Hej Ole,
It is possible. You connect the amplifier to the batteries and a current source (as charger) to the batteries as well. The current from the current source has to exceed the current drawn by the amplifier in average.
If you are afraid that the charging current may pull the battery voltage above the maximum supply voltage to the amplifier, use a shunt regulator to bleed off excessive voltage.
It is possible. You connect the amplifier to the batteries and a current source (as charger) to the batteries as well. The current from the current source has to exceed the current drawn by the amplifier in average.
If you are afraid that the charging current may pull the battery voltage above the maximum supply voltage to the amplifier, use a shunt regulator to bleed off excessive voltage.
Hej Ole,
The "Charger" is a current source circuit that operates from the 19V power line. At the cathodes of the two diodes, the amplifier is connected. The upper diode serves to supply the amplifier directly from the 19V line when that line is powered. At the same time the batteries are charged, through the "Charger" current source circuit, from the 19V line.
If the 19V power line is low, the amplifier is feed via the lower diode from the batteries.
It is important that the charging current to the batteries remains below the maximum charging current the batteries can stand. I looked at one brand of 18650 batteries and they have a maximum charging current just above 1A. If you connect the amplifier (like I suggested for a start) directly to the batteries (without diodes) and charge the batteries directly with the amplifier connected, the charging current should be no more than 1A. 1A because you cannot rely on the amplifier drawing any significant current. But, if the amplifier actually draws 1.5A, the charging current (1A) is not even sufficient to feed the amplifier and the last 0.5A has to be taken from the batteries (no charging but actually discharging).
The slightly more complex circuit proposed by WWense has the advantage that the battery charging current is not the residual of the charger current when the amplifier current has been subtracted. With this circuit, the amplifier can draw as much current as the 19V line can supply, and the charging current to the batteries can be set independently and does not depend on the amplifier current. It is a well conceived circuit.
Did that help on the understanding?
I assume 19V is for four 18650 elements.
The "Charger" is a current source circuit that operates from the 19V power line. At the cathodes of the two diodes, the amplifier is connected. The upper diode serves to supply the amplifier directly from the 19V line when that line is powered. At the same time the batteries are charged, through the "Charger" current source circuit, from the 19V line.
If the 19V power line is low, the amplifier is feed via the lower diode from the batteries.
It is important that the charging current to the batteries remains below the maximum charging current the batteries can stand. I looked at one brand of 18650 batteries and they have a maximum charging current just above 1A. If you connect the amplifier (like I suggested for a start) directly to the batteries (without diodes) and charge the batteries directly with the amplifier connected, the charging current should be no more than 1A. 1A because you cannot rely on the amplifier drawing any significant current. But, if the amplifier actually draws 1.5A, the charging current (1A) is not even sufficient to feed the amplifier and the last 0.5A has to be taken from the batteries (no charging but actually discharging).
The slightly more complex circuit proposed by WWense has the advantage that the battery charging current is not the residual of the charger current when the amplifier current has been subtracted. With this circuit, the amplifier can draw as much current as the 19V line can supply, and the charging current to the batteries can be set independently and does not depend on the amplifier current. It is a well conceived circuit.
Did that help on the understanding?
I assume 19V is for four 18650 elements.
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No, the 19v was just something I saw from Dayton Audio. I only want to use three 18650 (12,1 v). Do you imply that the power supply should also just be 12v ?
I am still unsure what a "charger" curcuit actually is (can you show a picture of a 12v charger) ? But it must somehow have separate input and output, otherwise the anodes of the two diodes would be directly connected.
I am still unsure what a "charger" curcuit actually is (can you show a picture of a 12v charger) ? But it must somehow have separate input and output, otherwise the anodes of the two diodes would be directly connected.
Please use a proper li-ion battery charging circuit with and not just a constant-current source. Li-ion does not work well with a simple constant-current source.
Charging Lithium-Ion Batteries – Battery University
...in fact no battery works well with a simple constant-current source, if you simply consider what happens when the battery is already fully-charged and you're still trying to push a current into it. That being said, most real-life chargers are a combination of constant-current + constant-voltage at the same time, or rather current-limited + voltage-limited. Battery charger ICs are widely-used and capable.
If in doubt, just buy a li-ion battery charger instead of making one from scratch.
1, 2 or 3 cells Lithium ion Battery 2A Charger Module 18650 Charging PCB SY6912 699901026556 | eBay
Charging Lithium-Ion Batteries – Battery University
...in fact no battery works well with a simple constant-current source, if you simply consider what happens when the battery is already fully-charged and you're still trying to push a current into it. That being said, most real-life chargers are a combination of constant-current + constant-voltage at the same time, or rather current-limited + voltage-limited. Battery charger ICs are widely-used and capable.
If in doubt, just buy a li-ion battery charger instead of making one from scratch.
1, 2 or 3 cells Lithium ion Battery 2A Charger Module 18650 Charging PCB SY6912 699901026556 | eBay
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Battery protection plus balance. Not absolutely necessary, but highly recommended for cells in series.
Battery protection boards may/should also include balance functionality even if not explicitly stated.
3s 11.1v 12.6v 25a W/ Balance 18650 Li-ion Lithium Battery PCB Protection Board | eBay
Battery protection boards may/should also include balance functionality even if not explicitly stated.
3s 11.1v 12.6v 25a W/ Balance 18650 Li-ion Lithium Battery PCB Protection Board | eBay
Thanks. I am totally new to lithium batteries and properly a bit paranoid. Can I just use normal (black) shrink tube, like I use for wires, or is it something special (like the blue stuff on all the chinese battery packs) ? What about heat and expandability of the lithium batteries (any concern) ? Should it cover the batteries completely with shrink tube ? Do I need to solder the batteries together or use something else to ensure the connections ?
I think a regular shrink tube will be fine, what they usually use for battery pack might shrink more. But the main goal is to keep the batteries together. If your batteries heat much or expand, that is concerning 
but no, in normal conditions that shouldn't happen.
You should solder the battery poles together with wires or tabs, if you only press the poles together, they might be separated at some point due to mechanical stress etc. Soldering might be tricky but doable, use enough heat and be quick that you won't damage the batteries.
If you hesitate to solder, there are single battery holders for 18650, you can use them.
but no, in normal conditions that shouldn't happen.You should solder the battery poles together with wires or tabs, if you only press the poles together, they might be separated at some point due to mechanical stress etc. Soldering might be tricky but doable, use enough heat and be quick that you won't damage the batteries.
If you hesitate to solder, there are single battery holders for 18650, you can use them.
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