====== Battery charge sequence ======


In ESS application, including but not limited by demand charge management, the power of charging the battery will be limited by 2 parameters:
  * maximum DC charging current (shown on the HMI as Max charging current)
  * active power setpoint (Target active power shown in settings-AC)

===== Constant current charge (aka fast charge) =====
When the battery voltage is much lower than constant voltage charging threshold, shown on the HMI as [[Slow charging voltage]], the inverter will charge it in a constant power or constant current mode, limited by the maximum charging current (Max charging current) and the given active power (Target active power) at the same time. The voltage of the battery will rise in the charging process.

===== Constant voltage charge (aka slow charge / topping charge) =====

When the battery voltage reaches the constant voltage charge threshold (Slow charging voltage), the PWS2-30K will charge the battery at constant voltage, the charging power and the charging current will reduce gradually till 0.


To make it easy to understand, here are two examples.

Example 1. The battery voltage is 600V in initial, the maximum charging current (Max charging current) is 100A, the requested charging power (Target active power) is 100kW, of course the PWS2-30K cannot execute in this power. It can only charge in $600V\times 100A=60kW$, and as the voltage rises, say 660V, the power can reach 66kW. But if 670V is the constant voltage charging threshold set by user, when the voltage reaches 670V, the power will reduce gradually till 0.

Example 2. The battery voltage is 600V in initial, the maximum charging current (Max charging current) is 100A, the requested charging power (Target active power) is 50kW, the PWS2-30K will charge in 50kW, because the charging DC current is just $50kW\div 600V=83A$, and as the voltage rises, such as 660V, the power is still 50kW, because the charging DC current is $50kW\div 660V=76A$. But if 670V is the constant voltage charging threshold set by user, when the voltage reaches 670V, the power will reduce gradually till 0.

===== Float charge voltage =====

The float charge is **ONLY for lead-acid or lead-carbon battery**. For lead batteries, the float charging voltage shall be a little lower than slow charge voltage (topping charge mode), and there is a threshold called "current threshold from topping charge to float charge" (legacy name: equal charge to Float charge current) , meaning that if the charging current reduced to this threshold, the inverter will change to float charge. if this option is set to 0, the inverter will never float charge the battery.

But lithium batteries shall not be float charged. So care must be taken to these parameters:

  * **float charging voltage** shall be set **as same as** **topping charging voltage**
  * **current threshold from topping charge to float charge** (legacy name: equal charge to Float charge current) MUST be set as 0

In order to maintain capability for both lithium-ion and lead-acid (carbon), Sinexcel inverters use above settings to differentiate them.