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8624Re: [solectria_ev] Thermal Management System

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  • Wade Perry
    Dec 3, 2012
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      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
      voltage)
      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)
      Wade



      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]
      >
      >
      >


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