I decided to waste a couple more days repeating the shot temperature thermometry on my two PID-modified Cimbali Juniors last week. A new test I devised was designed to measure shot temperatures delivered in the face of variable intervals in-between shots, with frothing mixed in. I did not do exactly the same test on both machines but it was pretty obvious that my almost 11-year old pourover Vibe Junior was much more temperature stable during this type of test than was my current vintage Rotary D1 Junior. I have learned previously that the rotary machine "recovers" shot temps quicker than the vibe and therefore the intershot intervals are 30 seconds longer on the closely spaced shots on the rotary machine. Here are representative shot temperature curves, with legends, that show what I mean:
Granted, the two machines are different, but they share identically sized boilers, identical groups, and identical heat exchangers. Both were PID'd in essentially the same manner. Why the difference? the only obvious difference that should matter for shot temperature stability is boiler AUTOFILL, present in the plumbed-in rotary but absent in the vibe machine, whose boiler must be manually refilled with the aid of a sightglass. Autofill tends to be sensitive and anyone who owns a machine with autofill knows that the autofill kicks in at unpredictable times. Anything that diminishes boiler fill (like frothing, or using boiler water for drinks) will increase autofill activity.
I discussed these findings initially with Jim Schulman, who agreed that the autofill was the likely culprit in making the plumbed in rotary machine less temperature stable on a complex shot series that included frothing. We discussed possible ways to defeat this such as having a switch one would use to defeat the autofill normally but allow the autofill to work once daily, or however often one desired and when one chose (i.e. not when making espresso drinks). The risk of that of course is that you forget to turn the autofill on again so the element eventually burns out when you empty out the boiler. Of course there are other options such as putting in on a timer, something Jim also brought up.
I had a conversation with Michael Teahan in Los Angeles today, who as always is a fount of espresso knowledge. Rather than using an on-off switch, Michael suggested using a relay to make sure the autofill doesn't actuate DURING A SHOT, but functions otherwise. He mentioned additional options for making this sort of thing work, such as slowing down the inflow into the boiler from the autofill, but the relay seemed the easiest to impliment.
Before actually trying to impliment this modification, however, I thought it would be worthwhile to repeat the shot series with the autofill bypassed. Here is a picture of the autofill circuit in my machine, on the left side of the boiler:
The autofill probe (as can be seen) is insulated in a sleeve and sticks into the boiler where it contacts boiler water; when it does, it completes a circuit with ground, and turns off the autofill as it senses the correct level. Here is how I defeated it, temporarily for purposes of conducting this experiment:
The temporary wire bridges the circuit and shuts off the autofill. This was confirmed by draining 8 oz of boiler water out and seeing that the boiler autofill did not actuate. I then reversed the change (removed the wire), obviously with the machine unplugged, then replugged in the machine and the autofill immediately acutated for about 15 or 20 seconds to refill the boiler.
With the autofill disabled, I repeated the shot series exactly as before. Here are the new shot curves:
As you can see, the shot temperature curves are now more tightly grouped, with a reduction in both the maximum and minimum shot temperatures. I haven't done any mathematical evaluation of these data, but visually it appears to me that the variability in shot temperature has been reduced by at least a third.
What remains to be determined is what is the best way to get this level of improvement in actual shot temperatures without risking burning out the element or causing a housefire :P My impression is that a simple relay, powered by the input solenoid wires (as suggested by Michael Teahan) is the right approach, however I'll have to install one and test again to confirm that this very simple modification in fact has the desired result.
ken p.s. this is crossposted on home-barista.com; please do not replay in both threads.
> I discussed these findings initially with Jim Schulman, who agreed that the > autofill was the likely culprit in making the plumbed in rotary machine less > temperature stable on a complex shot series that included frothing. We > discussed possible ways to defeat this such as having a switch one would use > to defeat the autofill normally but allow the autofill to work once daily, > or however often one desired and when one chose (i.e. not when making > espresso drinks). The risk of that of course is that you forget to turn the > autofill on again so the element eventually burns out when you empty out the > boiler. Of course there are other options such as putting in on a timer, > something Jim also brought up.
> I had a conversation with Michael Teahan in Los Angeles today, who as always > is a fount of espresso knowledge. Rather than using an on-off switch, > Michael suggested using a relay to make sure the autofill doesn't actuate > DURING A SHOT, but functions otherwise. He mentioned additional options for > making this sort of thing work, such as slowing down the inflow into the > boiler from the autofill, but the relay seemed the easiest to impliment.
<snip/>
> What remains to be determined is what is the best way to get this level of > improvement in actual shot temperatures without risking burning out the > element or causing a housefire :P My impression is that a simple relay, > powered by the input solenoid wires (as suggested by Michael Teahan) is the > right approach, however I'll have to install one and test again to confirm > that this very simple modification in fact has the desired result.
I'm not sure how many shots you would normally pul in succession (when using normally nit testing..) but you might also consider a solution that embodies a combination of Jim's and Michael's suggestions: a time delay relay powered by the input solenoid wires that switches the autofill off for a predetermined period of time say 2 minutes or whatever is reasonable.
> I'm not sure how many shots you would normally pul in succession (when > using > normally nit testing..) but you might also consider a solution that > embodies a combination of Jim's and Michael's suggestions: > a time delay relay powered by the input solenoid wires that switches the > autofill off for a predetermined period of time say 2 minutes or whatever > is > reasonable.
Why do something simple when a complex option exists?
:-)
In reality, my usage pattern is mostly making shots for myself, which tend to be spaced at greater intervals than 10 minutes and hence this is all irrelevant:-) When I have friends over they almost always ask for milk drinks. The acceptable variation in brew temperature for espresso going into a milk drink has to be hugely greater than for a straight shot, so again this is probably irrelevant. It would be more important if you were having a bunch of alties over and you had to build a complex drink order, some milk drinks and some straight shots. The likelihood of that happening in my town is zero. I don't think I know a single person who regularly drops by who would notice a brew temperature difference of 3 degrees F, even in a straight shot. Like most people, they drink stale plonk most of the time and my drinks, made from fresh coffee with acceptable barista skills far surpass anything else they drink the rest of the time, so they'd view this sort of stuff as amusing.
So, there is no practical application to any of this for me, where I live.
But it is an interesting question that I haven't seen discussed before so getting a better understand of it, while "fixing" my machine, may provide some cheap entertainment. There are reasons why dual boiler machines, especially 110v. dual boiler machines, can have some of the same temperature stability problems with a mixed drink menu. These would include the electronics in the brainboards which are setup to prevent the machine from drawing too much current and hence tripping the circuit breaker, due to trying to power both boiler elements at the same time if there is a lot of frothing going on. 220v. machines presumably would have less trouble with this.
I think this testing may shed some light on real usage situations that may show flaws in machines that would not be demonstrated on a simple shot series test that excludes frothing. Since milk drinks are the norm in N. America, this could result in an impression of better thermal performance than can in fact be obtained in typical usage.
> I think this testing may shed some light on real usage situations that may > show flaws in machines that would not be demonstrated on a simple shot > series test that excludes frothing. Since milk drinks are the norm in N. > America, this could result in an impression of better thermal performance > than can in fact be obtained in typical usage.
> ken
careful.. they'll be asking you to do beta testing ;-)
The first graph's vaguaries look right too. The initial shot temps aren't affected since they are determined by the group tempeature and the part of the HX in the steam. Performance degrades late in the shot showing the HX has recoivery problems after the autofill works.
In general, people's beef with autofills is not temperature problems, but them activitating in the middle of a shot and killing the pressure. BTW, locking it out while making a shot is a bit tricky. You cannot use the running of the motor as the lockout condition, since it would then shut itself off; instead, one needs to install a double pole brew switch, and use the extra pole to operate the lockout relay.
On Wed, 12 Jul 2006 17:32:31 GMT, "I->Ian" <some...@nowhere.com> wrote:
><snip> >>one needs to install a double >>pole brew switch, and use the extra pole to operate the lockout relay.
>Couldn't you wire the autofill through the NC contacts and use the >brew switch to open the NC contacts when pulling a shot?
Good idea! You'd still need an extra pole on the brewswitch, but it does make the relay unnecessary. Just short out the autofill wand through the NO side of the extra pole on the brewswitch.
My la Vittoria Single Group (full size commercial version of the la Valentina), says in the manual "The boiler filling function is disabled while coffee is being made. If at the end of the coffee-making cycle the boiler level probe is above the water level, the boiler filling function will be enabled to restore water level."
I just got this machine hooked up last night, so I can't confirm yet if the manual is accurate, but I thought it might add to the discussion since if true, others may want to check if their machines are already acting this way without the need for a relay. Cheers,
>What remains to be determined is what is the best way to get this level of >improvement in actual shot temperatures without risking burning out the >element or causing a housefire :P My impression is that a simple relay, >powered by the input solenoid wires (as suggested by Michael Teahan) is the >right approach,
I agree. For longevity & reliability, I'd also suggest using a triac-based electronic relay (eg; an Omron optical relay) instead of an electromechanical relay. There are standard mains-rated models with crimp lugs that'd be ideal for adding to your existing wiring.
> however I'll have to install one and test again to confirm >that this very simple modification in fact has the desired result.
As you've noticed, the danger is that the boiler could go dry if the operator forgets to re-enable the switch after pulling a shot. To me, there are two obvious ways to solve the problem:
(1) Use a relay/optoswitch with an NO (normally open) contact in place of the jumper you have in your photo. Drive the coil via a pushbutton on the front panel or on the counter. You could even use a standard footswitch on the ground. The operator would hold the switch or tread on the pedal while pulling the shot to prevent a fill cycle during the process. You'd need to make sure they understood the importance of letting the switch go as soon as they finish the shot.
(2) Use a timer circuit (eg; 10-15 seconds) to drive the above relay, & trigger the timer with one of the above switch options. If it were me, I'd tap a threaded hole into the group housing & bolt on a microswitch, so that the tank-fill solenoid would be disabled for X seconds after locking in the portafilter.
All the required parts are standard industrial controls that are easily obtainable & relatively inexpensive (well, much, much cheaper than a PID, at least. ;)
IMPORTANT SAFETY NOTE & DISCLAIMER: Unless you can prove that the fill solenoid & associated wiring is isolated from the mains, don't be tempted to eliminate the relay & wire straight to a standard push switch of pedal switch, as it'd be both a potential safety hazard & almost certainly illegal. A correctly wired up relay should be both legal & perfectly safe. ALWAYS DOUBLE & TRIPLE CHECK YOUR WIRING BEFORE RECONNECTING THE MAINS, & if in any doubt, have it checked by a qualified electrician. -- W . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^---------------------------------------------------------------
> ><snip> > >>one needs to install a double > >>pole brew switch, and use the extra pole to operate the lockout relay.
> >Couldn't you wire the autofill through the NC contacts and use the > >brew switch to open the NC contacts when pulling a shot?
> Good idea! You'd still need an extra pole on the brewswitch, but it > does make the relay unnecessary. Just short out the autofill wand > through the NO side of the extra pole on the brewswitch.
