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Pb-acid Battery Charging

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  • Tracy, Matt
    I am replacing a dozen, 12v, 125 amp-hour lead-acid batteries after some 500+ charging cycles, but less than two years after purchasing them. I would
    Message 1 of 8 , Apr 2 12:52 PM
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      I am replacing a dozen, 12v, 125 amp-hour lead-acid batteries after some
      500+ charging cycles, but less than two years after purchasing them. I
      would appreciate any wisdom / experience with optimal recharging.

      With this set of batteries, I drove 15 miles to work (using around 15-18
      amp-hours), recharged, and 9 hours later drove 15 miles home, and recharged.
      I read that Pb-acid batteries should be kept charged, and not left in a
      discharged state, to prevent sulfating (or whatever the chemical degradation
      process is called). This worked well, but would I be better off charging
      only once a day (in the evening, only 9-10 hours after initial discharge,
      vs. in the morning at work - on the company's meter - 14-15 hours after
      initial discharge), and cutting the number of charging cycles in half, and
      not worrying about the batteries sitting partially discharged for several
      hours each day? This would also push the depth-of-discharge twice as far,
      which I read also cuts down on the number of recharging cycles.

      FYI, I am using a Zivan NG-3 charger.

      Thanks for your help.

      Matt Tracy
      1992 Solectria Force, 144v
    • Tom Hudson
      ... How many miles did you get, Matt? I m guessing around 13,000, given the usage you mention. The pack in our 97 Force just went south after 12,500 miles,
      Message 2 of 8 , Apr 2 1:23 PM
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        > I am replacing a dozen, 12v, 125 amp-hour lead-acid batteries after some
        > 500+ charging cycles, but less than two years after purchasing them. I
        > would appreciate any wisdom / experience with optimal recharging.

        How many miles did you get, Matt? I'm guessing around 13,000, given the
        usage you mention. The pack in our '97 Force just went south after 12,500
        miles, so it sounds like you're probably right on track. I'm upgrading our
        car to NiCD batteries (see the web page covering the upgrade at
        http://asterius.com/solectria/ho/nicad.htm).

        > With this set of batteries, I drove 15 miles to work (using around 15-18
        > amp-hours), recharged, and 9 hours later drove 15 miles home, and
        > recharged.
        > I read that Pb-acid batteries should be kept charged, and not left in a
        > discharged state, to prevent sulfating (or whatever the chemical
        > degradation
        > process is called). This worked well, but would I be better off charging
        > only once a day (in the evening, only 9-10 hours after initial discharge,
        > vs. in the morning at work - on the company's meter - 14-15 hours after
        > initial discharge), and cutting the number of charging cycles in half, and
        > not worrying about the batteries sitting partially discharged for several
        > hours each day? This would also push the depth-of-discharge twice as far,
        > which I read also cuts down on the number of recharging cycles.

        As I understand it, the way you're using them is exactly how you should --
        recharge after every use, don't leave them discharged. Leaving them
        partially discharged 9 hours a day will age them. I suspect David Roden
        will have some better insight into this than me, though.

        -Tom

        Thomas Hudson
        http://asterius.com/solectria/ho -- Our Electric Vehicles
        http://asterius.com/solectria/ho/pvs.htm -- Solar Power
        http://asterius.com/solectria -- Solectria Owners Website
        http://asterius.com/pwgarden -- Port Washington Garden Club
      • william glickman
        I would try the standard power pulse units to get as much out of the batteries as possible unless you have already knocked the lead off the plates. On Mon, 2
        Message 3 of 8 , Apr 2 3:26 PM
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          I would try the standard power pulse units to get as much out of the
          batteries as possible unless you have already knocked the lead off the
          plates.

          On Mon, 2 Apr 2001 14:52:08 -0500 "Tracy, Matt" <mtracy@...>
          writes:
          > I am replacing a dozen, 12v, 125 amp-hour lead-acid batteries after
          > some
          > 500+ charging cycles, but less than two years after purchasing them.
          > I
          > would appreciate any wisdom / experience with optimal recharging.
          >
          > With this set of batteries, I drove 15 miles to work (using around
          > 15-18
          > amp-hours), recharged, and 9 hours later drove 15 miles home, and
          > recharged.
          > I read that Pb-acid batteries should be kept charged, and not left
          > in a
          > discharged state, to prevent sulfating (or whatever the chemical
          > degradation
          > process is called). This worked well, but would I be better off
          > charging
          > only once a day (in the evening, only 9-10 hours after initial
          > discharge,
          > vs. in the morning at work - on the company's meter - 14-15 hours
          > after
          > initial discharge), and cutting the number of charging cycles in
          > half, and
          > not worrying about the batteries sitting partially discharged for
          > several
          > hours each day? This would also push the depth-of-discharge twice
          > as far,
          > which I read also cuts down on the number of recharging cycles.
          >
          > FYI, I am using a Zivan NG-3 charger.
          >
          > Thanks for your help.
          >
          > Matt Tracy
          > 1992 Solectria Force, 144v
          >
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        • David Roden (Akron OH USA)
          You are right, shallower discharges mean more cycles. Normally the right thing to do is charge as soon as possible after ~any~ significant discharge. However,
          Message 4 of 8 , Apr 2 11:19 PM
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            You are right, shallower discharges mean more cycles. Normally the right
            thing to do is charge as soon as possible after ~any~ significant
            discharge.

            However, to some extent, a lot of very shallow cycles (say, 20-30% DOD)
            can be less efficient in terms of the mileage you get out of a battery.
            The optimal depth of discharge (optimal in the sense of giving the most
            total distance before replacement) is around 50% per cycle.

            That said, the sulfation resulting from sitting for several hours in a
            partly-discharged state may very well more than offset any gain.

            Use common sense. Consider the amount of energy used from the battery,
            and how long it will be before it's next charged. If you've used only
            10% of the charge, and you'll use the car again in 2-3 hours, I wouldn't
            charge. But if you've used 30% and it'll sit for 8 hours, I'd charge.

            A few thoughts:

            First, make sure your charger is set up appropriately for the batteries
            you are using. Gel, AGM, and flooded types all require different charge
            profiles. Heck, different manufacturers have different recommendations,
            so if you've changed type or brand since installing the charger, make
            sure you're still charging correctly.

            Second, it isn't necessary for your charger to perform a full or even
            partial equalization on every cycle. It might not be a bad idea to, when
            at work, pull the plug a half-hour or so after your pack reaches 14.2
            volts per module (for gel) or 15 volts per module (for flooded).

            Finally, 1.5 to 2 years' life from the 12-volt marine batteries these
            cars use is pretty decent. In hot southern climates, sometimes you're
            doing well to get more than a year. Good flooded marine batteries like
            the Trojan 27TMH are BCI-rated at only around 300 cycles, and that's in
            trolling motor service (lots less strenuous than hauling around a 2100 lb
            car).


            David Roden - Akron, Ohio, USA
            1991 Solectria Force 144vac
            1991 Ford Escort Green/EV 128vdc
            1979 General Engines ElectroPed 24vdc
            1974 Honda Civic EV 96vdc
            1970 GE Elec-trak E15 36vdc
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            NOTES: 1. Please do not send me virus warnings or anything else which
            suggests "forward to everyone you know." 2. I seek immediate punitive
            action against all spammers, regardless of the message.
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          • umarc@hippogryph.com
            ... I wish there were an easy way for me to tell, when I get out of my car and it says I m down 15 amp-hours, whether I m at 20% or 30% or 50% depth of
            Message 5 of 8 , Apr 3 6:05 AM
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              On Tue, 3 Apr 2001, David Roden (Akron OH USA) wrote:

              > However, to some extent, a lot of very shallow cycles (say, 20-30% DOD)
              > can be less efficient in terms of the mileage you get out of a battery.
              > The optimal depth of discharge (optimal in the sense of giving the most
              > total distance before replacement) is around 50% per cycle.

              I wish there were an easy way for me to tell, when I get out of my car and
              it says I'm down 15 amp-hours, whether I'm at 20% or 30% or 50% depth of
              discharge. The manual says I'm supposed to be able to go to 55 amp-hours,
              but the only time I've been down as far as 35 amp-hours the car started to
              lose power noticeably.

              Lately I've just been driving to work (about 6 amp-hours) and back (about
              8; it's mostly uphill).

              The manual also says, by the way, that I should charge until the amp-hour
              meter reads -4, but that is damned near impossible, as the charger
              sometimes (but not always!) shuts off at -1 or even +1, and because once
              it shuts off, if the meter reads below 0, it will reset to zero in about
              twenty minutes, leaving me scratching my head as to whether I'm at -.1 or
              -5.


              Rob Landry
              umarc@...
            • David Roden (Akron OH USA)
              ... It s standard to define 100% discharge as the point at which your battery voltage drops to 1.75 volts per cell while under load. If you have a 144v
              Message 6 of 8 , Apr 3 10:06 PM
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                On 3 Apr 2001, at 9:05, umarc@... wrote:

                > I wish there were an easy way for me to tell, when I get out of my car and
                > it says I'm down 15 amp-hours, whether I'm at 20% or 30% or 50% depth of
                > discharge.

                It's standard to define 100% discharge as the point at which your battery
                voltage drops to 1.75 volts per cell while under load. If you have a
                144v nominal pack, that would be 126 volts; if it's a 156v pack, 136.5
                volts.

                Connect a good quality accurate digital voltmeter to your pack (careful,
                insulate well!) and drive until the voltage on the flat at about 35 mph
                is at that level. Read your amp-hour counter. This is your real-world
                battery capacity right now (not the manufacturer's rated capacity or
                something theoretical).

                > The manual also says, by the way, that I should charge until the
                > amp-hour meter reads -4, but that is damned near impossible ...

                Assuming your amp-hour counter is accurate, it would be normal for it to
                run past zero when charging, because batteries aren't 100% efficient. An
                overcharge of 8-10% wouldn't be too far out of line. If it doesn't do
                that, there are a couple of possibilities.

                One is that the counter is not accurate. I have one here which reads
                actual amp-hours in and out differently!

                Another is that your charger really is undercharging the pack. This is
                probably happening if you have flooded batteries and the charger is set
                up for gel batteries. Long-term undercharging is as bad as long-term
                overcharging, so you should investigate this.

                The best way is to use a known-accurate amp-hour counter. There are some
                issues of concern with the Solectria/Brusa amp-hour counters; some people
                have suggested that they may sometimes miss a fraction of an amp-hour
                when the current peaks during acceleration. You might consider getting
                the newer design Brusa counter, or a Cruising Equipment E-meter.

                Another way would be to measure the actual battery state of charge. This
                isn't 100% accurate, but it's close enough to give you a good idea.

                After charging, let the car sit for 24 hours.

                If you have flooded batteries, read the specific gravity with a good
                quality temperature compenstated hydrometer (available from large battery
                vendors). A reading of 1.275 to 1.285 would indicate a fully charged
                cell. Take readings in all the cells and average them.

                Note that if your pack is old and sulfated it will not come up to full
                specific gravity. Also, if you find unusually low cells it indicates a
                need for equalization and/or possible weakness in those cells.

                If you have gel cells, with no load at all on the battery, read the
                voltage with your accurate digital voltmeter.

                12.85 - 12.95 volts => fully charged
                12.65 volts => 25% discharged
                12.35 volts => 50% discharged
                12.00 volts => 75% discharged
                11.80 volts => 100% discharged

                These values are approximate and again will be lower for old batteries.

                Again take note of any batteries that are appreciably lower than the
                others in the pack, and consider them either in need of equalization, or
                possibly they are sulfated weak links.

                If the SG or voltage in most batteries seems low, perform a long, slow
                equalization charge. I don't think your Zivan can do this, so you will
                need to either find a manual (adjustable) high-voltage charger, or charge
                the batteries individually with one or more 12-volt chargers. Charge at
                around 1 amp until the on-charge voltage stops rising. It may take days.
                Be careful to keep the current at or below 1 amp! Then repeat the above
                test. If you can't get the open-circuit voltage up to 12.6 volts or so,
                or specific gravity up past 1.250, it's probably getting on toward time
                for replacement.

                Solectria recommends a simple test which may be useful. Drive the car
                until it won't exceed 35 mph on level ground. Park and turn on the
                heater and some other stuff to keep the load going and immediately
                measure the voltage of the batteries (yeah, I know, it's a pain to open
                up the box under the hood in this situation; I recommend adding some
                external plugs to measure them). Any battery that reads under 10.5 volts
                should be considered suspect.

                There are people who have reported good experiences with the pulse
                "desulfators," but I believe that what they really do is essentially
                identical to the above-described regimen -- a long, slow equalization. I
                don't think they're worth the money, but as I say, some people like them.

                Whew, I wrote more than I thought I would. I hope this isn't more
                confusing than helpful. And I'm sorry if some of this seems vague.
                Unfortunately there's almost as much art as science in lead battery care!


                David Roden - Akron, Ohio, USA
                1991 Solectria Force 144vac
                1991 Ford Escort Green/EV 128vdc
                1979 General Engines ElectroPed 24vdc
                1974 Honda Civic EV 96vdc
                1970 GE Elec-trak E15 36vdc
                = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
                NOTES: 1. Please do not send me virus warnings or anything else which
                suggests "forward to everyone you know." 2. I seek immediate punitive
                action against all spammers, regardless of the message.
                = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
              • Gordon Stallings
                ... Hmm... I have the same behavior. When I first got the Force, charging went just as described in the manual -- after charging, the meter would read
                Message 7 of 8 , Apr 4 6:32 AM
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                  At 09:05 04/03/2001 -0400, you wrote:
                  >The manual also says, by the way, that I should charge until the amp-hour
                  >meter reads -4, but that is damned near impossible, as the charger
                  >sometimes (but not always!) shuts off at -1 or even +1, and because once
                  >it shuts off, if the meter reads below 0, it will reset to zero in about
                  >twenty minutes, leaving me scratching my head as to whether I'm at -.1 or
                  >-5.

                  Hmm... I have the same behavior. When I first got the Force, charging went
                  just as described in the manual -- after charging, the meter would read
                  negative about 1/10 the amp-hours that I had displayed before charging.
                  However, a few months after I bought the car, Solectria sent me a
                  replacement charger, saying that the one I had was defective. The
                  replacement behaves differently. The final value on the meter after
                  charging is unpredictable. It may be positive, zero, or negative. The
                  charger itself cycles during the night, starting and stopping its fan.
                  This is the 3KW charger.

                  However, the batteries seem to be doing well after one year of use. So I
                  can't find fault with the replacement charger. Today is a mild day, and I
                  drove 5.5 miles to work on 3.75 amp-hours. (This is lower than the typical
                  5.00.) I don't recharge at work and the car sits in the sun all day.
                  Summertime is punishing on the batteries, I'm sure. The rear fan doesn't
                  shut off at all during the summer. Solectria suggested that I might want
                  to add a temperature comparator to the fan control so that the fan doesn't
                  pull in air that is hotter than the batteries.

                  Gordon Stallings
                  1999 Solectria Force
                • David Roden (Akron OH USA)
                  ... I keep this from happening on mine. Most folks on this list probably have the old-design counter, not the one that s been out for a year or two. On the
                  Message 8 of 8 , Apr 4 8:13 AM
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                    On 3 Apr 2001, at 9:05, umarc@... wrote:

                    > once
                    > it shuts off, if the meter reads below 0, it will reset to zero in about
                    > twenty minutes, leaving me scratching my head as to whether I'm at -.1 or
                    > -5.

                    I keep this from happening on mine. Most folks on this list probably
                    have the old-design counter, not the one that's been out for a year or
                    two.

                    On the old ones you can inhibit the automatic reset to zero (it happens
                    when something draws current from the pack) by connecting pins 5 and 6 on
                    the counter's plug. I added a small, low-current relay that closes those
                    pins when the ignition switch is off. That way, the counter doesn't
                    reset to zero until I switch the car on again.


                    David Roden - Akron, Ohio, USA
                    1991 Solectria Force 144vac
                    1991 Ford Escort Green/EV 128vdc
                    1979 General Engines ElectroPed 24vdc
                    1974 Honda Civic EV 96vdc
                    1970 GE Elec-trak E15 36vdc
                    = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
                    NOTES: 1. Please do not send me virus warnings or anything else which
                    suggests "forward to everyone you know." 2. I seek immediate punitive
                    action against all spammers, regardless of the message.
                    = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
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