Pid + Timer ? How To Wire?

[komodo]

Just a quick question...

If I was to use a PID to control HLT could I put a timer in between the PID and the element or would that mess with the PID (I've only ever used a PID on a coffee machine so not real familiar with them)?
If not could I put a timer before the PID - but then would I not loose the temperature settings I set?

Any help / advice appreciated.

Not really a morning person - I figured that if I could have the HLT on a timer a.) it would mean I wouldnt have to get out of bed too early on my day off and b.) would make me get out of bed cause the water is upto temp and ready to go.

Cheers,
Kirk

 

[newguy]

Introducing a delay between your PID and the element would be bad. A timer on the PID itself would be okay. There are many different types/makes of PID controllers - I don't know if all/any would remember the last setting after a power cycle. You'd have to try it or find the model you really want and email the manufacturer to ask.

 

[Justin]

You'd have to check the specific function of your PID controller and see if it has a memory for the temp setting. My Omron E5CS ones do, so I can just plug the controller power into the timer. Once the timer turns on the PID turns on with the last temp setting and away it goes.

Set the temp on yours, unplug it, plug it back in and see if it turns on with your set temp.

Otherwise your other method should work (plugging the heater into the timer). I dont know PID really but I wouldn't assume it would cause any problems. Most PID controller have the option to turn off the PID function anyway and make it a simple on/off controller, honestly that is all you need. Nothing complex about heating up a HLT.

One thing you may want to consider is thermal layering in your HLT, if you could stir it during the heat up you'd be right on your desired temp when you got up. But if you can handle giving it a stir in the morning and waiting a little longer for the temp to settle (heat up or add cool water) then that's an option too. I've just found that the water below the element can be quite cold while the above temp is on the money. Stir it and the whole temp drops. FWIW my tap draws from the colder area so that's why I think it's important to consider if you want to be ready to go right away.

Cheers, Justin

 

[newguy]

I dont know PID really but I wouldn't assume it would cause any problems. Most PID controller have the option to turn off the PID function anyway and make it a simple on/off controller, honestly that is all you need. Nothing complex about heating up a HLT.

Ye gods, NOOOOO! PID = proportional integral derivative. The power delivered to the heater is a function of the present error (set temp - actual temp), the change in the error, and the sum of the error since the controller was turned on. Putting a timer between the PID and the heater is BAD BAD BAD. Imagine your bewilderment if someone put a timer on your lights, downstream of your light switch. You'd eventually figure out the problem, but that's because humans are much smarter than most machines. The PID controller won't catch on quite so fast.

If, however, you turned off the PID functionality and used it as a thermostatic control unit, putting a timer downstream of the controller would be fine.

 

[komodo]

Cheers guys I'll see if I can find a PID that retains the last setting.

Justin good suggestion - might look into someway to keeping the water moving to prevent thermal layering!

 

[schooey]

:huh:

I'm a little stumped here at what you are actually trying to achieve... Every PID I have come across recalls the last temperature set when it turns on, or are you after some other kind of setting?

 

[JasonY]

PID is really overkill in our application, if you are using SSR's perhaps you can take advantage of the algorithm a bit but your only boiling water As Justin said if it retains the last setpoint then put the timer at the power source and you have no problems.

If this is not the case then you can still put it between the PID and the element. What will happen is the integral action will increase the output since the temperature is not reaching setpoint (it should have anti-windup protection to limit to output to 100% at which point the integral action is stopped) so when the timer kicks on it will likely be flat out but as it. Since you are only heating some water this isn't going to be a big deal. Depending on the way you are heating, volume of water and other factors at worst you will get some overshoot (hotter water ).

 

[Thirsty Boy]

Check e-bay. I've bought two from e-bay from tw different companies, and both retain their settings after power off. My criteria for buying... that they were cheap and were able to control a mechanical relay as well as a SSR. The cheapest ones fulfilled these requirements. I couldn't find a simple on/off for less.

One of mine was from here - they dont look to have the same model atm, but the cheapest ones there look functionally identical, I would consider ramp/soak models in retrospect... then you can program in your mash and walk away. Not that I am unhappy with what I have.

I often run my HLT (which is an electric urn) on a timer... nothing compex, just a $10 timer from bunnings, it simply gets plugged into the wall and everything else is downstream from there. Easier than mucking about with wiring it in. I assume you only really want it so that the HLT is hot when you get up/get home ?? In which case all you do is unplug - remove timer - re-plug, when you decide to start to brew.

I was a little shy about the PIDS and elements etc coming on when I was in bed though - I have done a thorough job with my electronics.... but I am no tradesperson and I didn't trust homemade electronics to not burn down my house while I slept... ergo the commercial urn as HLT. That I trust, its designed to sit behind the counter of some footy club bar for 20 years and tick away - I trust it to come on and not fuse out while I am in bed. Might be worth thinking about.

Thirsty

 

[komodo]

Newguy and Thirsty boy you guys are on the ball - only wanting to use it as a thermostatic control unit. PIDs seem to be cheaper and easier to come across than a simple digital temperature control. Plus the ability to handle solid state devices makes them more attractive also. Plus I definitely want to use a PID for HERMS so matching controllers would add to brewery bling

As for stirring the water to prevent thermal layering - would a simple cheap variable speed drill with set to a slow speed driving a stainless "paddle" be adequate. Im guessing you wouldnt need to create a whirlpool mearly keep the water turning to prevent hot spots and get a more accurate temp reading

 

[Justin]

Or hook up your pump (maybe on a seperate timer switch even, so it runs for 15min on/off cycles after the first hour of heating if you dont want it to run continuosly during heat up) to just recirculate back on itself in the HLT, drawing from the bottom, whirlpooling in from the top. If you are building a HERMS you have one anyway. If you are after brewery bling this one looks quite neat.

That's personally what I do, just have my March pump hooked into the HLT and place the output back in the top with a length of hose (secured, so it doesn't fall out ). I will eventually install a fitting through the side near the top as a permanent solution.

Beats jimmy rigging a drill into the system that will look a bit cheesy. Another option is a 12V windscreen wiper motor, but honestly the pump is a better idea.

Cheers, Justin