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3393Re: Prius NiMH Batteries

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  • Bill Swann
    Dec 24, 2007
    • 0 Attachment
      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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