Float switch in Recirculating EBIAB?

[RocketBrewer]

I'm building a Recirculating Electric BIAB kettle and I'm a little concerned after reading about scorching that can occur when recirculating faster than the grain bed is flowing, exposing the element to air. Has anyone used a float switch under a false bottom to prevent this from happening? I was thinking about using this float switch under my false bottom. My false bottom will be 3 1/2" from the bottom of the kettle and the top of my element should be no higher than 1 3/4". I was thinking I could mount it right below the false bottom and interupt the DC side of my SSR with it. I plan to use a pair of PWM controlled 24V solar hot water pumps, 1 to recirculate through the mash, and one to maintain a small WP under the false bottom to help avoid any scorching or hot spots.

If you have experience with this type of float, how far below mount does liquid have to get to cut off switch? How has it held up and is it a problem to keep clean?

Also, the listing says it is 1/2" PT threads (couldn't find any with NPT), and from what I can gather, that is the same as BSP or BSPT threads. I found these couplings which I think will work. My plan would be to cut the coupling in half and weld to the kettle. Can anyone confirm this or know of a NPT mount float switch?

The other option would be to mount a weldless style with a nut and gasket like this one.

Thanks for any input

 

[CascadeOK]

Interesting idea, but I'd not want to put another hole in the side of my pot. I've had recirc issues using a pump like you described and learned 2 things.

1) You can restrict the pump OUTFLOW (never pump inflow) and control this. I had visible wort in my biab bag and didnt notice the level dropped to the heating element then smelled smoke. Shockingly the wort didnt taste smokey and the batch was great. I do now restrict the flow, and I when I clip my bag around the pot I leave a gap. so I can see fluid levels in bag and in pot.

2) My recirc output from pump comes into pot from flexible tube. I had also experimented with letting the pump recirculate outside the bag. Fluid levels seemed to be the same inside and outside the bag, temp seemed consistent inside and out

I've ended up doing both because I do walk away from the pot and do other things in the garage (i have an electric/PID controlled brew panel I built) and I no longer worry I'll burn up my pump, heating element or ruin a batch of beer. And this is easier than pot modifications and having one more thing you'd have to clean and sanitize.

A completely different approach would be to use a current monitor. A pump under load draws a pretty consistent amount of current. If that pump starts sucking air (which may be at a level lower than you want) there should be a noticeable drop in current as the pump will have less work to do pushing air than a liquid. We use these at work, think I'll ask one of our engineers about it. Benefit would be you'd be monitoring the electrical side with no contact of the wort.

 

[augiedoggy]

How would the air get there? If it's sucking from the false bottom and depositing on top how is the air getting under the false bottom? I recirculate in a similar manner with the 24v food grade tanks water fountain pumps thru my rims and never had an issue with sucking air? Granted I only see about 1.8 gallons a minute through my flowmeter with the grain for an 11 gallon recipe restricting flow. Are we talking about steam traped from the element boiling ? In that case wouldn't the PID be limiting the cycle time to prevent this?

 

[doug293cz]

Interrupting the SSR control signal with a float switch will work, until the SSR fails (they usually fail to the on state.) At that point the float switch will not shut off the SSR when the liquid level falls.

Brew on

 

[BrunDog]

You need a flow switch, not a float switch.

 

[RocketBrewer]

How would the air get there? If it's sucking from the false bottom and depositing on top how is the air getting under the false bottom? I recirculate in a similar manner with the 24v food grade tanks water fountain pumps thru my rims and never had an issue with sucking air? Granted I only see about 1.8 gallons a minute through my flowmeter with the grain for an 11 gallon recipe restricting flow. Are we talking about steam traped from the element boiling ? In that case wouldn't the PID be limiting the cycle time to prevent this?

I would assume air might get around the sides of the bag, or maybe just creating a void/vacuum. Perhaps the steam theory could be a cause of some of the scorching issues I've read about, maybe causing pressure under the bag stopping flow? Might only be a problem when element is very close to false bottom. I'm still considering using a float switch to keep from dry firing my element at any time. I use a float switch like this in my HLT on my main system and have been considering adding one to my BK after nearly dry firing twice heating strike water for mash and pumping it out while still on. There's just not a lot of room under a false bottom for that style of switch, that's why I'm wondering if anyone has experience with the style I brought up.

Interrupting the SSR control signal with a float switch will work, until the SSR fails (they usually fail to the on state.) At that point the float switch will not shut off the SSR when the liquid level falls.

This is a risk no matter what.

You need a flow switch, not a float switch.

It could flow well after the element is exposed.

Thanks to everyone for your input! I'd still love to here from anyone who may have experience with the switch I asked about.

 

[doug293cz]

...

This is a risk no matter what.

...

If there is a contactor controlling power to the elements, it is possible to use a float switch to interrupt the contactor coil circuit (may require a separate relay) so that power is positively interrupted to the elements, even in the event of an SSR failure.

Brew on

 

[augiedoggy]

If there is a contactor controlling power to the elements, it is possible to use a float switch to interrupt the contactor coil circuit (may require a separate relay) so that power is positively interrupted to the elements, even in the event of an SSR failure.

Brew on

This is a good idea...
I use 24v dc coil relays and actually I could wire the rims flow switch I use up easily in this fashion since its capable of acting as a 1 amp switch... currently its wired to my ssr I believe.

 

[RocketBrewer]

This is a good idea...
I use 24v dc coil relays and actually I could wire the rims flow switch I use up easily in this fashion since its capable of acting as a 1 amp switch... currently its wired to my ssr I believe.

Thanks, but i'm not sure this would be worth the extra expense in my case as a float switch activation AND failed SSR at the same time I would assume would be highly unlikely. If A SSR fails at any time, it will require a shut down and replacement of the SSR (I do keep a spare on hand). Failure of a SSR will become evident pretty quickly with the temp rising uncontrolled. The float switch wired in the DC control circuit of the SSR requires no additional parts other than the switch and a little wiring and works very well for stopping power to the element (I've tested it in my HLT). I can see where that method would be a VERY good idea with a RIMS and flow switch as an out of control element in that confined space could become dangerous.

 

[swimIan]

Instead of a float switch you could use something similar to the Blichmann Autosparge. It trims the flow of a pump so as not to overfill or underfill a vessel. This allow the wort the finish draining through the grains and help prevent dry firing.

 

[augiedoggy]

Instead of a float switch you could use something similar to the Blichmann Autosparge. It trims the flow of a pump so as not to overfill or underfill a vessel. This allow the wort the finish draining through the grains and help prevent dry firing.

The blichman autosparge is just a mechanical float switch... the pump goes on when the ball drops though..

none of these would work because hes worried about air somehow displacing the liquid at the bottom of the kettle under the mash bag and false bottom...his wort level would always be the same because hed be recirculating.
The only way I could see this happening while recirculating is if the element was so high power or density that it creates localized boiling under the false bottom... In that case better temp control or a lower density/wattage element would be the best bet.
otherwise unless your attempting to run the pump at much to fast a speed this is a non issue.... Ive been doing the same thing in my setup for four years I dont recall ever seeing air get pulled through my grainbed instead of liquid. but I recirculated at 1.5-2gpm tops for even heating and to prevent channeling. most recirculate around 2 to 3 gpm tops from what I read here.

 

[TexasWine]

The only way I could see this happening while recirculating is...

When this happened to me the culprit was the steamer basket I was using. Because the steamer basket holds the bag away from the sides of the kettle the level on the pump side of the bag can be pulled down very quickly, exposing the element if you're pumping faster than the bag is draining. I remember brewing some batches where the liquid level was above the rim of the basket and I could actually hear the wort falling and splashing between the basket and the kettle wall. When I got a sight glass I verified that the level on the pump side of the bag was indeed significantly lower than the grain side.

So, my two cents to the OP are that if you're not using something that holds your bag away from the kettle wall, then you most likely have nothing to worry about. Install a sight glass and watch the level there. If it drops you're pumping out too fast. This is exactly what I do and after a few batches it's super easy just to set the pump flow and peek at the level after about 5 minutes. If it's not dropping, I'm good.

But if you're bent on doing this, is there a way to instead connect your level switch to an external sight glass? That'd give you a lot more warning that something it going wrong.