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24v rechargeable battery to power a class D amp?

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  • #16
    Originally posted by Matt Clara View Post
    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?
    There will be a way.

    One issue with the 24V pack is that it requires some higher voltage (>26 V?) in order to fully charge the batteries.

    Explanation: 24 V is the nominal 6S pack rating. Fully charged a 6S Li-Ion pack is 25.2 V. And you need some extra voltage for semiconductor losses through the charge electronics. 26 V is not a problem for the TPA 3118 or TPA 3116 class D chip amps on the KAB boards. And the KAB amps have 35 V PS bypass capacitors so they should be good at that voltage as well (I've run other TPA3116 boards at 26 V without issue). But a 26 V PS is uncommon.

    Possibly the best way is to use a common 24V AC PS "brick" to power the unit when plugged in and a small buck inverter (PE Part # 320-614) installed in the box to to up the voltage a couple volts to charge the batteries. However, given the 1.5 A maximum output of that buck inverter, it's possible that playing the box at maximum volumes while plugged in may continue to drain the batteries (rare scenario in my opinion). And there are other ways to insure the 24 V AC PS is powering the amp and not the 25.2 V from the batteries while charging. A charge/play versus battery switch (to your original question) or a simple relay, or several internal series diodes to insure the amp always sees 24V AC PS as the higher voltage than the batteries (a little wasteful on power but "automatic").

    Me, I'd go with the buck inverter. If the battery drain while plugged in and playing becomes an real issue, then I'd implement a correction after the fact.

    Edit: Lastly, this is DIY. I might build the box-speakers-KAB amp without batteries for now. And test it on 12 V (readily available from a car battery) to see if it gives you sufficient volume. Then you can just add the KAB battery board/18650 cells (or two for extended play time) and a 19 V PS brick (old laptop supply) and be done with it.


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    • #17
      Ceiol has built a boombox similar (if not the same) as you are contemplating. I've asked him to post in this thread his power source (Volts, batteries, etc.) and his impressions on maximum volume for a reference. If you don't see it in a day or two, perhaps you could PM him.

      Having thought about Ben's suggestion some more, I think if you could find a 20 V or 18 V tool pack that has the battery management with the batteries, it would be very simple set up: 24 V AC PS, when plugged in batteries charge and box plays off the PS, when not plugged in, batteries will run the unit. A simple on/off switch to keep the batteries from draining when not in use or leave it plugged in and the battery management should keep the batteries topped-off.

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      • #18
        Use 2 12V batteries. Have a switch (or relays) that wires them in series when being used as a power source for 24V. When the switch is flipped, then they are wired in parallel, which then allows a standard 12V charger to be used (just take longer).

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        • #19
          Originally posted by Millstonemike View Post
          Ceiol has built a boombox similar (if not the same) as you are contemplating. I've asked him to post in this thread his power source (Volts, batteries, etc.) and his impressions on maximum volume for a reference. If you don't see it in a day or two, perhaps you could PM him.

          Having thought about Ben's suggestion some more, I think if you could find a 20 V or 18 V tool pack that has the battery management with the batteries, it would be very simple set up: 24 V AC PS, when plugged in batteries charge and box plays off the PS, when not plugged in, batteries will run the unit. A simple on/off switch to keep the batteries from draining when not in use or leave it plugged in and the battery management should keep the batteries topped-off.
          Just to clarify, the Kobalt batteries have BMS boards that balance and protect, but they do NOT have charge circuits built in. A charger that will supply a proper charge profile is necessary (constant current/constant voltage/termination). Also, while it is convenient to leave batteries on a charger and have them topped off, Li-Ion batteries will have a longer life-span if left in a state of charge less than 80%.

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          • #20
            Originally posted by 1100xxben View Post

            Just to clarify, the Kobalt batteries have BMS boards that balance and protect, but they do NOT have charge circuits built in. A charger that will supply a proper charge profile is necessary (constant current/constant voltage/termination). Also, while it is convenient to leave batteries on a charger and have them topped off, Li-Ion batteries will have a longer life-span if left in a state of charge less than 80%.
            Yes, the 80% is the storage charge. My beach boombox is packed away for the winter (NJ) and I have them on the storage charge for those 6-7 months. But I presume the boombox will see somewhat regular use throughout the year.

            There are PCB "MPPT" controllers that can be dialed in for the proper voltage and current limit via trim pots (<$10). I've looked at those to build a custom pack/charger before my friend gave me customer pack and charger.

            And to Wesrock2000's post ... Yes, I would use the KAB built-in battery management (MPPT on amp, battery protection on the battery extension board) with some XP2T switch to accomplish that.

            Li-ions are difficult for DIY due to their nature. A lot of customer engineering by really big companies has gone into the smart phones/laptops and they've had their share of issues.

            Long gone are the days when you could abuse NiCads and they would perform regardless

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            • #21
              Hi Matt,

              At millstonemike's suggestion, here is info on a boombox that I made

              http://techtalk.parts-express.com/fo...pepper-boombox

              works well -- plenty loud with just the KAB amp board and 12v lithium ion battery pack

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              • #22
                Originally posted by ceiol View Post
                Hi Matt,

                At millstonemike's suggestion, here is info on a boombox that I made

                http://techtalk.parts-express.com/fo...pepper-boombox

                works well -- plenty loud with just the KAB amp board and 12v lithium ion battery pack
                Thank's Ceiol. Really pretty box.

                Matt, I really feel I accidentally steered you in the wrong direction. When we started, you were looking at the 8 ohm version of the Heliums on the KAB2x30 (IIRC). I pointed out that the amp ratings are mostly immaterial as PS voltage and driver impedance determines power and gave some examples. Somehow that turned into the need for 24 V and all the issues the go along with it.

                Ceiol's boombox uses the NS3 drivers. They are pretty much the same as the ND9x series. And the NS3s are 8 ohm in his box while your using the 4 ohm version of the NDs. So at 12 V like Ceiol uses, you'll get 3 dB SPL more out of each driver, 6 db total. And that type of system has well integrated electronics/battery mgt plus all the user friendly functionality that goes along with it. And that will allow you to concentrate on the box build and aesthetics. Plus, any 19 V laptop PS can be used as you AC power source (if you don't have one, I can send you one to you - I've been saving them for some 20 years and have several extras laying around). Something to consider ...

                The KAB battery system requires Li-Ion 18650 batteries, very common. Beware of eBay and the like as the maH ratings are not to be trusted. Go with a respected vendor, I like the Panasonic 3400 maH batteries, pretty much the highest capacity that can be made into a 18650 cell. Gordy likes the Samsung 18650 cells at 3500 maH. They's run ~$5 each.

                Where is Gordy? Haven't heard from him in several months, hope he is ok.

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                • #23
                  what about a 6s bms like this
                  https://www.ebay.com/itm/6S-15A-PCB-....c100506.m3226

                  and some 18650 batteries?

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                  • #24
                    Originally posted by Millstonemike View Post
                    Thank's Ceiol. Really pretty box.

                    Matt, I really feel I accidentally steered you in the wrong direction. When we started, you were looking at the 8 ohm version of the Heliums on the KAB2x30 (IIRC). I pointed out that the amp ratings are mostly immaterial as PS voltage and driver impedance determines power and gave some examples. Somehow that turned into the need for 24 V and all the issues the go along with it.

                    Ceiol's boombox uses the NS3 drivers. They are pretty much the same as the ND9x series. And the NS3s are 8 ohm in his box while your using the 4 ohm version of the NDs. So at 12 V like Ceiol uses, you'll get 3 dB SPL more out of each driver, 6 db total. And that type of system has well integrated electronics/battery mgt plus all the user friendly functionality that goes along with it. And that will allow you to concentrate on the box build and aesthetics. Plus, any 19 V laptop PS can be used as you AC power source (if you don't have one, I can send you one to you - I've been saving them for some 20 years and have several extras laying around). Something to consider ...

                    The KAB battery system requires Li-Ion 18650 batteries, very common. Beware of eBay and the like as the maH ratings are not to be trusted. Go with a respected vendor, I like the Panasonic 3400 maH batteries, pretty much the highest capacity that can be made into a 18650 cell. Gordy likes the Samsung 18650 cells at 3500 maH. They's run ~$5 each.

                    Where is Gordy? Haven't heard from him in several months, hope he is ok.

                    Thanks Mike, I came into this worried about underpowering the system, so you're not to blame for that. What I've learned through all the discussion--other than there are ways to do 24v if you are willing to go to those lengths--is that I'm overly concerned about underpowering the system. It seems that "enough power" is relative to what you'll be using it for. I just turned 50, and I'm no longer trying to blow the roof off the house. I make payments on that roof. ;)

                    I too hope Gordy is okay. Like you and many others on the site, he's been very generous with his time, and I really appreciate the help and the spirit of generosity in general.

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                    • #25
                      Originally posted by videsh View Post
                      what about a 6s bms like this
                      https://www.ebay.com/itm/6S-15A-PCB-....c100506.m3226

                      and some 18650 batteries?
                      Yes, For future reference ...

                      A battery managemengt module BMM (for protection and cell balancing as in your link) along with a MPPT module (for voltage and current management) and you can build a pack using unprotected 18650 cells. For these 24V chip chip amps, I would recommend a 5S pack (21V fully charged). Then it would charge on a standard 24 V PS feeding the box when plugged in. There are low cost BMMs for any combo from 1S to 6S (5S shown below) for a few bucks as well as a variable MPPT module that can be dialed in for the pack size and cell capacity.

                      Li-Ion Mgt.png.

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                      • #26
                        Originally posted by Millstonemike View Post
                        Thank's Ceiol. Really pretty box.



                        Ceiol's boombox uses the NS3 drivers. They are pretty much the same as the ND9x series. And the NS3s are 8 ohm in his box while your using the 4 ohm version of the

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                        • #27
                          Originally posted by ceiol View Post

                          Mike, I’m actually using the ND90-4 which is the 4 ohm version of the NS3

                          I chose 4ohm for the extra amp output and a few more dB!
                          Huh, I took the NS3 from you XO drawing.

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                          • #28
                            Originally posted by Millstonemike View Post
                            Huh, I took the NS3 from you XO drawing.
                            yup, "NS3-4 / ND90-4"

                            4 ohm for sure

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                            • #29
                              Originally posted by ceiol View Post
                              Hi Matt,

                              At millstonemike's suggestion, here is info on a boombox that I made

                              http://techtalk.parts-express.com/fo...pepper-boombox

                              works well -- plenty loud with just the KAB amp board and 12v lithium ion battery pack
                              Thanks Ceiol. Because of the issue with the gain on the KAB250 and because I was worried that the KAB230 would be just adequate to drive the helium speakers, I opted for a 50w per channel TDA7492 board from Sanwu. I used three of their boards in my Christmas boombox(s) build for my nephews and daughter, and they work as advertised, so I'm pretty sure I know what I'm getting. It also has the "rubber ducky" antenna, as Mike calls it, which I can relocate to the outside of the boombox, hopefully extending its range beyond 12 feet! And it has aptX bluetooth and an aux-in. I did originally want to go with the KAB line, and appreciate their modular nature. After that I started looking at the TPA3116 boards, because lots of people like them, but when I started reading reviews comparing the two, many people prefer the TDA7492 as being less raw and rough, smoother. I don't listen to much punk any more, and never cared for speed metal, so I went with the TDA7492 board. Appreciate you sharing, I've looked at your build when I was planning the one for the kids at xmas. It's very cool.

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                              • #30
                                Originally posted by ceiol View Post
                                yup, "NS3-4 / ND90-4"

                                4 ohm for sure
                                And it says right on the XO ND90-4. I has looked up NS3 on PEs site and they only carry the -8 versions. I must be getting old.

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