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3397Re: Prius NiMH Batteries

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  • Mike Phillips
    Dec 25, 2007
    • 0 Attachment
      There are a few directions to approach the Prius packs for use in an EV.

      Energy content is about 1.0-1.2 kwhrs per pack from the testing that I
      did. Five in parallel give you 5.0-6.0 kwhrs of energy. That might get
      you 20-25 miles of range if you drain the pack dead. I'm assuming 250
      watt-hours per mile. Following the rule of thumb to not go lower than
      50% state of charge, you might have a range of 10-12 miles. Imagine
      having this kind of range after spending the time it takes to
      mechanically restrain every module so they don't expand and wiring it
      all up. A 1 amp charge rate will ruin an unrestrained Prius module.
      Then there is how to charge nimh in parallel. Some say it's
      impossible. Ask them how many times they have tried it. It can be done
      but requires even more of a complicated pack. The built in relays in
      the Prius packs make parallel charging and it's associated maintenance
      possible. Every now and then the pack needs to be separated into
      individual packs and charged separately.

      Then there is the cooling issue. That's an entire page all by itself.

      The Prius modules are rated to last 150k miles because they do in fact
      run in a narrow band of soc. I forget the exact number, if I ever knew
      it, but guessing at 40-80% is pretty close. That tight band is how
      they get millions of very shallow charge/discharge cycles. In an EV
      one hopes to get to 1000 cycles. The plates that make up each module
      are just thinner looking to me, than say the EV95 in the RAV4/Ranger
      nimh cells. That relates to being more efficient at accepting
      regen energy. Not all batteries are good at taking short dumps of
      energy and actually converting it chemically and storing it as
      electrical energy. Some of it is absorbed and turned into heat instead.

      Having several packs in Parallel will help distribute the load. But
      you only get a very short range for all of your work. I can tell you
      that having 5 Prius packs in parallel gave me the lowest pack
      impedance I will ever have. My regen was so severe it would almost
      break the rear tires lose on deceleration.

      Anyway, it sure is fun to tell your friends that your EV drives on
      Prius batteries. Unless the EV is something light like a golf cart, I
      suspect the lifetime will be short. If nothing else the range is just
      not worth the effort, to me anyway. I started to figure this out after
      spending weeks making up fan control circuits and lots of testing.

      The guy I sold all of my perfectly good packs to, smoked several of
      them right off the bat. I can promise you he is much more educated
      than I am. A professor in fact. The bottom line is that these
      different versions of nimh batteries, Cobasys, Prius, Sanyo, are so
      different in chacteristics that each should be considered a completely
      different chemistry.

      Here is a pic of the packs in the bed of my truck. There are more in
      that folder.

      http://www.rotordesign.com/s10/priuspack/P5270196.JPG

      Mike







      --- In solectria_ev@yahoogroups.com, "Bill Swann" <dbswann4@...> wrote:
      >
      > Thanks for the feedback. And for alerting me to the pitfalls of re-
      > engineering a battery pack. I do not fully understand your comment "
      > the Prius batteries have been optimized for efficiently accepting
      > regen energy". Are you suggesting that making a Solectria battery
      > pack with 5-6 Prius packs is ill advised because the Prius battery is
      > not designed for this? The price is certainly right for used packs,
      > assuming a high % of the cells are good.
      > Thanks, Bill S
      >

      > --- In solectria_ev@yahoogroups.com, "Mike Phillips"
      > <mikep_95133@> wrote:
      > >
      > > This information was derived from experience driving several hundred
      > > miles in a vehicle with 5 Prius packs in parallel for the pack.
      > There
      > > were 11 packs total used in testing.
      > >
      > > Mike
      > >
      > >
      > >
      > > --- In solectria_ev@yahoogroups.com, "Mike Phillips" <mikep_95133@>
      > > wrote:
      > > >
      > > > The absolute most important thing with these Prius modules is
      > cooling
      > > > them. Just 1 amp during charge can smoke them without cooling. If
      > you
      > > > look at the side view of the chassis you will see a slope in lower
      > > > plenum. It keeps the airflow rate the same across all of the
      > cells.
      > > >
      > > > The second most important thing is that the cells must absolutely
      > be
      > > > held in compression. Even when they are stone cold, just 1 amp
      > during
      > > > charge causes them to pressurize and expand a lot, thus ruining
      > them.
      > > >
      > > > If you overheat the modules they will not flow KOH into the black
      > > > overflow tubes that go across the top of the cells. The thermal
      > vents
      > > > will each crack and thus vent gaseous and liquid KOH.
      > > >
      > > > The 4 thermistors on the top of the cells are 10k NTC types. Using
      > > > them to adjust air flow is important.
      > > >
      > > > That sheetmetal chassis that they come in from the factory is
      > > > engineered the way it is for list full of reasons.
      > > >
      > > > You have to ask yourself if you have enough room for all of the
      > > > support hardware in each battery box.
      > > >
      > > > That 'current measuring coil' is for telling the hardware how much
      > > > current is being put into or taken out of the pack.
      > > >
      > > > These are not the same NIMH cells that you can read about in
      > books and
      > > > on the web. They are in the same family but have been very
      > optimized
      > > > for efficiently accepting regen energy, far better than anything
      > else
      > > > on the planet. That makes them less energy dense and more prone to
      > > > thermal failure.
      > > >
      > > > I'm buried up to my eyeballs in projects now, so I cannot give you
      > > > much more than this right now.
      > > >
      > > > Good Luck.
      > > >
      > > > Mike
      > > >
      > > >
      > > >
      > > > --- In solectria_ev@yahoogroups.com, "Bill Swann" <dbswann4@>
      > wrote:
      > > > >
      > > > > I dis-assembled a Prius battery pack. What I understand about
      > the
      > > > > design I like. The cells are bolted to a common baseplate.
      > There are
      > > > > series copper jumpers between the 38 cells. I saw a 125 amp
      > fuse and
      > > > > a computer, into which the 5 temp sensors and 19 voltage
      > measurments
      > > > > were fed. Also there are 2 single pole relays to disconnect the
      > pack
      > > > > from the outside world. I saw what would appear to be a current
      > > > > measuring coil, but I do not undestend what it might do in a DC
      > > > > system except to verify the the reley worked. There are thermo
      > wells
      > > > > in every cell, where the temp sensors are placed. Additionally,
      > all
      > > > > 38 cells were vented into a common tube to carry off gasses.
      > There
      > > > > was one temp sensor in a plenum below the pack to verify air
      > flow.
      > > > > And all of the cells had dimples on the sides so there would be
      > a
      > > > > gaps between cells for cooling air flow. My next step is to see
      > how
      > > > > many series combinations will fit in the Force battery boxes.
      > It is a
      > > > > squeeze, but 4 might fit in the front battery box.
      > > > > Bill S
      > > > >
      > > > > --- In solectria_ev@yahoogroups.com, Dorothy Swann <dbswann4@>
      > > > > wrote:
      > > > > >
      > > > > > Thanks for the math. I have not gotten around to doing that
      > yet. I
      > > > > had just looked at the watt-hours per pound which was
      > favorable. I
      > > > > inquired at a local surplus parts dealer, and battery packs in
      > > > > wrecked Priuss are available beginning at $ 400. My plan will
      > be to
      > > > > acquire enough packs and build up a series/parallel combination
      > on
      > > > > the bench, and start doing some load tests. The Prius pack I
      > have
      > > > > seems to look at the voltage of 2 modules at a time. The
      > voltage
      > > > > sampling electronics is being developed. First for 13 batteries
      > for
      > > > > the Force, then for a higher number of cells.
      > > > > > Bill S
      > > > > >
      > > > > >
      > > > > > ----- Original Message ----
      > > > > > From: Todd Martin <larsthelean@>
      > > > > > To: solectria_ev@yahoogroups.com
      > > > > > Sent: Friday, November 30, 2007 7:47:57 AM
      > > > > > Subject: [solectria_ev] Re: Prius NiMH Batteries
      > > > > >
      > > > > > Hi Bill,
      > > > > >
      > > > > > This sounds like an interesting project.
      > > > > >
      > > > > > I took the liberty of checking the specs on the Prius Nimh
      > modules:
      > > > > >
      > > > > > Each module is 11" long by 5" wide by 3/4" thick and require
      > a 2mm
      > > > > > gap between modules for forced air cooling. They weigh 2.3
      > lbs and
      > > > > > have 6 cells that total 7.2V at 6.5Ahr. With a standard 80%
      > depth
      > > > > > of discharge for Nimh, 5Ahr are usable.
      > > > > >
      > > > > > A Solectria Force has battery boxes that can accommodate 13
      > group
      > > > > 27
      > > > > > batteries (size 12-3/4" long by 6-3/4" wide by 9-7/8" tall).
      > This
      > > > > > works out to about 1119 sq. inches of battery box floor space.
      > > > > >
      > > > > > IF you can orient the Prius Nimh modules so they the 11" long
      > is
      > > > > > vertical (not a real problem in the back box since you can
      > always
      > > > > > add a spacer between the bottom and lid if necessary, but it
      > MAY be
      > > > > > a real problem for the front box), then I figure you can fit
      > > > > roughly
      > > > > > 270 modules into a Force. This is a rough calculation without
      > doing
      > > > > > an actual layout.
      > > > > >
      > > > > > Since you will need to arrange the modules into multiple sets
      > of
      > > > > > strings of around 156V, I see the math as:
      > > > > > 22 modules * 7.2V = 158.4V string linked in series.
      > > > > > 12 strings linked in paralles * 5Ahr = 60Ahr usable.
      > > > > > 264 modules used total weigh 264 * 2.3 lbs = 607 lbs.
      > > > > >
      > > > > > In comparison, a Lead Acid Gel pack weighs 821 lbs. So, you
      > will
      > > > > > save 214 lbs by making the switch and increase your range
      > from 50
      > > > > > miles to approximately 60 miles.
      > > > > >
      > > > > > Provided you still have a BRUSA NLG4 (or got an NLG5)
      > charger, I
      > > > > > don't see a real problem with charging the batteries. You
      > just need
      > > > > > to find out the charging profile and set the program using
      > the free
      > > > > > DOS program. For a Zivan charger, you'd need to send it to
      > the
      > > > > > manufacturer for a re-programming.
      > > > > >
      > > > > > I agree that a BMS would be a big obstacle. Perhaps placing a
      > > > > > Powercheq between each string would be enough to get by.
      > Otherwise,
      > > > > > that is a LOT of regs to be installing if you have to do
      > every
      > > > > > module.
      > > > > >
      > > > > > I'm curious as to the market rate for used Prius Nimh
      > modules. If
      > > > > > you can share the price for them, we can compare them to
      > other
      > > > > > battery choices.
      > > > > >
      > > > > > Thanks!
      > > > > >
      > > > > > Todd Martin
      > > > > > 1997 Solectria Force
      > > > > > VP, FVEAA
      > > > > >
      > > > > > --- In solectria_ev@ yahoogroups. com, "Bill Swann"
      > <dbswann4@ .>
      > > > > > wrote:
      > > > > > >
      > > > > > > I understand all the precautions you enumerate. I may
      > purchase
      > > > > the
      > > > > > > first of several surplus Prius battery packs tomorrow. Is
      > there a
      > > > > > > chance I can e-mail the person who put together a NiMH pack
      > for
      > > > > > the S-
      > > > > > > 10. I am open to tips and tricks/opinions.
      > > > > > > Thanks,Bill S
      > > > > > > --- In solectria_ev@ yahoogroups. com, "Jerry Pohorsky"
      > > > > <Pohorsky@>
      > > > > > > wrote:
      > > > > > > >
      > > > > > > > Howdy,
      > > > > > > >
      > > > > > > > The batteries in the Prius are not very suitable for the
      > Force
      > > > > > > unless you disassemble the pack, rewire the modules and
      > come up
      > > > > > with
      > > > > > > a suitable charger and BMS. NiMH batteries have a unique
      > charging
      > > > > > > profile and the standard lead acid battery chargers are not
      > > > > > > appropriate. The batteries themselves are an odd physical
      > size
      > > > > > and
      > > > > > > voltage. I believe they are something like a 7.2 volt
      > battery
      > > > > > with a
      > > > > > > 6.5 Amp-hour rating. That amp-hour rating is suitable for
      > > > > > > intermittent duty in a hybrid but totally inadequate for an
      > EV.
      > > > > > > >
      > > > > > > > You would need several strings in parallel to get the amp-
      > hour
      > > > > > > rating you need. A fellow EAA member bought several used
      > Prius
      > > > > > packs
      > > > > > > on eBay and wired them in parallel for use in his US
      > Electricar S-
      > > > > > 10
      > > > > > > pickup truck. He needed to invent a battery management
      > system as
      > > > > > > well as a fan-forced cooling system. The weight reduction
      > gave
      > > > > > him
      > > > > > > an improvement in acceleration over his old lead acid pack
      > and
      > > > > > > slightly more range, but eventually he got rid of them.
      > They took
      > > > > > up
      > > > > > > the entire bed of the truck. He is now running a flooded
      > NiCad
      > > > > > pack
      > > > > > > that he got from a military surplus supplier. He was able
      > to
      > > > > > mount
      > > > > > > the NiCads under the bed of the truck.
      > > > > > > >
      > > > > > > > Not all non-lead packs are series parallel combinations.
      > I saw
      > > > > > > someone selling Thunder Sky 90 Amp-Hour LiFePO4 batteries.
      > With
      > > > > > > these, you would just have a series string although there
      > would
      > > > > be
      > > > > > a
      > > > > > > large number of cells - they between 3 and 4 volts each.
      > > > > > > >
      > > > > > > > Stephen Taylor has a series string of the Valence Lithium
      > > > > > batteries
      > > > > > > in his Force.
      > > > > > > >
      > > > > > > > Similarly, I have 95 Amp-hour NiMH batteries in my RAV 4
      > EV.
      > > > > > > Unfortunately, these Panasonic batteries have been taken
      > off the
      > > > > > > market due to a lawsuit filed by Chevron - but it is
      > another
      > > > > > example
      > > > > > > where a series parallel combo was not needed.
      > > > > > > >
      > > > > > > > Adios,
      > > > > > > >
      > > > > > > > Jerry Pohorsky
      > > > > > > >
      > > > > > > > ----- Original Message -----
      > > > > > > > From: Bill Swann
      > > > > > > > To: solectria_ev@ yahoogroups. com
      > > > > > > > Sent: Tuesday, November 20, 2007 6:13 PM
      > > > > > > > Subject: [solectria_ev] Prius NiMH Batteries
      > > > > > > >
      > > > > > > >
      > > > > > > > I am surprised that someone has not taken some surplus
      > > > > > batteries
      > > > > > > from a
      > > > > > > > Prius and adapted it to the Force. The energy density is
      > > > > > double
      > > > > > > over
      > > > > > > > lead. As it is with battery packs other that SLA, the
      > pack
      > > > > > ends
      > > > > > > up
      > > > > > > > being a series/parallel combination.
      > > > > > > > Bill S
      > > > > > > >
      > > > > > > >
      > > > > > > >
      > > > > > > >
      > > > > > > >
      > > > > > > > [Non-text portions of this message have been removed]
      > > > > > > >
      > > > > > >
      > > > > >
      > > > > >
      > > > > >
      > > > > >
      > > > > > [Non-text portions of this message have been removed]
      > > > > >
      > > > >
      > > >
      > >
      >
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