Frequently Asked Questions about Solid State Relays
1. The relay is not disconnected:
(1) The load current is greater than the rated switching current of the SSR, which will cause a permanent short circuit of the relay. In this case, an SSR with a higher rated current should be used.
(2) Under the ambient temperature of the relay, if the heat dissipation is not good for the current it bears, the output semiconductor device will be damaged. At this time, a larger or more effective heat sink should be used.
(3) The line voltage transient causes the output part of the SSR to break through. At this time, an SSR with a higher rated voltage should be used or an additional transient protection circuit should be provided.
(4) Use a line voltage higher than the rated voltage of the SSR.
2. The SSR is disconnected after the input is cut off:
When the SSR should be disconnected, measure the input voltage. If the measured voltage is lower than the must-release voltage, it indicates that the release voltage of the breaker is too low, and the relay should be replaced. If the measured voltage is higher than the SSR must-release voltage, it is The wiring in front of the SSR input is faulty and must be corrected.
The method of judging the quality of solid state relay
(1) Discrimination of AC and DC solid state relays: Usually, beside the input and output terminals of the DC solid state relay shell, there are marked " ", "-" symbols, and the words "Dc input" and "DC output" are marked . The AC solid state relay can only be marked with " " and "-" symbols on the input end, and the output end has no positive and negative points.
(2) Distinguishment of input terminal and output terminal: Unmarked solid-state relay, multimeter R×10 k files, by measuring the positive and negative resistance values of each pin to distinguish input terminal and output terminal. When the forward resistance of a certain two pins is small and the reverse resistance is infinite, these two pins are input terminals, and the other two pins are output terminals. In a measurement with a small resistance value, the black test lead is connected to the positive input terminal, and the red test lead is connected to the negative input terminal.
If the measured forward and reverse resistances of a certain two pins are both 0, it means that the solid state relay has been broken down and damaged. If the measured forward and reverse resistance values of each pin of the solid state relay are infinite, it means that the solid state relay has been damaged by an open circuit.
Precautions for using solid state relays
1. The resistive load cannot exceed 60% of the rated current.
2. The inductive or capacitive load cannot exceed 40% of the rated current. When controlling the inductive load, the startability of the load must be considered. Try to choose a product with high withstand voltage, because the inductive load has about 6 times the reverse peak voltage.
3. When the solid-state relay is turned on, there is always a voltage drop at both ends, which will generate Joule heat, especially when working with high current. When the current is 10A, a radiator must be installed. When the current is greater than 40A, fan cooling or water cooling is required.
4. Overcurrent and load short circuit may cause permanent failure of SCR internal thyristor, so a fuse or air switch must be installed, and a fuse with a small capacity can be used.
5. Parallel varistors can be used for overvoltage protection, and built-in varistors can also be used according to user requirements.