I have a 24V audio amplifier that is powered by 8 packs of 6x protected 18650 batteries connected in series to produce 24V, and then all the packs are connected in parallel.

The amplifier powers a subwoofer and a pair of speakers. The issue was that when subwoofer kicks a deep note, the system just cuts out.

I introduced 2x47000uf capacitors to the circuit in parallel. Problem I have now, is that the batteries just shut down. I tried it with just one capacitor, and then it worked.

I'm guessing the capacitors drain the batteries too fast and they just switch off.

Is there anything I can add to the circuit to prevent this? Perhaps a resistor? What rating?

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    \$\begingroup\$ Inrush current! \$\endgroup\$ – winny Jun 1 at 11:48
  • \$\begingroup\$ Perhaps a 300W light bulb to charge up the cap \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 1 at 12:45
  • \$\begingroup\$ @winny My thoughts exactly. Solution? \$\endgroup\$ – Mladen Jun 1 at 12:48
  • \$\begingroup\$ If the Caps have an ESR of 100 mOhms then the peak current is 24/0.1=240 A So choose any light bulb in series to connect then keep it charged up always. Define what causes "System cuts out" Low batt voltage will not be corrected by adding caps \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 1 at 13:02
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    \$\begingroup\$ You could probably add a MOSFET with an RC on the gate. As to the details, it depends on what your peak and average load currents are. \$\endgroup\$ – Spehro Pefhany Jun 1 at 15:38

It is due to high inrush current in to the system.

The batteries shutdown due to over current. I think you are exceeding the rated current of the protection circuit.

Add an NTC thermistor to limit the inrush current. This is a simple and off the shelf option.

  • \$\begingroup\$ Any idea at all what specification NTC Thermistor should I use for the battery pack I described? \$\endgroup\$ – Mladen Jun 1 at 13:25
  • \$\begingroup\$ @Mladen Depends on your battery and ESR. None of which you have provided details for. Find out from the datasheet and set it up in your simulator. \$\endgroup\$ – winny Jun 1 at 13:29
  • \$\begingroup\$ what winny is saying is true. with out details of battery and the protetcion cirucit it is not possible. \$\endgroup\$ – Satish Singupuram Jun 1 at 13:35
  • \$\begingroup\$ @winny so it would be something that would limit the flow of electricity from the battery to the capacitors under 16 amps @ about 25v. I appreciate what you guys are saying, but I'm a beginner \$\endgroup\$ – Mladen Jun 1 at 14:00
  • \$\begingroup\$ How about using an inductor instead and building a proper LC filter? \$\endgroup\$ – Simon Richter Jun 1 at 14:53

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