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Educational Articles
Extending the Life of…
Batteries
By Scott Bernard
Conditioning Extends Battery Life and Reliability
It is well known that frequent and/or repetitive charge/discharge cycles produce an apparent inability in the battery to provide more than a portion of its normal capacity beyond a certain discharge level. This means if you do not use-up the full charge on a battery before you recharge it, you can build-up a memory wall at that point. So in future use of that battery, it will fail at that wall.
This is where recycling machines come into play. LSC sells one of the best units on the market, a unit from URDC. The following is from an article by William Todd, Product Manager at URDC Measurements. The article is entitled “Why Battery Conditioning Extends the Life of NiCads.”
Since the time they were first noted, the memory effect and the deep discharge cure have become two of the best-known attributes of NiCad batteries. Because NiCads have become so popular for use with portable radios, countless radio technicians have tried various methods of curing battery memory, and have freely shared their methods with each other and with non-technical radio users.
Some commonly used methods include forced discharge across a passive resistive load, such as a light bulb or large resistor, and forced discharge in the radio itself by turning up the squelch control and leaving the radio turned on for a long period of time.
It is also possible to reduce dendritic short circuits by discharging a large capacitor once or twice through a battery. All of these techniques have serious shortcomings, however, due to lack of precise control, and may cause more harm than good by driving cells into reverse polarity or damaging the plate separator.
Remember that it is harmful for a multi-cell battery to be discharged at too low a level because of the danger of cell polarity reversal. For this reason, manufactured discharge equipment all offer an automatic discharge cut-off, accomplished either by a timer or by sensing a predetermined voltage level.
Since the deep discharge itself may not always have the desired effect of restoring battery capacity, some direct measurement of actual capacity is also important. Incorporating the two features of discharge cut-off and capacity measurement into a single machine has resulted in the modern battery conditioning equipment now available.
What happens to a battery when it is processed by one of these machines? Generally, it goes something like this:
The battery is connected to the machine, given a top-off charge, and then a deep discharge. The discharge parameters are accumulated and displayed, the battery is recharged, and the process is repeated on another battery. Not all machines provide the initial top-off charge.
Connection is made by placing the battery in a receptacle, by clamping to a set of contacts, or by lead wires and connectors. The charge is controlled either by sensing battery temperature, detecting peak battery voltage, or measuring the rate of charge of battery voltage.
Charge current may be straight DC, rectified AC, or pulsed. A pulsed charge is best, since it has the effect of reducing the size of the dendrites over and above what the deep discharge can accomplish. Discharge is controlled by elapsed time or by battery voltage. Discharge parameters may be displayed in terms of time, current, or percent of specified capacity.
As with so many other things, it is easier to prevent a battery from going bad than to repair one which has failed. That is why it is recommended that batteries receive periodic, scheduled discharge treatments beginning when they are new. This way, discharge conditioning will correct minor problems before they are noticeable, as well as provide a complete record of battery history.
To put a new battery into service, first give it three complete charge/discharge/charge cycles to eliminate the passivation layer and provide an adequate first working charge. Thereafter, give the battery a complete charge/discharge/charge cycle at monthly intervals and record the discharge parameters.
The results of this type of program will extend average battery service life, pinpoint weak batteries, identify faulty charging equipment, and help people learn why not to inadvertently mistreat batteries. Even so, no battery will last forever. Plate separators will eventually break down, cases will break if dropped, and minute physical deterioration will eventually add up to failure. But an honest effort in this area can have important and beneficial results.
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