Aoyi Variable SSR Automotive Solid State Relay SSR-25DV Control Voltage

Resistive load:

The simplest application for SSR is invariable resistive load. As long as the rated steady-state current and breaking voltage of the circuit are within the allowable range of SSR, the relay could work reliably.

Lamp Load:

Incandescent lamp, which is although basically belong to resistive load, also has some special problems.This is because that the resistance of cold tungsten filament is about 1/10 of the one of hot tungsten filament, there will be a very high start current.Therefore, the start current must be limited within the endurable range stipulated by solid state relay.

Capacity Load:

Although the capacity load is not so common.it is applied sometimes.Take particular care for capacity load of low impedance, and do not exceed di/dt of SSR.if there is no extra limiting impedance, capactive load di/dt could reach near infinite during charging, it is a very useful way to limit capacitive load di/dt by zero-voltage conduction. Pay attention to the safety range of maximum blocking voltage during SSR using, it will result in a quite destructive di/dt value when it discharges near peak line voltage, which will easily make the load conduction, so transient voltage of capacitvie load must be limited. For large capacitive load, it is very necessary to limit the di/dt within the stipulated value by series circuit impedance, which can protect the SSR suffering accidental and unavoidable high transient voltage

Inductive Load:

Although AC SSR is cut off during zero current, there is still problem due to other phenomenon. On the moment of zero current, SSR will "change over"(reverse current direction). SSR does not make conduction on the moment of reverse, and all of the transient line voltage is bridged over on the connection terminal, which produces a high dv/dt (voltage variation velocity) capable to make the SSR conduction immediately and "lock up"  state appear without release. Most AC solid state relay has RC for enhance of resistance performance to dv/dt, there will be very high counter-electromotive force when DC inductive load is open, and the DC SSR can control inductive load reliably by adding freewheeling diode in the two terminals of the load

Transformer load:

When SSR is used to control primary load of transformer, the characteristic of secondary load should be examined, as the primary load can be made as one part of effective load of SSR, meanwhile, the transient voltage of secondary load circuit is transferred and applied to SSR. According to magnetic flux condition during transformer breaking, there may be a special problem, namely, the transformer may be saturated in the first half cycle of consecutive voltage application, this saturation phenomenon may cause a very high current(10 to 100 times of rated primary current) applied on SSR, which exceeds the surging value of half cycle. In such condition, compared to zero-voltage conduction SSR, random conduction SSR has stronger life force, as it generally required tat the transformer should only bear one part of first half cycle voltage, by contraries, zero-voltage conduction SSR usually closes in zero-voltage point (starting point of half cycle), so that the SSR must endure the worst condition, namely,saturated current.There is a big differences of severity degree for transformer's saturated current, and it is mainly subject to magnetic material of transformer, saturated primary impedance, circuit impedance, etc.