双金属热开关 : 类型 & 应用

什么是双金属热开关?
双金属热开关使用 双金属片是由两条不同金属的条带组成的条带，这些金属条在加热时以不同的速率膨胀. 它们用于将温度变化转换为机械位移. 它创建了一个圆弧, 像彩虹一样. 随着温度的变化, 金属继续发生不同的反应, 操作热切断开关.

Bimetal thermal switchs are widely used inside heating pads, blankets, medical pads, 电热水壶, and in some other devices where the application demands a cheap temperature controller mechanism.

Inside most home electrical appliances, we can generally find bimetal thermal switchs (temperature Snap Action switches) in two varieties – high voltage (Hi Amp) thermal switchs which directly control the flow of electric current to the load, or low voltage thermal switchs which indirectly control the current flow to the load. Schematic symbols for the common bimetal thermal switchs are shown below.

High voltage (Hi Amp) thermal switchs are rated for the voltage, current and power ratings of the loads they can handle safely. 例如, a thermal switchs rated at 250V and 10A can be used to control a 2500W(max) load.

Low voltage (and Low Amp) thermal switchs are comparatively smaller and cheaper, but they are more sensitive to changes in heat than high voltage thermal switchs. That means since they are only intended to handle the control current and not the load current, low voltage thermal switchs are highly responsive and can provide more precise control than their high voltage counterparts.

A bimetal thermal switchs opens or closes an electric connection at a predefined temperature. Here is the inside view of a bimetal thermal switchs lifted from an old coffee maker machine. See how everything is put together!

The online customized thermal switch factory in China provides the following complete bimetallic thermal switch parameters and selection:

The first is a 10A~60A/250V resistive load disc bimetal thermostat switch from the KSD301 /KSD302 series. operating temperatures ranging from -40°C to 280°C. Some of them have normally-open contacts, while others have normally-closed contacts.

KSD301 series bimetal thermostat thermal switch

Normally closed KSD301 thermal switch

高功放 – High voltage KSD302 bimetal thermal switch

Next is the TO-220 PCB-bimetal disc thermal switch from the JUC-31F series (PCB-bimetal thermal switch ). Currently, JUC-31F 95°C H This is the most common PCB mounted thermal switch with normally-open (close on rise) contacts.

凯斯达-01F/JUC-31F 0°C~130°C PCB mounting thermal switch

KSD-9700 most common and the cheap series thermal switch. consists of dish shape high sensitive bimetallic elemeng,活动接触头,静触头,底板,外壳,耐热铅等. When operation,the bimetallic element is in free state and movable contact-head and static contace-piece are closed and the circuit is on. normally-closed KSD 9700-A 250V 5A 70°C thermal protectors ( KSD-9700.pdf).

高温切断廉价KSD9700双金属热开关

定制17AM-D+PTC热保护器参数及线缆, 并对线束进行处理以添加热熔断器. 17AM-D+PTC热保护器 (德州仪器 KLIXON) 是电流敏感的, 与电机线圈串联的感温保护装置. 保护器根据线圈温度和电机电流而变化.

17是 + PTC overheating and overcurrent bimetal thermal switch

Knowledge of bimetallic strips:
A bimetal switch changes its switching status relative to the temperature. If the temperature is sufficient, the bimetall bends, thereby actuating a snap-action switch. This switch can open or close a circuit and in so doing start or stop a process (e.g. heating, cooling, pumping).

A bimetallic strip or bimetal strip is a strip that consists of two strips of different metals which expand at different rates as they are heated. 它们用于将温度变化转换为机械位移. The different expansions force the flat strip to bend one way if heated, and in the opposite direction if cooled below its initial temperature. The metal with the higher coefficient of thermal expansion is on the outer side of the curve when the strip is heated and on the inner side when cooled.

Bimetallic switches are used as part of the control engineering in the electrical industry, especially in auto-temperature control and temperature -indicating devices and appliances like heating, cooling, and pumping. Bimetallic thermal switches work on the principle that different metals bend at different temperatures. When the set temperature is achieved, one of the metals in the bimetallic switch bends to cut off the circuit and protect the appliance from extreme temperatures.

The TB02 series protector is a thermal switch with small dimensions（Referred to as battery pack thermal protector）, insulating case, high temperature sensitivity and long lifetime, which is widely used in lithium batteries, 灯光, 变形金刚, 电加热器具, and other fields.

最小尺寸电池组热敏开关 TB02

特征:
Snap action type bimetallic disc has the characteristics of high reliability and repeatability.
Small dimension is suitable for appliances which compactly installed upon winding or inside winding.
Steel structure bracket makes performance more stable.
Automatic temperature calibration process makes it has a high precision of temperature control.
The bimetallic disc overflow structure solves the technical difficulty of current transient overload and the temperature response lag.

Custom specifications according to customers’ req thermal switch
A key advantage of this concept is that the thermal switch can be installed in any desired local/remote location as it demands nothing but a simple two-core low-voltage cable for the interconnection. The low-voltage control circuit can then be used to drive an appropriate electromagnetic relay module (or a solid state relay module) to safely deliver power to the isolated high-voltage load, a mighty heater wire for example.

Basically, the circuitry switches on and off at different thresholds, so there is no leaping between one state and the other as the capacitors charges. That worked very reliably, no tweaking of the basic setup required. I have used this on a few Various electrical appliances designs now, and they have always proven very reliable.