larryroohr Senior Member Joined: 10 Aug 2009 Posts: 15 Location: colorado Expertise: Just starting
Posted Sat Sep 26, 2009, 6:04pm Subject: Le'Lit PL041 mod's
Did a couple things to my PL041 today.
Installed the Auber PID (Sylvia version). Only immediate hindsight "oh shait" was I could have removed that ridiculous tamper and mounted the box next to the grouphead instead of on the side, and saved me one drilled hole and the cost of a stainless-steel worthy drill bit. Oh well.
Have the temp sensor on the boiler with a 3" hose clamp and thermal grease. No convenient screws to attach it to and my boiler doesnt have the thermal well I saw mentioned in another thread, seems fine though, it's just below the water inlet and across from it.
Set the PID to 206deg for now, thats where I see 202 peaking in the basket. Drilled a hole in a basket and snaked a thermocouple up there, measured with coffee and without (with a plastic bottle cap in there to subtract some volume). Dont trust all these rube-goldberg hack measurements but it's completely adjustable now so I can dial it in to what tastes best, assuming I have any taste at all. I did cal my thermocouple meter with boiling water and it's on the money for 5250 ft and todays barometric pressure off a weather web site, and matches the Auber dead nuts, so thats good.
I think tomorrow I'll plug the bimetal thermal sensor back in and see how bad it's hysterisis is, watch it be tight and on the money, that'd piss me off (nahhh).
Also stuck 25 ohms in series with the vibe pump, 2 50 ohm 10w resistors in parallel. Before doing that I measured 10.5 bar at 2oz/30sec, now it's down to 7-8 bars at the same flow. I have no idea how to cal a pressure gauge, so thats a hail-mary. Interesting that before I stuck the resistor in I didnt notice any effect from the heater turning on or off, now thats whats responsible for the 7-8 bar variation, vibe pumps must be pretty non-linear at lower voltages. Might not be done messing with this one yet, could cut off the heater while the pumps on. The 33.3 ohms I used first dropped my voltage 12 volts, so the 25 should be dropping about 9, my outlets are at 122V here.
So now we'll see. The whole reason for this is the warmup time on my Anita hasn't worked out for the way I operate in the morning through the week, after Le'Lit cools off completely I'll check and see where I'm at for power on to reasonable stability time. Been thinking another control that turned it on in steam mode for the first x minutes, then dropped to the pid, might be a good idea for getting the grouphead where it needs to be quick. If Anita wasn't so danged purty I'd dump her in a heartbeat, seriously though, not comfortable with HX yet, even with Eric's thermo-probe. I'm keeping her just in case.
The Auber is factory set to 221 degrees for sylvia, delta of 19 deg to 202 at the coffee, if my hacking is correct LeLit is set at 206, quite a difference a few inches makes, all in all a tighter system if you ask me, only good if you can control it (pid).
The Auber is a bit under damped with sylvia loop parameters, understandable with the smaller boiler and higher wattage heater in the LeLit, higher gain with the same phase lag to the outside of the boiler for the sensor. I'll see if I can address that when time permits, it still converges in a couple minutes.
Hope someone finds this useful. Don't know if it was worth the time,money, or trouble yet. Cant say I didn't enjoy my day though 8^).
Wow Larry, you went right to work on this! The 25 ohm seems a bit too much voltage drop for the pump. (what is the voltage at the pump?) You weren't that far off to begin at 10.5 bar. Either 3 50ohm or 2 33ohm in parallel will get you 16 ohm. That might be better.
On your 206F boiler temp, that sounds reasonable. Is the probe on the top, middle, or bottom of the boiler side? (You will see lower temps towards the bottom.) Having the group form the bottom of the boiler makes for a much tighter delta here and easier to get stable brew temps than Silvia. Good luck on the project and please keep us updated. A bunch here are interested to know more on how this machine behaves. Thanks!
Yeah, I might take your advice on the voltage drop, still mulling it over. Still leaves you with pressure depending on grind/tamp, dependent variables, I'd still prefer an opv set at whatever. I'm sure I'm thinking about all this too much as it is, and I want to try lower pressure so this should be fine. My grinder is set for the standard shot time on Anita with her set at 9 bars, I'll see what it does in the morning. The resistor plugs in and out pretty easily.
The thermocouple is about half way down the boiler, it was either that or right at the top.
Caveat, I know better than to be sure about any of this at this point, so please point out anything I may have wrong about any of it. I wont be able to get back to it until next weekend. Definitely appreciating the issues involved with espresso machine's. All this was done with the lid off, so ambient temp around the boiler is lower than normal and there is more air flow over the surface.
Stuck a thermocouple (that matches the PID and cal'ed out correct in boiling water) on the top of the boiler, mashed it down with a chop-stick, steady state there's a 5 degree F difference between the top and halfway down where I put the PID sensor.
Looked at the parts diagram and even though the boiler is attached to the grouphead at the bottom there is a tube from the bottom of the boiler up to the top, I assume, and it makes sense, that the water feed is via this and so the water does come from the top of the boiler, maybe the top would be a better place for the pid sensor.
Then I plugged the bimetal thermostat back in and watched it cycle with the PID and the thermocouple on top of the boiler, this was interesting.
a. heater turns on with pid sensor at 187degF, top of boiler at 193 b. heater turns off ~20 seconds later, pid at 196, top at 213 c. top continues to rise for 30 seconds, max at 226, pid at 213 at this point d. another minute later pid max'es at 214, top has dropped to 221 e. 1.5 minutes later the pid is reading 206 deg, top is at 212.
This point is close to where my temp measurement in the portafilter said 202deg, and the top to pid delta is close to the steady state delta of 5 degrees, means things have settled out in there. Thats 3 minutes after the heater turned off. So if my portafilter measurement was correct (which I'm doubting), surfing my Lelit in my house, with the cover off the machine, would require a 3 minute wait after the heater turns off. If you try to flush the temp down instead you'll have to be very quick about it, as the temp drops fast and the heater turns on very quickly.
Some things I assume/observe from all this.
The stock thermostat is in contact with the water (?). Is it? Heater on/off behavior indicates so.
The water itself max temp was hotter than the max temp I measured of 226 degrees at the top of the cycle on the top of the boiler, has to be.
The heater itself possibly has enough thermal mass relative to the 220ml boiler to keep pumping significant calories into the water after it is shut off.
The heater is spec'ed at 1050 watts at 110V, at my 122V thats 1290 watts, which should raise 220cc of non boiling water 30 degrees in about 22 seconds, fits ballpark with the 20 seconds on time I observed and the 30 degree hysteresis on the bimetal thermostats I've seen (someplace, may be wrong), and the 34 degree max temp on top to 'heater on' temp. I'm assuming there is no conversion to steam in there.
Heater on time to the next heater on time was 8 minutes (lid off the machine).
So thats what i did today, right or wrong. I'm surprised at how hot things got with the thermostat in place "IF" my portafilter measurement and therefore delta temp between the boiler and the coffee is correct. My shots this morning (pid) seemed an improvement from what I've gotten before, but still nothing like the two times I've been blown away at a coffee shop, prolly a zillion reasons for that though.
I'm really doubting my portafilter measurement. Flow rate would be real important with this small boiler, the boiler water inlet looks like it's halfway down and not at the bottom, if thats true the cold water would mix faster towards the top it seems.
Ought to take the cover off, plug the thermostat back in and do the styrofoam cup measurement at different times after heater off with half an ounce of water or so, that would be a quick way to tell if my 3 minutes is close or if I'm out to lunch here.
This machine is up to temp in 10 minutes or less, the boiler is steady at 5, and the group in 10. Sweet, thats what I'm looking for. Now I just want to be confident I have the pid set right, and while I'm at it maybe gather some useful info for non-pid users (hope I havnt done the opposite here).
Good stuff Larry! Your temperature numbers look typical to what I see on the Venus. Offsets, cycle times etc. (you may notice some differences when the covers are on and the machine is fully warmed up for 30 minutes or more. The losses are slower. )
So for the temp surfer watching that thermometer overshoot your boiler temp, you soon loose patience with the thermostat. You know the btu output of the heater, you know you want the boiler 10F hotter than it is now (for instance) .... How long do you need to turn the heater on to get the boiler to settle where you want it 30 seconds later? (Do some test to figure out how many degrees rise in boiler temp you get per second the heater is on. Include the rise after the heater shuts off) This should be fairly consistent over a reasonable wide range. (hint hint, Larry already provides this answer in his data above.)
Even with your PID, you will still have a boiler at 260F or so after you finish steaming milk. How long do you need to run the pump to flush enough cool water to bring the boiler back to 210, grouphead back to 193F so you can pull the next shot?
This is how I ended up doing temp surf on Venus using a thermometer. I have a cycle for straight shots and one to get back and forth to steam temps. When the machine sits idle, I let the thermostat handle it.
One more thing to check here is to see how much the brew temp drops during the shot, as cool water enters the boiler, how quickly does in make it's way into your shot?
Sorry I forgot to address a couple issues/questions....
The thermostat is not in direct contact with the boiler water (at least any that I have seen.. I don't think Le'lit has a thermo-well into the boiler) It just screws into and measures the boiler surface temp.
In regards to measuring actual brew temps at the shower screen, during actual brew flows and pressures. That is the toughest measure to get accurate. I put together a crude basket with feed through for bare tip probe. I used it 6-8 times before I broke the probe tip. My over the basket attempts didn't go so well, then I quit trying to do any more with it. Styrofoam cup will get you close, but will not give you the resolution on how the temperature changes during a shot.
Getting real accurate here is not needed to dial in your shot temperature anyway. Once you are fairly close and repeatable, then you go by shot taste.
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