Id like some feedback on an idea to improve temperature stability during the shot in a gaggia classic. Its an electrical question so Im hoping Mal will chip in (btw, thanks for saving me from wasting my time with some other half baked electrical ideas on the roaster
)
Im already planning on putting in a pid to stop the wild temperature swings that the thermostat gives but Im wondering about stability during the shot with cold water coming in to the boiler. My recently retired sunbeam em4800 used to turn on its element whenever the pump was running (i think) so Im thinking of doing this on the Gaggia. Kind of.
skip the physics if you like:
<physics>A quick calculation on the back of an envelope tells me that given 4.2 joules/gram/degreeC as the specific heat of water and assuming incoming water is 75 degrees cooler than the boiler then I need 315 joules of energy to heat every gram of cold water. so if Im pulling 60 ml in 30s, thats 2grams/second, I would need 630 joules/second </\/physics>
So I need to heat the boiler at a rate of 630 watts. The sticker on the case says the classic is 1400 watts so I want to half that.
Im thinking of connecting an old phone charger or similar in parellel with the pump and using it to activate the same SSR that the PID will operate. Im also thinking that 700w will be enough to heat the boiler to brew temp (but not steam) so I could put a high voltage diode in the AC cuircuit that the SSR is switching. This will halve the element power whenever the pid or my little dc supply switches it on. Steaming should be unaffected.
So, my questions are:
Will a diode here cause problems for the pump and the PID that cant be fixed by a capacitor?
Will improving temperature stability improve my shots or is a slight decline in temperature during a shot a good thing?
Anything else I need to consider?
Ive read on other forums that a pid will stabilise temperature during a shot but Im sceptical of this claim because the temperature sensor and the element are both outside the boiler while the water is obviously on the inside. The pid might stabilise the temperature of the outside of the boiler wall but I suspect it wont make much difference to the inside in the time the shot is pulled.
any suggestions?...
:
Conan
)Im already planning on putting in a pid to stop the wild temperature swings that the thermostat gives but Im wondering about stability during the shot with cold water coming in to the boiler. My recently retired sunbeam em4800 used to turn on its element whenever the pump was running (i think) so Im thinking of doing this on the Gaggia. Kind of.
skip the physics if you like:
<physics>A quick calculation on the back of an envelope tells me that given 4.2 joules/gram/degreeC as the specific heat of water and assuming incoming water is 75 degrees cooler than the boiler then I need 315 joules of energy to heat every gram of cold water. so if Im pulling 60 ml in 30s, thats 2grams/second, I would need 630 joules/second </\/physics>
So I need to heat the boiler at a rate of 630 watts. The sticker on the case says the classic is 1400 watts so I want to half that.
Im thinking of connecting an old phone charger or similar in parellel with the pump and using it to activate the same SSR that the PID will operate. Im also thinking that 700w will be enough to heat the boiler to brew temp (but not steam) so I could put a high voltage diode in the AC cuircuit that the SSR is switching. This will halve the element power whenever the pid or my little dc supply switches it on. Steaming should be unaffected.
So, my questions are:
Will a diode here cause problems for the pump and the PID that cant be fixed by a capacitor?
Will improving temperature stability improve my shots or is a slight decline in temperature during a shot a good thing?
Anything else I need to consider?
Ive read on other forums that a pid will stabilise temperature during a shot but Im sceptical of this claim because the temperature sensor and the element are both outside the boiler while the water is obviously on the inside. The pid might stabilise the temperature of the outside of the boiler wall but I suspect it wont make much difference to the inside in the time the shot is pulled.
any suggestions?...
:

Conan

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