Quantifying secondary reactions in VRLA batteries. What purity standards and other factors are necessary to prevent negative plate discharge?
In a VRLA cell with a fully developed oxygen cycle, the negative plates will suffer discharge during float service if their self-discharge rate is too high to be balanced by the corrosion rate of the positive grids. Positive grids have been developed with very low corrosion rates. However, there is little quantitative data available on negative plate self-discharge rates that are required to balance such low corrosion rates. This paper presents values measured from several different battery brands, American and European. The data shows clearly that some production batteries have high negative self-discharge rates that account for the observed tendency for self-discharge in service. Surprisingly, the data also shows that other brands have achieved extremely low self-discharge rates-low enough to be compatible with the best positive grids that the authors have tested. These results are very encouraging for VRLA technology and confirm that the principle can be realized. The focus now shifts to the practical issues: finding the source of the impurities that increase hydrogen evolution and weighing the cost and practicality of reducing them.
Float life verification of a VRLA battery utilizing a high purity electrochemical system
Claims made at INTELEC battery workshops suggest that VRLA batteries may have a reliable life limited to as little as 2 years in standby applications. Furthermore, several published papers propose that one of the inherent failure modes is loss of capacity of the negative electrode. This paper examines float life verification of commercially available high purity VRLA batteries in light of this concern regarding negative electrode capacity loss and includes data from real-time room temperature float testing which has been ongoing well in excess of 10 years. The condition of the negative electrode, from both new and real-time aged product, has been carefully examined by both electrochemical measurements of the product and also by analyzing the morphology and crystallography of the plates. The condition of the positive grid has also been examined to determine the extent of corrosion. In conclusion, this paper demonstrates that by using a high purity VRLA technology, which has been commercially available for 25 years, it is possible to far exceed 2 years of reliable service. Properly designed batteries using this technology have been proven to deliver greater than 13 years in real-time float service.
Hobbes and the Reception of Leviathan
Although there has been much discussion of the reception of Hobbes’s work, Hobbes’s response to his own reception has rarely received much consideration. This article looks at Hobbes’s engagements with his critics. Far from being rearguard actions by a philosopher under siege, or disingenuous attempts to curry favour with those in power, they can be read as moments when Hobbes in fact sought to convert what he saw as the “truth of speculation into the utility of practice.”