Since we have several C9 users showed up in the thread, I'll start to explain more operational side of C9. Someone has asked whether you can charge while you are listening, so let me started here.
Charging and Protection Circuit
The 18650 is very different from the 3.7V Lithium battery that are commonly find in mobile phone. Overcharge and discharge of lithium-ion batteries will cause permanent damage to the positive and negative electrodes. Excessive discharge leads to the collapse of the negative carbon layer structure, and the collapse will cause the insertion of lithium ions in the charging process; overcharging will cause too much lithium ions to be inserted into the negative carbon structure, causing some of the lithium ions to no longer be released. (Extracted from
HERE)
A fully charged 18650 is around 4.2V and a discharged battery should stay at around 3.0V. A deeply discharged cell has fallen below 2.75V, it goes into a sleep mode and the battery is essentially useless.
- The Battery module and the C9 audio circuit did not share a common ground, so it is likely that there will be potential different between the two grounds. Therefore it is very important to charge the battery with a separate USB charger. Using the USB from connected audio source equipment (such as computer or media player) to charge up the C9 batteries will trigger the short circuit protection, and might even damage the device and/or connected source equipment.
- In case your C9 (or the battery module) entered protection mode, you need to remove everything and connect C9 or the battery module to a charger, charge it for at least 10 seconds and the device or battery module will revoke from protection mode and resume normal operation.
- After replacing or dismounting the battery, the battery module enters protective mode, you need to connect the battery module to a charger, charge it for at least 10 seconds, and the battery module will then revoke from protection mode and resume normal operation.
- Do not charge and playback both C9 and the connected source (let’s assume that is a DAP) at the same time. The four pieces of 18650 batteries are connected as a +8.4V and -8.4V power supply for the amplification circuit, and there is a set of ground line in between and that is connected to the C9 chassis. The charging circuit via USB-C has its own reference Ground connected to the USB socket. Be reminded that these two Ground are completely independent. If C9 and the DAP are charge and play at the same time, the power supply Ground (C9 Chassis) and charging Ground (USB socket) will short circuit by the charging cable and interconnect between C9 and DAP. C9 will enter protected mode. You can revoke C9 from protection mode by disconnecting everything and charge it for 10 second.
- You can charge and playback C9 at the same time before the batteries is fully charged. 18650 Lithium battery charge control is divided into two phases. The first phase is constant current charging. When the battery voltage is lower than 4.2 V, the charger will charge with a constant current. The second stage is the constant voltage charging stage, when the battery voltage reaches 4.2 V, due to the characteristics of the lithium battery, if the voltage is high, it will be damaged, the charger will fix the voltage at 4.2 V, and the charging current will gradually decrease. Therefore, if you charge and playback at the same time and your charging rate is faster than discharge rate, the 18650 batteries will reach 4.2V eventually. The problem is, when you continue to charge and playback at this moment, C9 power management cannot enter the constant voltage charge stage, this will put C9 into protection mode. You can revoke C9 from protection mode by disconnecting everything and charge it for 10 second. You are advised to disconnect C9 from charging when the fourth battery LED is flashing in these circumstances.
- If you charge and playback C9 at the same time and your charging rate is slower than discharge rate, your battery will consume slowly. At certain point, the batteries will drop below 3V and triggered the protection circuit to power off the C9. . You can revoke C9 from protection mode by disconnecting everything and charge it for 10 second and charge up the 18650 batteries. Since deep discharge might damage your battery, you are advised to stop your playback and start to charge up C9 when only 1 charging LED remains flashing.
- Please do not use USB charger from Huawei mobile device to charge up C9. Huawei has it own quick charge protocol that is not compatible with C9.