them in their own
series string, with their own separate controller that can keep the
current they deliver constant despite their drastically varying voltage.

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Re: Super caps revisited.

Lee Hart
In reply to this post by Evan Tuer
Bill Dube wrote:
>> The next best solution is to parallel each of the low-rate cells with
>> very high-rate cells of similar chemistry (voltage range), such as
>> A123ASystems cells. Folks talk about this, seemingly endlessly, but
>> none ever actually does it.

Evan Tuer wrote:
> I know someone who has done it (who is/was a member of this list).
> What the outcome was, I'm not sure...

It's an interesting idea, but so far it's just that -- an idea. It has
only been tried briefly, by a few people, and the results aren't really
known (publicly, at least). This could be a good approach if you like to
experiment. But simply sticking them in parallel isn't likely to work
very well.

Likewise, combining supercaps with batteries is a promising idea that
hasn't really been tried. It can be useful in theory; but you need to
understand the characteristics of each, and design the system to use
them to its benefit. Like batteries, simply connecting them in parallel
isn't the way to do it.
--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Re: Super caps revisited.

Seth Rothenberg
This relates to a question I had asked
a friend who is an EE....
What if you built a controller that
can take two inputs, each programmed
with different limits?

Or, could you build a
Parallel Discharge Management System,
that could be programmed to distribute
the draw on two power sources -
useful if you have supercaps and LiFePO4
or LifePO4s and SLAs....or even two
sizes or two designs of the same type.

My friend's answer was a (colorful)
comment about my insanity...basically
you would need  $timulu$ dollar$.
I'm not convinced that it is so hard.
Just put all our favorite EEs in a room
for a while...

(Don't airplanes do this? Deplete the
fuller tanks first?)

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Re: Super caps revisited.

Roland Wiench
In reply to this post by drdhdmd

At 09:33 AM 7/16/2010, you wrote:

Can a super Capacitor in parallel with a lithium ion battery such as a 100ah
ThunderSky help increase the maximum 20 second discharge
rate past the 3-4C (300-400amps) of the ThunderSky itself to supply at least
1500 amps?

How does one calculate the value of the Capacitor needed.

Thank you,

David Delman
eLectricDeLorean.com
evalbum.com/1482


Hello David,

You can contact Tavrima Canada Limited at:

               http://www.tavrima.com/contact.html

     Fill out the Feedback and Request Form and they will send you a spread
sheet on the application purpose and power/energy you need.

There type of capacitors are normally for storing REGEN energy and then
discharging the energy during acceleration.

Another type of supercapacitor is design for a EV only, not for a hybred,
which can actually drive the EV for a certain distance.  Is ideal for short
distance delivery vehicles or in town buses.

The source for these are from the ESMA company at:

             http://www.exma-cap.com

They will also provide a spread sheet on characteristics of the capacitor
system which is required for the performance of a vehicle.

Roland

 

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Re: Super caps revisited.

Lee Hart
In reply to this post by Seth Rothenberg
On 7/16/2010 11:01 AM, Seth Rothenberg wrote:

> What if you built a controller that
> can take two inputs, each programmed
> with different limits?
>
> Or, could you build a
> Parallel Discharge Management System,
> that could be programmed to distribute
> the draw on two power sources -
> useful if you have supercaps and LiFePO4
> or LifePO4s and SLAs....or even two
> sizes or two designs of the same type.

This is basically what you need to do in any system with two energy
sources, so you can independently control the energy you are getting
from each. It could be an ICE-battery hybrid, or an EV with two battery
packs, or a battery pack and supercaps, or fuel cells and supercaps, etc.

Your friend is right that it will cost more and be more complicated.
But, that doesn't mean it's impractical. There are advantages to be
gained by controlling things so you get your energy from whichever
source is the most effective for the particular load at the moment.

Consider the popular ICE-electric hybrids like the Toyota Prius. They
use the ICE when you need high power, and shut it off and use the
batteries when you need low power. The result is better than you could
get with either system alone.

With an EV and two battery packs, you'd need two normal motor
controllers. If these are the usual PWM controller with a single series
motor, then you'd also need two separate inductors, one on the output of
each controller (because they are designed to use the motor's inductance
as a key part of the controller. Or, you could have two motors, each
running on one of the controllers. This setup would be more expensive
than one motor and controller; but maybe not *double* the cost because
each one can be smaller.

With batteries and supercaps, the battery controller is normal. The one
for the supercaps is rather special, as it has to work with a very wide
range of input voltages. The energy in capacitors is proportional to the
square of the voltage. A 2:1 range gives you 25%-100%, i.e. you can get
75% of the stored energy out. A 3:1 range is 11%-100% or 89% of the
stored energy.

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Re: Super caps revisited.

Cor van de Water
In reply to this post by drdhdmd
I think Viktor has documented his setup quite extensively for this CRX.
The issue there was the (too) high internal impedance of his Lithium Ion
batteries at that time, so when he got a deal for Supercaps, he jumped
on it to give his Lithiums some support for a quick launch.

First order approximation of the value of the caps: say that you
have a 300V pack that sags to 200V at a 500A discharge, so using
the formula I x t = V x C
(Current times Time equals Voltage(change) times Capacitance)
and knowing that your hard-launch does not need to last longer than
for example 10 seconds:
500A x 10s = 100V x C
C = 5000As / 100V = 50 Farad.
Note that supercaps typically have a working voltage of a few volts,
so you need about 60 in series to get 300V with 5V caps.
This means that each supercap must be 60 times larger than 50 Farad,
or 3000 Farad, 5V.
This is a big bank of caps...
Today this is not needed as Lithium Ion batteries have reduced their
internal resistance low enough to easily beat an equal volume of caps.

Regards,

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Lee Hart
Sent: Friday, July 16, 2010 9:23 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Super caps revisited.

Bill Dube wrote:
>> The next best solution is to parallel each of the low-rate cells with

>> very high-rate cells of similar chemistry (voltage range), such as
>> A123ASystems cells. Folks talk about this, seemingly endlessly, but
>> none ever actually does it.

Evan Tuer wrote:
> I know someone who has done it (who is/was a member of this list).
> What the outcome was, I'm not sure...

It's an interesting idea, but so far it's just that -- an idea. It has
only been tried briefly, by a few people, and the results aren't really
known (publicly, at least). This could be a good approach if you like to
experiment. But simply sticking them in parallel isn't likely to work
very well.

Likewise, combining supercaps with batteries is a promising idea that
hasn't really been tried. It can be useful in theory; but you need to
understand the characteristics of each, and design the system to use
them to its benefit. Like batteries, simply connecting them in parallel
isn't the way to do it.
--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Re: Super caps revisited.

EVDL Administrator
In reply to this post by Lee Hart
Solectria built an experimental EV about a decade ago, using supercaps to
reduce the peak load on the lead batteries for better range.  It had a wide-
range bidirectional DC:DC converter (probably the one then offered by Brusa)
to prop up the caps' rapidly falling voltage as they discharged.  

They reported some modest success, IIRC, but the implementation cost was
astronomical.

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: Super caps revisited.

Jack Murray
The issue with using batteries as booster is this increases their cycle use by 10x, so they will not last long.

It is important to note that us DIY building one-off cars can build things differently than what is "cost effective" for GM or any production car.
In other words, if someone has two motors, two controllers and a bank of capacitors available to them at low-cost, it can be cost effective to build an EV using them, so telling them it is too costly isn't exactly
the best advice.  The OP asked how to size them, haven't seen that answer yet.

--- On Fri, 7/16/10, EVDL Administrator <[hidden email]> wrote:

> From: EVDL Administrator <[hidden email]>
> Subject: Re: [EVDL] Super caps revisited.
> To: "Electric Vehicle Discussion List" <[hidden email]>
> Date: Friday, July 16, 2010, 11:12 AM
> Solectria built an experimental EV
> about a decade ago, using supercaps to
> reduce the peak load on the lead batteries for better
> range.  It had a wide-
> range bidirectional DC:DC converter (probably the one then
> offered by Brusa)
> to prop up the caps' rapidly falling voltage as they
> discharged. 
>
> They reported some modest success, IIRC, but the
> implementation cost was
> astronomical.
>
> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> EVDL Information: http://www.evdl.org/help/
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> Note: mail sent to "evpost" an "etpost" addresses will not
>
> reach me.  To send a private message, please obtain my
>
> email address from the webpage http://www.evdl.org/help/ .
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>
>
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