Hi Tymo

the maximal intensity that can be cut by the pressure switch (CEME, Mater, Campini), is 15 Amper(opening the switch)

the intensity of your heating element is around 11.5 A, so the switch can on be open without burning.

but I don't know about the life time, it may depend on the using time of your lever machine.
In France we have 220-240 V, I have no idea because the time between a switch failure is'nt linear with the current.

You can use a relay (a contactor ) with a higher capacity, the switch of the Pstat is in serie with the relay'sinductor and connected to 120 v and on the other hand, the contacts of the relay is in serie with the heating element (instead of the Pressure switch).
The relay is a nosy solution and need more space.

Regards

Jacob wrote:Have anyone tried to put two pressure stats in series (for smaller dead band and better safety)?

My machine has a safety thermostat which cuts power to the heating element should the pressurestat fail. The conditions that might cause the first pressurestat to fail (e.g. mineral scale) could also cause the second one to fail too. Using a different technology for the failsafe seems like a better idea to me than having redundant pressurestats.

How would two pressurestats provide a narrower deadband? I don't understand how that works.

Regards
Timo

Christophe wrote:the maximal intensity that can be cut by the pressure switch (CEME, Mater, Campini), is 15 Amper(opening the switch)

the intensity of your heating element is around 11.5 A, so the switch can on be open without burning.

but I don't know about the life time, it may depend on the using time of your lever machine.
In France we have 220-240 V, I have no idea because the time between a switch failure is'nt linear with the current.

You can use a relay (a contactor ) with a higher capacity, the switch of the Pstat is in serie with the relay'sinductor and connected to 120 v and on the other hand, the contacts of the relay is in serie with the heating element (instead of the Pressure switch).
The relay is a nosy solution and need more space.

Thanks Christope. Is there a surge-consumption with a resistance heating element when it first comes on, greater than the ongoing operating load (in my machine's case, 11.5A)?

My father-in-law is a retired electrical engineer -- he did industrial controls for factories. I will ask him. Not that I haven't asked him questions about electrical circuitry in the past. But this time I won't nod as though I am understanding his explanations, and I won't give him another beer at the picnic until he puts his answer in language I understand

Regards
Timo

timo888 wrote:How would two pressurestats provide a narrower deadband? I don't understand how that works.

Adjust the two stats so the two dead-bands only overlap in the heigh end on one and the low end on the other.

Say two stats each with a dead-band of 0.2 bar. One adjusted for 0.8 to 1.0 bar and the other adjusted to 0.9 to 1.1 bar would result in a combined dead-band of 0.1 bar (0.9 to 1.0 bar).

I have not seen this comfiguration before, so maybe I have overlooked something

The thing that I have overlooked is fact that the first stat won't kick back in before the pressure comes down to 0.8 bar - sorry.

Hi,

My father-in-law is a retired electrical engineer -- he did industrial controls for factories. I will ask him. Not that I haven't asked him questions about electrical circuitry in the past. But this time I won't nod as though I am understanding his explanations, and I won't give him another beer at the picnic until he puts his answer in language I understand

Oh it's funny because I'm a process control engineer , so after a good beer (because my english is'nt fluent that I hope)
I think that you try to explain me that you change the heating element by a more powerful one ?

In all case your pressure control by switch or relay or contactor, is the same for the heating element i.e. ON or OFF
the heating is a resistor not an inductor so there no surge current when the switch open (if I understand your question but I affraid to be in the bad way )

If you have a element power greater than the initial heating element
it's modify (reduce) the ON time but the average consumption don't change significantly.

Jacob why do you want to reduce the dead band ? For a closed boiler like in major lever machine it's not good for extraction beacause The period time of ON/OFF would be too short, so the temperatures top and bottom (beacause of turbulence)would be closed and the top will be at the thermodynamic equilibrium more than 105°C if the boiler is under pressure.

So you have a "dileme" you need pressure for first step injection (the piston is at the top) and a "low temperature " that's why it's interresting to wait during the off aroud 2 minuts to have a gradient beetween the top and the bottom of the boiler
to reach around 87-90°C to have something like that :


with a 0.3-0.4 bar of dead band you have robust process and adapt the shot temperature by waiting more or less during the off time of the Pressure switch (adapt the temp to the coffee if your roast your been for exemple).

You have an excellent topic at the below links but it's in french

http://www.planetcafe.fr/forums/viewtopic.php?t=4

Regards (and good coffee ...and beers)

Christophe wrote:Jacob why do you want to reduce the dead band ?

The dead band thing were just a idea that came to mind as I were about to suggest the double stat for safety - but please forget that one

Christophe wrote:... the heating is a resistor not an inductor so there no surge current when the switch open (if I understand your question but I affraid to be in the bad way )

Yes, that is my question, and you have answered it clearly: "The heating is a resistor not an inductor so there is no surge current". So, if my machine's heating element is 1350W / 120V = 11.25A, a pressurestat rated for 15 amps should suffice.

You are probably familiar with the Jaeger pressurestats, Christophe. Jaeger Controls emailed me the Fiche Technique, mostly in French (with some English and German translation). The Jaeger specifications do not indicate the temperature rating of their pressurestats. The Barksdate pressurestats, for example, are rated to 165°F only, and require a cooling loop.

#1 Jaeger PS 20.10
POUVURE DE COUPURE: 15(2.2)A 250V~/8(1.3)A
ETALONNAGE
Centrer la plage 0.4 - 2.6 bar

#2 Jaeger PS 15.01
POUVURE DE COUPURE: 15(2.2)A 250V~/8(1.3)A 380V
ETALONNAGE
Centrer la plage 0.9 - 1.7 bar


Regards
Timo

Hello Timo,

I'm sorry I've no technical specification about temperature and never use these trade mark parts for espresso.

I took a snap about a CEME with 1/8 " fitting.



As you can see it's rated for 120°C and 15 amper at 250 volt
The midle screw can tune the pressure switch and the righ tune the dead band



Regards

Christophe wrote:I took a snap about a CEME with 1/8 " fitting.

As you can see it's rated for 120°C and 15 amper at 250 volt
The midle screw can tune the pressure switch and the righ tune the dead band

Thanks, Christophe. I like the dual control and will try to use one of these CEME pressurestats to set a wide deadband on my Club.

Do I understand correctly, that when the pressurestat is rated for 15 amps at 250 volts, the pressurestat could drive a resistance heating element of up to 3750W @ 250V and a resistance element of up to 1650W @ 110V?

Regards
Timo