[ausev] Batteries not getting up to charging voltage?

[Goel, Gaurav]

Brian, very interesting report.  Thank you for sharing this with us.

All lead acid batteries will wear down due to corrosion at the internal
lead and lead oxide terminals.  Water consumption may not be a good
indicator of the level of wear of the battery, because it only reflects
evaporative losses.  Heat and the number of charge cycles are positively
correlated to reduced current and voltage, and the further symptoms you
will experience will ultimately include cell failure due to corrosion,
sadly.  This is pretty much inherent in the design of a lead-acid
battery.

For an excellent explanation of design issues, see Firefly Energy's
website FAQ (www.fireflyenergy.com).  Firefly (a spinoff from
Caterpillar) is designing a new type of battery terminal that will
extend life and vastly increase energy density, but alas, they are not
planning to sell to the general public anytime soon, if ever.

You may find that individual batteries have different voltages, though
that might be a pain to check in your EV.  Note that EV load cycling is
a tremendous acceleration of a typical lead-acid starter battery design
life span.  You may want to investigate if you can directly access a
battery recycling facility, instead of going through the retail supply
chain.

Good luck,
Gaurav


Gaurav Goel, Registered Patent Agent
Jackson Walker LLP | 100 Congress Avenue | Suite 1100 | Austin, Texas
78701 
(512)236-2360 direct | (512) 691-4423 direct fax | ggoel at jw.com |
www.jw.com


-----Original Message-----
From: ausev-bounces at austinev.org [mailto:ausev-bounces at austinev.org] On
Behalf Of Brian Lasseter
Sent: Tuesday, June 09, 2009 2:56 PM
To: AustinEV News Announcements and General Discussion
Subject: [ausev] Batteries not getting up to charging voltage?

My batteries have been losing range for a while now...  i.e. The voltage
sags more under high current load limiting my effective electric vehicle
range.  However now I'm starting to see a new issue, which I presume is
also related to my batteries being past their prime.  The batteries are
not really getting up to the charging or acceptance voltage, so the PFC
charger just keeps charging them all night.  This happens about once a
month, that I get an unplanned equalization charge for my car.

At 80F the US8VGC batteries that I have should be charging at 186V
(2.583V * 72 cells as per http://www.usbattery.com/usb_faqs.html ).
At the end of March, I dropped the charge voltage to 184V (the 90F
charging voltage, since it was not reliably hitting 186V).  At the end
of April I dropped it to 181V (the 100F charging voltage, since it was
not hitting 184V).  Now at the end of May, it seems that my batteries
will not get much above 175V.

At first I thought it was temp or water issues (which it may have been),
but I have been checking the water fairly often through this process.  I
last refilled the water a month ago, and at the end of April the 18
batteries and 72 cells only needed 3 gallons of water (from the previous
6 weeks of car usage).  I actually have noticed that as the effective
range of the vehicle has been dropping (so I charge it more often, and
can not discharge the batteries as far) the water used by the batteries
has decreased from the amount of water that I used to use in my
batteries.  I spot checked a few batteries last weekend for their water
and they seemed pretty high, and the batteries have always been very
consistent in their water usage (from cell to cell, and battery to
battery).  I'll be watering them again this coming weekend.

Anyways, I guess my main question was if not getting up to the charging
voltage was a known issue as batteries age.  Mine are at about 300
cycles now.  I was also curious what other signs would crop up as the
batteries age further.


--
TTFN,
Brian "Lasso" Lasseter

"No Sane man will dance."   -Cicero (106-43 B.C.)
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