Application Advantage Of PTC In Small Household Appliances
- Oct 29, 2018 -

   In the soybean milk maker, blender, such as egg mixer in the small home appliance, to avoid a "tough" big motor locked-rotor and burned caused by design engineers usually design temperature or over-current protection measures, the commonly used are: 1 time over-current protection, recoverable temperature protection (also called bimetallic thermostat), now also use PTC do locked-rotor protection.

   When motor blocked in turn, flows through the armature current will be normal working current for several times, usually can achieve at least 4 ~ 5 times or more, such a large current flows through the motor armature, will cause the motor temperature rise sharply, lead to a significant reduction in the electrical insulation performance, finally cause the enameled wire insulation layer of the stator or rotor winding to melt, cause electrical short circuit burning and other dangerous phenomenon.

   Because the motor is started, in order to overcome the friction torque, moment of working current is big, and completion of launch, in the absence of blocked in turn, working current is a constant value, because once the fuse in its 2 times rated current, quickly action, expression is burn out, open circuit, the motor start failure, so the early use of one sex as a motor over-current protection, 1 to overcome the shortcomings of insurance, usually choose one of the fuse will be greater than the rated current of the motor's normal working current, so while avoiding the motor start the instantaneous error protection problems,However, if the motor is blocked or overheating, the protection will not be timely, affecting the protection effect.

   If choose bimetal thermostat as motor blocked or overheating protection, the impact of the moment motor start current before the heat of the engine does not translate into motor, bimetallic thermostat will not action, although can effectively avoid to choose 1 times the disadvantages of the fuse, but the installation position of bimetal thermostat is very exquisite, need to the thermostat clingy or exciting winding of the stator of the motor, otherwise, if the motor is blocked in turn, although the armature temperature is higher than the set value, but because of the heat conduction, not in time or the quantity of heat conduction to the thermostat is not enough, not enough to cause the thermostat action, will lead to protective effect.Bimetallic thermostat as locked-rotor protection of small home appliance, there is a problem, is that if the temperature controller action, cut off the motor power supply, electric opportunity to stop at the moment, so no longer fever, the overall heat loss, as the motor temperature controller will automatically restore conduction, the motor will rotate again, if at the moment the user is just in the cleaning blade, so automatic recovery rotating blades, will lead to users of the danger.

   If use PTC as locked-rotor protection of motor, will effectively avoid the above problems, first of all, PTC as recoverable fuse of polymer materials, internal depend on joule's law Q = 2 irjt action, I see its internal heat and is proportional to the square of the flow of electric current, when the current is added, internal heat to the square of the current relationship has increased dramatically;The high current of the motor at the moment of starting, because the concentrated heat is not enough to cause PTC action, so there will be no wrong protection.Once the motor is blocked, since the current is several times the normal working current, PTC can start protection as long as the current flowing through is two times the normal working current.Power protection, need human intervention, the PTC heat dissipation can be restored to the factory after low resistance state, if not to cut off the current, the PTC will always have a small residual current flows through the PTC for a high resistance, even at this very moment users are electric cleaning mixer blade, also ensure that the motor does not rotate, thus protecting the personal safety of users.

   Because PTC is not polarized, it is only required to be connected in the load loop, free from space limitations, and extremely flexible and convenient to install. Therefore, it has been recognized by more and more customers.