08-23-2016, 06:11 AM
(This post was last modified: 08-23-2016, 07:16 PM by pfeerick.
Edit Reason: typo
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(08-22-2016, 10:11 PM)Boring Wrote: Do you also need a diode when using a solid state relay?
Solid state relays (SSRs) do not need diodes as they do not kick back (EMF) when triggered. Unlike electromechanical (traditional) relays, they don't use a coil/electromagnet to 'switch' - hence the name 'solid state'. Instead they use generally use SCRs or TRIACs for for AC rated SSRs, or MOSFETS for DC rated SSRs. J
Just like with cheap relay boards like this one, they are have an optically isolated control signal, meaning you don't have to worry about feedback (so no diodes for the control signal, although one is still needed on the relay board) or some catastrophic failure which somehow connects the high voltage (typically your AC mains) to the low side (your control board - pine64 in this case)... killing both the board, and potentially you if touching it when it goes bang.
SSRs are better than electromechanical relays in that they are silent, can switch on and off faster, and because there are no moving parts, can last a lot longer. Only real gotcha with SSRs is that there are AC and DC ones - unlike traditional relays you can't use them for both. Plus with low loads (think a 3W led lamp) they don't always switch off properly... there is some leakage current when they are in their off state. But that may be becoming less of an issue with better manufacture techniques.