Re: Ultra capacitors

[jdbachman]

I'm probably preaching to the choir. Here's an interesting take on ultra
capacitors:

http://www.metricmind.com/ac_honda/main2.htm

None of us could afford it of course.

JD Bachman
Lancaster, PA
------------------------------

Message: 23
Date: Mon, 21 Jul 2008 13:18:21 -0500
From: Glen Hoag <hoag@...>
Subject: Re: [EVDL] Ultracapacitors
To: Electric Vehicle Discussion List <ev@...>
Message-ID: <200807211821.m6LILJ8x1218841@...>
Content-Type: text/plain; charset="us-ascii"; format=flowed

The idea is that the ultracapacitors can increase the available peak
power.  Can we believe that you can actually draw on the LiFePO4
batteries at a 10C rate without significant sag?  The ultracaps could
reduce sag at peak demand.

There is another NASA/Glenn (Lewis Research Center at the time)
report from 1999 on the Hybrid Electric Transit Bus (HETB) project
that discusses
using  ultracapacitors.
<http://gltrs.grc.nasa.gov/reports/1999/TM-1999-208890.pdf>  The
advantages claimed are better acceleration and ease of recapturing
energy using regenerative braking.

--Glen Hoag
   hoag@...



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[Roger Heuckeroth]

He never states how he made out with the Utracaps.  It just says "to  
be continued".

On Jul 21, 2008, at 6:49 PM, John Bachman wrote:

> I'm probably preaching to the choir. Here's an interesting take on  
> ultra
> capacitors:
>
> http://www.metricmind.com/ac_honda/main2.htm
>
> None of us could afford it of course.
>
> JD Bachman
> Lancaster, PA
> ------------------------------
>
> Message: 23
> Date: Mon, 21 Jul 2008 13:18:21 -0500
> From: Glen Hoag <hoag@...>
> Subject: Re: [EVDL] Ultracapacitors
> To: Electric Vehicle Discussion List <ev@...>
> Message-ID: <200807211821.m6LILJ8x1218841@...>
> Content-Type: text/plain; charset="us-ascii"; format=flowed
>
> The idea is that the ultracapacitors can increase the available peak
> power.  Can we believe that you can actually draw on the LiFePO4
> batteries at a 10C rate without significant sag?  The ultracaps could
> reduce sag at peak demand.
>
> There is another NASA/Glenn (Lewis Research Center at the time)
> report from 1999 on the Hybrid Electric Transit Bus (HETB) project
> that discusses
> using  ultracapacitors.
> <http://gltrs.grc.nasa.gov/reports/1999/TM-1999-208890.pdf>  The
> advantages claimed are better acceleration and ease of recapturing
> energy using regenerative braking.
>
> --Glen Hoag
>   hoag@...
>
>
>
> _______________________________________________
> For general EVDL support, see http://evdl.org/help/
> For subscription options, see http://lists.sjsu.edu/mailman/listinfo/ 
> ev

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[EVDL Administrator]

On 21 Jul 2008 at 18:49, John Bachman wrote:

> I'm probably preaching to the choir. Here's an interesting take on ultra
> capacitors:
>
> http://www.metricmind.com/ac_honda/main2.htm
>
> None of us could afford it of course.

Actually, that WAS one of us!  Victor, are you listening?

David Roden - Akron, Ohio, USA
EVDL Administrator

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[Metric Mind]

EVDL Administrator wrote:

> On 21 Jul 2008 at 18:49, John Bachman wrote:
>
>> I'm probably preaching to the choir. Here's an interesting take on ultra
>> capacitors:
>>
>> http://www.metricmind.com/ac_honda/main2.htm
>>
>> None of us could afford it of course.
>
> Actually, that WAS one of us!  Victor, are you listening?

Sorry, I don't monitor EVDL that closely lately, but
I am listening. I paid $9,600 for the stack of 160 2.7kF capacitors;
or $60 a piece. That was 70% off liquidation sale of then discontinued
model Maxwell wanted to get rid of. They sold few pallets of them
this way, I think around 5000 capacitors, to whoever was interested.

Is this what John wanted to know?

Victor

> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
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[Doug Weathers]

On Jul 22, 2008, at 6:58 AM, Roger Heuckeroth wrote:

> He never states how he made out with the Utracaps.  It just says "to
> be continued".

He (Victor Tikhonov) told the list about it.

As I recall, he was very pleased with the improved performance and the  
much more even load on the pack both from acceleration and regen.

There should be details in the archives.

--
Doug Weathers
Las Cruces, NM, USA
<http://www.gdunge.com/>


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[Metric Mind]

It might say "to be continued on the web site" for a while. It was
continued in life, just ACRX the site never got updated. Now I have even
less time, but eventually will update it.

Basically caps (the way I connected them, straight parallel to the pack)
helped TS cells by
taking peak loads and absorbing peak regen. It was especially
noticeable during regen, it was strong and you cold feel
the bank soaking up the energy getting ready for the next acceleration,
while TS cells were loafing along just slowly charging the caps
to the pack,s terminal voltage. Without caps because cells had very high
R_int, as soon as I engage regen, current injected into the pack caused
voltage rise to the top programmed limit for the inverter (380VDC)
without any meaningful current going into the cells. So the inverter cut
down motor regen current not to allow voltage overshoot, so you feel
loss of regen. With the caps the voltage stayed far more constant, they
are far stiffer.

Some hard data:

http://www.metricmind.com/ac_honda/line_art/test1.gif
first part of the plot - capacitors are connected,
second half - disconnected. I tried to keep test runs
drive patterns the same - accelerations and decelerations
(regen) to full stop, repeat.

You can see how much stiffer voltage is in first half, and how much
power (40kW easy) inverter puts out into the caps. TS only was incapable
to absorb, it so generally no more than 15kW could be generated.
It was one blip close to 30kW. Data was recorded with Siemens inverter
tracing facility (part of SIADIS software) and stored to a disc.

Zoomed in plots, compare:
http://www.metricmind.com/ac_honda/line_art/caps.gif
http://www.metricmind.com/ac_honda/line_art/nocaps.gif

In light of discussion about voltage sag: here is the test
of initial 2 100Ah cells TS sent to me, after which I
thought this is good representative of what their product is
and took the plunge. I would be pretty happy if the cell would
keep performing like this:
http://www.metricmind.com/ac_honda/line_art/liion.gif

Green and pink trace - voltage on two cells conencted in series and being
loaded with 100A (1C) current. You can see, these cells perform very
alike. Voltage sag is 0.56V, it is ~0.375V at 50A. (test was done
at 75% SOC, room temp, with entry level Dataq data acquisition system).
R_int = deltaV/deltaI=0.0037 Ohm, very good value.

For those interested how the caps hold up:
http://www.metricmind.com/ac_honda/line_art/ultracaps_balance.gif
Data was collected from last 10 caps in the stack.
Once the stack settles with balancing resistors, voltages are
close enough. R_leakage for the caps is not controlled parameter and
so was varying wildly, sometimes 2x. Resistors value of 39 Ohm
was chosen to dominate this variation - it is 10 times less
than average R_leakage (measured to be ~400 Ohm). You can see that whole
stack "breathe" up and down as charged/discharged, without disturbing
relative voltages ratios at resting condition. This tells me that
capacities of individual caps were very close (same ch/disch rate) and
leakage was no longer the dominating factor - it stayed balanced like
this for more than 2 years until I decommissioned the stack out of the car.

This was interesting experiment I wanted to conduct, and practical
conclusion (for this type of connection only!) was that there is no
need for capacitors if your battery is stiff enough and can absorb your
regen rate. They won't have chance to work. Spend money in more
batteries instead, it's more beneficial per weight.

It makes sense to use the caps (again in parallel to the pack)
only if your battery is low power. Low power cells may be deliberately
chosen option for whatever reason (say, someone can get them for free).
Then the caps will make vehicle driveable.

If you use DC-DC converter between the pack and the battery or connect
the stack in series with the battery, for instance like this:
http://www.metricmind.com/audi/line_art/_0002_capacitor_concept.gif ,
this is entirely different animal, and most of above discussion does not
apply.

--
Victor
'91 ACRX - something different
'01 in-AUDI-ble - handsome car with 0.4MW AC drive (work in progress)


Doug Weathers wrote:

> On Jul 22, 2008, at 6:58 AM, Roger Heuckeroth wrote:
>
>> He never states how he made out with the Utracaps.  It just says "to
>> be continued".
>
> He (Victor Tikhonov) told the list about it.
>
> As I recall, he was very pleased with the improved performance and the  
> much more even load on the pack both from acceleration and regen.
>
> There should be details in the archives.
>
> --
> Doug Weathers
> Las Cruces, NM, USA
> <http://www.gdunge.com/>
>
>
> _______________________________________________
> For general EVDL support, see http://evdl.org/help/
> For subscription options, see http://lists.sjsu.edu/mailman/listinfo/ev
>
>
>

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