Common causes of unstable output current of portable power supply (mobile energy storage) mains charger
Phenomena: The charging current is fluctuating, jumping, charging is intermittent, and the power fluctuates back and forth, which is not constant current charging. It is divided into four categories: charger itself, portable power supply terminal, external environment and wiring contact.
First, the charger (adapter) itself
The input mains voltage fluctuates, the voltage of the home power grid is unstable, and there are high-power appliances (air conditioners, induction cookers and electric water heaters) on the same circuit. The input voltage of the adapter fluctuates, and the output current fluctuates accordingly. Old plug-in and low household voltage will also appear.
The over-temperature protection of the adapter reduces the internal temperature of the power charger for a long time, which triggers the over-temperature protection and actively reduces the output current; The temperature drops and recovers, showing that the current jumps back and forth. Hot environment and poor heat dissipation of stacked packages of chargers are easy to occur.
Aging damage of adapter components
Electrolytic capacitor bulging and capacity attenuation: switching power supply is the most common, filtering fails, output ripple becomes larger and current jumps.
The switch tube and feedback circuit are faulty, and the voltage stabilizing loop works abnormally, which makes it impossible to stabilize the constant current/constant voltage output.
Insufficient power margin of the adapter: the portable power supply needs a large charging current, but the rated power of the adapter is small, and the full-load work enters the overload critical point, and the current fluctuates.
Adapter specifications don't match. Use a non-original charger: the voltage is right, but the maximum output current is not enough and the protocol is incompatible. The portable power supply and the adapter shook hands abnormally, and the charging power was repeatedly negotiated, and the current kept beating.
Second, the portable power supply body failure
Battery state problem
The batteries are aging, the internal resistance is inconsistent, and the pressure difference between single battery cells is large. BMS battery management system frequently adjusts the charging current to balance the batteries, and the current fluctuates.
Abnormal battery temperature: the battery is too cold/too hot, BMS temperature control protection, automatically limit and adjust the charging current. The charging current will change repeatedly in low temperature environment.
The battery is close to full charge: at the end of charging, the lithium battery itself will gradually reduce the current, which is a normal phenomenon, not a fault.
BMS battery management system abnormal BMS sampling circuit failure, sampling resistance drift, inaccurate detection of voltage and current, constant adjustment of charging input, resulting in output current jump; This phenomenon can also occur in BMS firmware bugs.
The charging input interface is damaged, the DC charging socket of the portable power supply is loose, the shrapnel is oxidized, the welding is virtual, the contact resistance is large and small, the equivalent load changes, and the charging current jumps back and forth.
Three, connecting wire, connector, poor contact
Excessive loss of charging wire, thin wire core, long length and large wire resistance; When charging with high current, the voltage drop on the line is large. When the adapter detects the voltage change, it will change the output current. Inferior DC lines are most likely to appear.
Plug oxidation, loose mains plug, adapter input, DC plug, metal oxidation, wear and tear, unstable contact resistance, slight vibration will cause current jump, and the charging state will change when touching the connector.
Fourth, other external factors
The heat dissipation problem (both of them need heat dissipation) is not only the charger, but also the portable power supply itself charges and heats up. If the shell is wrapped, the inside will heat up, the BMS will flow down and the current will be unstable.
Interference: The adapter and high-power equipment are placed in close proximity. Electromagnetic interference affects the feedback loop of switching power supply, and the output ripple increases and the current fluctuates slightly.
The portable power supply with load working at the same time is charged by mains electricity and discharged with load. The internal power is dynamically distributed, and the input charging current will change with the external load, so it seems that the charging current is unstable.
