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QUESTIONS
Q1 – Should I take my battery off charge to measure cell voltages?
Q2 – Should I specify a particular plate thickness for my batteries?
Q3 – Do I need forced ventilation for my battery area?
Q4 – Why do lead acid battery manufacturers use different alloys in their batteries (lead-calcium, etc.)?
Q5 – What is the memory effect in nickel-cadmium batteries?
Q6 – Is a VRLA battery a 'sealed' battery?
Q7 – What is the effect of temperature on battery life?
Q8 – When will lithium ion batteries be available for stationary applications?
Q9 - What are the main differences between nickel cadmium and lead acid industrial batteries?
Q10 -Can I use a conductance/impedance battery monitoring system designed for lead acid batteries with a Ni-Cd battery?
ANSWERS
Q1 – Should I take my battery off charge to measure cell voltages?
A1. No, you should take voltage readings with the battery stabilized on float charge. This shows whether the charger is set correctly, and how well the battery is responding to the charge. Open circuit (off charge) voltage readings are of little practical value.
Q2 – Should I specify a particular plate thickness for my batteries?
A2 - For lead-acid batteries, there is an inverse relationship between the high-rate performance and life expectancy. Designs with thinner plates have a greater plate surface area per ampere hour, and therefore superior high-rate performance. However, thinner plate grids are more susceptible to the effects of corrosion, and thin-plate batteries have shorter life. High-rate UPS batteries have lives of around 10 years, whereas thick-plate telecom batteries have lives of around 20 years on float. General purpose designs, with medium plate thickness, give around 15 years. While it is certainly possible to specify thicker-plate, longer-life batteries for high-rate applications such as UPS, the problem is that such batteries, when sized for a short-duration discharge, will be larger, heavier and more expensive than the thin-plate types. Nickel-cadmium batteries are also available in high-rate, medium-rate and low-rate versions. However, since the hardware in a Ni-Cd battery does not degrade over life, there is no life penalty involved with the use of thin-plate high-rate types.
Q3 – Do I need forced ventilation for my battery area?
A3 - In any battery installation, ventilation must be adequate to prevent the accumulation of explosive levels of hydrogen gas. The lower explosive limit of hydrogen is around 4% in air. However, to avoid the possibility of pockets of explosive gas mixtures, it is normal to specify a lower concentration and some codes call for a maximum level of 1%.. Hydrogen diffuses rapidly through most building materials, and it is quite unusual for fan-assisted ventilation to be required for gas removal. A fan may, however, be useful for cooling the battery room/enclosure.
Q4 – Why do lead acid battery manufacturers use different alloys in their batteries (lead-calcium, etc.)?
A4 - The composition of the plate grid alloy can have a major effect on operating characteristics, such as behavior on float charging and cycle life. Older lead-antimony designs have good cycling capability but require frequent water additions, particularly towards the end of life, due to antimony migration between the plates. Cells with lead-calcium alloys require far less watering, but tend to have a poor cycle life. Lead-selenium alloys are actually low-antimony types with the addition of selenium as a hardening agent. Such alloys promote good cycling capability, while maintaining a constant and fairly low level of water consumption. Many variants on these alloy types are commercially available.
Q5 – What is the memory effect in nickel-cadmium batteries?
A5 - The memory effect is a reduction in capacity of a Ni-Cd battery, which occurs after the battery has been subjected to repeated shallow discharges. Memory is an issue only with sealed Ni-Cd cells, and relates to the way in which they are charged. Vented Ni-Cd cells do not exhibit this phenomenon.
Q6 – Is a VRLA battery a 'sealed' battery?
A6 - The, so-called, 'sealed maintenance-free lead acid batteries' were introduced for stationary applications in the early 80s. While these batteries are 'sealed' to the extent that there is usually no access to the inside of the cell, the term was misunderstood and batteries were installed tin areas with no ventilation. In practice, this type of battery periodically release small amounts of hydrogen in normal service, and can produce large quantities of this flammable gas if overcharged. This led to explosions as ventilation is required, as is regular servicing. With this in mind, the industry moved away from the term, 'sealed maintenance-free' and has agreed on 'valve-regulated lead-acid' (VRLA).
Q7 – What is the effect of temperature on battery life?
A7 - When operated above 20-25°C, batteries have shorter operating lives. For vented lead-acid batteries, each 10°C temperature increase cuts the life by 50%. VRLA batteries are more sensitive to higher temperatures, and an 8°C increase will halve the life. Nickel-cadmium batteries are quite resistant to high temperature operation, with a 10°C increase cutting life by only 20%
Q8 – When will lithium ion batteries be available for stationary applications?
A8 - Lithium ion technology is currently being scaled up for applications requiring higher battery capacities, such as electric vehicles. However, it will be a few years before these larger batteries are commercially available, although they are in many demonstration applications.
Q9 - What are the main differences between nickel cadmium and lead acid industrial batteries?
A9 - This is too complex to answer in a few words. We have therefore produced a double sided pdf document which gives the main differences which results in their different uses. You can download this document by clicking here.
Q10 -Can I use a conductance/impedance battery monitoring system designed for lead acid batteries with a Ni-Cd battery?
A10 - If a battery monitoring system is required then a system measuring cell/block voltages and temperatures is sufficient for nickel-cadmium cells. Systems that measure internal resistance or impedance give little additional benefit. These work on the basis that the lead acid plate corrodes during its lifetime and there are fundamental changes in performance and the expected lifetime is unpredictable. With the steel plate structure of the nickel cadmium cell these changes do not occur, the performance is maintained and the lifetime is entirely predictable.
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