Cheap Temperature Control For Open Boiler Espresso Machines

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Postby DJR » Jan 26, 2011, 3:10 pm

I thought this might be generally helpful. It is only for open boiler machines (La Peppina, Caravel, Mini Gaggia, etc.).

I use a router speed control. (You can get them anywhere, but I got mine at Amazon Less than $30.00


I removed the clip from the back. I also shortened the cord, but neither modification is necessary. The beauty of the device is its simplicity and reliability. Just plug it in between your machine and the outlet.

To calibrate, I measure, not at the group, but in the boiler. I just use a Thermapen digital thermometer. Any good thermometer will work.

1. Turn the rocker to "FULL". Let it come to a full boil.
2. Switch the rocker to "VAR". Measure the temperature at each number and make yourself a little table of equivalents. ) eg. 4=199 degrees. You could also make a new dial, mark the old dial, put a piece of tape on the dial, etc.

To use, just turn the rocker to FULL. When it boils, turn to VAR and turn the dial to the number you want. In the La Peppina the change of temperature is almost immediate. Nothing could be easier, no wires hanging out and the device has its own internal fuse, adding a layer of protection.

It also makes it possible to keep the machine at a controlled temperature for some time without furious boiling, unplugging etc.

When done, turn the rocker to "OFF" and power is off. No need to turn the switch on your machine to "OFF".


PS. I've now used this with my La Peppina for almost a year on an almost daily basis and have had no issues. In practice, I don't worry much about the numerical temperature. I taste the first shot. If it needs more heat, I turn the knob a bit to increase the temp. And so on. The response to temp rise or fall is faster than it takes for me to grind, pack and pull another shot, so it works very well. Frankly, something in me rebels against using a numerical readout/computer with an open boiler machine. This solves that.

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Postby sweaner » Jan 26, 2011, 9:09 pm

Dan, would this work with an electric kettle? Do you think this would result in more wear to the element than a PID to control the temperature, or would they be about the same?
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Postby DJR » Jan 26, 2011, 10:18 pm

I'm not an electrician, however, my understanding of normal PIDs is that they pulse the power 100% on and 100% off to creep towards the destination temperature. This on/off is governed by a computer which keeps it from ramping too fast and overshooting.

Kilns typically use this method of pulsing to control temperature. If you don't, you have to have a voltage reducer which at high voltages/amps/watts is very expensive.

In any event, used in a device that doesn't have a computer which relies on certain voltages, a dimmer won't damage the elements and might cause them to last longer since they are not being heated to max all the time on and off.

So, yes, it would work fine with a kettle unless it has a computer on board. It works well with lights which do last longer at lower voltages. It also works with some motors, but not all. Capacitor start motors could be a problem.


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Postby newmanium » Jan 26, 2011, 11:14 pm

Wouldn't this work less precisely as the volume of the water changes after a few shots? Suppose this depends on whether the heat loss is variable to different water volumes - if it's constant, this dimmer switch will maintain a nice equilibrium.

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Postby kmills » Jan 26, 2011, 11:27 pm

The difference in heat loss due to a few square inches of water contact with boiler walls should be imperceptibly small. Thats the only variable heat loss mechanism I can imagine as long as the surface area of exposed water (to air) is the same. Heat loss due to latent heat of vaporization should be greater than that of conduction and thus would reduce the temperature dependence on water volume. If you had a PID, rates of heat absorption would be an issue (might need to auto tune for a different height), but this is a blissfully simple solution that only cares about the steady state solution.

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Postby hbuchtel » Jan 27, 2011, 9:07 am

Nice - thanks for posting!

I had the same concern as Louie, but Kendall's response seems reasonable.

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Postby kmills » Jan 27, 2011, 10:01 am

If you do notice there is an actual difference, all you have to do is put some sort of graduated height marker in the boiler and plot the different temperature curves on the same graph. It would look an awful lot like this:


Only the X-axis will be dial number, Y-axis is temperature and each curve would represent a different water level.

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Postby DJR » Jan 27, 2011, 10:38 am

Or.....when you pull a shot or two...add a shot or two of agua! That's what I do. Open boilers seem to want that. By the time you pack the next shot it is stable. The point of this method is to keep it simple and repeatable. The less I spend measuring temperature the more I spend concentrating on what's important. Taste.

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Postby five and dime » Jan 27, 2011, 1:07 pm

Would this device work for those of us using a 220 peppina with a step up transformer? It sounds great!
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Postby yakster » Jan 27, 2011, 1:42 pm

I use a PID with my La Peppina (with the lid on) and love it, but I'm tempted by the compact size and simplicity of this. If only the case were black instead of red. :shock: I wouldn't really need to buy this if I just knuckle down and put my PID in a more compact case.

I do find that my La Peppina likes to have the kettle about half-full, but with the PID it'll maintain the temp as long as the probe is still under water.