Define "Boil"

[PaulCa]

Lets say you have a thermostatically controlled wort boiler.

If you leave the element at full it will be on all the time and water will never get to be more than boiling. It will never be above 100*C. No mater how powerful your boiler is.

But, based on the latent heat capacity of water, any energy applied at 100*C results in evaporation. The wort remains 100C.

All that maters is the amount of energy you need to supply to maintain a temp of 100C, after loses. Any more energy will result in evaporation.

So, how do you configure a setup to boil, but only boil a volume of water?

Wort that is boiling is 100C (give or take a few tenths maybe), it might take only 1Kw to keep that boil, but your boiler provides 3Kw. Your choices are, boil the wort with +2kw of evaporation power or turn the termostat down and not get a rolling boil.

EDIT: Gas users can turn down the propane valve to produce a lower amount of heat and match the point at which it just boils. Electric boiler users are kinda screwed.

 

[PaulCa]

Practically, what difference would it make to a boil if it was cycling between 99C and 100C? I mean spending a lot of time not rolling in a boil but more simmering between 99 and 100C?

If acceptable for quality, it would say a lot in electricity and a lot in "boil off".

 

[BIGJIM72]

Erm, I can turn my boiler down to less than half power & it holds a rolling boil,so your electric boiler user comment is bunkum. Though I can see what you are getting at if you are trying to set up an automated system.

 

[PaulCa]

My boiler only has one element, so it's on or off, like a kettle. Hard rolling boil or dead calm.

 

[rpt]

This doesn't help answer your question but wort doesn't boil at 100C as it contains sugar. Even water doesn't boil at 100C unless it's pure and at sea level.

 

[PaulCa]

This doesn't help answer your question but wort doesn't boil at 100C as it contains sugar. Even water doesn't boil at 100C unless it's pure and at sea level.

I agree with your science, but experimental evidence suggests (my instance of) wort does boil at 100C (+/-1C). I live at about 15 feet above sea level.

 

[PaulCa]

My main problem is the huge amount of evaporation I get even with the lid half on and half off it was raining beer in my kitchen and I mean "literally" raining beer. There was a brown puddle on the ceiling and drips falling.

 

[chastuck]

Erm, I can turn my boiler down to less than half power & it holds a rolling boil,so your electric boiler user comment is bunkum. Though I can see what you are getting at if you are trying to set up an automated system.

Ditto ................. If you are using a PID you can control the output just like a pot on an electric ring.

 

[bobsbeer]

Depending on how much automation you want to put in, you could go down the pid/ssr method. While the element is still 3kw, the pid via the ssr turns the element on and off to maintain the temperature are wanting.

 

[PaulCa]

But... 100C is 100C at 99.9C is won't be boiling at 100C it will. A thermostatic approach won't work. I tested this with very fine movements of the thermostat, turn it down a "hair" until it clicks and the temp drops to about 98C before it clicks back on, that stops the boil fairly instantly and it stays not-boiling for a good 5 minutes before clicking back on when it clicks off again before getting to boil again.

A 3Kw potentiometer is a large and hot affair and I doubt practical.

Cycling a relay on/off on a timed interval to give, say 50% on, might work. (Similar to a switching PSU, which I suppose could work).

The only other option I can think of is to use a smaller immersion element that I can lower in to keep the boil and switch the main element off.

I'm not really looking for "automation", just a more relaxed boil and not have it raining in the kitchen. The boil is seriously intense, I wouldn't call it a rolling boil more of a pumping, jumping frantic boil. To give you a comparison, take the lid off your kettle, put it on and hold the switch down. Actually I don't recommend this as you'll get japped with boiling water, but it's close to what I mean and there is noway you could get the boiler close to full and be safe.

 

[theboytony]

PID is totally the wrong thing to use in this application. You do not want to be trying to work to a set temperature. If you want to control the boil vigour to try and cut down on evaporation then you need something like this PWM controller

 

[PaulCa]

PID is totally the wrong thing to use in this application. You do not want to be trying to work to a set temperature. If you want to control the boil vigour to try and cut down on evaporation then you need something like this PWM controller

Ah ha! Someone who gets what I mean :) I'll check this out later, but if PWM stands for Pulse Width Modulation, then it's exactly what I need. Thanks.

I was thinking raspberry PI, but my relays are underrated at 10A with a 12.5A element. That linky is rated to 40A and over 3Kw. Just need to make a mount for it and hope it has a 1:0 ratio setting for heating the water.

 

[jonnymorris]

Ta da!
viewtopic.php?f=23&t=37878

 

[theboytony]

Yeah it is pulse width modulation, I've been using one of these for a while now and it works spot on :thumb: I fitted mine in a plastic box along with an ammeter so I've got some sort of reference (also something to look at lol) You could also go for one of the pricier phase angle controllers like this but for me the cheapy chinese option has worked fine for 25+ boils, although thinking about it I might actually order another as a spare just in case :pray:

 

[chastuck]

PID is totally the wrong thing to use in this application. You do not want to be trying to work to a set temperature. If you want to control the boil vigour to try and cut down on evaporation then you need something like this PWM controller

I've seen this said before in this beer forum, but you are totally wrong to say that using a PID is totally wrong. Using a PID in a pure resistance circuit, such as a heater, is very similar to PWM in terms of the outputted heating effect. The PID uses Time Proportional Control. The current build up in the heating element never reaches full peak before the timing cycle of the PID cuts it back again - rather like a wave effect. To quote from the SYL 2352 PID manual: "Almost all high power control systems use time proportional control because amplitude proportional control is too expensive and inefficient". A further quote from the PID manual: "One application example is controlling the strength of boiling during beer brewing. You can use the manual mode to control the boiling so that it will not boil over to make a mess."

 

[theboytony]

PID is totally the wrong thing to use in this application. You do not want to be trying to work to a set temperature. If you want to control the boil vigour to try and cut down on evaporation then you need something like this PWM controller

I've seen this said before in this beer forum, but you are totally wrong to say that using a PID is totally wrong. Using a PID in a pure resistance circuit, such as a heater, is very similar to PWM in terms of the outputted heating effect. The PID uses Time Proportional Control. The current build up in the heating element never reaches full peak before the timing cycle of the PID cuts it back again - rather like a wave effect. To quote from the SYL 2352 PID manual: "Almost all high power control systems use time proportional control because amplitude proportional control is too expensive and inefficient". A further quote from the PID manual: "One application example is controlling the strength of boiling during beer brewing. You can use the manual mode to control the boiling so that it will not boil over to make a mess."

Sorry but you are talking absolute rubbish, quoting from a manual is no comparison to working experience. PWM is often used in conjunction with the output from a PID so maybe you are confused.

 

[chastuck]

PID is totally the wrong thing to use in this application. You do not want to be trying to work to a set temperature. If you want to control the boil vigour to try and cut down on evaporation then you need something like this PWM controller

I've seen this said before in this beer forum, but you are totally wrong to say that using a PID is totally wrong. Using a PID in a pure resistance circuit, such as a heater, is very similar to PWM in terms of the outputted heating effect. The PID uses Time Proportional Control. The current build up in the heating element never reaches full peak before the timing cycle of the PID cuts it back again - rather like a wave effect. To quote from the SYL 2352 PID manual: "Almost all high power control systems use time proportional control because amplitude proportional control is too expensive and inefficient". A further quote from the PID manual: "One application example is controlling the strength of boiling during beer brewing. You can use the manual mode to control the boiling so that it will not boil over to make a mess."

Sorry but you are talking absolute rubbish, quoting from a manual is no comparison to working experience. PWM is often used in conjunction with the output from a PID so maybe you are confused.

Sorry, but you are talking rubbish to say I'm talking rubbish. Maybe you are confused as you have not used a PID in manual mode. I've used a PID to control boil intensity in my brews for many years with great effect. I'm not just quoting the manual, I'm speaking from working experience. You have your opinion, I have mine. Nothing more to be said from my perspective. You can have the floor. I'm off elsewhere.

 

[theboytony]

Using a PID in manual mode? Can you explain what you mean by that because PID in manual is pretty pointless, it kind of defeats the object. What do you use as the setpoint for your PID? Why would you want to go elsewhere, if you have a valid argument then fight your corner?!?

 

[BIGJIM72]

Boil:-noun:- a painful spot with or without a head that may need to be lanced by a medical professional. Is there a prize?

 

[PaulCa]

As a non-layman but having never studied PIDs I looked it up. It seems that inherently a PID has a target. It has 1, 2 or 3 'current/past' parameters and it adjusts based on 1, 2 or all of those to meet the target.

(I have spent some time working out similar control loops in software to determine if the house heating should be switched on or off, without over reacting and cycling the heating if the temperature flucuates due to various reasons such as opening internal doors and creating drafts. Not saying I achieved anything as elegant as a PID, though. I used a rolling buffer of past results and just averaged them, which might be akin to the "i").

To control the vigor of a boil, what would be the target? It isn't temp, we ruled that out. In fact there is little that can be measured that will tell you the vigor of the boil.

I suppose if there was a large enough capacitor and an ammeter as the "P,I and/or D" parameter(s) and the output was a PWM switching voltage regulator then it might be able to adjust the voltage to meet the consumption amps required, thus achieving the required effect. However, why then not just use a switching voltage regulator knob manually?

The PID would provide a clever way to control the amps (or voltage), but as both are going to stable values that don't tend to fluctuate in the case of an element, the PID sounds superfluous. I assume it also requires the PID is controlling the voltage regulator, thus if you remove the PID completely and just add a manual voltage regulator you would achieve the same effect.

Now I think I can see both of your points. If the PID is being used to control the temp of the boiler by varying the voltage based on temperature, but happens to have a manual way to alter the output voltage, then adjusting that manually would achieve a variable boil.... but ultimately the PID isn't required, just it's output setting manually.

Thus if you had a PID already controlling voltage, with a manual output mode, you could use it for this. Which is more expensive?