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18650 battery 14.4V battery charging and use

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  • 18650 battery 14.4V battery charging and use

    I want to use 8 18650 batteries to make a power supply for a portable boom box project. I plan to use two batteries in parallel in a series of four pairs. My problem is what type of charge / overcharge / discharge device to use. I plan to use a 19VDC PC power supply to charge the system and need to know if I can use this power supply to charge while using this to power a Kenwood auto Media Player.
    I know quite a bit about these systems, it is what I may not know that scares me.

  • #2
    You need protection circuits on each of the cells and an intelligent charger that reads and balances all the cells in the pack during charge. The circuits manage each cell's charge voltage, discharge cut-off voltage, max amp draw, etc.

    The most cost effective products will be targeted at hobby (RC) electronics. Both the battery packs (with balance circuits embedded in the pack) and the intelligent charger to manage the charge as shown below from HobbyKing.

    Auto electronics were never made to be efficient as a car's electrical system can supply power "almost forever". You may find the Kenwood unit draws a lot of power significantly reducing run time. And if it's audio output circuitry is class A-B, it will be very inefficient powering the speakers. It depends on the age of the unit's design.

    Do not try to charge LiPos using experiences learned with lead acid or NiCad batteries. They will catch fire.

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    • #3
      I just linked this one because it has 8 bays, Battery Junction has numerous chargers, I have made several purchases from them.PE has one and two bay 18650 chargers, to be fair.

      https://www.batteryjunction.com/klarus-c8-charger.html

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      • #4
        i was wanting to build the batteries into the device and charge it with an external power supply. I was planning to use this.

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        • #5
          i was planning on using a new media player, I found a JVC that has an easy to read display and runs off a 10 amp fuse.

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          • #6
            Originally posted by kduggan View Post
            i was planning on using a new media player, I found a JVC that has an easy to read display and runs off a 10 amp fuse.
            Model #?

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            • #7
              Originally posted by kduggan View Post
              i was wanting to build the batteries into the device and charge it with an external power supply. I was planning to use this.
              There are many of these protection boards available. But I don't believe the basic protection circuits boards manage charge voltage or current (stated current is the module's maximum current capability). I believe you need a MPPT to manage charge voltage and charge current based on the cells' capacity / spec. Individual 18650 cells will specify maximum charge current (ex. 0.5C). Of course lower charge currents (longer charging time) extends battery life / cycles.

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              • #8
                i had been powering the unit with a 7 Ah 12V battery driving a Dayton chip amp but I burned up 3 amps in less than two years, I think because of low power to the amp as the battery became overly discharged. I need something that will turn itself off when it is under powered. I can use as many as 16 18650 batteries but I need to protect them somehow.

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                • #9
                  Originally posted by kduggan View Post
                  i had been powering the unit with a 7 Ah 12V battery driving a Dayton chip amp but I burned up 3 amps in less than two years, I think because of low power to the amp as the battery became overly discharged. I need something that will turn itself off when it is under powered. I can use as many as 16 18650 batteries but I need to protect them somehow.
                  I used digital voltmeter to tell the battery voltage. Never let it go below 10.5 V (not below 11 is better).

                  Panel Meter.png

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                  • #10
                    I had considered a similar item, but teenagers do not follow directions well. I guess I have a little more research in my future. Thank you for your help!

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                    • #11
                      Originally posted by kduggan View Post
                      I had considered a similar item, but teenagers do not follow directions well. I guess I have a little more research in my future. Thank you for your help!
                      You could try a 12V low voltage cut-off, below. Over draining the battery is one of the worst things for battery's life cycle. Second only to leaving a lead-acid battery discharged for any length of time.

                      I'm surprised the amps blew. Which model were you using? Many of the newer chips have auto shutdown for over temp, over current, etc.

                      Low V Cutoff.png

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                      • #12
                        I was using the Dayton DTA2 #300-385. It would run for about 10 hours on the 7 Ah battery but I had no way of monitoring voltage drop.

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                        • #13
                          http://batteryuniversity.com/

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                          • #14
                            http://batteryuniversity.com/ This is a great resource, Thanks for the link

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