Going halvsies

[Sean Korb]

Hi listers,

I found the disk brake upgrade for my Metropolitan and an S-10 rear
axle with 4:11 gearing.  I was originally going to load it up
with 10 12v lead acid batteries but the Lithium Ion batteries
have so much momentum and buzz and.... well, success behind them
that I thought 2 strings of TS 100AH batteries would get me the
50 mile round trip commute I was targeting.  That would be 34
batteries in series and another 34 in parallel.  That's pretty
expensive compared to 10 T-1275 batteries.

If I started with 34 batteries for a single string, I thought I
could get 15 or 20 miles out of that with 2/3 the investment
and a chance to learn the technology, but would I toast the
batteries with the current I would draw?  When this motor
and controller was in a S-10 pickup it would occasionally draw
over 200A. It doesn't seem like a lot to draw from lead cells
but the TS batteries seem a little fragile.

thanks,
sean

--
Sean Korb [hidden email] http://www.spkorb.org
'65,'68 Mustangs,'68 Cougar,'78 R100/7,'60 Metro,'59 A35,'71 Pantera #1382
"The more you drive, the less intelligent you get" --Miller
"Computers are useless.  They can only give you answers." -P. Picasso

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[Seth Rothenberg]

Sean,
I am using similar logic - I bought 50 of them,
am wiring them now.
Once I see how my range is, and check
Curb Weight compared to GVWR,
I'll see if the second pack can be the
same size.    If not, it will be lighter cells,
same voltage.  (50 cells is the max I
can put to my controller)

My analogy for this model is,
there are gas vehicles that carry
two tanks.  When one is empty,
open this valve, close that one...

It's not ideal, but it allows
the step-in approach....

(Of course, I might not need the second pack,
once the President of the company sees
what I made, maybe he'll get me an outlet :-)

Seth

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[Mike Nickerson]

Hi Sean,

I'm just curious:  If you are thinking of going with two strings of TS 100AH
batteries, why not just go with a single string of 200AH batteries?  It
seems like it would be a lot easier to manage a single serial string, same
price for the cells, and cheaper on battery management since you would only
need 1/2 the cell management hardware.

Also, you would know that a 200A draw is only 1C on the cells and wouldn't
always be wondering whether 1 string is providing more current (and
therefore taking more of the load) than the other.

Of course, there could be physical size reasons this wouldn't work, but it
seems a lot simpler.  Obviously, with this approach, you couldn't get 1/2
the cells now and 1/2 later.  I doubt your truck will run very well on 60
volts!

I like the way the cells are being priced by the Ah.  That makes these kinds
of design tradeoffs easier, since you aren't paying a price penalty to move
to larger or smaller cells.

Mike

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Sean Korb
Sent: Wednesday, November 11, 2009 7:56 AM
To: Electric Vehicle Discussion List
Subject: [EVDL] Going halvsies

Hi listers,

I found the disk brake upgrade for my Metropolitan and an S-10 rear
axle with 4:11 gearing.  I was originally going to load it up
with 10 12v lead acid batteries but the Lithium Ion batteries
have so much momentum and buzz and.... well, success behind them
that I thought 2 strings of TS 100AH batteries would get me the
50 mile round trip commute I was targeting.  That would be 34
batteries in series and another 34 in parallel.  That's pretty
expensive compared to 10 T-1275 batteries.

If I started with 34 batteries for a single string, I thought I
could get 15 or 20 miles out of that with 2/3 the investment
and a chance to learn the technology, but would I toast the
batteries with the current I would draw?  When this motor
and controller was in a S-10 pickup it would occasionally draw
over 200A. It doesn't seem like a lot to draw from lead cells
but the TS batteries seem a little fragile.

thanks,
sean

--
Sean Korb [hidden email] http://www.spkorb.org
'65,'68 Mustangs,'68 Cougar,'78 R100/7,'60 Metro,'59 A35,'71 Pantera #1382
"The more you drive, the less intelligent you get" --Miller
"Computers are useless.  They can only give you answers." -P. Picasso

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General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev

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