SSR ratings
(I’m asking for a friend) Lets say you want a solid state relay that’d take a 3.3v input to switch the load for the heater cartridge on a 12V hotend…any suggestions on what amperage it’d have to support?
I guess extra bonus points if it could handle 24 Volts.
You could drive a normal SSR with a ULN2003: http://www.bonebrews.com/solid-state-relay-with-a-beaglebone/
There are some SSRs that trigger at 3 volts and handle 3 amps:
To be honest, it probably be 5v trigger and 12v heater, but if I’m going through the trouble to create the design, it helps to accommodate the max and min possibilities.
Easy to work out! take the watts lets say 40 and divide by the 12 volts and the answer is 3.4 amps at 24volts 1.7 amps
A common DC to DC SSR would handle around 40 amps like this one http://www.amazon.com/JGX-40DD-Covered-Solid-Module-5-110V/dp/B009AQO894/ref=sr_1_1?ie=UTF8&qid=1440266121&sr=8-1&keywords=JGX-40DD
@The_Hozza a common SSR would not trigger at 3.3v.
Most SSRs are 3v rated. Ohms law says 40W@12v= 3.3333A of current. So overspec and go 4A or so.
@ThantiK quite a few of those ratings are optimistic. http://forum.allaboutcircuits.com/threads/ssrs-appear-not-to-work.92601/
"In testing, out of five of these relays, only one was able to switch on with direct GPIO voltage. "
http://www.bonebrews.com/solid-state-relay-with-a-beaglebone/
So following on this, a 5 amp fuse might not be a bad idea.
If you’re running your hot end from DC, then try a logic-level MOSFET board rated for 30V at 10A
The issue with most SSR input voltages is that while they will trigger at 3.3v, they require more current than most digital I/O pins can put out at that voltage without dropping the I/O voltage due to how they’re wired internally.
A switching transistor (eg: Darlington array or even a small FET) is all that is needed to get a decent output voltage.