Idea for a simple Run Dry prevent switch

[kenc_zymurgy]

I'm planning an Electric Brewery. For years I've been doing 5.5 G batches on the kitchen gas stove, splitting an ~ 7 G boil across two 5 G brewpots and two burners, which has worked OK ( ~ 20~30 minutes to go from mash to a boil with ~3.5 G per pot). So my thoughts are to add a 1650 watt 120V element to each 5 gallon brewpot, with each on a separate 120V circuit (so that I'm not dependent on a 240V circuit).

So I know you want to avoid running an element like that dry. I've seen some plans for float switches, but that seems like a bit of a pain, it's going to get in the way, has to be mounted, cleaned, etc.

So my idea was to use the weight of the water/wort in the pot to close a switch. That switch would go to the controller and would need to be closed to enable the element power. I envision a piece of plywood for the pot to sit on, with the momentary contact switch mounted near the middle of one edge, pointing down, set so that it is only closed when flush. A spring would push down a pin near the switch, adjusted so that the pot needs to have enough water to cover the element to compress the spring and close the switch.

Does that seem reasonable? It sounds easier than a float switch to me, but I haven't built it yet, so maybe I'm missing something?

 

[Bobby_M]

Sure that would work. You'd have to tune the counterpressure springs carefully and then likely put a calibration screw on the switch to fine tune the break point.

 

[kenc_zymurgy]

Sure that would work. You'd have to tune the counterpressure springs carefully and then likely put a calibration screw on the switch to fine tune the break point.

Thanks for the feedback. Yes, I figured I'd have some sort of knob to adjust the spring tension.

 

[Tobor_8thMan]

Could also put a sensor just above the element. Sensor detects no liquid, then element doesn't "fire".

 

[Tobor_8thMan]

Thanks for the feedback. Yes, I figured I'd have some sort of knob to adjust the spring tension.

"adjust the spring tension" depending on the time of the year...

 

[kenc_zymurgy]

Could also put a sensor just above the element. Sensor detects no liquid, then element doesn't "fire".

What kind of sensor would that be? This will also have wort in it, so that has to be considered.

"adjust the spring tension" depending on the time of the year...

And phase of the moon, local gravitational fields, ambient temperature affecting spring constants, etc

But seriously, I'm really trying to protect against a brain fart and turning it on when it is empty. I'm not trying to detect it with fractions of an inch of the element, I either have at least a couple of gallons ( ~ 16# added) in there or not. So I expect it should be pretty simple to have a switch turn on/off at about a 12# delta. But as I mentioned, I haven't tried it yet, and I am often surprised how difficult a simple idea is when it comes down to implementation. What's the old line?

"In theory, there is no difference between practice and theory. In practice, there is.”

 

[Tobor_8thMan]

"adjust the spring tension" depending on the time of the year... "

I wasn't giving a smarta*sed reply. I've noticed spring change due to the time of the year, humidity, etc.

There are plenty of liquid sensors. Search engines are your friend.

 

[kenc_zymurgy]

"adjust the spring tension" depending on the time of the year... "

I wasn't giving a smarta*sed reply. I've noticed spring change due to the time of the year, humidity, etc.

There are plenty of liquid sensors. Search engines are your friend.

No problem, I understand and agree - a spring setting will be a little 'tweaky". I think this will be a pretty coarse go-no-go, and not require *much* tweaking, but we will see.

I'll do some serahing for liquid sensors, I just thought maybe there were well known good/bad units when it comes to dealing with wort.

 

[Tobor_8thMan]

I searched for "brewing liquid level sensor" and found lots of results.

 

[TheMadKing]

A switch that responds to liquid pressure is called a pressure transducer.

The simplest way to prevent dry firing an element is a simple piece of logic code

Run "Look_in_your_pot"

If(pot_contains_water)=yes;
Set(turn_on_the_element) = true;
Else, don't turn on the element
Endif



Not being a smart ass is hard for me sorry.

Seems like using a scale with weight as your measured variable might be easier than finding a pressure transducer that can stand up to boiling wort and won't break the bank.

 

[Bobby_M]

It would be simple enough to tune it at the beginning of the brew day. Just back off the adjustment screw, fill the pot with water to just an inch above the element and adjust the screw until the element just turns on. That's probably a good spot.

 

[kenc_zymurgy]

A switch that responds to liquid pressure is called a pressure transducer.

The simplest way to prevent dry firing an element is a simple piece of logic code

Run "Look_in_your_pot"

If(pot_contains_water)=yes;
Set(turn_on_the_element) = true;
Else, don't turn on the element
Endif



Not being a smart ass is hard for me sorry.

Seems like using a scale with weight as your measured variable might be easier than finding a pressure transducer that can stand up to boiling wort and won't break the bank.

Good point - the only catch is, my own personal CPU is not as reliable as an ATmega32U4!

@Tobor_8thMan - I actually didn't find a whole lot of useful hits for "brewing liquid level sensor", but one suggestion was just a couple wires to test for conductivity (could feed an analog input of the Arduino with a little protective circuitry). That would be simple, though I was trying to avoid stuff in the brew pot, but I guess I could just hang them from the vent hood. Hmmm, that seems pretty simple, thanks.

 

[esdill]

You could use a modification to this to close a relay if the weight exceeds the programmed amount: Raspberry Pi Based Weight Sensing Automatic Gate.

 

[redllama]

ebrew supply has float switches (here) that would prevent the element from firing unless the liquid level is above the switch.

 

[kenc_zymurgy]

ebrew supply has float switches (here) that would prevent the element from firing unless the liquid level is above the switch.

Thanks, but that's $80 plus another hole in the kettle. Not really what I was thinking of.

You could use a modification to this to close a relay if the weight exceeds the programmed amount: Raspberry Pi Based Weight Sensing Automatic Gate.

Hmmm, interesting, but I can't really see the advantage over a switch with some spring loading.

 

[OneInTheHand]

Invite a friend over to have a beer and watch the water/wort level.

 

[RufusBrewer]

I see stainless steel water level float switches on eBay at reasonable prices. (~ $15.00) They are rated for 120 deg C. The contact ratings should handle a relay coil.

They come in different lengths so you have choices about how to deal with mechanics of mounting and installation.

You might need to deal with a rolling boil and the float bobbing around. Certainly there are timer & reset circuits that could be employed to ensure it does not give off a false alarm.

 

[mgalbus]

I am not sure if this will work on a heating element or not but I think the “power” principle may apply to this case.

As an example only... in the chemical industry we utilized dry run protection on most of our magnetic drive pumps. The power requirements would change based upon the amount of work being produced by the pump. Drying running had different power consumption versus pumps that were operating normally.

Here is an example of such a device:
Dry Run Pump Protection

I am surmising that you may see a similar situation happen with the heating element - a change in power (not amps). I am just not sure if it is a large enough change or if there will be false positives with hot and cold water

This assumption could be tested by an electrician with a muilti-meter (I say electrician because I don’t want anyone getting electrocuted!). You would see what it is like with it on versus off and hot water versus cold.

 

[mgalbus]

And one other way to consider... set your tank on a load scale. You don’t need a super accurate (Load cell) scale!

Measure the weight of the tank with enough water in it (meaning enough to easily cover t

If the weight is above that weight fire the element. Otherwise keep it off.

can also use this scale as a fail safe to turn off water if you have that automated as well.

 

[Tobor_8thMan]

I am not sure if this will work on a heating element or not but I think the “power” principle may apply to this case.

As an example only... in the chemical industry we utilized dry run protection on most of our magnetic drive pumps. The power requirements would change based upon the amount of work being produced by the pump. Drying running had different power consumption versus pumps that were operating normally.

Here is an example of such a device:
Dry Run Pump Protection

I am surmising that you may see a similar situation happen with the heating element - a change in power (not amps). I am just not sure if it is a large enough change or if there will be false positives with hot and cold water

This assumption could be tested by an electrician with a muilti-meter (I say electrician because I don’t want anyone getting electrocuted!). You would see what it is like with it on versus off and hot water versus cold.

Great idea... giving me ideas as you are correct. Interesting and possibly time to experiment. However, OP wants something simple. Even 2 probes hanging over the side of the brew kettle will not complete a circuit until the liquid level rises enough. This, then could tell a control to turn on the heating element.

 

[day_trippr]

Is the original concept trying to prevent literally running the element without having put water in the system?
Or simply to prevent firing the element when its recirculation pump isn't running?

If the former there may be bigger problems here
If the latter one could run an element fire enable circuit through a second set of contacts on the pump switch (ie use a dpst instead of an spst, or a dpdt instead of an spdt). Element can't fire if pump switch isn't in the On position...

Cheers!

 

[Tobor_8thMan]

All valid possibilities....