Category Archives: Batteries

Worked Calculation Example of Lithium Battery Capacity Versus Load

I frequently am asked to comment on data that other engineers send me. This morning I received some test data obtained from an engineer measuring the backup time of an Uninterruptible Power Source (UPS) containing multiple lithium-ion (Li-Ion) batteries. The engineer was disappointed with the backup time provided by this UPS and wanted to know if his test results were reasonable considering the battery capacity of the UPS. While there were numerous circuit parameters measured during this testing, the critical information was the battery voltage versus time. Continue reading

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Interesting Discussion on Lithium Battery Fire Hazard

We have all heard stories of the  fire hazards that lithium-ion batteries present – just to remind you, here is a partial list: Boeing Dreamliner Electric Cars Samsung Phones There have been many other documented "thermal events". I personally have … Continue reading

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Using a D-Size Battery String for a UPS Energy Source

Quote of the Day If there is one thing more than another for which I admire you, it is your original discovery of the Ten Commandments. — Thomas B. Reed to the youthful Theodore Roosevelt about his self-righteousness Introduction I … Continue reading

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Spline Interpolation Example Using Battery Capacity

Introduction I had a conversation with a customer recently who wanted to estimate the capacity and running time of their electronic systems when operating from batteries that are under various current load and temperature stresses. The battery manufacture had only … Continue reading

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Battery Life Dissipated Under Varying Temperature Conditions

Introduction I am not getting any younger. As I age, I have come to realize that certain activities age me faster than others. For example, I have no doubt that sitting in meetings for hours every day has deleterious effects … Continue reading

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Battery Freezing Math

I live in a cold climate -- so cold that under certain circumstances we can freeze our lead-acid batteries (Figure 1). A customer who lives in my region called recently and was wondering if I thought any of his batteries would have frozen over the winter. A number of his Internet service subscribers have vacation homes that are unoccupied over the winter. All of these vacation home owners turn off their AC power for the winter. Since all of our Optical Network Terminals (ONT) are connected to Uninterruptible Power Sources (UPS), they will begin operating off of their battery when the AC power goes away. If the home owner does not disconnect the battery, the ONT will run discharge the battery. This is important because a discharged battery will freeze -- a charged battery will not freeze. A battery that has been frozen is very likely a dead battery. Continue reading

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Battery Outgassing Math

I recently have received a number of questions about the outgassing of hydrogen gas that can occur from lead acid batteries when they are being overcharged. I thought it would be useful to review what is happening when a battery is outgassing. When being charged, batteries can release enough hydrogen gas to create an explosive hazard. Consider this report and Figure 1 as an example as to what can happen. With lead-acid batteries, hydrogen gas can be generated any time, but charging is when the greatest challenges are faced. Continue reading

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Battery Failure Rates and Continuously-Compounded Interest

While performing some routine reliability analysis, I noticed that there is a similarity between battery aging and continuously-compounded interest calculations. I had not noticed this similarity before, and I thought I would document it here.

Figure 1 shows a common lead-acid battery. This chemistry is my focus in this post. Other chemistries will behave similarly, but the constants involved will differ. I will be assuming that the failure rate of the battery is described by the Arrhenius equation. Continue reading

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Lead Acid Battery Life Math

Quote of the Day The key to effective goal-setting is being realistic about what you can accomplish. — Andrea Woroch Introduction It is difficult to dig trenches for fiber optic cable in many parts of the US and Canada during … Continue reading

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Battery Charge Capacity and Energy Math

Introduction I am doing some requirements analysis work on backup power systems for GPON ONTs. As part of this work, I need to perform an evaluation of a number of batteries for charge capacity and energy. As part of this … Continue reading

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