Really basic newbie questions


#1

Hey all,

I apologise if these basic questions are in the wiki, other posts in the community, or somewhere else, but I have made the effort to look and have come up empty :expressionless:

OK, so first off here’s some background. I have a working fermentation chamber made from a fridge - what seems to be a fairly standard setup i.e. thermostat bypassed, thermowell in the fermenter, 100W IR (reptile bulb type) heater, currently run by an STC-1000 controller.

I came across the BrewPiLess project and hence to the source of the goodness - BrewPi.

I have a very strong interest in improving my setup via BrewPi, a low cost way to try this could be brewpiless or a homebrew Arduino/RPi setup, but ultimately if it all looks good I rather like the look of the Spark as a final solution.

So, what i do not understand, is exactly how the BrewPi control works; I see implementations with relays and SSR’s so my first question is whether the control (whcih is mentioned as PID) is in fact switching the relays on/off at relatively long intervals of many minutes, and it has a PID action when viewed over a long enough time period, OR is it that when SSR’s are used, the system does “real” PWM for the heater? Of course you can not PWM a compressor.
This seems simple, but i am conflicted by seeing mechanical relay setups, but then comments such as BrewPi Noob has some questions and comments where Elco says "Note that this is heating at maybe 5% power. "

The next question seems to be on a very common theme - are there some sensible default paramters for the various delays and constants, or a library/thread of people’s setup and their parameters so that I can start with something closer to right than wrong? I note Elco is vociferous in helping foks who post thier graphs and ask for help, is that just the done thing?

Lastly - is it terribly rude to get my feet wet with BrewPiLess and ask for tuning help here? The thing is, it’s the weekend coming up, and i have the relays and ESP8266 needed to implement a BPL system to get testing and playing with the underlying brewpi control - and i guess i am impatient!


#2

Brewpiless is forked from the deprecated arduino version of BrewPi which did not have PWM.

The Spark version uses PWM with a configurable period. The default is 4 seconds for the heater and 30 minutes for the cooler. Additionally there are minimum on and off times to protect the compressor.

I don’t recommend mechanical SSRs, use a zero cross SSR instead and avoid the fotek brand.

I won’t be able to offer good tuning advice on the BrewPiless code because it differs drom the official version and is based on the 2 year old arduino version.

But if you want to play around with it, no one is stopping you. Just know that it forked off from the official version some time ago and is not the same.


#3

Got it, thanks. It looked like an easy way to mess with this stuff given i have the bits already, but i think i will order a Pi and do it properly :slight_smile:

I’m still not 100% clear on the PWM - can you tell me if this is correct:

  • The old branch - uses on/off switching, with deadtimes and delays for e.g. compressor protection.

  • The new code has PWM with SECONDS of on/off time periods, rather than what i think of as PWM - using kHz type frequencies. I do understand that this is still PWM, just on a much longer timescale, since we are dealing with large thermal inertias here. The advantage is more precise control.

Understood on the SSR vs relay, and I actually have seen the “fake” notices around the Fotek’s! Will get a reputable Omron or something.

Thanks for your wisdom!


#4

FWIW I have implemented a PWM PID controller in AppleScript for my temperature controllers (using the Mac XTension program). Works great.