Choosing a charger that can equalize

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  • Sunking
    Solar Fanatic
    • Feb 2010
    • 23301

    #16
    Originally posted by gardner
    Interesting. I read it as a current limit.

    I'm expecting be able to set my bench power supply to C/20 current limit and 2.58 VPC and let 'er rip.
    No reason to go that low, especially if you want to speed things up. C/8 is perfectly acceptable. All you have to is understand the difference between CC and CV.

    Constant Current is just what it sounds like. You pump in X amount of current without a respect to a voltage source. If you have a 100 volt power supply that you can control current limit say 20 amps, you can pump in 20 amps on a 12 volt 200 amp battery with no problem until the battery voltage reaches 15 volts. The battery voltage will rise to 100 volts if it does not blow up first. So in a Bulk or CC mode you pump in X amount of current until the battery voltage reaches a set point of say 2.4 vpc or 14.4 volts on a 12 volt battery. At that point the charger turns off and the battery should be at roughly 80 to 90% SOC.

    Constant Voltage is mostly like it says, but also has a Constant Current aspect to it. Lets say you use that bench power supply with current limit set to 10 amps, and voltage to 15 volts. With me so far?

    Now let's say we have a 12 volt 100 AH battery that is fully discharged and an OCV of 10.5 volts, and an Internal Resistance of .02 Ohms and connect it to the Power supply. Still with me?

    Initially when we connect the battery and if we monitor the voltage and current we will see a current of 10 amps, and a voltage of 10.5 volts + (10 amps x .02 Ohm's) = 10.7 volts. Not the 15 volts you set the voltage too on the DC power Supply. The reason is the Power Supply is acting like a Current Source of 10 amps. That 10 amps flowing through .02 Ohms is only .2 volts rise in the battery voltage. Understand so far?

    As we charge the battery voltage slowly starts to rise and the current remains a constant 10 amps. It does so until the battery voltage reaches 14.8 volts. At that point the transition from Constant Current to Constant Voltage begins. When the battery voltage reaches 14.9 volts the current has tapered to 5 amps. As the voltage continues to rise, the current tapers down and will continue to do so until we hit equalization saturation voltage occurs and the battery voltage can go no higher. At that point you are now equalizing cells and the current will be very small. It can take several hours to bring the weak cells up at such a slow pace.

    So don't be afraid to set the current limit above c/20. You can if you want, but it will just take a lot longer. Just don't set it any higher than C/8. Only other thing to guard against is over heating above 120 degrees which would be very rare under the right conditions on a hot summer day in the 100's, or low water levels.

    OK?
    MSEE, PE

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    • Cranky2981
      Junior Member
      • Feb 2015
      • 8

      #17
      my 2 cents....

      the xantrex c40 is a 40 amp charger 3 stage with auti or manual equalization.

      they seem to be well liked and reliable (i hope as I have one!)

      the x40 can be used across 12/24/48v but its bigger brother is 12v at 60amp (the X60)

      they are about 150 bucks I think!

      good luck

      ps - the bulk and float charger voltages are set by user with some linear pots under the skin of the charger

      Comment

      • Sunking
        Solar Fanatic
        • Feb 2010
        • 23301

        #18
        Originally posted by Cranky2981
        my 2 cents....

        the xantrex c40 is a 40 amp charger 3 stage with auti or manual equalization.

        they seem to be well liked and reliable (i hope as I have one!)
        That is really old antiquated PWM controller. For every 100 watts of panel, you only get 66 watts at very best. Just by changing it out to a MPPT model will give you roughly 30% more power. Lot cheaper than adding panels.
        MSEE, PE

        Comment

        • gardner
          Junior Member
          • Feb 2015
          • 21

          #19
          Originally posted by Cranky2981
          the xantrex c40 is a 40 amp charger 3 stage with auti or manual equalization.
          I think that's a solar panel charge controller. I should have been more clear that I am looking for a mains/AC charger that will run from my generator.

          The first mentioned B&D/Vector VEC1093 is really the kind of thing I was looking for.

          Thanks.
          --
          Gardner

          Comment

          • Bucho
            Solar Fanatic
            • Dec 2013
            • 167

            #20
            Originally posted by gardner
            The first mentioned B&D/Vector VEC1093 is really the kind of thing I was looking for.

            Thanks.

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