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Re: [solectria_ev] Cold and Thundersky cells

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  • d. Bouton Baldridge
    Hi Newton,  that is a great set of observations. I have found that the high temps, anything above 80 degress F is the best performance on my 4 year old  40
    Message 1 of 8 , Feb 17, 2013
      Hi Newton,
       that is a great set of observations. I have found that the high temps, anything above 80 degress F is the best performance on my 4 year old  40 Ah TSs, in fact they provide impressive power for their size, but the cold is "not so much" I have to rewind my stop watch for 0-60mph acceleration readings, but the waterbed heater does just enough for our mild winters to keep most of those following me from giving me the finger in traffic. Just as you have discussed, since the controller prevents the voltage from going too low when the pack is cold there does not appear to be much degradation from the cold performance. I would love to see another 4 more years, but we are going into uncharted territory now.

      From: Newton Hausermann <rclugnut@...>
      To: solectria_ev@yahoogroups.com
      Sent: Sunday, February 17, 2013 12:07 PM
      Subject: Re: [solectria_ev] Cold and Thundersky cells

      Hey Chip,

      I can back that performance up, at school we've done some testing on K2's
      26650P cells (2.6ah LiFePO4's) and we've found that freezing them results
      in poor current output until the cells heat up naturally. I've also noticed
      with my R/C cars LiPo's that they like to heat up to ~110*F and run at that
      no matter what the load/ambient temps. So it appears that the cold effects
      the chemical reaction within the cells, and the rate at which it occurs,
      therefore how much current the cell outputs. However we haven't noticed
      any degradation in capacity on that run, sadly we don't have the ability to
      continually freeze discharge and refreeze cells again. These are just my
      observations on batteries in general, hope this helps.


      On Thu, Feb 14, 2013 at 10:18 AM, cchandlerc66

      > **
      > Cold and Thundersky
      > This data is from August-December 2012 in 1997 Force with Elcon PFC 4000
      > charger, 49 160Ah Thundersky cells, miniBMS, 4210 test miles, 115 separate
      > trips/charges on average 36 miles/trip in central Maine. This data is from
      > one probe between the top of two cells in the middle of the rear pack under
      > 1 inch of foam touching the cell top edges under a 2" air space and the
      > plastic battery cover. The Force was driven mostly at the Normal setting
      > (120 -130 amps, depending on pack temperature). Charging at both 110 and
      > 220 volts, didn't seem to be any difference in cell temperature rise. There
      > were three trips of about 70 miles.
      > Data below is: average ambient temperature at trip start, average pack
      > temp at start, Ah/mile, average temp rise during trips, average temp rise
      > during chargings, total temp increase for trips plus chargings. All in
      > degrees F.
      > Aug: 75 degrees, 78 degrees, 1.2 Ah/mile, trips-6 degrees, charges-7
      > degrees, total-13 degrees.
      > Sept: 62 degrees, 71 degrees, 1.25 Ah/mile, trips-10 degrees, charges-5
      > degrees, total-15 degrees.
      > Oct: 56 degrees, 65 degrees, 1.28 Ah/mile, trips-8 degrees, charges-7
      > degrees, total-15 degrees.
      > Nov: 40 degrees, 53 degrees, 1.4 Ah/mile, trips-9 degrees, charges-4
      > degrees, total-13 degrees.
      > Dec: 34 degrees, 38 degrees, 1.5 Ah/mile, trips-13 degrees, charges-7
      > degrees, total-20 degrees.
      > Extremes:
      > July 28: 33.2 miles, 1.21 Ah/mile, starting ambient temperature-72
      > degrees, pack start temperature-88, pack end temperature-93, charge end
      > temperature-102.
      > Jan 2, 2013: 31.6 miles, 1.72 Ah/mile, starting ambient temp-16, pack
      > start temp-10, pack end temp-35, charge end temp-45.
      > Performance: I noticed only a slight decrease in power in November when
      > the pack start temperature was below 50 degrees. The January 2nd trip was
      > dramatically sluggish at first. The car wouldn't accelerate above 35 mph on
      > the level, however after 8 miles of driving, the performance improved to
      > the November level. Others with smaller capacity packs have reported poorer
      > performance in cool temperatures, so perhaps a larger capacity pack
      > performs better in the cold.
      > As the pack got colder, the start voltage at full throttle sagged from a
      > normal of 165v (80 degrees) to 134v at the coldest. My only voltage readout
      > is on a CleanPowerAuto EV display and it doesn't seem to record below 134
      > volts at its current settings. At the start of trips with a cold pack, the
      > low voltage alarm on the miniBMS often sounded at full throttle. The alarm
      > should sound at about 132 volts at nominal temperatures to signal charging
      > is needed.
      > While driving in temps below freezing, it wouldn't be difficult to keep
      > the pack internal temperature above freezing, helped by charging soon after
      > driving. Any insulation (or heating) surrounding the battery packs would be
      > helpful and benefit performance, but it my case doesn't seem necessary.
      > I've parked the car until March; the diesel heater is inadequate below
      > freezing and there are occasional blizzards and salt on the roads.
      > Chip Chandler


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