A Guide to Healthy Batteries

A Guide to Healthy Batteries

Nickel Cadmium. (NiCd) batteries offer an excellent way to power the various portable instruments made by Diagnostic Instruments. Since these batteries are re-chargeable, there are a number of useful tips to follow in order to achieve maximum performance. A number of ideas on how to obtain healthy batteries are proposed.

Natural Discharge

When NiCd batteries are left on the shelf, whether inside or outside the instrument, then they naturally discharge the energy that is inside. The discharge rate depends on how many cells in the battery pack and also the capacity of each cell so is difficult to quantify. However typically leaving the battery for one month on the shelf will cause discharge.

This phenomena is not uncommon particularly among Lead Acid batteries. A good analogy is to consider how difficult it would be to start a motor car if it had been left in the garage for one month.

If batteries have been left for a long time, then a good charge/discharge cycle (three times) is recommended as described below.

Memory Effect

NiCd batteries exhibit a phenomena known as the memory effect. The best way to explain this is to consider a battery (or instrument) that normally can operate for 8 hours.

If this battery is used for one hour then given a full overnight (12 hour) charge it will be topped up. If the operator continues to work in this way, each time the instrument is used, then the batteries start to believe they are only required to work for one hour. Any more operating time the operator tries to get is often in vain since the batteries REMEMBER they only have to work for one hour.

The above problem can be cured by going through a charge/discharge cycle three times.

Charge/Discharge Cycle

To cure problems such as memory effect and long time storage, a three times charge discharge cycle is suggested. To do this the following steps are recommended.

1. Switch on instrument and set Time Out to OFF. (This means the instrument will remain ON without shutting down after a few minutes if no key is pressed. Note that the PL33 has Time Out permanently set OFF).

2. Discharge Instrument by keeping it powered on. (Note that no charger is connected at this point).

3. After a certain time the battery voltage drops to a level where the instrument will switch off. When this happens, connect the charger and charge for 12 - 14 hours.

4. After the charge cycle return to step 1) and repeat the whole process 3 times.

Each time the above cycle is made the operating life should increase as shown below until it returns to the expected operating time.

Good Operating Practice

The people who get the best performance from their NiCd batteries are those who after operation, they fully discharge then charge overnight. Such a practice may be extreme if in the first instance the instrument was used for 15 minutes. In these cases, discharge may not be suitable but the operator must remember not to charge until the BAT warning appears. This avoids the memory effect as described above.

For people who use their instrument routinely (e.g. as part of a predictive maintenance program) then a full discharge (after collection and upload of data) may be the best solution.

Finally, it is worth noting that NiCd batteries do have a finite life span. They become worn our after frequent use and may need replaced. The typical life span is 2 years but this may be longer or shorter depending, on how instrument is used.

This article is provided courtesy of Diagnostic Instruments

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