Q:Why are there two current parameters for current sensing thermal protector?

A:It is a confusing question for some engineers. Actually, for current sensing thermal protectors, there are two current parameters. One is rated current. It is the nominal working current. The other one is tripping off current, also called over-loading current.

For the rated current, for examples, 3A or 5A, it means that the thermal protector can not trip off under this current. It would only cut the circuit off when temperature reaches the pre-set value.

But for the tripping off current, it means that the thermal protector has to trip off very quickly, like 4 to 10 seconds under this current. It is for overload protection purpose. General speaking, the tripping off current is around triple or 4 times of rated current. For example, if the rated current is 3A, the tripping off current should be set at 9A to 15A. It is only a rough estimation. The accurate value depends on the technical requirements of mock-up test and application.

Q: What’s the difference between creep action thermostat and snap action thermostat?

A: According to the action type of contacts, the bimetal thermostat can be divided into creep action and snap action thermostat. General speaking, creep action thermostat can only be used for heating pad or cushion. Our WAA2 series thermostat belongs to creep action type.The function of creep action thermostat is for temperature adjustment, not for heating or over temperature protection. Only USA and Canada accept this kind of temperature controlling device. In Europe, creep action thermostat is not allowed to use. On the contrary, most of bimetal thermostats are snap action. The main purpose is over heat protection. Our KW model is snap action.

Q:Why does the smaller size thermal protector have higher price?

A:Customers like to ask the question:” Why does the smaller size thermal protector have higher price?” It sounds that it does not make sense. In fact, there are some reasons:

1. For the small size thermal protector, all parts have to be more precise. It means that we need to use better manufacturing machineries. The equipment cost would be higher.

2. The yield rate of smaller size thermal protector is lower than common size. So, the final cost would be higher.

3. The material of small size thermal protector is different also. The material has to be more reliable. Accordingly, the price of raw material is higher.

4. For the small size thermal protector, we have to use different machineries and manufacturing process. Both the manufacturing cost and labor cost are much higher than common size.

Due to the above reasons, the final cost of smaller size thermal protector is higher than common size.

Q:Why is the thermal switch with lower temperature but higher price?

A:There are three reasons for thermal switch with lower temperature but higher price:

1. Thermal switches with lower temperature have to use some special materials, like bimetal strip and contacts. These materials have higher cost and better quality level;

2. In the process of manufacturing, both production and testing equipment for lower temperature thermal switches are different. The equipment cost of low temperature is higher than common temperature ratings.

3. The production yield of low temperature thermal switches is lower than standard temperature rating also. It would make the final cost is much higher.

Q:What’s the lowest action temperature of your bimetal thermostat?

A: The lowest action temperature of our bimetal thermostat is 0C. It is creep action type and the relevant model number is 17AME-H. The contact making type can be normally closed or normally open. The main function of this thermostat is to remain the temperature inside of a narrow range. For example, OFF at 5C, ON at 3C or 4C. It is widely used to temperature control device or PCB control system. The life endurance can be 100,000 cycles also. The terminal ends of this bimetal thermostat can be at the same direction or opposite direction. The insulation paper has Nomex or Nitto for your option.

The shortage of this bimetal thermostat is the current. The max working current can’t exceed 5A, normally less than 3A. Since the current is too small, we sometimes to use gilded contact to avoid contacts oxidization.

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