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Detection and Removal of internal Short Circuits from Plante Cells in Containers

Short circuit in lead acid cells are caused by any conductive material becoming lodged between two internal elements with opposite polarity.

Detection of short circuits in a cell is facilitated by noting:

• The colour of the positive and negative plates
• The voltage of the cell
• The relative density of electrolyte in a cell

If a cell develops a “short� the plates will show a visable deterioration in colour. Healthy positive plates are normally chocolate brown to black whilst negative plates are light grey.

The colour of the positive plates in a cell with “shorts� may range from sandy to mid- brown, while negative plates will have changed to dark grey.

The cell voltage and relative density of an affected cell will be lower than other cells in a battery. The best indication of a “short� is a progressive fall in the relative density when compared at intervals with other cells in the battery.

Before trying to remove a “short�, take the following precautions:

If possible, isolate the battery so that the affected cell or cells can be removed from circuit. Alternatively, if it is necessary to remove affected cells without breaking the supply from the battery, this can be done after connecting a number of cells of similar capacity in parallel across the affected section of the battery.

Remove any inflammable gas which may have accumulated under the cell lid during changing. To do this, remove the vent plugs, insert a small bore flexible rubber or plastic tube into the cell and blow steadily into the cell for two minutes.

Wear safety goggles and PVC gloves for protection against acid spillage.

The location and severity of the “short� will determine the method to be used for its removal:

If the material causing the “short� is small and clearly visible it may be possible to dislodge it into the sediment space below the plates merely by rocking or shaking the cell. Another method is to use a hydrometer and, with a pumping action, draw in electrolyte and expel it against the material to dislodge it.

If this falls, a non-conductive probe can be inserted through the hole and gently guided down between the plates and separators to dislodge the material. If the probe is of metal it should be completely covered with insulating material. Single-core PVC covered copper wire or PVC covered coil spring curtain wire are useful, but any exposed tip should be covered.

Once the problem has been remedied, the cell should be given a thorough freshening charge to ensure that it is once again in a fully charged condition before being put into the circuit. This charge should be at the finishing rate ( seven percent of the normal 10 hour capacity of the cell ) and should be continued until constant relative density is achieved.

Provided all “shorts� have been eliminated the RD reading should be higher than the previous readings when there was still a problem. If the gravity is outside the range 1.205 to 1.215 at 25c it should be adjusted, making sure that the electrolyte level is correct.