PID on a HX...this is my thinking, is it flawed? - Page 3

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coffee_monkey

#21: Post by coffee_monkey »

Switching the 3 way on mine involved lifting the top cover and twist. Takes a few secs.... I did modified my shell for free access though =)

The length/plumbing of the original machine is setup in such way that you can reach steady state in a normal shot pulling pace while keeping a reasonable boiler pressure. With the super-charged HX, you have to set the boiler at lower temp/pressure since now the efficiency of the HX went up (less delta T). That, of course, causes weak steam (which is already not a strength of these Isomac machines). The lengthened HX also changed the dynamic of the machine which causes it to do weird stuff. But please try it out and let me know how it behaves. I want to know if my prediction/speculation is correct.

I don't drink any milk drinks and only kept that option when I need to entertain guests who can't take espresso just yet. Just a nice option to have since I already went thru the trouble to tear out everything. Plumbing is really a major pain the ass...

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jesawdy

#22: Post by jesawdy »

HB wrote:You're thinking about the Cimbali Junior's HX. The Tea's HX is a straight horizontal copper tube (it's pictured in JimP's article Single Boiler vs. Heat Exchanger?).
Thanks for the pic link, Dan. I could not find one yesterday. I wrongly assumed the hot dog tube was the standard design.... before I knew anything about HX espresso machines, I envisioned them to be more like the Tea's design.
Another approach I've been mulling over is to automate the cooling flush. That is, combining an E61 thermocouple adapter, an inexpensive PID, and a SSR controlling the pump. Non-lever type E61s would be good candidates for this modification (e.g., Valentina and the Expobar Pulser).
Now that seems like a more worthwhile effort for non-Levetta folks.

Jason, have you considered EricS's thermocouple adapter and an inexpensive PID as a temp monitor?

jimoncaffeine, please update as to when your article is complete and thanks for the info.
Jeff Sawdy

jasonmolinari (original poster)

#23: Post by jasonmolinari (original poster) »

Jeff, i already have a thermocouple in the screw in the group head, that is how i do my flushing now, and i'm quite pleased with it.I didn't use EricS, since i had made my own before he sold them, i brazed a SS sheathed TC into a hex screw i had made a hole through.

It works OK, my thermocouple reader doesn't have the response rate of a fluke that Dan uses in his videos, so i sometimes overshoot my flush point...installing a PID would have done away with this external reader and wires coming out of my group, but it seems like it is a lot more work than i thought.

jason

lparsons21

#24: Post by lparsons21 »

The more I read about PIDing an HX, the more confused I get.

The article on HXs and flushing seems to indicate that a 20-30 second flush is needed, and then the cup and following cups, one after the other, will be at a consistent temperature. This on a stock HX machine.

From reading here, CG and alt.coffee, it looks like your PID is controlling the boiler temp, not the HX or tube temp. Reducing the boiler temp to something closer to brew temp. Of course, at that temp, steaming would be poor or non-existent, which takes away one of the major advantages of the HX to begin with.

So how about a simple explanation as to why a PID is a good thing on an HX, when the way I read it, it isn't unless you just want to do espresso and not steam.

I'm waiting for my Alex to get here so I can get some hands on, but I wouldn't be adverse to PIDing it IF it would allow more stable brew temp, do away with the flush (or at minimum reduce it) and still steam well.
Lloyd

jimoncaffeine

#25: Post by jimoncaffeine »

lparsons21 wrote: So how about a simple explanation as to why a PID is a good thing on an HX, when the way I read it, it isn't unless you just want to do espresso and not steam.
(My opinions only and I don't consider myself an expert so you probably shouldn't either...)

- In my experience, adding a PID to control the boiler temp will give you better control of your boiler temps. With a commercial pressurestat, in good shape, you may have 2 to 3 degrees of fluctuation in temperature - all the time.

- From what I have experienced and read, without doing some of the exotic mods mentioned, you won't be able to eliminate the cooling flush unless you don't mind not having much steam... If you don't steam milk, I'll bet that you can get pretty close to eliminating the cooling flush with the pid.

The H/X machine is a compromise. It allows one boiler to have hotter water than you want to use to extract coffee (but good for steam) while allowing you to get cooler water via the hx circuit. (allowing you to get cooler water = with the proper technique: cooling flushes, some experiments with temperature drop with use and rise when static over time, etc.)

Is it a good thing:
It is if you want tighter control of the boiler temps and easier ability to change the temps.
It is if you think it would be fun.

Is it a bad thing:
If you expect that it will eliminate cooling flushes and produce good steam - at the same time with no other modifications.

Regards,

Jim

lparsons21

#26: Post by lparsons21 »

You say about a 2-3 degree variation in boiler temp without PID. I wonder how that translates to the HX brew temp. I wouldn't think it would be a 1:1 ratio as the heat exchanger most likely isn't 100% efficient. I suspect, but do not know, that if the boiler has a 2-3 degree variation, that the brew temp swings would be more like 1 or 2 degrees. With my uneducated palate, I don't know that I would be able to tell that difference in the cup.

But the fun factor is certainly something to consider. As is another gizmo that looks important mounted on the machine. I might end up doing it for that alone.

thanks for the feedback, it did clear some things up.
Lloyd

jimoncaffeine

#27: Post by jimoncaffeine »

lparsons21 wrote:You say about a 2-3 degree variation in boiler temp without PID. I wonder how that translates to the HX brew temp. I wouldn't think it would be a 1:1 ratio as the heat exchanger most likely isn't 100% efficient. I suspect, but do not know, that if the boiler has a 2-3 degree variation, that the brew temp swings would be more like 1 or 2 degrees. With my uneducated palate, I don't know that I would be able to tell that difference in the cup.
I think that you are absolutely correct. The temp swing will be less in the H/X but there still will be one there... How much? Maybe only a degree. I do seem to be pulling better shots as time goes on. Is this due to the pid or because my technique has improved or both? Probably a bit of both. Since I am paying more attention I am likely being more careful and deliberate. Being more careful and deliberate means that I am being more consistent. I am the primary limiting factor on what ends up in the cup (I think that this is gong to be my new signature! :) ). The pid doesn't change that but I think that it makes my job a little easier.
lparsons21 wrote: But the fun factor is certainly something to consider. As is another gizmo that looks important mounted on the machine. I might end up doing it for that alone.

thanks for the feedback, it did clear some things up.
Even if you just want to try it out and then want to switch back to the pressurestat, use it as a cheap digital thermometer to watch the temperature to pressure relationship in the boiler. It's still pretty cheap and fun (you are only out the cost of the ssr that you aren't using). If you had another thermocouple you could modify your group head to take the thermocouple and use the pid to show extraction temps by simply swapping the connections between the boiler tc and the group head tc. (My nickname will soon be jim-the-enabler!) Some PID's come with two tc inputs so you might be able to just push a button and switch between the two but those (even used) seem like they run into a bit more money than the simple ones.

Besides it has cool flashing lights, buttons and changing numbers on the front! What's not to like about that? :lol: (Likely I was a Raccoon in a prior life.) Ok, if you don't like that side of it and want the traditional non-techno look you can hide the pid and its workings out of sight.

Good luck and have fun with it,

Jim

lparsons21

#28: Post by lparsons21 »

Flashy lights? Did you just say flashy lights? ;-) I LOVE flashy lights!

A quick, OT comment. I was at a computer show many years ago and one vendor had his setup going and behind his counter was this very neat looking, computerish panel, with tons of flashing lights. As I watched his demo, I noticed that the lights didn't seem to correlate to anything. So I asked him what they were showing.

His answer - nothing! they were hooked up to a random generator. He was only using it to draw attention.

Thanks for the feedback.
Lloyd

gscace

#29: Post by gscace »

jasonmolinari wrote:Jeff, yep, i think i can see your issues....but that doesn't mean i won't try:) I've also forgotten most of my fluids and heat transfer.

Hrm..another thing i thought about is that there is a run of tube outside the boiler, connecting the boiler HX tube to the group head. The water in there would not be at brew temp...that might be an issue.
Hi Jason:

The PID thing is very worthwhile. Unfortunately you'll have to keep the temp setpoint close to what it is now. One major problem with setpoints that are close to brew temp is that the thermosyphon loop is designed to keep the group hot by circulating overly hot water from the hx to the group and back to the hx. The thermosyphon both cools the water in the hx and heats up the group. If the water in the hx is near to brewing temp, then the group will be waaaay too cold. There's so much mass in the group that it'll take many ounces of flushing to heat it up. By that time the water in the hx itself will be too cold and you'll be in trouble. With PID you should be able to optimize the boiler temperature so that the group idles at just below desired brewing temperature. When brewing from idle one would then flush the hx of overly heated water and then happily brew away. The added heat to the group will raise the group temp to the correct value.

I did a bunch of work on this when I was tuning my Astra Gourmet. I have recently revisited some of this with another e-61 machine. The cold group thing is a real show-stopper.

-\greg

jasonmolinari (original poster)

#30: Post by jasonmolinari (original poster) »

Thanks for the tips greg. I was wondering if the thermosyphon would stop working if the water got too cool in the HX. Well, given the complications, i might just stick with my Tea as it is...and wait for the mystical magical PID dual boiler sub $1000 machine:)