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Thread: Hi from the UK - help with Bezzera BZ99 PID projec

  1. #1
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    Hi from the UK - help with Bezzera BZ99 PID projec

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi all,

    I usually post on toomuch coffee but thought you guys would be more likely to help me with this project.

    I have decided to fit a PID to my BZ99. I now have all the parts (CAL 1/32DIN controller, 25A SSR, T type thermocouple and brass collet for mounting the probe)
    http://www.omega.co.uk/ppt/pptsc.asp?ref=BRLK_SSLK
    http://www.omega.co.uk/ppt/pptsc.asp?ref=HTTC36

    I have a couple of questions, does anyone have an electrical schematic for the BZ99 as i cannot find one on-line.

    Also (I am just guessing here) do I just replace the preasurestat with the output side of the SSR? If so I dont need a diagram as this is fairly straightforward.

    Thanks in advance for your help guys.

    Here is my kit...
    http://www.toomuchcoffee.com/index.php?name=PNphpBB2&file=viewtopic&t=2632&high light=
    http://www.toomuchcoffee.com/index.php?name=PNphpBB2&file=viewtopic&t=3667&high light=

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by monkey66 link=1174149362/0#0 date=1174149362
    Hi all,

    I usually post on toomuch coffee but thought you guys would be more likely to help me with this project.

    I have decided to fit a PID to my BZ99. I now have all the parts (CAL 1/32DIN controller, 25A SSR, T type thermocouple and brass collet for mounting the probe)
    http://www.omega.co.uk/ppt/pptsc.asp?ref=BRLK_SSLK
    http://www.omega.co.uk/ppt/pptsc.asp?ref=HTTC36

    I have a couple of questions, does anyone have an electrical schematic for the BZ99 as i cannot find one on-line.

    Also (I am just guessing here) do I just replace the preasurestat with the output side of the SSR? If so I dont need a diagram as this is fairly straightforward.

    Thanks in advance for your help guys.

    Here is my kit...
    http://www.toomuchcoffee.com/index.php?name=PNphpBB2&file=viewtopic&t=2632&high light=
    http://www.toomuchcoffee.com/index.php?name=PNphpBB2&file=viewtopic&t=3667&high light=
    You could try www.barazi.com.au -- bezzera importers in Australia
    For discussion of hx and PID heres a good site:
    http://www.home-barista.com/forums/should-i-pid-my-heat-exchanger-t1109.html

    not sure if its as straight forward as single boilers or as repeatable

    All the best
    Brett

  3. #3
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Gday m66 and welcome to CoffeeSnobs [smiley=thumbsup.gif],

    Heres a link to the only schematic for Bezzera machines that I know about so it "might" be applicable, a bit of judicious checking will have to be carried out.

    Out of interest, why do you want to replace the P/stat with PID control? Sirai P/stats are pretty damn good and able to control the boiler temperature within about a 2 degree C envelope. If its not doing this then theres a chance that the diaphragm membrane needs replacing and thats a lot simpler (and way cheaper) to do than converting over to PID control. A mod that IS worth doing though, is to add a slave relay into the P/stat-Heater Element circuit so that the slave relay switches the high current of the element(s) and preserves the P/stat contacts (they will burn out over time otherwise). I guess if you wanted to, you could use an SSR for this job but it would be considerable overkill in my opinion.

    Anyway, since youve already started, all the best with your project and hope the linked schematic is of some use to you. All the best,

    Mal.

  4. #4
    Senior Member robusto's Avatar
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    I agree, Mal, the extra couple of degree stability a PID will bring to the boiler temperature is going to be absolutely meaningless as far as steaming milk goes, and practically immaterial to the brew temperature as well.

    The only practical reason youd consider a PID is if steaming is done away with and the boilers sole function then is to provide much lower brew-temperature water to the heat exchangers and group.


    Monkey66, its your prerogative of course, but what is your reason for the PID? If you still want to steam milk, Youll still have to do cooling flushes, and thats where the real temperature "control" comes in.

    --Robusto

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    OK, so Mal and robusto had the guts to say what I was thinking. Because I assume youd still need to do a flush from water being sitting in the hx pipes for too long etc
    That quote I gave
    :http://www.home-barista.com/forums/should-i-pid-my-heat-exchanger-t1109.html

    may suggest why but I dont think it would be the holy grail like PID on a single boiler.

    Brett

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Hi monkey66 and welcome to coffeesnobs....

    About the only things fitting a PID to your HX would result in is constant steam temp (and a much lighter wallet!!)...... and the steam temperature varies 2 deg C (sometimes less depending on the pressurestat) as has been said above...... Why would you want the steam temperature that well controlled?

    The brew temperature on the other hand (which you do want to control) is dependant on the percentage of HX in steam compared to water (varies as boiler level changes), but even more so with the time since last use / flush and the volume of the flush (just varies heaps - for example 93C to 125C in my case!!) - neither of which the PID will help..... and the boiler temp (which the PID will give you a little better control over)....

    So fitting a PID to an HX isnt really of any value other than to replace mechanical contacts (on the PSTAT) with a SSR (which you can do a lot cheaper than buying a PID).

    An HX machine is "Dynamically" stable - brew temperature is constant given the correct usage pattern...... a normal single boiler is Statically stable (within limits) and has poor dynamic stability - and the PID helps with these parameters.

    The quality commercial machines today do have PIDs - but they are not HX machines. They have at least a steam boiler and a brew boiler (which is controlled by the PID)..... with the very best having one brew boiler per group and a separate PID on each :) :)

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Thanks for all you replies guys.

    I am fitting the PID for a few reasons.
    1. I like the idea of tightening the range of the preasurestat system.
    2. Whilst i accept all your comments about stability (indeed i am a big fan of large lumps of brass to be the best route to temp stability) I would like the option to adjust +/- a degree or two to fine tune shots with different beans/blends. This is very haphazard with the preasurestat system.
    3. I got a great deal on the PID and i was getting PID envy from other peoples projects.
    4. I love an excuse to get my tools out and i havent for a while.


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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    monkey66,

    Well good luck with your project - but it wont allow you to change your brew temperature with any certainty - the effects caused by time since last flush, the amount of that flush, the water level in the boiler, the rate of flow through the HX - determined by the dose/tamp of the puck...... etc ..... etc will have far too great an effect. (about 30C to be exact- even if the boiler is held at EXACTLY the same temp/pressure !!!!!)

    You should really replace the temp sender with a pressure sender (far more sensitive than temperature.... which is why they are used in the first place - and this will also require you to change your PID characteristics) - which may/may not be possible with your PID....

    The normal way to change brew temp with a HX is by altering the length of the cooling flush...... and that works quite well.

    None the less an interesting project.

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Actually it was Ken Foxs article that encouraged me to go for it.

    "If you are considering modifying your HEX machine by putting in a electronic temperature control with a PID, I hope this post will encourage you to do so. Every machine is going to respond to PIDing differently, but I think it will be a rare HEX machine that does not have better inter and intrashot temperature consistency after the modification, plus you will be able to actually control the temperature of your straight shots with not a lot less accuracy than some of the mega expensive double boilers that are either now being sold or will soon be released on the market. When the occasion calls for frothing, just push up the boiler temp and froth away; temperature stability of shots going into milk drinks is not all that important, at least in my opinion."

    Thanks for the diagram, it is the first one i have ever come across (and none for the BZ99) but it appears to confirm what I had suspected that the SSR output will connect to the 2 black wires on the preasurestat. I will confirm all of this with my fluke before power of course :)

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    I saw the posts for the "study" on home barista, and I am interested in how the original data looked. I am also interested in the longer term data with/without PID over 20+ successive shots. HX machines are built to have inter-shot stability after initial flushing. Would the lag of the PID compared to the pstat make any sort of difference in this case?

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    monkey66,

    It sounds like Ken might have set the HX up a bit like a single boiler machine (like the Silvia)..... with a brew temp and a frothing temperature.....

    So as long as you dont draw too much from the HX it will be at boiler temp..... until the water in the HX is depleted - after which the temp will drop...... and then you switch to texturing temperature and wait for it to heat up (or just leave it on that temp for milk based shots).....

    Whilst it may improve the espresso shot temperature, you would have to wait for enough heat to transfer from the boiler to the HX after each shot (just like the Silvia reheating) and wait for it to get to steam temperature (just like the Silvia - only it will take longer as the volume is greater).....

    So you have just converted your HX into an expensive Silvia..... with possibly better tasting espressos...... as long as you are willing to wait between shots (It takes my HX 5 minutes to stabilise to boiler temp..... but I can extract shots at my ideal brew temp every 40 seconds or so.... and texture milk at the same time..... just as it is!) ;)

    Mmmmm...... I dont think I would bother. :-/

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by JavaB link=1174149362/0#10 date=1174223863
    Mmmmm...... I dont think I would bother. :-/
    Me either JB :-?....

    In my view, if the intention is to keep the machine running as a standard HX machine, then PID control is just not worth the trouble or the money. If you have access to plenty of money and machines, sure, buy another machine and set it up as a dedicated Steam Boiler and set your original up as a Brew Boiler. In the end, would be wayyy cheaper and more effective to buy an Expobar Minore which is designed to operate as a Dual Boiler machine and a more sophisticated PID controller could be used on the Brew Boiler.

    Mal.

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    I dont understand all this talk of brew and steam issues.

    My machine works fine for both brewing and steaming as it stands. All I want to achieve is a faster/shorter heating cycle and finer adjustability of the temprature.

    I accept the stability gains will not be ground-breaking but the flexibilty and consistancy should be improved.

    I am greatful for all the advice (especally the schematic) but I am a little supprised by the negativity towards this project. All i am doing is refining an already good product.

    I practically never make more than 2 shots at a time so 20-30 shot stability is largly academic. I (like most of us) have spent some years refining and practicing my grind/distribute/dose practices and am just looking for some improved temp control.

    I dont understand *how i am creating an expensive Silvia. The only component I am upgrading is the preasurestat, all the other virtues of the BZ remain. Currently the HX temp is directally changed by the boiler temp, hense changing the p-stat settings changes the temp. *The recovery time will be as it is now (if not a little faster as the PID should be quicker than the p-stat) so why would anything else be effected?

    How could buying a new machine be cheaper and more effective than an 80buck replacement/upgrade of the preasurestat? i am not looking to emulate a dual-boiler machine, just make the best of my existing one.

    I reciently replaced the Fulid-o-tech OPV with the new Exobar one which can actually regulate to 9bar (more than any of the standard fulid-o-tech opvs I have ever seen). This was a great upgrade and a significant improvement to my espresso, I recomend it to everyone using the standard part. Now I dont see a huge difference in upgrading the p-stat. Of course it is temp not
    preasure controlled but these are all relitive inter-related liniar values within an espresso machine.

    I have spent some time *using the Minore (or Brewtus II in the UK) and whilst it is a very nice machine I prefer the BZ99, less flushing issues and you can brew and steam at the same time (although I do like the looks).

    Perhaps i have got this all wrong and you guys are right. Do you have examples where an HX (like mine) has been Pidded and it was a step backwards?


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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Monkey 66:

    Pressurestat: boiler temperature 116 -118º
    Brew temperature: depends on length of flush

    PID: boiler temperature: 116º steady
    brew temperature: stiill depends on length of flush

    Youve stabilised the 2º boiler variation in the boiler to zero variation.... Great. But that wont affect your steaming.

    Heat exchanger water will be around 116º (variations because of the thermocycle effect) -- still way too hot for brewing coffee

    So youll have to do a cooling flush to bring it down to around 93º.

    What have you achieved in so far as superior temperature control goes?
    -Nothing, really.


    UNLESS: you want to use your expensive HX machine to make espressos only, in which case youd set a much lower PID temperature for the boiler which is stuitable for that sole purpose.

    --Robusto



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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by monkey66 link=1174149362/0#12 date=1174237423
    I dont understand all this talk of brew and steam issues.

    My machine works fine for both brewing and steaming as it stands. All I want to achieve is a faster/shorter heating cycle and finer adjustability of the temprature.

    I accept the stability gains will not be ground-breaking but the flexibilty and consistancy should be improved.

    I am greatful for all the advice (especally the schematic) but I am a little supprised by the negativity towards this project. All i am doing is refining an already good product.

    I practically never make more than 2 shots at a time so 20-30 shot stability is largly academic. I (like most of us) have spent some years refining and practicing my grind/distribute/dose practices and am just looking for some improved temp control.

    I dont understand *how i am creating an expensive Silvia. The only component I am upgrading is the preasurestat, all the other virtues of the BZ remain. Currently the HX temp is directally changed by the boiler temp, hense changing the p-stat settings changes the temp. *The recovery time will be as it is now (if not a little faster as the PID should be quicker than the p-stat) so why would anything else be effected?

    How could buying a new machine be cheaper and more effective than an 80buck replacement/upgrade of the preasurestat? i am not looking to emulate a dual-boiler machine, just make the best of my existing one.

    I reciently replaced the Fulid-o-tech OPV with the new Exobar one which can actually regulate to 9bar (more than any of the standard fulid-o-tech opvs I have ever seen). This was a great upgrade and a significant improvement to my espresso, I recomend it to everyone using the standard part. Now I dont see a huge difference in upgrading the p-stat. Of course it is temp not
    preasure controlled but these are all relitive inter-related liniar values within an espresso machine.

    I have spent some time *using the Minore (or Brewtus II in the UK) and whilst it is a very nice machine I prefer the BZ99, less flushing issues and you can brew and steam at the same time (although I do like the looks).

    Perhaps i have got this all wrong and you guys are right. Do you have examples where an HX (like mine) has been Pidded and it was a step backwards?
    I dont see the attitudes as negativity- the site has many members who come from technical and engineering backgrounds, and so the approaches come from there.
    The comments on this thread have been from a point of view of understanding the workings of hx machines and how, if at all, a PID would help.
    Im all for PIDs on a single boiler (love it on my Botticelli), but understand that balancing the hx flush to where the water no longer sizzles, is how I get appropriate temps- ones where the temp is set by hx tubes running through a boiler at a certain temp.

    A PID will control boiler temp and therefore ultimately the brew temp, but no more than adjusting the pressurestat. You can do the same by doing a google search on what each variation of boiler pressure corresponds to in temp.

    You still have the issue of needing the hx flush if water has been sitting in the hx tubes for more than a short while. After the flush the temp will settle to the temp created by water flowing through the tubes. This is no different to what is achieved by setting pressure via pressurestat.

    It will also not alter the other factors which make up your particular machines foibles- such as how much of the hx tubing is in the water in the boiler.

    None of the replies do anything other than explain the workings of hx machines. I for one would be happy to be shown where my reasoning is wrong- were all here to learn.

    Another alternative is what I do- the PID single boiler for weekdays on a timer, the hx for weekends and big family groups.

    Brett

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Off topic replies have been moved to [link=http://coffeesnobs.com.au/YaBB.pl?num=1174271804]This Thread[/link]

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    monkey66,

    We arent really being negative other than we (as owners of HX machines) cant see the value in what you are trying to do.

    In a single boiler machine or a machine with a separate brew boiler, the PID is closely coupled to the boiler and the water which it contains. Also the group is heated with this water..... so the whole brewing path is kept exactly at your set temperature. The unit wont heat up any faster once the unit has been fitted with a PID as the heater output is reduced as it approaches the set point rather than remaining "flat out" until the thermostat cuts off the heater (at which point the boiler temp has overshot and must be allowed to settle back to the desired brew temp). Both arrive at the brew temp at about the same time - the PID just prevents the initial overshoot. And this works excellently.

    With an HX the brew temperature is loosely coupled to the boiler temperature as is the group temperature..... water via the thermosyphon heats the group (E61) or conduction from the boiler with the other types of groups..... this requires the boiler to be much hotter than the brew temperature (also required to produce steam).... These units are designed for these parameters. So if you replace the pressurestat (maximum variation in boiler temp of second crack) with a PID you will reduce this variation.... only part of which affects the group temp and the HX temperature in any case.....

    But keeping a HX boiler at constant temp wont make the brew temperature stable as it depends on so many other factors (unlike the single boiler or the brew boiler in a two boiler machine). It also wont heat up faster (probably slower in fact) as heating will be reduced as you approach the set point (to prevent overshoot). You also must wait for the brew group to stabilise at the correct temperature before using (and that will take quite a bit longer than getting the boiler up to temperature with either the pressurestat or PID).

    So the best you can hope for is to eliminate a 2 deg C variation in boiler temperature...... but you have done nothing to reduce the 30 deg C variation between HX temp after idle for a period ( 125C) and the desired brew temp (93C).... which is still the major limitation with HX machines - requiring the cooling flushes etc..... and by careful control of the timing of these flushes you can determine the brew temperature (on a non modified HX)... On an HX with a PID you will still have to control these flushes to the same extent.... and you havent gained much, if anything...

    On a HX even the temperature of the water entering the HX will affect brew temperature...... Yet another variable over which the PID has no control.

    A HX is designed to make lots of coffees - one after the other (they are dynamically stable)...... and they do that very well - they are not designed to be a walk up and extract machine (requiring static stability) - and cant be modified to behave in that way......

    A single boiler or multiple boiler machine is designed to be statically stable..... and that stability can be enhanced considerably with a PID which provides excellent static stability- and massively improved dynamic characteristics as well.

    The latest commercial machines have a large steam boiler and one (small) brew boiler per group...... so each group can have its temperature set by the PID for that group. The PID is closely coupled to the boiler and therefore the brew water and provides excellent stability. You can walk up to one of these machines and extract a coffee straight away..... or do multiple coffees if you wish - and both will be perfect.

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Ill swing the other way. Im for PID control for a number of reasons. One is the increased stability of the group temperature. All macines have some form of group heating. In a HX machine, any swing in the boiler temp will somehow translate to a swing in the group temp. So you have some variability. The other issue is longevity of the pressurestat contacts. The BZ99 doesnt use a Sirai pressurestat, but a smaller lower rated pro-sumer unit. While Sirais have a 30A contact rating and are huge, the pro-sumer units are less so. So SSR switching will result in some longevity gains. Then there is the ability to lower the boiler temp to the regime used by Ken Fox in order to achieve single boiler-like operation. This regime is for the espresso purist, but its a quick and easy change to switch the machine from the low flush espresso mode to the higher flush milk steaming mode. So the machine is more versatile. Also adjustments to the steam temperature will also be easier to accomplish. So all in all, youre winning and having some tinkering fun in the process.

    Here are a few things to consider though. Id add the SSR in series to the active line coming out of the pressurestat and then set the pressurestat at some higher boiler pressure (say 1.4-1.5 bar). Then the pressurestat will act as a fail-safe for the PID circuit. Otherwise if the PID controller or SSR fails in the on-state, youll end up heating until the safety valve vents, then the water will escape from the boiler, the auto fill will kick in and itll end in a drained water reservoir, maybe a pump burned out and more... Of course the BZ99 has a low water cut-out in the boiler, so youll probably not fry your element... unless the steam stuff youre auto-fill electronics... Better to be safe than sorry.

    Next to consider is probe placement. The probe will probably respond faster if it is in the water of *the boiler rather than just the steam. But then you may be susceptible to hot/cold spots in the boiler, which will moot the gains that PID can give you. If the probe is in the steam only, it may not respond as fast due to the lower conductivity of the steam. Im really not sure what the best answer is for this one.

    Another issue is response. Youll want it to be quick for steaming. Make sure the proportional band isnt too large or the element wont swich fully on during steaming. So you can compromise your steaming performance if youre not careful. Therell probably be some optimising required to get all the responses and stability sorted out.

    BTW: Im considering using PID control in my machine as well. Currently my Sirai pressurestat swings more than 0.2 bar and the resultant temperature swing is detectable in the group (thermosyphon group). Then theres *the very loud pressurestat clunk that Id like to do away with, and finally the ease of adjustment. I do agree with the masses above that the gains arent as large as in single boiler machines, but they are still there and worth shooting for.

    And just for the record, the top of the line commercial machines from Reneka are HX machines that use PID control of the steam boiler for just the reasons Ive outlined above.

    So go for it and let us know the results.

    Cheers,

    Mark.


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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Adjustable temperature control, and the ability to just rock up and pull a shot without a cooling flush.

    Dont get me wrong, but isnt that going to change your HX machine to similar performance of the EM6910?

    I can understand wanting to be able to adjust brewing temperature for different blends/origins. But I think its going to take a lot more time and $$$ to convert your Bez into a Synesso or FB80.

  20. #20
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr


    Im sure its not going to be a magic bullet, but ease of adjustability and the ability to swap modes seems to me to be worth it. Especially if you already have the parts. Its certainly not going to perform any worse than the current configuration.

    I dont think the OP has any illusions that the PID mod will give Synesso-like performance.

    Monkey66, CS may not be the best site to get tinkering advice. This site is more concerned with home-roasting and getting some awesome beans at awesome prices. Most of the tech types post on home-barista, a.c., coffeed, TMC and the German Kaffee-Netz site (if you can read German).

    Cheers,

    Mark.


    BTW, I was thinking of converting the BZ into a dual boiler machine. In fact its still on the cards and is in the planning stage. I have an older Bezzera Mini bar which is in pieces. Im thinking of running the thermosyphon group off the BZ boiler and using the HX unit to preheat the water, which will then feed a mixer (to lower the temp) and then a Sunbeam EM6900 thermoblock, which will be PIDed. The thermoblock will feed into the thermosyphon reguated Bezzera group. That should give me very precise and active control of the brew temp and a decent head of steam for the milk drinks.

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by Sparky link=1174149362/15#17 date=1174277755
    One is the increased stability of the group temperature. All macines have some form of group heating. In a HX machine, any swing in the boiler temp will somehow translate to a swing in the group temp. So you have some variability.
    Mark,

    I hadnt given much thought to the change in Group temperature...... so I just did a check on the M20......

    I know the boiler varies a bit less than 2 degrees C..... so I expected a reasonable change in the group temp - but the variation measures about 0.4 degrees...... which I dont think will make any noticeable difference....

    The Cimbali group is very, very heavy brass and is passively heated by conduction from the boiler- and this may have something to do with the stability..... but Im not going to worry about a 0.4C variation. ;) I doubt my cooling flushes would be that accurate :-/

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Hi JavaB,

    Horses for courses. The PID mod may not that earth shattering on a HX and its effect will vary. My Sirai is still over 0.2 bar fluctuation and results in quite a few degrees variation in the group. Im in no hurry to modify the machine, as I have other projects, but to get rid of the relay click and stabilize the boiler temp, it seems like a good way to go, given my surplus of PID controllers and SSRs.

    Certainly to get the dual mode operation out of a HX machine, PID is the only wy to go. My only caution is that Ken Fox did the mod on his Cimbali Juniors. The BZ99 group is still conductively heated, like the Cimbali, but as they are different machines, the results may differ as well.

    Cheers,

    Mark.

  23. #23
    Mal Dimal's Avatar
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Hi All,

    My experiences with the MiniBar before I disassembled her for restoration replicate very closely with JBs numbers for his LC. I just dug out my notes for a range of temperature tests I carried out using a micro-bead K Type t/c sited on top of the coffee puck. I carried all of this out after exchanging info with Mark as a matter of fact, just to ensure that everything worked properly prior to stripping her (the MiniBar) down.

    The initial setting of the Pressurestat was at 1.2 Bar and this was sequentially reduced to 0.9 Bar over the 30 minute period. At this setting and after cooling flushes to steady state liquid from the Group over a period of approx 30 minutes, shot temperatures varied no more than 0.4-0.6+ C throughout the time of the shot. This is the average taken over 15 shots pulled during the 30 minute period and did not seem to be affected by the adjustments to the P/stat that I could measure.

    The instrument reading was particularly stable during the shot with barely discernible fluctuations being observed. I dont own a thermo-logging instrument so all readings were taken directly from the Fluke DMM I own, and with the able assistance of my son to start/stop and time the shots. Initial Group temperature prior to the cooling flushes was very stable at 116-118C at the commencement of testing and I imagine if I would have charted this against the operation of the P/stat, an intercorrelated cycle would have been noted. After cooling flushes and during the shot though, the temperature envelope was within the tolerances noted above.

    Needless to say, I am very satisfied with the performance of the little MiniBar and dont intend converting to PID Boiler management. I didnt really pay all that much attention to the switching noise of the P/stat but I dont think its going to be a huge problem as I suffer from a bad case of industrial deafness.... other members of the family may complain though, will have to wait and see ::). I have already installed a slave relay to switch the element load current and at this stage, thats about all I intend to do.

    As you say though Mark, horses for courses and I really just want to enjoy a great coffee at the end of the day, so thats my main driving passion.

    Cheers,
    Mal.

  24. #24
    Senior Member robusto's Avatar
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Theyre a beautiful set of numbers, Mal. Great thermal stability.

    The pressurestat cycling is one of those things that, if you become aware of it, you hear it. If youre not aware, you dont. The jury is out in my place as to whether it is annoying or can become so.

    --Robusto


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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by robusto link=1174149362/15#23 date=1174296092
    Theyre a beautiful set of numbers, Mal. Great thermal stability.

    The pressurestat cycling is one of those things that, if you become aware of it, you hear it. *If youre not aware, you dont. *The jury is out in my place as to whether it is annoying or can become so. *

    --Robusto
    At my place if the coffee flows and the hot waters available for tea, most things can be put up with!
    Brett

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by Mal link=1174149362/15#22 date=1174292013

    The initial setting of the Pressurestat was at 1.2 Bar and this was sequentially reduced to 0.9 Bar over the 30 minute period. At this setting and after cooling flushes to steady state liquid from the Group over a period of approx 30 minutes, shot temperatures varied no more than 0.4-0.6+ C throughout the time of the shot. This is the average taken over 15 shots pulled during the 30 minute period and did not seem to be affected by the adjustments to the P/stat that I could measure.
    Yep, Ive found my temperature to be as stable as I require it and when measuring the flow temperature from the group have found a similar very small degree of variation.

    I remember reading somewhere about a stability problem with thermosyphon groups at idle where the temperature of the groups became erratic. From memory it was fixed by a solenoid and some sort of sensor in the flow path so that when the machine was at idle the flow was stopped.

    The article said something like - The thermosyphon system is designed for dynamic stability (just like every other part of an HX coffee machine) and has problems with long periods at idle as the temperature differential required for steady water flow disappears, flow slows and eventually may even stop, the group cools, flow restarts etc....

    I would imagine this cycle would be a much longer period than the boiler cycle. I wonder if that is the effect Mark is seeing?

  27. #27
    Senior Member robusto's Avatar
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    JB, To test the extremity of a commercial HX, have you considered running water continuously through the group, and seeing what happens to the temperature? Im not talking about the 60-odd mls for a double shot, but a couple of litres.

    If the system stays in harmonious thermal balance, any worries about recovery would not be an issue then.

    Just a thought.

    --Robusto


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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Would be very similar to pulling 30 shots in succession. Not a continuous flow, but 60 ml, stop for 30 sec, 60 ml more, etc. until you reach about 2 l.

    Track thermal stability in that situation, do the mod, and compare the modded and unmodded data.

  29. #29
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by robusto link=1174149362/15#26 date=1174300558
    JB, To test the extremity of a commercial HX, have you considered running water continuously through the group, and seeing what happens to the temperature? Im not talking about the 60-odd mls for a double shot, but a couple of litres.
    --Robusto
    Robusto....

    Nope havent done a couple of litres but I did try about 150 ml per group and the temperature remained within the 0.4 degree from the start (after cooling flush)...... and seeing I normally only draw 60 ml every 45 seconds or so...... which makes it 150ml in about 2 minutes 30 seconds.... and it takes less than 5 minutes at idle for the water in the HX to reach boiler temp....

    I figured that is pretty damn good. During the Home Barista review of the La Cimbali Jnr they ran water from the group for a minute with less than 0.5C variation. Dan Kehn commented "No prosumer HX machine that I’ve tested is capable of such lengthy tail-end stability. "

    What makes that test most interesting is that the boiler (being much smaller than my 17L monster ;)) would almost certainly cycled on the pressurestat during the test - and it still maintained the brew temp within 0.5C :)

    Might try a larger volume soon just to see..... but Im totally happy with the 150ml test.

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr


    JavaB, the thermosyphon is designed to keep the group heated during idle periods. During operation the thermosyphon is interrupted.

    As for the oscillations, Ive havent seen them since. Now the group is stable to about 0.2 C during an element cycle.

    Im still getting used to the machine, so PID is not on the cards yet. The huge HX tubes mean that I can flush for ages and see very little change in temp. However, this is just an observation and not rigorous. Until I get a naked PF going and can use my thermo-filter contraption, the machine will remain a mystery, which I will continue to tryand feel my way through.

    Cheers,

    Mark.

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by Sparky link=1174149362/15#29 date=1174305104
    JavaB, the thermosyphon is designed to keep the group heated during idle periods. During operation the thermosyphon is interrupted.
    Ah.... maybe my recollection was back to front..... and it was a machine that didnt interrupt during the pour........ Old age makes you...... now what was I going to say..... ah thats right .... forget ::)

    As for the oscillations, Ive havent seen them since. Now the group is stable to about 0.2 C during an element cycle.
    WOW thats excellent! I cant seeing you do much to improve on that. I dont think a PID will make any noticeable difference in that case.

    The huge HX tubes mean that I can flush for ages and see very little change in temp. However, this is just an observation and not rigorous.
    Thats also the big plus with the La Cimbali. They use what looks like a mini boiler which is only slightly submerged in the water...... I think it holds well over 100ml of water mainly heated by the steam..... so that it is slower to heat up towards boiler temp than it would be if fully immersed in water (and also reduces the required cooling flush to a maximum of 120ml) :)

  32. #32
    Mal Dimal's Avatar
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by Sparky link=1174149362/15#29 date=1174305104
    However, this is just an observation and not rigorous. Until I get a naked PF going and can use my thermo-filter contraption, the machine will remain a mystery, which I will continue to try and feel my way through.
    I think we all know by now Sparky, that perfection is the only target that you consider worthy of attainment ;), and we all learn from your exploits, no doubt about that 8-)

    Mal.

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Thanks for all your input.

    I posted here as there is far more Bezzera users in Oz than the UK.

    To answer a couple of questions I am using a long t tyoe probe that will replace the p-stat in the boiler and reach into the water, not the steam. I like the idea of using the p stat as a safty device but I dont think there will be a spare hole in the boiler to achive this (but I will look at options). I am intending to use the PIDs secondary alarm output to shut the element at 150deg as an additional safety feature (but of course this will fail if the PID fails) but my understanding is the PID should fail off so there is some cover there (as well as the thermal protection trip on the element and the overpreasure valve on the boiler)

    I am not intending to alter the boiler temp to emulate a single brew boiler type setup, just to reduce the p-stat dead-band and have a more granular adjustment of the temp.

    The thermal dynamics and stability of the large coupled brass block is great and pretty consistant at the moment so I dont expect huge gains just small ones.

    Ill be going for the install in a few weeks and ill let you know my findings.

    Thanks again.

  34. #34
    Mal Dimal's Avatar
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by monkey66 link=1174149362/30#32 date=1174314033
    I am intending to use the PIDs secondary alarm output to shut the element at 150deg as an additional safety feature (but of course this will fail if the PID fails) but my understanding is the PID should fail off so there is some cover there
    Hi again m66,

    This "failsafe" mode of unit failure works ok in theory but in my personal experience over a few decades working in process control, is that the unit can fail just as often with the output high as it does with it off or low. Its better to use a second tier level of safety that is completely separate from the controller such as the P/stat method mentioned by Sparky.

    Anyway, hope you enjoy the exercise of doing the PID conversion and we will all look forward to hearing how it all works out when its up and running. All the best mate,

    Cheerio,
    Mal.

  35. #35
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Hi monkey66
    Id second Mals good wishes- as an inveterate tinkerer, if I thought there was any chance of a gain, Id PID my Bezzera. Ive been hugely impressed with what the PID has done with my Botticelli, except for one thing- Im worried that it may be giving me better flavour than the Bez- bit of tinkering to be done there!
    All the best
    Brett

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    As promissed here is the results...overall i am very happy :-)

    http://www.phpbber.com/phpbb/viewtopic.php?t=179&mforum=coffetimeboard

    many thanks for all your help guys.

  37. #37
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    monkey66,

    Those results are pretty much as Id expect (being a neigh sayer re PID on a HX ;))

    Pressure in the boiler and water temperature ARE linear - but only at steady state.... pressure varies more rapidly than temperature under dynamic conditions. :-/

    When you crack the steam valve... the steam pressure will start to fall instantly... and when it falls by 0.2 Bar (or thereabouts) the pressurestat will kick the heater back on.... and back to full pressure in seconds (12-15 sec in my case).... the water in the boiler will have barely dropped in temperature because of its large thermal inertia.

    With a PID, you open the steam valve- the pressure drops - and will continue to fall.

    As the vapour pressure above the water drops, the water will start to boil slowly, replacing the steam, this will absorb latent heat of evaporation from the water... slowly dropping its temperature..... there is a large thermal mass of water so the drop will be slow but eventually it will be sufficient to trigger the PID which will then turn on the heaters.....

    So a pressurestat is better for steam recovery! It is also better for constant HX temperature as the boiler temperature is more constant...

    But a PID with a pressure sensor will give a smaller dead band than the 0.2 Bar..... could also be adjusted for what ever pressure you desired (without taking off the side panel).... and you can get PIDs which take electronic pressure sensors....

    That would be the best of both worlds. :) :)

  38. #38
    Mal Dimal's Avatar
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Quote Originally Posted by JavaB link=1174149362/30#36 date=1176637364
    But a PID with a pressure sensor will give a smaller dead band than the 0.2 Bar..... could also be adjusted for what ever pressure you desired (without taking off the side panel).... and you can get PIDs which take electronic pressure sensors....

    That would be the best of both worlds. :) :)
    Sure would JB,

    But a decent pressure sensor working within this operating range would not be cheap (think $400+) and most do not come with a signal transmitter (can cost as much again) except at the very top of the range. I guess you could be lucky and pick up what you need from evilbay but that would be enormously risky in my view. As you say though, it would provide an absolute level of control over the boiler 8-), no doubt about that.

    I guess with a straight temperature controller as m66 is using, you would need to start out with a very high derivative setting and an extremely narrow proportional band to have any hope of achieving anything resembling useful control. Ah well, experimentation is lotsa fun. Hope you get it sorted to your satisfaction m66,

    Cheers,
    Mal.

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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    i gotta say it is working very well at the moment..once warmed up the temp stability is improved and so is the espresso. I just find myself tweaking up a bit for reliable steam.

    Being able to adjust the temp to fine tune blends is great.

  40. #40
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Update - I have been living with the PID for 4 months now and have learnt a few things. I am running a few degrees hotter than where I started. After repeated testing I concluded that my brew temp was too low with my current flushing regieme. I adjusted the cycle time and overshoot and now get a faster esponse from the PID.

    A big change was to install a 10mm longer low water probe (dropping the ammount of water and increasing the steam volume. Some of you will be aware that steam is a lot more efficient than water at transfering heat and this has significantly increased the HX efficiency and recovery time.

    Overall the machine is running great. I can adjust temp for different beans at will and also have a far more accurate reading of the temp (for instance after foaming milk) sobetter informed when to loack and load the pf.

    I am toying with the idea of a preheater coil of copper pipe around the boiler to heat up the water hitting the HX so it is not stone cold and does not have such a large thermodynamic swing.......of course Icould just be coming to the end of stability available from this design :-)

  41. #41
    Senior Member robusto's Avatar
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    Good to hear it is all to your satisfaction Monkey66. If youre happy, thats what counts.

    We had a lengthy discourse here some time ago on the efficiency or otherwise of steam as a thermal conductor.

    I would have thought that dropping the water level would REDUCE heat transfer to the exchanger. But if you are satisfied with the result, stick with it.

    -Robusto

  42. #42
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    Re: Hi from the UK - help with Bezzera BZ99 PID pr



    Hmmm, very interesting indeed. I think the PID readout for the boiler and the ability to easily and accurately adjust the boiler temp would be a bonus indeed. If you can get the steaming response in line with what youd get with a pstat, then all the arguements about fitting a PID are moot IMO.

    As for the preheat.... dont do it! A HX machine works by mixing cold water with superheated HX water. If you change this by pre-heating youll be flatout getting it to work, unless you drop the boiler temp dramatically and essentially have a large single boiler machine with little steaming capacity (similar to what Ken Fox achieved with his Cimbali).

    Thanks for posting the update.

    Cheers,

    Mark.


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    Re: Hi from the UK - help with Bezzera BZ99 PID pr

    To confirm, the steam is fine now the PID is correctly set up.

    Strange as it is to believe steam is about 5 times more efficient at transfering heat than hot water. There was some debate on a few forums but the scientists nailed it with some definitive maths and thermodynamics.

    So if you want to have a hotter HX drop the water level in the boiler (oboviously not so much as to expose the element and the hot water capicity wil be lowered).

    The issue with preheating HX water comes about because of the small HXs in home machines. Having spent some time with my fluke and thermocouple I believe (and certainly for the Bez) that in most shots from a small HX machine the temp reality is toohot/just right/too cold through the shot. the temp drop when that cold water hits the HX is great.

    It would seem the only way to get stable temp through the shot is a large commercial HX, or better still dual boiler......anyone got a spair GS3 :-)



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