Operation 4.1 PWM Technology (Series Pulse Width Modulation) The controller adopts the advanced series pulse width modulation. With range of 0-100%, it can charge the battery quickly and stably under any condition of solar photovoltaic system. The operating principle of PWM charging mode is as follows: The battery is firstly charged with pulse current and recharged after it stops charging for a while. It is repeated in this way for several times till the battery is fully charged. Intermissions allow some oxygen and hydrogen generated by chemical reaction can be chemically combined again and then absorbed, which can eliminate concentration polarizatio n and ohm polarization naturally, and reduce the internal pressure of the battery. Consequently, it makes next charging smooth and the more power is charged to the battery. Intermittent pulse current charging mode makes battery have more time to react, which reduces the gassing volume and makes battery improve the acceptance rate of charging current.