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24v rechargeable battery to power a class D amp?

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  • 24v rechargeable battery to power a class D amp?

    As I understand it, that would be teh best case scenario. The amp wants 24v to provide full power, and while a lot of people just use a 12v rechargeable system and let it be underpowered when on battery, is there any reason not to use a 24v rechargeable, other than size and cost? I used some TalentCell 12v 3000mAh rechargeables in my last build, and I see that they have a 24v option, too, for a cool $70. https://www.amazon.com/dp/B078T7M9HZ I'm told it's "about 1.5 x 3.1 x 5.4 inches", so it'll fit. Any reason not to use 24v, other than the cost? Am I thinking about this wrong? Thanks. Sorry for the constant barrage of newbie questions--I appreciate all of the help I've received!

  • #2
    Charging circuit to go with it?

    Edit: nevermind, I see it comes with an AC charger... looks like it would work great!

    I don't see any reason to stick with 12V other than simplicity and the wealth of availble 12V battery and charger options.
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music

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    • #3
      Yeah, the circuit is in the case with the battery, all powered by a wall wart. At least the 12v versions were, and this looks very similar, just bigger and with some additional functionality. I underestimated how much space they would need and ended up having to remove the cases from them. They consisted of a bright blue pack of AA sized batteries wired to a circuit board with a power switch and some LEDs.

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      • #4
        Look at the spec.'s closely. It's not 22.4 aH at 24 volts. The description says seven 3.7V cells and each cell is 3.2 aH. So it won't last very long at 24 V. Also, the Li-ion 18650 cells, when fully charged, are 4.2 V. Seven would put the voltage over 29 V. So if they charge fully, the "24V" output will likely near/exceed the absolute maximum ratings on many chip amps.

        I would look to RC hobbies for a 6s LiPo pack and compatible charger. RC batteries are competitively priced and have good performance lest they get a bad rep in the hobby.

        Look for the 6s (6 cell) 10 aH (10000 maH) "Multistar High Capacity 10000mAh 6S 10C Multi-Rotor Lipo Pack XT90" on hobbyking.com ($49). A compatible charger may be: "Turnigy Accucel-6 80W 10A Balancer/Charger LiHV Capable" ($30). They'll be two connectors: + power and 9-pin dbm for cell balancing.

        I have a 6s, 20 aH pack that reaches 25.2 V at full charge. It was custom built by a friend as a gift and uses a $60 computer charger. That connects with power leads and the 9-pin dbm connector. The computer charges and balances each individual cell (60 cells total in a 10 x 6s arrangement). That pack will run my boombox all day at the beach (9+ hrs) with pleny of capacity to spare. It's a TPA3116 2.1 system with 4 ohm drivers and supplies sound for a 25 to 30 person beach group (with dancing). So 10 aH should be good to go. You may consider an even lower capacity 6s pack depending on the boom box. I run a lot of power through mine all day long and have plenty to spare.

        Dunes Tunes - Small.jpg

        Powered by two 12V 18aH SLA-AGM's prior to the Li-ion pack.

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        • #5
          Thanks Mike, unfortunately, at that cost ($140?), I'm stuck with 12v.

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          • #6
            Originally posted by Matt Clara View Post
            Thanks Mike, unfortunately, at that cost ($140?), I'm stuck with 12v.
            The battery I referenced is nominal 24V 10aH for $49. You only need one. Plus the charger at $30 for a total of $79 (plus shipping if applicable). You likely could get away with the Multistar 24V 5.2aH for $25 - total $55 with smart charger.

            Refresh my memory on the details of the boombox. I doubt you need anywhere near the capacity I use with mine.

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            • #7
              If you want cheap 24V power and don't need the capacity Mike is talking about, check out the 24V max Kobalt batteries at Lowes. They're not high capacity, but they are super inexpensive, so you can always just buy a bunch and swap them out.

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              • #8
                Originally posted by Millstonemike View Post

                The battery I referenced is nominal 24V 10aH for $49. You only need one. Plus the charger at $30 for a total of $79 (plus shipping if applicable). You likely could get away with the Multistar 24V 5.2aH for $25 - total $55 with smart charger.

                Refresh my memory on the details of the boombox. I doubt you need anywhere near the capacity I use with mine.
                I'm sorry, Mike, when you listed your laptop charger for $60, I thought that was a third thing to buy, bringing the total to $140. I'm building the boombox with a pair of Scott Sehlin's helium micromonitors, which contains a pair of 30w 4 Ohm full range and a pair of 6 Ohm tweeters, driven by a 50w per channel class d amplifier. And a pair of vu meters at 12v via a buck convertor.

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                • #9
                  Originally posted by 1100xxben View Post
                  If you want cheap 24V power and don't need the capacity Mike is talking about, check out the 24V max Kobalt batteries at Lowes. They're not high capacity, but they are super inexpensive, so you can always just buy a bunch and swap them out.
                  Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

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                  • #10
                    Originally posted by joeybutts View Post

                    Ben, I was looking at this option before but couldn’t figure out how you use the pack other than deconstructing it....
                    Yeah, Joey has a point on interfacing with the pack's proprietary configuration. And the pack is $50 for 24 V at 4.0 aH - less capacity per $$$s. Plus you need the cobalt charger for $40.

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                    • #11
                      The KAB supports the 12 V Li-ion battery board. And it supports multiple battery boards for extra capacity, not higher voltage. I bet there is a way to use a DPDT switch to change between (1) Playing off an AC PS while charging the batteries; and (2) Playing off the batteries in a series configuration for 24V. But first ...

                      You'll get about 96 dB SPL out of each ND-91 at 12V, 99 dB total (before BSC). That may satisfy the portable performance goal. That SPL will approximately double on the 19V AC PS. I'd start with a 12V battery board (or 2 in the standard parallel config for extended play time) and see how it goes. If need be, you may be able to reconfigure to 24V as above. Get good sound with an integrated system with Scott's design is a given. Worst case, you may not be able to compete with a pair of Statements on a Crown

                      Alternatively, pick a 4 ohm design with more efficient drivers which likely translates to bigger woofers and a bigger box. I've played with an integrated 24V design and it's a PITA. My 24V Li-ion pack is external to the box and only charges when not playing. That works for it's dedicated beach a use, not so convenient for a generic plug-and-play boombox for the young'uns.

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                      • #12
                        Originally posted by joeybutts View Post

                        Ben, I was looking at this option before but couldn’t figure out how you use the pack other than deconstructing it....
                        Well, they are super simple to deconstruct (4 screws to remove the outer shell and you can solder wires directly to the contacts). Or, you can actually use a couple female quick disconnects and stick them in the terminal slots. Another cool feature is the 4 LED charge indicator. If you keep it, then with the press of a button, you can see how much charge is left in the battery.

                        Originally posted by Millstonemike View Post
                        Yeah, Joey has a point on interfacing with the pack's proprietary configuration. And the pack is $50 for 24 V at 4.0 aH - less capacity per $$$s. Plus you need the cobalt charger for $40.
                        I was referring to the 1.5 Ah pack for $10 and the 2.0 Ah pack for $20. They aren't super high capacity, but they are very inexpensive options for someone wanting a cheap battery solution. Also, there's no need for a Kobalt battery charger. Anything that can charge a 6S Li-Ion pack should work. I have a couple of the $10 packs and I use a generic hobby charger to charge them.

                        Again, they're not a perfect solution, just a really cheap option and they're readily available at your local Lowe's.

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                        • #13
                          Originally posted by 1100xxben View Post

                          Well, they are super simple to deconstruct (4 screws to remove the outer shell and you can solder wires directly to the contacts). Or, you can actually use a couple female quick disconnects and stick them in the terminal slots. Another cool feature is the 4 LED charge indicator. If you keep it, then with the press of a button, you can see how much charge is left in the battery.



                          I was referring to the 1.5 Ah pack for $10 and the 2.0 Ah pack for $20. They aren't super high capacity, but they are very inexpensive options for someone wanting a cheap battery solution. Also, there's no need for a Kobalt battery charger. Anything that can charge a 6S Li-Ion pack should work. I have a couple of the $10 packs and I use a generic hobby charger to charge them.

                          Again, they're not a perfect solution, just a really cheap option and they're readily available at your local Lowe's.
                          Well that makes it a little easier. I presume the cell protection and balancing electronics are in with the batteries as there doesn't seem to be enough contacts between the charger and battery module to perform that function. Hopefully, the cells' charge current limiter is also included with the pack (Li-Ion cells are finicky and prone to fire if not charged in accordance with tight tolerances).

                          If all that is true, then the $50 for the 24V 4.0 aH pack is not a bad deal at all.

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                          • #14
                            Originally posted by Millstonemike View Post
                            Well that makes it a little easier. I presume the cell protection and balancing electronics are in with the batteries as there doesn't seem to be enough contacts between the charger and battery module to perform that function. Hopefully, the cells' charge current limiter is also included with the pack (Li-Ion cells are finicky and prone to fire if not charged in accordance with tight tolerances).

                            If all that is true, then the $50 for the 24V 4.0 aH pack is not a bad deal at all.
                            That is correct, there is a BMS board inside the plastic case.

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                            • #15
                              When unplugged, do all of these rechargeable options automatically switch between providing power to the amp from the mains to the batteries (and vice versa), and charge the batteries when plugged in while providing power from the wall outlet to the amp?

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