[Oeva-list] OSU Solar Car needs BPS help for A123 prismatic cells

Kat Han kathyhan4 at gmail.com
Wed Jun 6 13:27:05 PDT 2012


Hello friends from the EV community,

This is a request for help from anyone who has the time, experience, and
knowledge to lend a hand.

As some of you know our solar car team is finishing up their third vehicle,
the Phoenix, for the American Solar Challenge that is next month (a 1600
mile race from New York to Minnesota).  Everything is going really
smoothly, but we have ran in to a problem with our batteries  (unlike the
last battery problem we had).  A123 is supplying us with batteries and a
protection system (BPS), but since they just had a major recall and have to
redirect their efforts there is a significant chance that they won't get to
reconfigure the software to work with our pack and testing requirements
before we leave on June 29th.  So, we are left without a battery protection
system, though they can provide the hardware if we can program it.

A123 is supplying the battery pack.  The pack has already been built in the
30 in series 2 in parallel configuration for a total of 60 of their 20Ahr
prismatic cells.

*Our BPS is required to perform the following tasks:*

Sense and open circuit under these conditions:
Over Temperature: 62 deg. C
Over Current: 120 A discharge, 40 A charge
Over voltage: 3.65V per cell
Under voltage: 2.4V per cell

ASC test procedure:
http://americansolarchallenge.org/wordpress/wp-content/uploads/2010/03/ASC2010_Protection-System-Test-Procedure.pdf


*Our team has decided to work on several BPS solutions in parallel and see
which one comes through first.  Our options include:*

1.) Work with Bob Simpson's BMS (from EV Drive, up in Banks, Oregon) and
adapt it to the A123 battery module. Bob has an integrated BMS that will
sense voltage and temperature and will talk RS485. Matt Knoop will get an
Arduino board to interface Bob's BMS and also get a current shunt to sense
current, and then it will throw the contactors open and closed,
appropriately. *We are looking to get this done in under 10 days (before
June 16th).*

2.) Use the existing hardware that A123 Systems is providing us (the
voltage, temperature, and current sensor systems) and build a "master" that
throws contactors open and closed based on the voltage, temperature and
current. The difficulty of this solution is that the devices talk through
the CAN protocol, which is a difficult protocol to program for.

3.) A123 Systems will still try to get the Battery Control Module built in
the next 3 weeks, so in case we don't have the first two solutions, we may
yet be saved at the last second by an overnight shipment of a fully
functional BCM from A123 Systems. This is a shot in the dark, but it may
end up saving us.

If you have experience with these things and you would like to help, please
contact us ASAP!  Our group is not that familiar with programming for CAN
bus, and if we can get that programming done more easily than this task is
not as big.

Thank you for your support!  We are very lucky to have such an active EV
community in Corvallis and Oregon!

Sincerely,

Kat Han
Co-captain
OSU Solar Vehicle Team
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