How to Monitor Your Telecom Batteries 7x24x365

Let's walk through the reasons for high-quality battery monitoring. We'll look at the the inherent difficulties. We'll also review one possible solution that walks the line between "ineffective" and "too expensive to justify".

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Your batteries MUST be protected

UPS batteries for telecommunications systems are used in many industries:

• Telecom
• Electric generation & distribution
• Transportation
• Police/Fire/EMS radio
• Government & military

The BVM G3 uses newer D-Wire sensor technology to monitor 3 key battery values at once: voltage, temperature, and internal resistance. I include more details at the end of this article.

In their own ways, each of these industries protect human lives. That makes every remote site they use in telecom applications absolutely critical.

UPS battery strings are used as a backup power source to keep telecommunications equipment online at all times. This protects you when commercial power fails. That makes them just as deserving of protection as the communications equipment they power.

You need good remote visibility of your batteries to protect against:

• Sudden battery failure.
• Thermal runaway.
• Undetected normal discharging that eventually drains your batteries completely.
• Long-term reduction in battery life
• Gradual deterioration that leads to internal shorting.

Some monitoring solutions just don't work

Unfortunately, monitoring your batteries isn't always easy. There are plenty of optons that won't do the job, for one reason or another.

Scheduling recurring visits with a handheld tester is a waste of time and money. Your skilled technicians have much better things they could be doing. They shouldn't be driving for hours just to check on remote site UPS batteries. This also can't protect you from sudden failures (full discharge, thermal runaway) at sites you don't visit extremely often.

Buying expensive monitoring systems that are impossible to justify will never work. I've heard from many DPS clients a common (entirely serious) comment.

"For the price of most battery monitoring systems, I'll just replace the battery strings more often," they say. Perhaps that's an overreaction, but there's no doubt that budget constraints are real.

What you can never forget, though, is that the people you serve need your services to be 100% reliable. Replacing batteries is hardly the only cost of a service outage.

For that reason, not monitoring at all and having to replace your batteries will not work. Even if that's the "right" choice in the face of ultra-expensive monitoring systems, it's still wrong. With equipment failures, you have to price in the risk and impact of service outages.

You won't just be replacing a battery string. You have to contend with upset (and possibly lost) customers. If you work in "government" or telecom, the lives of your "customers" (residents) might actually depend on your network reliability.

Your shopping list for high-quality battery monitoring:

So, what DOES work for keeping track of your battery status? The right solution will help you solve the problems above without dooming you to the pitfalls above.

Whatever battery monitoring system you choose, make sure that it:

1. Monitors the "Big 3" elements of battery health: voltage, temperature, and internal resistance.
2. Provides 7x24x365 protection - without requiring repetitive site visits.
3. Is reasonably priced, but also highly reliable. Look for a manufacturer with a history.
4. Is adaptable to your battery types, whether they're 12-volt, 2-volt, or some other voltage. You should also be able to handle lithium-ion batteries, AGM batteries (Absorbed Glass Mat batteries), or thin-plate-pure-lead batteries.
5. Takes advantage of the opportunity for monitoring efficiency. Sure, you have to monitor your batteries, but what about fuel levels, equipment alarms, door sensors, and everything else? If you pick the right system, you can monitor every important thing within your remote telecommunications facility with one box.

Recent Solution: The BVM ("Battery Voltage Monitor") G1 & G2

These are the considerations I had in mind when I helped the Engineering team here at DPS. We revised our BVM ("Battery Voltage Monitor") system into the G3 model.

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The birth of the BVM was, as the name implies, focused around voltage only. The device had 24 analog inputs for monitoring up to 24 cells. You simply wired leads to each battery in the string. That was great, but what about thermal runaway?

The BVM G2 incorporated temperature monitoring and our newer "D-Wire" sensor technology to support daisy chaining. You'd place one on each battery to get BOTH voltage and temperature readings. The gear is also 100% DPS-manufactured, giving us more control over quality.

This was a big improvement, but the D-Wire bus had limited power for running a lot of sensors. This was fine for 4-battery strings, but 24 batteries became unworkable. Also, the temperature sensor, being in the aluminum sensor chassis, had some moderate lag in detecting temperature spikes.

Solution Example: The Revised "Battery Voltage Monitor G3"

In , I helped DPS Engineering to create a new BVM model. It would address "really serious battery monitoring", which encompasses long-term battery health. You can't simply detect this with voltage and temperature. You need more.

Like any good successor, the BVM G3 added a new measurement: internal resistance.

It sends brief pulses of AC through a battery every few minutes (or even hours). You get an updated reading of how much power is lost to internal resistance. This tells you whether you have internal cells that are starting to fail and short.

The BVM G3 is:

• A system that will perform continuous battery checks on your batteries (2-4 battery strings at typical sites). It shouldn't require site visits and time spent putting on clamps and downloading data. It provides automated continuous battery monitoring with sensors connected directly to each of your batteries. Temperature, voltage, and internal resistance is monitored for each battery.
• Alarm and status reporting to your existing T/Mon LNX or any SNMP manager.
• A monitoring device that is independent of your existing RTUs, but that can also monitor some external equipment and sensors if needed.
• A device that you can easily manage via its built-in web interface.

The choice is yours

You have to determine which battery management device you want to purchase and implement in your network. I've given you a general outline of criteria you can apply when talking to any manufacturer or vendor.

DPS engineers and I designed the BVM G3 to be well-suited to real-world concerns you're likely to face. Only you can make the call.

When Sony introduced the first lithium-ion battery in , they knew of the potential safety risks. A recall of the previously released rechargeable metallic lithium battery was a bleak reminder of the discipline one must exercise when dealing with this high energy-dense battery system.

Pioneering work for the lithium battery began in , but is was not until the early 's when the first non-rechargeable lithium batteries became commercially available. Attempts to develop rechargeable lithium batteries followed in the eighties. These early models were based on metallic lithium and offered very high energy density. However, inherent instabilities of lithium metal, especially during charging, put a damper on the development. The cell had the potential of a thermal run-away. The temperature would quickly rise to the melting point of the metallic lithium and cause a violent reaction. A large quantity of rechargeable lithium batteries had to be recalled in after the pack in a cellular released hot gases and inflicted burns to a man's face.

Because of the inherent instability of lithium metal, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density, the lithium-ion system is safe, providing certain precautions are met when charging and discharging. Today, lithium-ion is one of the most successful and safe battery chemistries available. Two billion cells are produced every year.

Lithium-ion cells with cobalt cathodes hold twice the energy of a nickel-based battery and four-times that of lead acid. Lithium-ion is a low maintenance system, an advantage that most other chemistries cannot claim. There is no memory and the battery does not require scheduled cycling to prolong its life. Nor does lithium-ion have the sulfation problem of lead acid that occurs when the battery is stored without periodic topping charge. Lithium-ion has a low self-discharge and is environmentally friendly. Disposal causes minimal harm.

Long battery runtimes have always been the wish of many consumers. Battery manufacturers responded by packing more active material into a cell and making the electrodes and separator thinner. This enabled a doubling of energy density since lithium-ion was introduced in .

The high energy density comes at a price. Manufacturing methods become more critical the denser the cells become. With a separator thickness of only 20-25µm, any small intrusion of metallic dust particles can have devastating consequences. Appropriate measures will be needed to achieve the mandated safety standard set forth by UL . Whereas a nail penetration test could be tolerated on the older cell with a capacity of 1.35Ah, today's high-density 2.4Ah cell would become a bomb when performing the same test. UL does not require nail penetration. Lithium-ion batteries are nearing their theoretical energy density limit and battery manufacturers are beginning to focus on improving manufacturing methods and increasing safety.

Recall of lithium-ion batteries

With the high usage of lithium-ion in cell phones, digital cameras and laptops, there are bound to be issues. A one-in-200,000 failure rate triggered a recall of almost six million lithium-ion packs used in laptops manufactured by Dell and Apple. Heat related battery failures are taken very seriously and manufacturers chose a conservative approach. The decision to replace the batteries puts the consumer at ease and lawyers at bay. Let's now take a look at what's behind the recall.

Sony Energy Devices (Sony), the maker of the lithium-ion cells in question, says that on rare occasions microscopic metal particles may come into contact with other parts of the battery cell, leading to a short circuit within the cell. Although battery manufacturers strive to minimize the presence of metallic particles, complex assembly techniques make the elimination of all metallic dust nearly impossible.

Figure 1: Lithium-ion battery damages a laptop.
Safety issues are enticing battery manufacturers to change the manufacturing process. According to Sony, contamination of Cu, Al, Fe and Ni particles during the manufacturing process may cause an internal short circuit.

A mild short will only cause an elevated self-discharge. Little heat is generated because the discharging energy is very low. If, however, enough microscopic metal particles converge on one spot, a major electrical short can develop and a sizable current will flow between the positive and negative plates. This causes the temperature to rise, leading to a thermal runaway, also referred to 'venting with flame.'

Lithium-ion cells with cobalt cathodes (same as the recalled laptop batteries) should never rise above 130°C (265°F). At 150°C (302°F) the cell becomes thermally unstable, a condition that can lead to a thermal runaway in which flaming gases are vented.

During a thermal runaway, the high heat of the failing cell can propagate to the next cell, causing it to become thermally unstable as well. In some cases, a chain reaction occurs in which each cell disintegrates at its own timetable. A pack can get destroyed within a few short seconds or linger on for several hours as each cell is consumed one-by-one. To increase safety, packs are fitted with dividers to protect the failing cell from spreading to neighboring cells.

Safety level of lithium-ion systems

There are two basic types of lithium-ion chemistries: cobalt and manganese (spinel). To achieve maximum runtime, cell phones, digital cameras and laptops use cobalt-based lithium-ion. Manganese is the newer of the two chemistries and offers superior thermal stability. It can sustain temperatures of up to 250°C (482°F) before becoming unstable. In addition, manganese has a very low internal resistance and can deliver high current on demand. Increasingly, these batteries are used for power tools and medical devices. Hybrid and electric vehicles will be next.

The drawback of spinel is lower energy density. Typically, a cell made of a pure manganese cathode provides only about half the capacity of cobalt. Cell and laptop users would not be happy if their batteries quit halfway through the expected runtime. To find a workable compromise between high energy density, operational safety and good current delivery, manufacturers of lithium-ion batteries can mix the metals. Typical cathode materials are cobalt, nickel, manganese and iron phosphate.

Let me assure the reader that lithium-ion batteries are safe and heat related failures are rare. The battery manufacturers achieve this high reliability by adding three layers of protection. They are: [1] limiting the amount of active material to achieve a workable equilibrium of energy density and safety; [2] inclusion of various safety mechanisms within the cell; and [3] the addition of an electronic protection circuit in the battery pack.

These protection devices work in the following ways: The PTC device built into the cell acts as a protection to inhibit high current surges; the circuit interrupt device (CID) opens the electrical path if an excessively high charge voltage raises the internal cell pressure to 10 Bar (150 psi); and the safety vent allows a controlled release of gas in the event of a rapid increase in cell pressure. In addition to the mechanical safeguards, the electronic protection circuit external to the cells opens a solid-state switch if the charge voltage of any cell reaches 4.30V. A fuse cuts the current flow if the skin temperature of the cell approaches 90°C (194°F). To prevent the battery from over-discharging, the control circuit cuts off the current path at about 2.50V/cell. In some applications, the higher inherent safety of the spinel system permits the exclusion of the electric circuit. In such a case, the battery relies wholly on the protection devices that are built into the cell.

We need to keep in mind that these safety precautions are only effective if the mode of operation comes from the outside, such as with an electrical short or a faulty charger. Under normal circumstances, a lithium-ion battery will simply power down when a short circuit occurs. If, however, a defect is inherent to the electrochemical cell, such as in contamination caused by microscopic metal particles, this anomaly will go undetected. Nor can the safety circuit stop the disintegration once the cell is in thermal runaway mode. Nothing can stop it once triggered.

What every battery user should know

A major concern arises if static electricity or a faulty charger has destroyed the battery's protection circuit. Such damage can permanently fuse the solid-state switches in an ON position without the user knowing. A battery with a faulty protection circuit may function normally but does not provide protection against abuse.

Another safety issue is cold temperature charging. Consumer grade lithium-ion batteries cannot be charged below 0°C (32°F). Although the packs appear to be charging normally, plating of metallic lithium occurs on the anode while on a sub-freezing charge. The plating is permanent and cannot be removed. If done repeatedly, such damage can compromise the safety of the pack. The battery will become more vulnerable to failure if subjected to impact, crush or high rate charging.

Asia produces many non-brand replacement batteries that are popular with cell users because of low price. Many of these batteries don't provide the same high safety standard as the main brand equivalent. A wise shopper spends a little more and replaces the battery with an approved model. Figure 1 shows a cell that was destroyed while charging in a car. The owner believes that a no-name pack caused the destruction.

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