Temperature PID causing brew pressure drop

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
bscandanavia

#1: Post by bscandanavia »

Hi all,

I'm in the process of debugging an issue with my older Lelit Anna series machine. I've found that when the temperature PID is actively heating the boiler, it results in a power fluctuation to the pump. Using an oscilloscope, I can see that the voltage only drops by about 2V across the 120v AC, but there is a noticeable effect on the pump's output. Presumably there is amore significant current drop (which I have yet to try and measure).

When the PID is actively heating, I can also hear a noticeable change in the pump vibrations and measuring the pressure output shows about 1 bar drop.

I'm actually a bit surprised that the heater current draw is enough to cause such a significant power drop.
Has anyone seen this before? Does it seem like an issue with the AC mains line not delivering enough power to the machine, or is there something else at play?

It's causing quite a bit of frustration as I attempt to mod the machine for pressure profiling, and finding that the PID activity is interfering with the pressure control.

Any help would be appreciated.

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HB
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#2: Post by HB »

You could install a relay to cut off the heating element when the pump is running. That's what Chris' Coffee did for the Quickmill Alexia; it was discussed way back in 2007 in the Buyer's Guide to the Quick Mill Alexia:
jesawdy wrote:...I believe that under normal operating conditions, the new PID kit heater-cutoff relay does not make a drastic difference to the temperature profile. It may lengthen the minimum recovery time needed, but probably not by much. For those folks that already have a PID-controlled Alexia, I wouldn't feel cheated. However, as mentioned in the last post, the pressure fluctuations and noises associated with the simultaneous vibe pump and heater load are a thing of the past.
Dan Kehn

bscandanavia (original poster)

#3: Post by bscandanavia (original poster) »

Oh interesting to see that the problem has been seen before. Many thanks for the tip!

I would still love to better understand why the machine can't source enough current to supply both the pump and the heater tho.
Is it just a function of the internal resistance of slightly under-rated wiring?

JRising

#4: Post by JRising »

bscandanavia wrote: I'm actually a bit surprised that the heater current draw is enough to cause such a significant power drop.
Has anyone seen this before? Does it seem like an issue with the AC mains line not delivering enough power to the machine, or is there something else at play?
It's causing quite a bit of frustration as I attempt to mod the machine for pressure profiling, and finding that the PID activity is interfering with the pressure control.
Don't be too surprised, it's the way all machines like this are.
Make sure there are no significant voltage drops elsewhere that you can eliminate, for example on older machines with a power switch or a brew switch of 0.4+ ohms of resistance, fix that right away, but you'll still notice the element's effect on the pump's sound.

If you really want to try to eliminate all external effect on the pump while still using a little vibe pump machine, maybe replace all wiring to the brew switch and to the pump with 12gauge, replace the power cord with as short a 12 gauge as you can, and find it a 20A receptacle to draw from. It seems like kind of a lot of effort, but stranger things have been done.
Cutting the element completely on an SBDU while brewing may have worse effect on the flavour of the coffee than any barely detectable variance in flow/pressure of a pump noise changing.

bscandanavia (original poster)

#5: Post by bscandanavia (original poster) »

Thanks for lending your expertise. The pressure fluctuation has never been noticeable - but now that I'm attempting to control the pressure for profiling with a PID controller, I'm finding the 1bar fluctuation to be an issue (10% pressure change is not insignificant really).
I'll try upgrading the internal wiring and check the resistance of any suspect components.

thanks again

ragdoll serenade

#6: Post by ragdoll serenade »

I have an Anna, 2.5 years old. Just for your reference, I do get a change in the the pump sound when the PID activates the heating element during extraction. I can also see the needle move on the manometer but nowhere near 1 bar. It is really just a barely discernible fluctuation, maybe one-tenth of a bar. I have a the machine on a 20 amp circuit with no other real load on it. I do kind of wonder if it is possible that this is due to an ageing pump?
Would grind and consequent flow rate have an effect on this as well? Good luck.

bscandanavia (original poster)

#7: Post by bscandanavia (original poster) »

That's helpful info. I recently replaced the pump so I don't think that is the likely issue. I actually went through some trouble and rewired quite a bit of the machine (which turned out to be quite a bit of work)- that helped reduce the pressure fluctuation a bit, but it's def still there... tho to completely rule that out as the source I would need to check all the switches and replace the remaining wires as well.

I'm also using a digital pressure gauge so I wonder if it might have less damping / more sensitive to fluctuations than a mechanical gauge.

It could also partially be the old wiring in my apartment. I've tried different outlets, but there could be some systemic resistance upstream.