Contents
What is zero cross function SSR?
The zero-cross type SSR switches on when the load voltage is close to zero volts. The zero-cross type SSR has a built-in zero-cross circuit, it’s switch on at close to a zero-voltage point of alternating current even if a signal is input to the SSR at not close to the zero-voltage point.
What is the difference between SCR and SSR?
The SCR power control module also provides more accurate control of the process compared to contactors and solid-state relays. The SCR provides much finer control resolution compared to the SSR and electro-mechanical contactor.
Which is better a random fire or a zero crossing SSR?
The Zero-Crossing SSRs seem much more readily available than the Random-Fire kind. The Zero-Crossing SSRs have extra circuitry which “delays” your trigger signal until the NEXT zero-crossing. Otherwise they would fire ANYWHERE, even in the middle of the wave. (Which is what “Random-Fire” means).
How does zero crossing work in a relay?
The zero crossing only refers to when the switch closes (or opens). So when you apply a control voltage, the relay waits until a zero crossing and closes and remains closed. When you remove the control voltage the relay waits until a zero crossing and opens. The delay is only a part of one 60Hz cycle on each end.
Are there SSRs with a lower voltage drop?
There are SSRs that have lower voltage drop by using FETs, but these usually don’t handle much current and are usually more expensive. If you’re not planning to switch often, then perhaps a mechanical relay might be more suitable. These don’t have one nice features of SCR and triac SCRs though, which is to turn off at the current zero-crossing.
How many TRIACs are used in a random SSR?
Some SSRs give trouble with large inductive loads as the current lags the voltage. If your fan is less than a couple of hundred watts you should be OK. Figure 1. Random SSR and zero-cross SSR. The random SSR usually uses two triacs. The first is a small photo-triac.