Batteries back up every part of our digital society. They are complex electrochemical devices that take up a lot of expensive real estate in data centers, and their use presents environmental concerns.
Battery monitoring/testing is an excellent way of mitigating some of the risks associated with the use of this crucial product. The mission critical world uses UPS, engine start, and station batteries constantly, but we also find thousands of other battery applications in our cell phones, iPods, watches, etc.
During a discussion of the Deepwater Horizon oil spill, my colleague, Tom Leonard of BTECH Inc., reminded me that most failures are a result of a string of events, and no one event is typically responsible. Most reports point to the failure of a blow-out preventer as a major contributing factor leading to the oil spill, but few reports identify a dead battery as a possible reason that the blow-out preventer failed.
There are several compelling reasons to employ a battery monitoring system in the mission critical environment.
Since the 1970s, efforts have been under way to find a better failure prediction mechanism. The term settled on, which best reflects the health of a battery is “ohmic value.”
In the simplest technical terms, ohmic value is based on Ohm’s law, which expresses the relationship of volts, amperes, and ohms in an electrical circuit. Ohm’s law can be expressed as follows: E (volts) = I (amperes) x R (ohms). If any two of the three values of are known, the third value can be calculated using Ohm’s law.
E = I x R
R = E / I
I = E / R
Thus, the ohmic value of a battery is determined by using voltage and current to determine the resistive characteristic of a battery. Higher resistance equates to a reduced ability to produce current. This characteristic is translated into a measurement of impedance (ohms).
Opinions of best method for determining the ohmic value of a battery vary by manufacturer. There is agreement that the common goal is to develop trending of quality data over time that can reliably predict a failure far enough in advance so that an orderly resolution can take place vs. an unplanned failure at a critical time. Three of the common methods for determining ohmic value are: