A solid state relay don’t switch off the same way as a relay with moving parts in.
When a ‘normal’ relay is switched off, it is switched off, and absolutely nothing going through it.
But when a solid state relay is off, it is still a bit on, but with such a high resistance that most things wont be able to do anything. But if you connect a power saving bulb, neon light, or something like that, they might just turn their brightness down when you switch them off.
SSR’s would be nice, but (yes, there must be a but) they seem expensive. I checked ebay, and they’re $8 each… Doesn’t seem like a lot, until you realise that I’ll use it 1 moth of the year, and that I need over 10.
If you know of a cheaper source for ones rated at 3~ and 15~ amps, please share.
SSRs are nice and I have used a few to good effect. But as you have seen they tend to be a little costly compaired to surplus relays. Once in a while I’ve seen some $2-3 surplus ones but they tend to have one amp ratings or so. Also something that many miss is that to use a SSR at anywhere near full current ratings requires that you mount it to a substantial heat sink, just like with large power transistors. This adds size and costs to projects and makes the old elecromechanical relay worth looking at again.
Well I tend to like All-electronics and electronics goldmine. These tend to be surplus or new old stock as the prices are below normal retail, however they may not be available the next time you look to buy a specific model.