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Author Topic: Low water level switch question  (Read 1239 times)

Tex

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Low water level switch question
« on: January 10, 2013, 12:54:00 PM »
I want to setup an auto-off switch in case the water level in the boiler drops low enough to damage the heating element. Low water is the primary cause of element failure and an auto-off switch would be an extra layer of protection.

Does this rough diagram look feasible?
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Offline MMW

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Re: Low water level switch question
« Reply #1 on: January 10, 2013, 01:06:58 PM »
Maybe a fuse (or a fusible link) inline somewhere in the DC portion?  I'd set that rating under the rating of your DC Power supply.
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"During the early 19th century, most Americans subsisted on a diet of pork, whiskey, and coffee.  ----- Where did we go wrong?

Offline MMW

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Re: Low water level switch question
« Reply #2 on: January 10, 2013, 01:10:17 PM »
As another thought to ponder (and I'm not an expert in this)...what about corrosion concerns? running current between two pieces of metal through water does funny things sometimes...
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"During the early 19th century, most Americans subsisted on a diet of pork, whiskey, and coffee.  ----- Where did we go wrong?

Tex

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Re: Low water level switch question
« Reply #3 on: January 10, 2013, 01:20:45 PM »
Quote from: MMW on January 10, 2013, 01:10:17 PM
As another thought to ponder (and I'm not an expert in this)...what about corrosion concerns? running current between two pieces of metal through water does funny things sometimes...


Most commercial espresso machines use stainless steel probes in their auto-fill circuits, and have current passing through the boiler to ground.

I'm not sure what DC voltage they use, but corrosion issues don't seem to be a problem in this application?
« Last Edit: January 10, 2013, 01:33:18 PM by Tex »
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Tex

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Re: Low water level switch question
« Reply #4 on: January 10, 2013, 01:51:42 PM »
Quote from: yakster on January 10, 2013, 01:46:19 PM
Since it is DC, they may arrange the polarity to prevent corrosion, making the probe the sacrificial anode instead of the tank.

The boilers are usually copper or nickel plated copper (I don't know if the plating is exterior only?). The probe is always stainless steel and I've never heard of one corroding?

Galvanic corrosion is never an issue with commercial machine that uses an autofill probe/circuit.
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Tex

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Re: Low water level switch question
« Reply #5 on: January 10, 2013, 07:39:51 PM »
Someone reminded me that autofill circuits in espresso machines are triggered by conductivity probe circuits, not electricity. Now I'm racking my brain trying to recall something I heard about or read about a long time ago.

THX
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jimec3

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Re: Low water level switch question
« Reply #6 on: January 21, 2013, 02:00:45 PM »
we used to use a three probe system at work to initiate pump activity.  The top probe was overlow the middle probe was pump on and the bottom probe was pump off.  Currnt ran from the bottom probe to the top ones through the product (toothpaste etc) the entire system was stainless and corrosion free.  We use level sensors now as some of our product did not have a significant enough amount of water
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