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Re: (ET) Fully charged pack voltage

It actually can take up to 24 hours to get to resting voltage. And I don't think you can 'hurry' it up by momentarily applying a load.

Here's a good reference:


- SteveS

Michael S Briggs wrote:

On Thu, 23 Apr 2009, John J Casey wrote:

In my experience, the onboard ge charger takes my newish T-105's up to
44-45v over an 18 hour cycle, the last 3-5 hrs between 44.4 and 45v for cell equalization. End the charge cycle and in a short time the voltage settles
back to 39v.Jack

So, the fully charged pack then has a voltage of 39 V (since that is what it settles to after charging). One thing that is troubling me - what does it take a while for the battery's voltage to gradually drop from the elevated charging voltage down to its resting voltage. I know that while charging the voltage applied will be higher than the battery's voltage due to the voltage drop across the internal resistance of the battery (batteries) - but once the charger turns off, I would think that the battery pack voltage would drop rather immediately down to its resting voltage (the potential difference that the chemical reactions taking place at the electrodes produce). BTW, this has some interesting information about how the internal resistance of the electrolyte changes with state of charge, which gives lead acid batteries their unique voltage vs. state of charge curves:
The main thing I'm trying to figure out right now is what to set my Landis charge controller to to make sure that the pack gets fully charged (and doesn't take 3 days to get there). It would seem that the default 38V setting is too low, since the pack should be higher than that when fully charged.


On Apr 23, 2009, at 8:13 AM, Michael S Briggs wrote:

      I just got a nice new pack of Trojan T-605s (slightly lower
      capacity than T-105s, with a proportionately lower price). I'm
      trying to figure out what the voltage of a fully charged new
      pack *should* be, and I have seen very different things as
      skimming through the archives.
      My understanding is that the chemical reactions taking place in
      a lead-acid cell produce a potential difference of 2.13 Volts,
      so a fully charged lead-acid battery measured with a very high
      impedance voltmeter should measure that 2.13 Volts per cell, or
      6.39V for a 6V battery, and 38.34 V for a 36V pack.
      But, I have seen statements in the archives saying that a fully
      charged pack should have a voltage of 42V or so (various posts
      saying anywhere from about 40V up to 44V).



      Michael S. Briggs, PhD
      UNH Physics Department
      (603) 862-2828

      Elec-trak mailing list
      Elec-trak cosmos phy tufts edu


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