Refer to the Previous Article:
Battery Systems for Mission Critical Infrastructure - Design, Maintenance and Testing (3)
Vented Nickel-Cadmium Batteries
Just like the name suggests, these batteries are a vented (flooded) type, where the positive plate is made of nickel hydroxide and the negative plate is made of cadmium hydroxide. These batteries are often preferred because they:
- Have a high cycle count
- Can be charged very fast
- Have a long shelf life
However, these batteries have the following drawbacks:
- The NiCd batteries have lower voltages (1.2 V instead of 2 V for lead-acid batteries), which could be a problem for space. For a 120 V system, we would need 60 lead-acid cells, but 100 NiCd cells.
- Cadmium is toxic, so these batteries are not easy to dispose.
- NiCd batteries have memory, which means they remember the capacity delivered the last time and don’t deliver more than that. Because of this, they need to be discharged to lose the memory and then fully charged again.
IEEE has developed a standard for this type of battery: IEEE 1106-2015, Recommended Practice for Installation, Maintenance, Testing, and Replacement of Vented Nickel-Cadmium Batteries for Stationary Applications (
https://standards.ieee.org/findstds/standard/1106-2015.html).
As with other kinds of batteries, personal protective gear, such as goggles, gloves, and aprons, are recommended when servicing the NiCd batteries.
IEEE 1106-2016 recommends a quarterly inspection, which is the same as the vented lead-acid batteries’ monthly inspection:
A visual inspection of:
- The general condition of the area
- The battery cells, looking for cracks
- The electrolyte levels
- The battery terminals for corrosion
A measurement of:
- The float voltage at the battery terminals
- The float current
- Room or area temperature and ventilation
There is a semiannual inspection as well. This inspection encompasses what the quarterly inspection requires and adds cell voltage measurements. The yearly inspection also requires looking at the condition of the cable connections and measuring the resistance.
A list of simple corrective actions to a few abnormalities
The NiCd batteries can be submitted to a high-rate charge. Normally, they are charged at around 1.4 to 1.47 V per cell, but in a high-rate charge, the voltage can go to 1.55 V for a maximum of 1.8 V.
A NiCd battery is more tolerant of higher temperatures. The NiCd battery life and temperature correlation is shown below.
The relative correlation of nickel-cadmium (NiCd) battery life expectancy and temperature.
NiCd batteries, if operated at 20 to 25°C (68 - 77°F), can last a long time. Their capacity drops slowly, reaching 80% after 20 years. Even after that, they can be used in less-demanding applications.
Summary: The Importance of Design
Maintenance is especially important for mission critical systems because of the importance of the reliability of these systems. Indeed, maintenance does not start when problems with the equipment arise; rather, maintenance starts with the design of the systems. The design professional always needs to keep maintenance in mind when designing electrical systems, and the same goes for battery systems.
Keep the following tips in mind when designing and specifying batteries in mission critical facilities:
- Decide early, in conjunction with the owner, what type of battery to use. Choosing the battery type early helps with nailing down the design and operation conditions of the battery system.
- Design a cooling system in accordance with the manufacturer’s recommendations. As mentioned, the ambient temperature plays a big role in the battery lifespan.
- Design a ventilation system to properly refresh the air in the area to not allow hydrogen concentration in the area.
- Design proper clearances around the battery racks.
- Design proper containment in case of a leakage of the battery solution.
After the system (or facility) is up and running, it is critical to make sure that the design conditions mentioned above are enforced. It is also critical to follow IEEE recommendations for weekly, monthly, and yearly inspections (add a semiannual inspection for NiCd batteries). A visual inspection, as simple as it might seem, is very important to catch early what could become a serious malfunction.
It is best for the maintenance team to prepare a standard form for each type of inspection. These forms could have boxes for check marks and spaces for notes where certain conditions observed can be explained. Having a log of the inspections helps in tracking certain conditions and compiling a plan of action if the conditions deteriorate.
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For other design considerations / topics in data center and critical infrastructure, please visit
(1) Site Selection,
(2) Space Planning,
(3) Cooling,
(4) Redundancy,
(5) Fire Suppression,
(6) Meet Me Rooms,
(7) UPS Selection,
(8) Raised Floor,
(9) Code & Standards,
(10) Transformers and Harmonic Distortion,
(11) Multi-mode UPS Systems,
(12) Electrical Rooms,
(13) Generator Systems,
(14) Generator Fuel Systems,
(15) Battery Systems, etc.
