In the battery system industry, some companies provide charger and battery systems to smaller, mission-critical applications; for some years, it has been clear that reducing the impact of battery failure is the best way to increase the user’s overall system reliability. In contrast to power electronics that can achieve MTBF in the range of 1 million hours, all VRLA batteries will fail between “now” and perhaps a little more than a decade. Giving users advance warning of an event of this certainty ought to be standard procedure.

We perceived a shortage of battery assessment solutions for the types of products our customers use. We believed we could remedy some of these shortcomings by embedding a battery assessment function in a microprocessor controlled battery charging system for these reasons:

1. At AC powered sites a charger (or UPS rectifier) is always supplied with the battery.
2. Chargers contain the right sort of electronic hardware (e.g. power handling capability, accurate voltage and current metering) to implement a battery monitor.
3. Chargers/DC UPS typically contain alarms. Adding one more (battery failure) alarm makes no demand on the user to change his existing remote monitoring procedures.
4. The battery charger controls DC bus voltage. This is significant because the charger’s output can be changed when desired to cause a change in behavior of the battery

Choice of Battery Assessment Method:

Two INTELEC papers from the ‘90s discuss the battery failure predictive capability, and limitations, of a technique called “battery middle point voltage comparison”. This technique continuously compares the voltage of each half of the battery to the other, and sets an alarm if the deviation exceeds a predetermined value. The principle of operation is that voltage drop in healthy cells tracks the others during discharge. In contrast, weak cells show early, and faster voltage decay. A weak cell would create an imbalance between strings, activating the failure alarm.

Glad, Waltari and Suntio determined that demonstrating a battery can deliver some useful capacity by detecting catastrophic failures is a lower cost, but still useful alternative to attempting to prove the battery can deliver its full-rated run time. The ability to detect catastrophic failure gives users the ability to avoid system downtime if they act before their next AC outage. Although not perfect, this function is an enormous advancement for users with no former battery assessment capability!

Our design team determined that demonstrating the battery can deliver useful capacity was a reasonable performance target for a charger-based battery heath assessor. For the sake of simplicity and cost, we chose to ignore the question of whether the battery could deliver its full rated capacity. Although the middle point comparison scheme has limitations (i.e. useful information is generally available only during discharge), we chose to implement it for the following reasons:

1. The technique’s performance characteristics and shortcomings are documented.
2. It is inexpensive to implement: the charger already includes voltage and current measuring instruments of the accuracy required for battery assessment.
3. The charger control system can be easily programmed to cause discharges from time to time while remaining at a high enough voltage to safely power the load should the battery fail. This eliminates risk of dropped loads during testing.
4. Middle point voltage measurement detects bad cells earlier than could a simple gross load test without middle point voltage measurement.

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Conclusion:

EverExceed has vast experience when it comes to battery solutions, and we are satisfying our partners' and customers’ pain points with the most efficient and precise state of art battery packs consistently. If you have any requirements or any kind of query regarding the battery solutions, feel free to communicate with our dedicated team at any time at marketing@everexceed.com