Temp controller (NOT PID) HELP

[TRAXX]

Ok I have gone over what temp controller to use for my oven and Iam just sick of looking for something that will do this.Iam using four 3000watt elements I want all four elements to stage on 10sec apart that way i dont have 50amps of draw all at once.Then when the oven is up to temp lets say 450deg when it drops i want only two of the four elements to stage on and maintain the temp.My other oven i used a robertshaw knob style controller that runs two elements and it has aways worked fine.I was going to use a PID controller from ebay but i was told that they wont stage on and off,Are they hard to set and program?? ANY IDIAS

[chromo]

Well with my limited 400 years of knowledge this does not sound correct to me. LOL.

If all your elements are on at the same time then you WILL have the max AMP draw all at once! No real way from this, either use it or don't!
The only way I would know to not have max amps all at once would be to run less elements at one time. If your not going to run them, then why have them

So if you have 50amps of elements, perhaps you can turn on and off only 25amps to run at any one time total, but you see what I mean, you still only have 25 amps running at any time, so why have the other 25 amps at all?

You could use a controller to run 2 elements set for say 350F, a second controller for 2 set for 400F.
This way when you first turn your oven on, all elements will run full blast to about 350F, 2 will shut off and the other 2 will heat to 400F then shut off. To maintain heat then from about 350F to 400F only 2 elements should run, the other two should not turn on again unless you drop below 350F for some reason like open the door for awhile and loose all the heat.
So with 2 controllers you could run 4 elements max amps to 350F heat, then shut off 2 and run only 2 after 350F.

I don't see any way (or reason) to run 50 amps of elements at half power or so at all times with out ever using max amps all at once.

[ed_denu]

Chromo has pretty much defined what needs to be done if you want the 4 elements to cycle on and off at different times.

The PID's sold on ebay and other sources are not very complicated in most senses. During heat-up, the DC voltage signal from the PID driving the SSD(s) is always on. Once the set point is reached it cycles the SSD on and off to maintain the set point. I'm not sure what your concern is with only using 2 elements to maintain the set point. The PID will do this for you.

Either way, as chromo stated, if you have 50amps you need a circuit capable of supporting 50 amps. Why not just let the PID control the on/off function of the elements?

[TRAXX]

What is the diff between SSR and a contactor I want to use one for each pair of elements like maybe a 30amp for two elements.Thanks I might be just using one controller and two SSR or contactors.

[ed_denu]

I'm not an ee but here is my understanding. A contactor can be either electro-mechanical or solid state.
An electro-mechanical contactor has contacts which normally you can hear open and close. Eventually they can burn up but the advantage is they can handle large electrical loads.

Solid State devices, either contactors or SSR's, have no contacts and switch electronically. Solid state devices turn on and off at the zero crossing mark on a sinewave so electrical surges and noise spikes are greatly reduced(probably not important in oven construction). Since there are no moving parts in a solid state device, they can be cycled on and off many times per second.

I don't believe there is much if any difference between solid state contactors and solid state relays, they basically are the same thing. SSC's often incorporate heatsinks and are usually of industrial strength. Depending on load, either should normally be connected to a heatsink. Maybe someone else can elaborate more on the differences, but either should be suitable for use in a PC oven.

My personal opinion is that an electro-mechanical contactor would not be a good choice to use with a PID. When temperature approaches the set point my PID cycles the elements on and off frequently, probably to often for an electro-mechanical switch.