kolektiv
Member
Hi folks,
Just looking for a quick sanity check. I'm planning on building a system which has (to start with) two 3kw heating elements (HLT and BK - they're only little). Being in the UK, that means 12.5A per element, so 240V/12.5A to switch. I'm also planning on using a Raspberry Pi as the core controller for this, so need to drive switching (effectively a software PID in all likelihood). Obviously an SSR to switch each element using mains power will be needed.
Now I could, feasibly, find some DIN rail SSRs which will have a low enough switching voltage/current that I could drive them directly from the GPIO pins on the Pi, but it seems more sensible to use a relay expansion on the Pi (switching, say, a 12V DC supply) to drive the actual mains relays. This should mean that there's a bit more isolation between the mains relays and the Pi, and that I can pick relays which need a bit more switching voltage/current than a Pi can provide (and that widens the availability dramatically, and should make the switching more reliable than being right on the lower limit of switching voltage for most SSRs available).
Does this sound sensible/feasible? Effectively (assuming a DIN rail type approach) I'd have one DC PSU with a suitable switching voltage, a distributor, and a couple of DIN rail SSRs. The DC could then be distributed to a couple of relays on the Pi relay board, and then to the main SSRs which would switch mains power for the elements.
I've not drawn up a wiring diagram but can do a quick sketch if useful! Basically any opinions welcome. (And yes, I'll be getting a proper electrician to look over the plans! Just trying to get everything straight in the designs first...)
Just looking for a quick sanity check. I'm planning on building a system which has (to start with) two 3kw heating elements (HLT and BK - they're only little). Being in the UK, that means 12.5A per element, so 240V/12.5A to switch. I'm also planning on using a Raspberry Pi as the core controller for this, so need to drive switching (effectively a software PID in all likelihood). Obviously an SSR to switch each element using mains power will be needed.
Now I could, feasibly, find some DIN rail SSRs which will have a low enough switching voltage/current that I could drive them directly from the GPIO pins on the Pi, but it seems more sensible to use a relay expansion on the Pi (switching, say, a 12V DC supply) to drive the actual mains relays. This should mean that there's a bit more isolation between the mains relays and the Pi, and that I can pick relays which need a bit more switching voltage/current than a Pi can provide (and that widens the availability dramatically, and should make the switching more reliable than being right on the lower limit of switching voltage for most SSRs available).
Does this sound sensible/feasible? Effectively (assuming a DIN rail type approach) I'd have one DC PSU with a suitable switching voltage, a distributor, and a couple of DIN rail SSRs. The DC could then be distributed to a couple of relays on the Pi relay board, and then to the main SSRs which would switch mains power for the elements.
I've not drawn up a wiring diagram but can do a quick sketch if useful! Basically any opinions welcome. (And yes, I'll be getting a proper electrician to look over the plans! Just trying to get everything straight in the designs first...)
