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I am trying to build a DIY Bluetooth speaker using a 18650 battery cell, a TC4056A battery charger board, an XY-016 that raises the voltage to 6.5 V, a 2200 μF capacitor, and a CSR8645 board. I am using two speakers rated at 5W, 4 Ω. The components are very similar to the ones used in the aukits DIY kit, an older version.

The problem I am having is that at maximum volume, on some more punchier songs, the assembly shuts off and the TC4056A board outputs only 1.5 V. I have to shut it off and turn it back on, then it goes back to normal. I also have a 3 mm LED in parallel with the output of the TC4056A board and when the bass kicks, it dims following the rhythm.

Many people have built a similar speaker and didn’t have any issues so I am expecting for this configuration to be OK. Do you have any suggestions?

ocrdu
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Andrei-Eduard Lică
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  • Do you know the peak current consumption of the device and do the modules/boards have manuals that say they can provide the peak current? – Justme Aug 27 '22 at 22:28
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    Overcurrent and short-circuit protection - the module will cut the output from the battery if the discharge rate exceeds 3A or if a short-circuit condition occurs – Tony Stewart EE75 Aug 28 '22 at 01:37

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The data sheet for the TC4056 module shows that it has a shut-off current limit of 3 amps, which corresponds to 12 watts at 4 volts. The cell voltage may drop to 3.5 volts, which would be 10.5 watts. Your XY-016 voltage booster, and your amplifier, may be 80% efficient, so at the full rated 10 watts RMS of your speaker system, you are certainly causing the overload you experience.

If these overloads are brief, you may be able to get higher instantaneous power surges by adding a much larger capacitor on the 6.5 volt supply. You can estimate what is required by using the formula:

V(t) = I * t / C

If you would like the 6.5 V supply to drop to 5.5 V in 1 second for 3 A:

C = I * t / V or C = 3 * 1 / 1 = 3 Farads

Another way to look at it might be by using the RC time constant, although that would correspond to a 63% voltage drop to 2.4 V. If the amplifier draws 3 amps at 6.5 V its resistance is about 2.2 ohms, and 1 second TC would indicate about 0.5 F. But in reality you would need to use about 1/6 TC, perhaps related to a drop of 1 volt down from 6.5 volts. A simulation shows what is going on:

Capacitor time constants

A 3 Farad 10 V supercapacitor should be available for a reasonable cost.

PStechPaul
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  • It really makes sense now. Thank you for the in detailed answer. The problem is that I can’t seem to find a suitable supercapacitor in any shops from Romania .. Do I have any other options like replacing the TC4056 with something that allows higher amp output? Or could I modify it so that it would allow more than 3A? Or replace the XY-016 with something more efficient? – Andrei-Eduard Lică Aug 28 '22 at 07:57
  • You will have to search for alternative components yourself. Such capacitors are available from China, and you can try a wide range of values as long as the voltage rating is sufficient, and suitable protection circuits are used for capacitors in series. – PStechPaul Aug 28 '22 at 09:02