I am building an electric RIMS, but I only have one 120V circuit and that circuit has other loads on it (lights, motors, etc). I want to avoid tripping the breaker with the RIMS. I could use PWM to control an SSR, but since the SSR is either "on" or "off", and not "in-between", in the "on" state my heating element could trip the breaker.
I believe that SCRs might be the answer. They can control the load power from 0%-100%, so I could program my software to only use 100% if there are no other loads (my software is also controlling the pumps). If the pumps are on, the software will tell the SCR to only use some percentage of the max, say 80% (or whatever I determine is safe to avoid tripping the breaker).
But there are things I don't understand. I read somewhere that SCRs only pass current in one direction, which would only give me half of the power from my 120V circuit. Is that correct?
Do SCRs need a separate power supply, or is it just two terminals for voltage in and two terminals for voltage out (like an SSR)?
How efficient are SCRs? Will an SCR controlling the same load as an SSR require a heatsink that is larger than what the SSR would require?
Where are the cheap SCRs? I found some expensive ones on omega.com. I did some googling with wild variations in price, and I could not understand what the tradeoffs were.
Is anyone on HBT using an SCR in this kind of application?