Many applications require a battery for use in hazardous areas and for the batteries and /or equipment to be intrinsically safe. Univercell are capable of making these batteries to detailed designs approved by the customer and the various external approval bodies such as BASEFA and SIRA.
These designs often include a number of technical features.
Resistors are used to limit maximum current on discharge.
Thermistors are used for thermal sensing to switch off charge when the temperature rises. Thermistors can be NTC (negative temperature coefficient) or PTC (positive
temperature coefficient) and are selected to be compatible with the charging circuit.
Polyswitches are resettable devices to limit the current and the polyswitch goes high resistance when current limit is exceeded (eg in a short circuit situation). The polyswitch resets itself when the
fault condition is removed.
Thermal switches are used to switch the battery off completely if a given temperature is exceeded and the switch can reset when the temperature returns to normal.
Fuses are a third level of safety that switches the battery off completely in a fault condition.
The fuse can be thermal (tripping at high temperature) or current limiting.
Intrinsically safe batteries often require specified insulation between positive and negative terminals or specified insulation thickness on wires or between components in the battery.
The battery may need to be filled with epoxy resin or similar material with particular characteristics such as flameproof qualities. These designs include provision for maintaining venting of the cells.
In all intrinsically safe applications Univercell will ensure that the agreed designs are strictly followed. Drawings are marked with the details of the approval and include a comment that no changes are permitted without reference to the customer.