8624Re: [solectria_ev] Thermal Management System
- Dec 3, 2012Hi 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!
> 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
> > Bouty
> > ________________________________
> > From: Wade Perry <perrypeas@... <mailto:perrypeas%40gmail.com>>
> > To: firstname.lastname@example.org <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
> > 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.
> > 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-
> > 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
> > because on especially cold days there'd be +1.00 or +2.00 Ahr still left
> > the counter when the charger shut off. Warmer days I'd be back to -0.14
> > 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.
> > 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
> > 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
> > 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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