Laptop battery Safety circuits
A modern laptop battery is a delicate device that requires protection against damage. The most common protection is a fuse that opens if there is a too onerous. Some backups will lead to a permanent opening for the battery disable, for example if the fuse wire is blown. Other safety devices are resettable. The polyswitch ™ is such a resettable fuse. Incorporated into the current path of the battery, this device is a high impedance at too high a burden. The polyswitch ™ returns to its normal function as soon as the situation returns to normal.
Batteries in an explosive environment must be explosion proof. Hazardous environment includes oil refineries, mines, grain elevators and fuel stations at airports. Such zones are predestined for the use of wireless communications and mobile computing. Non-explosive Toshiba PA3399U-1BRS to prevent too great heat and may cause electric sparks with defective equipment. Due to the strict licensing requirements, the cost of battery explosion two are three times higher than for standard batteries.
Another battery that provides the highest protection devices is the lithium-ion battery. This is done to provide security in all circumstances, because it is in the hands of a wide audience. Typically, a field-effect transistor (FET) will be opened if the charging voltage is reached from any cell 4.30V. A separate fuse opens when the cell temperature reaches 90 ° C. In addition, a switch will interrupt permanently in each Toshiba PA3451U-1BRS cell of the charge current when the pressure safety threshold has been exceeded the value of about 10bar (150 psi). To protect the battery against overload, the load path is interrupted by the fuse circuit at approximately 2.50 V / cell. Longer storage at voltages of 1.5 volts per cell and deep damage to the lithium-ion battery can, and create security problems when trying to recharge the battery.
Each parallel string of cells in a lithium-ion battery requires an independent voltage monitor. The more cells are connected in series, the more complex the security posture. Four Toshiba PA3465U-1BRS cells in series, the practical limit for commercial applications.
The internal protection circuitry shall be designed so that the lowest resistance is built into the load path. The circuit in a Zellulartelefonbatterie consists of two FET switches in series. A FET is responsible for the upper, the other FET for the lower voltage switching threshold. The joint resistance of the two FETs is idle 50-100 milliohms (mW). This virtually doubles the internal resistance of the Toshiba PA3107U-1BRS battery.
A critical problem arises if static electricity or a faulty charger destroyed the protective circuit of the battery. This can lead to permanent ON state of the circuit breaker, without which the operator knows anything about it. A battery with a faulty protection circuit may function normally, but offers no further protection. If a charge is about the safety threshold, eg by a defective charger, a leakage of gas made with inflammation. Such a situation must be avoided at all costs. Such a Toshiba PA3331U-1BRS battery to close shortly, can lead to an explosion.
Small lithium-ion batteries containing magnesium chemicals that contain one or two cells may include a fuse as protection. Magnesium is more tolerant than cobalt, and these cells are regarded as safe when they are small.
Although less expensive, the absence of a protection circuit brings a new problem. Zellulartelefonanwender we'll have access to Toshiba PA3450U-1BRS chargers that rely on the protection circuit to stop the load. Without a protective circuit, the cell voltage will rise too much and thus damaging the battery. Too much heat, even the swelling may be the result. The use of the battery and the charger should be halted when a lithium-ion battery is hot.
To ensure safety, manufacturers sell lithium Toshiba PA3534U-1BRS batteries, not separately, but always assembled into a battery, fully integrated with the safety circuit. The circuit is often the object of a special examination before the producer cells, and circuitry for assembly at liberty. Although there were several incidents involving leaks and infections, should the lithium-ion batteries are known to be safe.