Inconsistant boiling

[kevreh]

I just ran a virginal brew session with my new 4kW, Omega PID controlled, 12gal BIAB system. Still some flaws to work out, but definitly a step up from propane!

One thing I need to figure out is boil consistancy. No matter if I set my Omega pid to 211°/212°/or 213° I get a boil thats on/off, relevant to the element firing. 211° means a little boiling, then about 15 seconds of off time. OTOH, 213° means very violent boiling then maybe 5 seconds of off time.

I tried to set the manual % power output but that didn't seem to make a difference.

I know this is a PID most people don't have. But I *did* do an autotune from ~140° to ~155°.

Is this a common problem?

 

[heckels]

Yeah, it's common. I set my BCS to 45% and get a good boil for a few seconds and then it dies to a simmer for a couple. Unless you set the element to 100%, you'll end up with some down time.


Sent from my iPhone using Home Brew

 

[mattd2]

What model Omega PID do you have, and do you have a link to the manual? Setting the boil to 211/212/213°C is not the best way to achieve a consistent boil. If the PID you have has a manual mode then you need to use that, otherwise look at a separate PWM or SSVR control for the boil.

 

[stevehaun]

I use an omega PID. Set cycle time to 1 second and use the manual mode. Start at 100% and then back off once you have a vigorous boil.

 

[kevreh]

It's the cn9500. Can't find the manual online right now. It says it has a manual output % in proportional mode only, not sure what that means. Either way, when I tried adjusting the manual output % it didn't change the element power.

A seperate knob for control would be easier than going into the settings for the pid. Does the type of pid I have dictate whether I can use a ppm or ssvr controller?

 

[mattd2]

It's the cn9500. Can't find the manual online right now. It says it has a manual output % in proportional mode only, not sure what that means. Either way, when I tried adjusting the manual output % it didn't change the element power.

A seperate knob for control would be easier than going into the settings for the pid. Does the type of pid I have dictate whether I can use a ppm or ssvr controller?

Yeah that manual I found was confusing as hell (http://www.omega.com/Manuals/manualpdf/M2897.pdf) but it seems the SP1 manual percentage power control parameter (hAnd) is so that if the sensor fails the controller reverts to a nominated set point - I assume this is so a sensor failure doesn't have an immediate catastrophic failure of the process. You could fudge the boil control by setting the sV to 250°F (anything greatly above boiling) and then control the power by limiting the Set SP1 power limit percentage parameter (PL.1). This will "trick" the controller into wanting to be in full 100% on but the controller will then limit the maximum % down to what you have set - if that makes any sense

 

[kevreh]

mattd2-

Thanks for that insight, I'll do a test to see if the PL.1 setting is the right one.

I'm leaning towards a reostat from Auberin. That way during mash, I can turn it down to ~10% and not worry about the grain bag touching the lwd element.

Going into the sub-sub menus in the Omega is cumbersome and not prone to easy changes.

 

[kevreh]

I use an omega PID. Set cycle time to 1 second and use the manual mode. Start at 100% and then back off once you have a vigorous boil.

Thanks for the cycle time tip. Default was 20 seconds(!), so yeah, not good for maintaining temps very well with a smaller vessal (vs. a large vessal used in commercial applications).

 

[stevehaun]

Any cycle time > than 2 or 3 seconds will lead to "pulsed" boiling.