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8624Re: [solectria_ev] Thermal Management System

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  • Wade Perry
    Dec 3, 2012
      Hi Tom.
      The cells cannot be "undercharged", in any sense that would cause them
      damage anyway. Totally different from Lead. In fact it's better to
      undercharge them a bit, or as Bouty says "stay away from the knees".
      Charging to 3.4v is good. Very conservative, you'd probably be fine
      charging to 3.5v, and get a little extra capacity on the top end.
      (although there's risk of exceeding the operating voltage of the
      controller, which is theoretically 190v, if you interrupt the end of a
      charge and try to drive without letting the cells settle down to resting
      I'm charging up to ~192v right now when the charger enters the Constant
      Voltage phase of the charge. I'd thought that was a little low but based
      on my "pack emptying" experiment and getting a full 60 Ahr out, why change
      anything? (Of course that last Ah wasn't really usable for much, but I did
      make it to 60!) I do plan on setting my new charger to go to 196v though.
      Congratulations by the way on your own transplant. Very impressive and
      very neatly done! (I'm envious actually- looking at the snarl of wires
      beside my own pack)

      On Sun, Dec 2, 2012 at 9:58 AM, Tom Hudson <tdhudson@...> wrote:

      > **
      > The Ah "precession" is something I have been very curious about. Our car
      > is up to 2Ah now
      > after charging, and it's pretty cool out in the garage (in the 50s). So
      > it's not real
      > warm, which seems to be what you're indicating causes the charge to
      > terminate before the
      > Ah counter reaches zero.
      > What is your charge profile setup? Mine charges to 3.4V per module
      > (190.4V) at 20A then
      > switches to 190.4V until the current drops below 1A, then the charger
      > turns off. I'm
      > wondering if this is similar to what you're using to charge your pack, and
      > want to make
      > sure I'm not chronically undercharging or something. I was tempted to
      > change the charge
      > so that it used a lower termination current, just in case stopping at 1A
      > was too early and
      > causing undercharging.
      > At least I know that others see a similar precession on charge, so I'm
      > less concerned than
      > I might be, but I'd like to know what your charge profile does. You are
      > doing very well
      > with your pack and I could do worse than emulate you!
      > -Tom
      > On 12/2/2012 9:26 AM, d. Bouton Baldridge wrote:
      > >
      > > Hi Wade,
      > > In my opinion, the balance thing has been greatly over blown and your
      > readings are
      > > perefectly acceptable especially after using so much capacity having
      > only +/-.1 v or so
      > > from the mean is fantastic. The big thing is avoiding going beyond the
      > knees and your
      > > system seems to be working just fine doing that. As for the Ahmeter
      > issue, It has been
      > > my experience that voltage is not a reliable means for determining
      > capacity. In my case
      > > I have found the reaching the limiting voltage was caused by the pack
      > warming up; for me
      > > it was the sun. Now that the ambient temperature is lower in the winter
      > season my charge
      > > resets closer to zero, but in summer it stops on the plus side by .1 ah
      > each cycle when
      > > the outside temp is above 80 degrees. My guess for you is that when you
      > charge for a few
      > > hours, the pack temp increases higher than when you were driving and the
      > voltage is
      > > slightly higher as a result this stops the charger earlier than the
      > previous Ahour
      > > reading. I am not sure if this is happening as a function of breaking in
      > or aging. But
      > > it was not an issue with lead since it woul be overcharged routinely and
      > had the
      > > automatic reset. I am a few months shy of 4 years and this slight
      > precession is only an
      > > annoyance it has not seemed to impact the utility of my pack. Since I
      > have a pretty long
      > > warm season I would just occasionaly reset the Ah meter to zero just so
      > I wouldn't have
      > > to remember every time. Now that my cells are getting twice as old as
      > any Pb pack would
      > > last, I am getting into new territory for longevity and at some point I
      > might find some
      > > of these answers, but for now I am saying congratulation on your project
      > FWIW,
      > > Bouty
      > >
      > > ________________________________
      > > From: Wade Perry <perrypeas@... <mailto:perrypeas%40gmail.com>>
      > > To: solectria_ev@yahoogroups.com <mailto:solectria_ev%40yahoogroups.com>
      > > Sent: Sunday, December 2, 2012 1:47 AM
      > > Subject: [solectria_ev] Thermal Management System
      > >
      > >
      > > Greetings all- I've driven over 1,000 miles on lithium now.
      > >
      > > I drove a fair bit today, it was mostly empty when I was coming back home
      > > from the last errand so I thought I'd take the long way home and
      > discharge
      > > a bit more than I usually do. Until today the maximum I'd taken out is
      > > probably around 45 Ahr. I had set my limit around 50 to be safe.
      > > So after I got home I drove the block a few times with the heater on.
      > Went
      > > well past 50. I measured pack voltage and some individual cells while I
      > > did this and felt fairly safe as I was getting down towards the bottom.
      > > Finally drove it around one last time in econ with no heater and it was
      > > around 57.5 when I was done. Then I ran the heater by itself to get it to
      > > 59. Took the voltage on each cell.
      > > Made a new column to my battery balancing spreadsheet, it's here-
      > >
      > https://docs.google.com/spreadsheet/pub?key=0An5nm8itUMMcdHhQV3RsSUdfbzRTQkFlNmtaSy05MHc&output=html
      > >
      > > The cells were springing back as I was measuring them. When I was done I
      > > went back and measured CK, where I'd started measuring the pack. it was
      > > .04 volts higher than I'd written down the first time. By the time I was
      > > finishing measuring, all the cells were coming in around 3.04 or 3.05. So
      > > they're reasonably well balanced.
      > >
      > > One cell stands out. JA. It measured 2.93 when its adjacent cells were
      > > measuring an entire ~0.10 volt higher. I haven't figured it out yet.
      > > Other than it happens to be the one that I noticed arrived from the
      > > factory at 4.23% below 50% SOC. You can see that on the sheet. It stood
      > > out at the time because all the other cells came in at 1 or 2% over 50.
      > > This was the only one that was below, and by a fair amount.
      > >
      > > Anyway then I ran the heater some more, watching JA in particular. It
      > > would have been cool to have a graph of all the cells at once. But they
      > > were falling off quite quickly. Some dipped down to 2.75 or so. JA dipped
      > > all the way down to 2.50. But I discharged down to a full 60.00 Ahr on my
      > > counter! Finished with a pack voltage of around 160. (which was
      > > undoubtedly springing up also. I didn't wait around to check but plugged
      > > in the charger so I can drive again tomorrow)
      > >
      > > This is great, because I had feared I was losing capacity permanently by
      > > charging below freezing. I'd hoped this wasn't the case, but was
      > concerned
      > > because on especially cold days there'd be +1.00 or +2.00 Ahr still left
      > on
      > > the counter when the charger shut off. Warmer days I'd be back to -0.14
      > or
      > > something like that. I'd been worried that I was gradually damaging the
      > > cells.
      > >
      > > Apparently I'm not. Or at least not to the extent I'd feared. This is
      > > with a battery box that's not even put together yet- the 60 Ahr cells are
      > > taller than the gels I took out, so when I finally do get things put
      > > together properly, I'll need to shim the cover over the battery box.
      > Right
      > > now it rests on top of the cells, so there's probably a 1" space all
      > > around, letting cold air in. I did put in a 60watt incandescent light
      > bulb
      > > back there to keep things warmer (and bright and cheery) in the battery
      > > box, whenever the car's plugged in.
      > >
      > > So. What I'd really like to do is hook up the Solectria heating mats to
      > AC
      > > power, so I can be more setup for winter. I myself took it apart back in
      > > August, but obviously didn't pay much attention to what I was doing. I've
      > > searched this list repeatedly but can't find anything that talks about
      > > where the AC power hooks up to the heaters / sensors... Can anyone point
      > > me to a resource about this?
      > >
      > > Thanks for the help!
      > >
      > > Wade Perry
      > > 1998 Force
      > > 56 CALB CA 60 Ahr
      > >
      > > [Non-text portions of this message have been removed]
      > >
      > > [Non-text portions of this message have been removed]
      > >
      > >
      > --
      > Thomas Hudson
      > http://portev.org -- Electric Vehicles, Solar Power & More
      > http://klanky.com -- Animation Projects
      > [Non-text portions of this message have been removed]

      [Non-text portions of this message have been removed]
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