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3352Re: Prius NiMH Batteries

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  • Mike Phillips
    Dec 2, 2007
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      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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