How do you switch between 2 elements using 1 pid

[bf514921]

So i have 1 pid, and 2 elements, plugs, ssrs etc. is there a way to switch control of the pid from 1 element to the other without unpluging and plugging things in? what kind of switch is this?

 

[Fletch]

Yes, it can be easily done. All you need is a Single Pole, Double Throw toggle switch (or any SPDT switch: toggle, rotary, even a slide switch). Wire the negative side of the two SSR inputs together, connect them to the negative DC connection on your PID. Connect the positive side of each SSR to one of the NO terminals on your SPDT switch. Connect the Common (center) terminal of the SPDT to the positive output of your PID. If you're using a PID that simply has a relay output, with a separate transformer to produce your SSR switching control voltage, then the negatives from your SSRs connect to the negative side of the transformer, and the Common (center) terminal on the SPDT connects to the NO terminal on the PID relay output, with the Common on the PID connected to your transformer positive.

Also, using this setup, with the SPDT in the center position, neither SSR will be energized by the PID. This can be convenient, as you can leave the PID powered up to monitor temps while having the output in override, as it were.

 

[MrH]

Are these two elements in the same vessel? If not, do you need independent temp control for both? If you have a PID with manual proportional control and one of the elements is for boiling, then you can pull this off. Otherwise, no. If you try to switch between two temp probes, you'll have issues, not only with increased resistance across the switch, but each heating task will require a different set of P-i-d parameters, so you'll never get very good accuracy. Unless you're using one element for boiling, you're better off just getting a second PID.


MrH

 

[Fletch]

Guess I should have started by asking what you are trying to do, specifically. If you want to control two different vessels, it can be done, if you manually set your parameters, and disable the "autotune" function on the controller. This is not a big deal, the I found autotune pretty worthless for HERMS temp control, as there were too many variables from batch to batch for my brewing. Resistance across the switch is not an issue if you switch the output, as I described, and of course you would have to move your sensor from one vessel to the other. You cannot use a switch and two thermocouples for the input.

 

[limoges]

I asked about this a few days ago

here`s the link best of luck

https://www.homebrewtalk.com/f51/pid-controller-mlt-e-kettle-166373/

 

[passedpawn]

So i have 1 pid, and 2 elements, plugs, ssrs etc. is there a way to switch control of the pid from 1 element to the other without unpluging and plugging things in? what kind of switch is this?

Here is a decent solution.

https://www.homebrewtalk.com/f51/electric-brewing-question-167052/#post1931368

 

[bf514921]

so to switch the ouput of the pid, somthing like this might work?
http://www.radioshack.com/product/index.jsp?productId=2062518&CAWELAID=107593083

 

[passedpawn]

so to switch the ouput of the pid, somthing like this might work?
http://www.radioshack.com/product/index.jsp?productId=2062518&CAWELAID=107593083

Absolutely!