Battery Choice Advice (electrathon)

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Battery Choice Advice (electrathon)

Reinkens, Kirk
Hello,
I'm working with a team of young college students who have been competing in local Electrathon races. For those unfamiliar with this...these are smaller, nearly go-kart sized vehicles with reasonable roll-over protection. The challenge is 1-hour...as far as you can go with 73 pounds of Lead Acid. This amounts to approximately 1 KWhr of energy. Fun for students who have not designed, built or tested much.

Scenario: The typical vehicle is a 24V DC 1-2 hp system. The battery weight is consistent with 2 RED(SC25A,SC35A or SC75/35) or YELLOW(D35 or D75/25) Optimas. My students have been building and racing an AC vehicle using a traditional Siemens industrial VFD. Our battery pack is tied to the DC bus of the drive and protected by shunt regulators during charging. It has taken time, but they/we have become more familiar with the drive settings and feel that the performance is limited by the battery choices we have made and not the controller or motor.

Question 1: Our pack is a set of 26 12 ~3.2-3.4aHr SLA @ 2.8 pounds each. We have selected essentially generic batteries. We suspect that the quality of the SLA's is not consistent with the level of quality of the Optimas regarding energy density. Can someone suggest a specific lead acid battery model that might move our overall battery pack to a similar available energy of the 2 Optimas?

Question 2: We could also use a 15 pound pack of Lithium-Ion or Lithium-Polymer. This would be new territory for us. Suggestions for a 1-KWhr pack at ~370 volts and 15 pounds would be great.

Kirk
Pullman, WA

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Re: Battery Choice Advice (electrathon)

Elithion
Reinkens, Kirk wrote
We could also use a 15 pound pack of Lithium-Ion or Lithium-Polymer.
Suggestions for a 1-KWhr pack at ~370 volts and 15 pounds would be great.
You won't find an off-the shelf Li-ion battery; you'll have to build your own.

For ease: use prismatic cells (CALB, Sinopoly, or the like).

For higher performance, you'll have to go to pouch (not ANY pouch, just some particular models) or small cylindrical (A123 M1 26650). Either one will require a steep learning curve, and a LOT of work.

You'll need a BMS. Here is a selector that has all the commercially available BMSs: http://liionbms.com/php/bms-selector.php Choose the one that is right for you.

To learn how to do a Li-ion battery, and use a BMS, you can read the Li-ion BMS book for free on Google Books: http://books.google.com/books?id=o-QpFOR0PTcC

Davide Andrea
Elithion
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Re: Battery Choice Advice (electrathon)

EVDL Administrator
In reply to this post by Reinkens, Kirk
On 6 Nov 2012 at 19:39, Reinkens, Kirk wrote:

> Question 1: Our pack is a set of 26 12 ~3.2-3.4aHr SLA @ 2.8 pounds each.
> We have selected essentially generic batteries. We suspect that the
> quality of the SLA's is not consistent with the level of quality of the
> Optimas regarding energy density.

With a fixed battery mass devoted to multiple modules, you have more mass in
battery cases and separators, and less in active material.

It would be an interesting exercise to run the numbers on whether a DC:DC
upconverter between the canonical Optimas and your controller would be more
or less efficient than all that non-active material.  

David Roden
EVDL Administrator
http://www.evdl.org/


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Re: Battery Choice Advice (electrathon)

Cliff
In reply to this post by Reinkens, Kirk
Kirk,

We are running in the Electrathon of Tampa Bay series in Florida. This form
of racing presents challenges that forces one to rethink the basics of
making an electric vehicle fast. It is very interesting racing.

I would like to hear more about how your very high voltage set up is
working. Running high voltage seems like a great idea for efficiency but
what about torque?

You also might want to post your questions on the Electrathon of America
discussion forum. There are many experienced Electrathon racers there who
might have ideas.

<Question 1: Our pack is a set of 26 12 ~3.2-3.4aHr SLA @ 2.8 pounds each.
We
have selected essentially generic batteries. We suspect that the quality of
the SLA's is not consistent with the level of quality of the Optimas
regarding energy density. Can someone suggest a specific lead acid battery
model that might move our overall battery pack to a similar available energy
of the 2 Optimas?>

So you are running 312 volts and an average current of 3.5 amps? Have you
done any testing to see what the one hour rate of one of your SLA is?

The 20 hour rate rating makes them sound great with around 1,382 Watt hours
but what do they deliver at the the 1C rate? Yellow tops test out at around
800 Watt hours.

I would guess that Cyclon (Enersys) batteries such as their D or DT model
would give better 1 hour performance. They would also have the added
advantage of allowing you to monitor each cell as opposed to each battery
block. I can tell you from experience (having run a 400 volt string on
Cyclon's in the Electric Imp) that I suspect that even LiPoly will be
cheaper and
less complicated.

<Question 2: We could also use a 15 pound pack of Lithium-Ion or
Lithium-Polymer. This would be new territory for us. Suggestions for a
1-KWhr pack at ~370 volts and 15 pounds would be great.>

I would check the R/C plane forums and see what is available. You will be
working with small cells so I would agree with David's <you have more mass
in
battery cases and separators, and less in active material.>

In the long term, I think Lithium is a good choice. You get to run a lighter
vehicle and, as long as you do not over discharge the cells, you will get
better cycle life than are likely from deeply discharged lead acid.

Cliff

www.ProEV.com




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