Posted Mon Sep 16, 2013, 7:38am Subject: Re: Do GICARs usually pulse the pump on power up?
Specific volume of water changes with temperature, i.e., it expands slightly in relation to its increase from 0C. For example, the specific volume of water increases about 5-7% when going up to espresso machine boiler temps (93-123C). So, when it cools back down after you turn it off, the water level lowers ever so slightly...enough to trigger the fill mechanism? That I don't know, but if so, this may explain what you're seeing when you turn it back on. I'd be interested to hear if there is another reason.
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jimboc Senior Member Joined: 25 Feb 2013 Posts: 14 Location: Sydney Expertise: Just starting
Espresso: mypressi twist Grinder: Baratza Precico
Posted Mon Sep 16, 2013, 3:27pm Subject: Re: Do GICARs usually pulse the pump on power up?
I'd discounted the reducing volume of the water with cooldown because the pump runs every time I turn the machine on, which would mean the water level is kept always around the high level.
I thought the idea of the high and low sensor pair was for hysteresis, only filling the boiler when low but right up to the high point, to avoid the constant pulsing that would happen with turbulent boiling water or the machine being bumped.
But thinking about it further now that you've also mentioned the volume reduction, I'm now thinking the GICAR instead waits for the water to be under the high sensor and just fills for a short preset time (giving the hysteresis), and the low sensor only used as a failsafe to interrupt heating.
That would also stop the protect the pump being on for too long and give less variation as to how much of the HX tube was covered with boiling water, hence easier brew temp control.
calblacksmith Moderator Joined: 25 Nov 2007 Posts: 6,809 Location: Riverside, Ca, U.S.A. Expertise: I live coffee
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Posted Wed Sep 18, 2013, 5:27am Subject: Re: Do GICARs usually pulse the pump on power up?
I could be wrong as I have not seen every machine there is but any I have seen only have one sensor, the system senses either on or off. If there is conduction through the sensor circuit, the boiler is not topped off, if there is no conduction, the pump is turned on and the boiler gets a shot of water.
There should be only one probe, it is either through the side of the boiler or down from the top, the boiler shell is grounded so if the current flows, the water is high enough. It is a simple on/off sensor, not two for min/max.
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jpboyt Senior Member Joined: 28 May 2010 Posts: 27 Location: Washington, USA Expertise: I love coffee
Posted Wed Oct 2, 2013, 7:09pm Subject: Re: Do GICARs usually pulse the pump on power up?
It would be easy enough to test. Pull the lead off of the high level sensor and ground it to the boiler or frame. Turn the machine on and see what happens. If you get a second or two of pump action it is probably due to the electrical voltages in the box working their way to steady state. I see a lot of relays that click for a second or so due to inrush currents. Especially in older electronics with capacitors that may be getting a bit low in value. jpboyt
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