Between floating and intermittent floating: Low-current self-discharge under compensation

Abstract

Standby lead acid batteries maintained under a constant float voltage to compensate self-discharge often encounter the problem of short service life. One of the reasons limiting battery life span is the corrosion of positive electrodes. It is known that the rate of corrosion is the lowest when the polarisation of positive electrodes is between 20 mV and 80 mV. When applying the float voltage, the battery is permanently overcharged, the current is several times stronger than the self-discharge current and the polarisation far exceeds the zone of minimum corrosion.The new method proposed here is intended to maintain the full charge of stationary batteries using low-current and periodic charges. It has the advantage of reducing overcharge thus keeping the battery voltage in the minimum corrosion zone. The applied low-current need to exceed the rate of self- discharge but are much smaller than the usual float currents. Laboratory experiments point at examining the rate of self- discharge of flooded and VRLA batteries and the effect of low- current on reducing self-discharge. Three different cases were operated: floating, low-current self-discharge under compensation and open circuit. The new low-current method is tested in several UPS systems at Electricite de France (EDF), using flooded battery technologies.