Poor Man's Flow Switch

[Maritimer]

Hi RonH,

So if you put two SSRs in series, the probability of them both failing closed would infintesimal, no? In the situation of controlling the contactor with a microcontroller, how would you interface it?

M

[RonH3154]

I am thinking of a totally separate safety circuit independent of the SSR (SSR controls power to boiler) that would be controlled by the flow switch and/or other safety devices. I would use a contractor/relay controlled by the safety devices to remove the power source. I would have a manual emergency kill switch and any other safety devices control this contractor/relay.

[Maritimer]

Hi RonH,

This is the saftey circuit that I developed with cholme.

Contactor Circuit.pdf

(50.99 KiB) Downloaded 227 times

It is pretty much as you describe. The microcontroller activates a relay through an optocoupler (not an SSR , just an LED/optotransistor). The contactor circuit has its own power supply independent of the micrcontroller's.

I had forgotten about the SSR's fail-closed problem, which I had discussed with cholme. This led to the use of a MID400 AC Line Monitor Logic-Out Device http://www.fairchildsemi.com/ds/MI/MID400.pdf" onclick="window.open(this.href);return false;" rel="nofollow to monitor the boiler SSRs.

There is an external watchdog which is fed from pulses generated by the main loop of the microcontroller. This is also optically coupled to the contactor circuit and keeps a retriggerable monostable low, powering another relay.

Various temperatures are also monitored by the microcontroller. The flow switch is not currently within the contactor circuit because the flow is controlled by the microcontroller--it is not used while bringing the boiler up to boiling. When the liquid starts to boil, the vent and reflux condenser case temperatures will rise which will start the coolant pump. (This is also a test of these sensors.) The boiler temperature is also monitored.

Comments?

M

[heartcut]

The logic path shows NC contacts, should be NO energized under non-fault conditions. Looks good otherwise. Pictures?

[Maritimer]

Hi heartcut,

The schematic is intended to show the path under no-fault conditions. True, Ry1 would be energized under no-fault conditions and the contact would be NO. I debated whether to show the contacts NO, but then the current path would not be obvious to someone without your understanding.

M

[RonH3154]

I see nothing wrong with the circuit. I would ensure that the 6 contacts shown as NC fail in the open position. For example in the case of the flow switch when there is no water flowing the contact should be open (NO) once the minimum flow of water has been established this open contact will close and allow RY3 to energize assuming all other interlocks are satisfied.

[RonH3154]

Hi heartcut,

The schematic is intended to show the path under no-fault conditions. True, Ry1 would be energized under no-fault conditions and the contact would be NO. I debated whether to show the contacts NO, but then the current path would not be obvious to someone without your understanding.

M

Where I am from we typicall draw contat states as the would appear if no power were applied to the circuit.
Then if further clarification is needed we would say a contact is "NO energize to close" or "NC energize to open".

[Maritimer]

Hi RonH, heartcut,

Here is a revised Contactor Cct diagram:

Contactor Circuit Rev 1.pdf

(57.72 KiB) Downloaded 203 times

Thanks, guys. Here is the current controller:

The boiler has four 1000W teakettle elements which are fed via the grey plugs. there are four SSRs attached inside the box where the heat sinks are. These are raw zero-crossing type SSRs http://www.sharpsma.com/webfm_send/321" onclick="window.open(this.href);return false;" rel="nofollow , $6.52 from DigiKey. Every half-cycle of each element is controlled, so that there are 1024 linearly spaced power levels. I've used the DIN jacks to play around with temperatures to measure the instantaneous reflux ratio (with a one-minute transient).

The microcontroller is a Zilog eZ8 encore! development board, programmable in C. There is an RS232 connector on the board that communicates with a Hyper Terminal.

M

[RonH3154]

Maritimer

Nice looking controller. Does the one pot controll all of the elements such that each one is outputting the same amount of power?

[Maritimer]

Hi RonH,

Yes, the power goes through the elements in a round-robin fashion. It's outlined in this thread: http://homedistiller.org/forum/viewtopi ... 1#p7023135 . The pot is converted to 10-bit binary, then the program counts off the number of half-cycles set by the pot out of each batch of 1024 half-cycles, distributed over the four elements. The new controller will have to be in a larger box to accommodate the contactor and the extra circuitry. If I can afford it, I'll put an LCD readout on the box. I used one in a previous project; it is fed information by the other RS232 interface on the development board. Something like this: http://www.matrixorbital.ca/products/lk_series/" onclick="window.open(this.href);return false;" rel="nofollow .

Edit: In the previous post, that was four 1000W elements, not 100W elements.

M

[heartcut]

Good stuff, Maritimer. Looks clean, too. Might just get me to do something with my system.

[Maritimer]

Hi heartcut,

The thing I miss most about retirement is working with other people. There's nothing quite like having a colleage with whom to share a project to give it life and new ideas. I'll happily chip in ideas and what knowledge I have if you want to get your project moving. And vice versa.

Might as well fill out my very safe still project with the last of the information cholme and I worked on. Here is a list of the states that the still can assume and inputs inputs and outputs:

States of Still and Their Parameters.pdf

(85.71 KiB) Downloaded 197 times

And here is the state diagram:

State diagram.pdf

(71.18 KiB) Downloaded 256 times

M

[junkyard dawg]

Very cool project, fella's...

[lampshade]

The attachment The first Controller.jpg is no longer available

Maritimer, where did you get the chassis and heat sinks for your controller and how much did they cost?

~

[Maritimer]

Hi lampshade,

I buy all my electronics from DigiKey, or Newark if DigiKey doesn't have what I need, which is rare.

The heatsink is "half brick" size. Here is the search page:
http://www.digikey.ca/scripts/dksearch/ ... ageSize=25" onclick="window.open(this.href);return false;" rel="nofollow

The chassis is 2X10X12 inches. Here is the DigiKey page:

http://www.digikey.ca/scripts/dksearch/ ... ageSize=25" onclick="window.open(this.href);return false;" rel="nofollow
Scroll down to the bottom of the page to get a cover for it.

Here is the chassis search page:
http://www.digikey.ca/product-search/en ... ?k=chassis" onclick="window.open(this.href);return false;" rel="nofollow

M

[Maritimer]

Here is an update on the flow switch. I made a gantry out of plywood to hold it over a pail. There is a copper pipe to place the water into the switch's little bucket.

The bucket is now bigger, changed from crescent-shaped to circular.

The top was also reinforced by gluing on another layer of yogurt-container to its bottom. You can also see a little 45 degree brace under the switch. This makes the top quite rigid. Everything is glued with hot glue. The changes make the switching action more positive. The drain hole was changed from 1/4 inch to 3/16. In the area behind the little bucket, the bottom was drilled out to drain any water that might get there.

The gantry can be disassembled. The microswitch is wired to a circular DIN jack. The signal goes to a GPIO port on a microcontroller. If the switch opens, all power to the elements is cut off.

The switch has been used for two stripping runs and is pictured in use on the first spirit run.

M

[heartcut]

Good, simple job. Ought to be reliable and easy to make.
Could be used for Easter eggs, too...

[Maritimer]

Hi heartcut,

My number one fear--a workshop full of ethanol vapour--has been allayed.

M

[lampshade]

aaaarrrgghhh

I just lost my second 5-gallon wash to cooling loss. My sink and still are 10 feet apart and I only watch the still, assuming that nothing can go wrong at the sink. Boy was I wrong. When I smelled tails, I knew that all of my hearts were gone (evaporated) due to cooling water loss.

I will soon a install water flow indicator at my still and a home-made water flow alarm somewhere between the sink and still. I will post pictures later.

aaaarrrgghhh

[Maritimer]

Hi lampshade,

The flow switch has worked OK as it is shown, but it could probably be improved by turning the yoghurt container over so that the switch is glued to the bottom and the filling goes into the wider part of the container. I added some 45 degree supports under the switch to strengthen the top, as you can see if you look closely. But now I see that it would have been more rigid if the switch had been attached to the bottom of the container.

If you can manage it, try to put the switch in your heater controller. Here is a suggestion for sambedded's controller:

http://homedistiller.org/forum/viewtopi ... 6#p7257521

Looking forward to your implementation.

M

[Maritimer]

Hi lampshade,

The reason that I called this thread Poor Man's Flow Switch was that when I looked for flow switches for industrial purposes, they started at about $50 and required 10 micron filtering. But badbird has found consumer flow switches on ebay for $4 http://www.ebay.com/itm/AC-220V-3A-22mm ... 1e85cfd350" onclick="window.open(this.href);return false;" rel="nofollow . He found that they required a little modification to work at low pressure: http://www.aussiedistiller.com.au/viewt ... 40#p126690" onclick="window.open(this.href);return false;" rel="nofollow .

Check out ebay. There are hundreds of flow switches available. Finding the right one might take a little buying-and-trying. If you find something good, let us know!

M

[Jacksonbrown]

Heaps of bargains on ebay!

Perhaps not a poor man’s option but I use something like this on my set up. You also get a bit of a flow indicator with the LEDs too, which is nice.
This is pretty similar.

That broken bit is just the lead that unscrews so make a stupid offer and you might just end up with it.

I have plenty of spare IFM leads here if someone were to snap it up.
Or this one?
Or this?
They might be a touch more expensive but you get industrial quality & very resilient, you could just about pump porridge past them if you like. Here is how they work. With the Endress one I think you get that added benefit of an accurate temp transmitter too. Great if your montering dephlegm outlet temps as well.
Just looking now I found this too. Hmm, add one of these for some serious CM fun.

Lot of links, sorry. May have got a bit carried away I'd love to take this stuff to next level but need to be careful how much cash (and time) I burn.

[Jacksonbrown]

I might add, there's little point putting in a safety measure if there's a chance it might fail when it actually matters.

Also, any flow switch should obviously be downstream of your condensers and the type I linked too should have a check valve added as flow draining back when your pump stops will still register as flow.

[lampshade]

Perhaps not a poor man’s option but I use something like this on my set up. You also get a bit of a flow indicator with the LEDs too, which is nice.
This is pretty similar.

Thanks Jacksonbrown.

I noticed from the specs that power must be applied from an external source. Also, I assume that you monitor the ON(flow)-OFF(no-flow) signal output from the flowmeter to tell you when flow stops; perhaps you have an external buzzer that is activated when the flowmeter signal indicates no-flow. That being said, I assume that you have an outboard flow monitoring assembly that houses a power supply and a buzzer. Can you provide details about your outboard flow monitoring assembly.

Thanks, again.

[Jacksonbrown]

Yeah, my control box has 24VDC in it so I just used that.

You can set the on/off point on the fly very easily.

The green LEDs show your flow rate and you just move the red one left or right to set the trip point. I guess far left is no flow but I have it set to the point where the condensers just start to get overwhelmed.
You just hold down the right arrow on max flow for a few seconds to calibrate the range.
Very simple.

I use it to drive a (TPDT?) relay. When off, the power to the pump is killed and so is the SSR signal. The relay also drives a flashing buzzer (although I killed the noise bit).
That's why I had to add a start button to override it and get the pump going.

Some details are here
I will go a different way if 2.0 ever happens but this thing works fine for now. I just drive the PID controller on manual.
It was also intended to run a HERMs system but I'm not done making rum yet (I've even done a few meals with it as a sous vide cooker )

Looks like I accidentally bought that proportional valve for 50 bucks too , I just hope the flow rate is useful.
It'll probably be fine with a pump but I'll have to do the numbers before I try to use it on anything.

Edit to add - I may have misunderstood your question, check out the output on the data sheet. You only get a visual indicator of flow rate with this model. It's just a fancy switch.
The flowphant gives a 4-20mA flow (& temp) output but they cost a lot more and I don't think they're very accurate.

[bdizzle6969]

Love this idea maritimer, I'm currently working on a somewhat form of this however I'm monitoring the temp of my cooling water right now and using that info to control my arduino PWM controller running my circ pump. As temp increases I have found so must the flow. I plan on adding a SSR to cutoff power at danger levels. This setup still leaves the possibility of pump failure so I will be adding a flow switch similar to yours in future.

[Maritimer]

Hi bdizz,

There was a post recently about controlling coolant flow rate using PWM on the coolant pump: http://homedistiller.org/forum/viewtopi ... 6#p7285247 . Check it out.

As temp increases I have found so must the flow.

Don't know if I would agree with this, unless you are running very hot. What are your conditions?

A flow switch removes a lot of the anxiety of running a still. I wouldn't think of running without one.

I'm doing a lot of coding these days to implement every safety feature I can think of. Once the still is safe, automation won't be far off. What are your plans?

M

[bdizzle6969]

Thnx for the link I hadn't seen that thread but it very similar to what I'm doing, lots of useful info.
My final setup will be a 5 gallon res and a 12v pump controlled by my arduino which will monitor the temp and the flow switch like yours. I only say it must increase flow with temp because when my cooling water is cold I need very little flow to condense and too much causes huffing in my Liebig, however when my coolant gets hotter I increase flow. This of course is only the case at the beginning and only to a certain temp at which my pump will stay fairly constant. I just picked up a couple small radiators today I'm going to use and I plan on using the arduino to PWM control the fans for those. I also have a 100w peltier cooler I'm going to use that my controller will turn on at a certain temp. All of these things will be attempting to keep the res temp as constant as possible and prevent water changes any more than necessary. I'm not looking to automate my still as I find it fun to run but I also love programming and building gadgets so I'm bringing the two worlds together.

How does your 5 gallon res work for you? I was worried that it might not be enough for longer spirit runs. How long are your runs and what kind of coolant temps are you seeing/ how many water changes?

[Maritimer]

I'm using a submersible 120 VAC pond feature pump. It puts 50ml/sec through my system. At maximum, the elements operate at 4000 W. I have a car air conditioner condenser (looks like a radiator) and two 18" table fans mounted under it. The fans have three speeds, and in the summer, doing a stripping run at 4 kW, with the fans on HI, the reservoir can get warm, but not too hot. I let the pump and fans run while I'm changing the charge for the next strip, and that brings the temperature down quite quickly.

I use a pot still head for stripping and a VM column for spirit runs.

In the winter, I keep the shop at 40*F, so I like to warm up the reservoir by running the equilibration time without running the fans. To tell you the truth, I'm not really having any problems with the reservoir temperature, but since I'm automating the still, and I can turn the fans on and off, I figure I might as well keep the reservoir temperature at some standard temperature, just to have consistency from run to run.

On long spirit runs, which can take ten or more hours, the reservoir settles at a constant temperature, sort of tepid.

M

[bdizzle6969]

That's awesome news for me as your using way higher power... rather than get off topic here, is there a thread or post somewhere with pictures of your set-up?