by GTE Government Systems
Mid-Atlantic Regional Support Facility
Chesapeake, Va. USA
I. Summary *
Engineering technical assistance was provided to NISE-EAST Detachment, Norfolk, VA for the purpose of developing a battery maintenance program that will cause improved performance of Nickel-Cadmium (NiCd) batteries used by the Navy, specifically those batteries used in areas considered critical for safety of equipment or personnel.
Historically new batteries have, after just a few months of service failed to provide their rated ampere-hour capacity. This "lowered capacity" is caused by the effects of crystalline formation, we call it "MEMORY". Crystalline formation can cause battery self-discharge and, if severe enough cause a shorted cell, thus rendering the battery useless.
Recent data from batteries tested on three U.S. Navy ships (referred to as Ship A, Ship B and Ship C), plus the NiCd performance history, prompted the need for development of a battery maintenance program. Eleven of twenty-two batteries tested on U.S. Navy Ship A had capacities below 10%. These batteries were removed from the chargers approximately eighteen hours prior to testing. Use of radios with these batteries could have been detrimental to the ship and its crew had an emergency occurred.
Studies have shown a marked difference in the number of batteries requiring replacement when using charging only, exercising only, or deep discharge reconditioning only as the charge maintenance method.
Based on these studies and replacing batteries when they reach 80% capacity or less, would, at $60.00 per battery pack cost:
U.S. Navy Ship A, with approximately 1500 batteries on board
U.S. Navy ship B, with approximately 600 batteries on board
U.S. Navy Ship C, with approximately 500 batteries on board. Maintenance Method Annual % of Batteries
With these costs in mind it is imperative that a battery maintenance program be incorporated, specifically one that incorporates Deep-Discharge Reconditioning.
III. Battery Analyzer Requirements
A. For proper NiCd battery maintenance, the Battery Analyzer must be able to perform the following:
1.Evaluate the battery based on system-stored battery-specific parameters.
2.Employ reverse load pulse charging for cooler battery charging and less gas build-up.
3.Employ multiple charge-termination methods for safe charge termination.
4.Prime new batteries to exercise and match cells.
5.Automatically recondition batteries that fail to reach a user pre-determined capacity.
6.Serve multiple battery technologies or chemistries.
7.Identify shorted or mismatched cells.
8.Identify soft cells (cells that rise in voltage too fast during charge, indicating damaged electrolyte.
9.Simulate user-defined discharge conditions.
10.Have a computer interface for manipulation, reporting and archiving of battery condition data.
11.Have a printer interface for printing of service reports and battery service labels.
12.Provide capacity reading as a percentage of rated capacity.
13.Have pass-fail indicators for non-technical users.
14.Be capable of providing a programmable trickle-charge rate that is between 1% and 10% of the rated battery capacity.
15.Employ password protection to prevent unauthorized program entries.
NOTES: 1.Temperature sensors in are recommended if the batteries are being serviced outside of their recommended range of 5 degrees Celsius to 45 degrees Celsius (41 to 113 degrees Fahrenheit). If the battery is being serviced at room temperature, sensing of the battery temperature (by the CADEX unit) is not required. The sensor inhibits fast-charge when the battery is outside its operational temperature range of 5 degrees Celsius to 45 degrees Celsius. NiCd batteries should not be serviced if the temperature is above 45 degrees Celsius (113 degrees Fahrenheit)
2.The "Reverse Load Charge Method" is the recommended method of charging a NiCd battery. This method intersperses discharge currents between the charge pulses. This push-pull action promotes the recombination of gases generated during charge. Best results are achieved when a 9% reverse charge current is used. For example, a 1700mA battery should be charged with a reverse load current of 153mA.
3.The recommended trickle-charge settings on batteries with a rating of 1800mAh and below is between 5% and 10% of the rated capacity. For larger batteries a lower percentage is used. A 5% trickle-charge at 20% Celsius (68 degrees Fahrenheit) compensates for NiCd battery self-discharge, 10% keeps the NiCd fully charged.
A. Batteries that are to be placed into a maintenance program must be analyzed and/or under-go a recondition discharge to remove crystallization (memory), establish the capacity of the batteries, and weed out those batteries that are no longer useful. A separate test for self-discharge will have to be made and those batteries that have developed excessive self-discharge must be replaced as well.
B. Once the batteries have been restored to capacity and the bad batteries (poor capacity or high self-discharge batteries) weeded out, they need to be serialized and then analyzed.
1.Those batteries that are used daily and charged periodically should be analyzed, at a minimum, every 90 days. This will cycle (and if needed recondition) the battery and provide a record of battery capacity.
2.Those batteries that are charged continuously and used periodically (i.e. the Damage Control Locker batteries) should be analyzed, at a minimum, every 30 days. This will cycle the battery and provide a record of battery capacity.
C. Records of battery capacity must be maintained, by battery serial number, to ensure that batteries with capacities below 90% are not installed on radios to be used in areas considered critical to safety of personnel or equipment (i.e., Flight Deck or Damage Control Lockers). Batteries with capacities as low as 50% may be used for general communications but not for critical communications. The only way to ensure this is to maintain a database of the battery status by serial number.
NOTES: 1.Analyzed means, analyzing the battery based on system-stored battery-specific parameters to determine capacity.
2.Reconditioning is a slow deep discharge applied below the end-of-discharge voltage threshold. During this gradual depletion of the remaining energy, the crystalline build-up on the cell plates dissolves and the NiCd battery is commonly restored. Typically the End-of-Recondition voltage is 0.2 - 0.4 volts per cell.
3.There are two types of memory:
a. Crystalline Formation (what we call memory), caused by lack of proper exercise. The active material (chemicals) grow crystalline structures which limit the capacity of the battery. b. Cyclic Memory, meaning the NiCd remembers how much discharge was required on previous discharges and will not discharge below that level . With the modern NiCd technology this form of memory is almost immeasurable. 4.Self-discharge, is caused by the current leakage across the plates of the thin insulator isolating the positive and negative cell plates. A NiCd typically loses 10% of its charge within the first 24 hours after being charged, after which it loses approximately 10% per month. A problem arises when self-discharge causes the battery to drain within a day. High self-discharge is caused by excessive crystallization that punctures the thin insulator. Once punctured, it cannot be repaired, instead the battery must be replaced. The method for determining self-discharge is to analyze the battery, let the battery sit for 24 hours, and then analyze it again to determine what charge the battery retained after the 24 hour period. Currently no battery analyzer performs this function automatically. (Editor's note: Actually, the CADEX C3000, C4000 and C7000 can all be custom-programmed to perform self-discharge tests automatically.)
V. Analyzer Comparison Study
The following provides a comparison of the specifications/capabilities of some of the analyzers/optimizers on the market.
1.The MOTOROLA Conditioner can analyze, condition, and charge a battery. Motorola's condition mode cycles the battery through three DC charge/discharge/charge cycles. It does not "Recondition" a battery. The Motorola conditioner is made by HME.
2.The HME Conditioner can analyze, condition and charge a battery. HME's condition mode cycles the battery through three DC charge/discharge/charge cycles. It does not "Recondition" a battery.
3.The ALEXANDER Optimizer can analyze, condition, and charge a battery. Alexander's condition mode cycles the battery through three charge/discharge/charge cycles. It does not "Recondition" a battery.
4.The CHRISTIE Optimizer can analyze, condition and charge a battery. Christie's condition mode cycles the battery through three charge/discharge/charge cycles. CHRISTIE does use a "Reverse Pulse Current" charge mode. It does not "Recondition" a battery.
5.The CADEX Analyzer can analyze, recondition, and charge a battery. CADEX's recondition mode is a deep-discharge applied below the end-of-discharge voltage. It does "Recondition" a battery. The CADEX analyzer is the only analyzer, discovered to date, that meets all battery analyzer requirements listed in paragraph III.
NOTE: The DC Charge Method places a DC voltage on the battery until the battery is charged at which time the charger shifts to a trickle charge. Typical charge currents are 200 - 500 mA and typical trickle charge currents are 50mA.
VI. Battery Maintenance Management
The current industry battery-management standard is to analyze all batteries every 30 days. For a ship the size of U.S. Navy Ship A with 1500 batteries on board, this is almost unmanageable. For example:
Based on a monthly maintenance schedule of two batches of batteries per unit per month, an analyzer analyzing four batteries every 4-8 hours can maintain 160 batteries per month. This translates to 10 four-position units if each of Ship A's batteries is to be analyzed every month. This is not feasible.
For a battery maintenance program to work effectively, the batteries must be divided into critical and non-critical requirements.
Critical batteries will be for personnel whose radio's must provide reliable communications because they are in areas where the chance of personnel injury or equipment damage is high, such as for Damage Control and Flight Deck operations. They must be >90% certain that the battery on their radios will provide the advertised ampere-hour life. To ensure a 90% ampere-hour life the battery must be analyzed each month.
Non-critical batteries will be for personnel who are not likely to suffer personal injury or cause equipment damage if their radio quits functioning because of a dead battery.
Using the critical-non-critical criteria and U.S. Navy Ship A's 1500 batteries for example: Approximately 160 batteries then are considered critical and need to be analyzed each month. The remaining 1340 batteries for non-critical communications can be analyzed every three months.
Figuring, worst-case scenario, it will take about eight hours to recondition a battery. This means that a four-position unit can service eight batteries in a sixteen-hour (two-shift) day, or forty batteries in a week, or 160 batteries in a month.
This works out to 607 batteries per month (160 + 1340/3) or a need for four, four-position analyzers.
VII. The Battery Maintenance Program
A.Serialize all batteries
B.Analyze and/or recondition discharge all batteries to establish the initial capacity of the batteries, and weed out the batteries that are no longer useful.
C.Test each battery for self-discharge and discard those batteries that have developed excessive self discharge.
D.Identify via serial number which batteries will be critical and non-critical.
E.Establish recall list for the critical and non-critical batteries, keeping in mind that only eight (8) batteries can be serviced per analyzer per day (based on the maximum 8 - 10 hour recondition cycle) on a four-position analyzer.
NOTE: Accomplishing steps B and C will require approximately five and one-half months using four-position analyzers based on the information above.