Liquid level indicator

[MarkMc]

Hi Chris

Thanks once again for a very detailed response. I really do appreciate
you giving me your time on this.

In response to your post.

Thanks for the insights regarding EMI. I was aware of the EMI produced
by the pump, and I managed to buy a joined 100R resistor and (can't
remember) I think 0.1uF capacitor rated at 400v in one package,
specifically for the purpose of protecting relay contacts. Hopefully
these will be ok.

I'm not sure what current rating the pump is, but it's afairly hefty
s/s cellar pump. I bought it reconditioned, but the home brew shop I
bought it from said that I should fit a 5A fuse. The pump is indeed
A/C, 240v. I'm going to buy a controller from RS to control the flow
rate, so I think this fits in series with the pump load IIRC.

Of course, the heater, pump 'logic' is a perfect solution, as is your
suggestion of a 3-way switch for the on/off/override requirement - such
simplicity! I have about 14 years experience in my job (computer
programmer), and one of the first things I try to teach inexperienced
guys is "simple is best".

You use the short-hand "FF", but I can't see for the life of me what
this is refering to! Can you explain?

Also, I have no idea what a MOV is, can explain what this does?

Following your advice, I'll place the 240v stuff and relays in one
metal enclosure, and mount this as far away as possible from the 12v
logic stuff, which I'll obviously place in a separate enclosure - I
assume metal will be best for this too?

I amazingly knew to put a bypass cap from VCC to gnd to help with
voltage fluctuations, but thanks again for the professional advice.

Regarding the FE33L, I already have one of these, but the documentation
is pretty poor. The 'probe' that can be bought to fit the device is
soldered (by the user-i.e. me) on the the board, so I was wondering if
I could make a food safe probe of my own by fitting the wires to a
piece of stainless steel rod?

I've been planning on testing this thing in the lab before using it in
anger with water and beer from a can. I assume I'm best to include a
preset resistor in the sensor ccts, and make any adjustments by
adjusting this?

Thanks once again for the help.

Cheers!
Mark

 

[Chris]

Hi Chris

Thanks once again for a very detailed response. I really do appreciate
you giving me your time on this.

In response to your post.

Thanks for the insights regarding EMI. I was aware of the EMI produced
by the pump, and I managed to buy a joined 100R resistor and (can't
remember) I think 0.1uF capacitor rated at 400v in one package,
specifically for the purpose of protecting relay contacts. Hopefully
these will be ok.

I'm not sure what current rating the pump is, but it's afairly hefty
s/s cellar pump. I bought it reconditioned, but the home brew shop I
bought it from said that I should fit a 5A fuse. The pump is indeed
A/C, 240v. I'm going to buy a controller from RS to control the flow
rate, so I think this fits in series with the pump load IIRC.

Of course, the heater, pump 'logic' is a perfect solution, as is your
suggestion of a 3-way switch for the on/off/override requirement - such
simplicity! I have about 14 years experience in my job (computer
programmer), and one of the first things I try to teach inexperienced
guys is "simple is best".

You use the short-hand "FF", but I can't see for the life of me what
this is refering to! Can you explain?

Also, I have no idea what a MOV is, can explain what this does?

Following your advice, I'll place the 240v stuff and relays in one
metal enclosure, and mount this as far away as possible from the 12v
logic stuff, which I'll obviously place in a separate enclosure - I
assume metal will be best for this too?

I amazingly knew to put a bypass cap from VCC to gnd to help with
voltage fluctuations, but thanks again for the professional advice.

Regarding the FE33L, I already have one of these, but the documentation
is pretty poor. The 'probe' that can be bought to fit the device is
soldered (by the user-i.e. me) on the the board, so I was wondering if
I could make a food safe probe of my own by fitting the wires to a
piece of stainless steel rod?

I've been planning on testing this thing in the lab before using it in
anger with water and beer from a can. I assume I'm best to include a
preset resistor in the sensor ccts, and make any adjustments by
adjusting this?

Thanks once again for the help.

Cheers!
Mark

Welcome back, Mark. This type of conversation should be of some use to
a lot of beginners in electronics.

Your pump is a lot beefier than I had guessed. Your snubber of 100
ohms + 0.1uF may help some, but if you remove the cover from the relay
and watch it switch off, you'll still get an arc. It might be best to
move the relay physically to another enclosure if you have problems
with electrical noise.

We mentioned in an earlier post that "FF" is shorthand in electronics
for Flip-Flop, the basic memory storage unit in electronics. It holds
1 bit of information, and can be a logic 0 or 1. The RS (Set-Reset,
and don't ask why it's always called RS instead of SR, I don't know) FF
is the most basic one that can be cobbled together, with only two logic
gates. You can use NOR or NAND gates to make one. They operate a
little differently from each other, but that's another story. You've
got a NOR RS FF in your control circuit.

An MOV is a Metal Oxide Varistor, a device developed by the wizards at
General Electric Semiconductor during the early '60s, when men were men
and women were glad of it. An MOV is a device that doesn't conduct at
all until its in its breakover region. At that point, it conducts and
acts something like a bidirectional zener. It's commonly used as
device protection across the line. The problem is that the crystalline
structure of the zinc oxide breaks down when it absorbs energy, so they
can be destroyed instantly if there's no series impedance to limit the
current in the event of a line voltage surge. An MOV is a wear part,
and should be replaced occasionally.

Since you've got a 400V cap, you want an MOV that will conduct before
the voltage across the cap gets to that voltage. The bigger the MOV
the better, but you might want to look at Maplin HW13P Suppressor
250VAC 308 in Stock £0.69. Here's a reference which starts in on an
explanation of the MOV:

http://www.currenttechnology.com/paper_5.htm
http://www.currenttechnology.com/paper_6.htm

GE wrote the bible, an applications manual on MOVs, but I don't think
it's available online.

For your application, just put your snubber across the relay contacts,
and put the MOV in parallel with the snubber, and you should be OK.

Using a metal enclosure for both boxes should be OK. Be sure that, if
you've got line voltage in a metal box, you make sure to earth the
chassis as well as fusing as necessary. Use a GFCI is mandatory where
water and line voltage are in proximity. Make sure that, even if the
box drops on the floor, there won't be loose wires with line voltage in
the box. You also might want to get someone knowledgeable to take a
look at your work before you plug it in.

Your probe might be a bit of a problem, as we mentioned before.
Anything used in a food service application should be able to be washed
down and sterilized. The probe shown in the .pdf article doesn't look
like it will fill the bill. If you have a description of the sensor
and/or part number (is it an LM35?), I might be able to give you more
help.

The .pdf article on the FE33L is somewhat descriptive, but it isn't a
data sheet and it doesn't have a schematic of the controller itself.
Possibly if you have a better reference, I might be able to give you a
hand.

* Heater Wattage?
* FE33L additional documentation?
* Sensor type? (If it looks like a TO-92 transistor, you could just
copy down the numbers)

I'm looking forward to seeing your work in progress on your website.

Cheers!
Chris

 

[MarkMc]

Hi Chris

FF - yes of course, just didn't twig! Obviously, too much home brew
has killed some brain cells!

Thanks for the info about the MOV, I've heard of varistors, but never
knew what they were.

The relay is a tiny (ultra miniature they call it) PCB mount thing.
I'm not sure if the cover is removable. I can vandalise one as part of
'research' I suppose!

The .pdf file on the Maplin site is new - it wasn't there when I bough
my unit a few months ago. Would've been useful. I've been developing
a cct for temperature control using a PIC microcontroller which
interfaces to the FE33L, and spits out an RS232 signal for a PC to read
- I'm using the FE33 mainly as a tempsensor and LCD display - all of
which I'd probably implement using discrete components for version 2
now I've learned a bit about PIC's.

I did have a .pdf file of the manual for FE33L, but I can't find it (a
USB memory stick got trashed), otherwise I'd stick it on the web site.
If I get time, perhaps I can scan in the paper version. It's very low
on detail though, and certainly isn't a datasheet and doesn't have a
schematic. It basically has two outputs for temperature control - too
hot or too cold, so you can control a heat and cool source.

By the way, the relay (YX97 - maplin) is rated to 10A

The temperature probe is the FE34M, and I have one of them. I wouldn't
want to put it in hot wort. Hence I'd like to make something from s/s
if that's at all possible.

I just looked through my Maplin order history, and I see that I ordered
RG23 500v 0.1uF capacitors, and also RG22Y Contact Suppressor 100R and
0.1uF in series 250v max.

Using your suggested 'relay logic' setup, would I need to put two
suppressors in the cct, one across each, or can I still stick with your
original suggestion of having these across the load? Any reason for
your change here?

The heat source will be controlled by RS#655-622, as will the pump.
Well, that's the intention anyway. But I am yet to decide on what to
use for the heat source. I haven't yet found my s/s containers for
this application, so the size will dictate the heat source to a certain
degree.

I was thinking about using an electric kettle element 2kW or similar.
I will be needing to heat about 25L of liquid from ~50C to 65C, fairly
rapidly, while recirculating with the pump.

Sorry Chris, what is GFCI?

I'm getting an old coal shed converted to use as the brewery, and it'll
have it's own consumer unit, earth rod and RCD main switch...

Cheers,
Mark

 

[Chris]

Hi Chris

FF - yes of course, just didn't twig! Obviously, too much home brew
has killed some brain cells!

Thanks for the info about the MOV, I've heard of varistors, but never
knew what they were.

The relay is a tiny (ultra miniature they call it) PCB mount thing.
I'm not sure if the cover is removable. I can vandalise one as part of
'research' I suppose!

The .pdf file on the Maplin site is new - it wasn't there when I bough
my unit a few months ago. Would've been useful. I've been developing
a cct for temperature control using a PIC microcontroller which
interfaces to the FE33L, and spits out an RS232 signal for a PC to read
- I'm using the FE33 mainly as a tempsensor and LCD display - all of
which I'd probably implement using discrete components for version 2
now I've learned a bit about PIC's.

I did have a .pdf file of the manual for FE33L, but I can't find it (a
USB memory stick got trashed), otherwise I'd stick it on the web site.
If I get time, perhaps I can scan in the paper version. It's very low
on detail though, and certainly isn't a datasheet and doesn't have a
schematic. It basically has two outputs for temperature control - too
hot or too cold, so you can control a heat and cool source.

By the way, the relay (YX97 - maplin) is rated to 10A

The temperature probe is the FE34M, and I have one of them. I wouldn't
want to put it in hot wort. Hence I'd like to make something from s/s
if that's at all possible.

I just looked through my Maplin order history, and I see that I ordered
RG23 500v 0.1uF capacitors, and also RG22Y Contact Suppressor 100R and
0.1uF in series 250v max.

Using your suggested 'relay logic' setup, would I need to put two
suppressors in the cct, one across each, or can I still stick with your
original suggestion of having these across the load? Any reason for
your change here?

The heat source will be controlled by RS#655-622, as will the pump.
Well, that's the intention anyway. But I am yet to decide on what to
use for the heat source. I haven't yet found my s/s containers for
this application, so the size will dictate the heat source to a certain
degree.

I was thinking about using an electric kettle element 2kW or similar.
I will be needing to heat about 25L of liquid from ~50C to 65C, fairly
rapidly, while recirculating with the pump.

Sorry Chris, what is GFCI?

I'm getting an old coal shed converted to use as the brewery, and it'll
have it's own consumer unit, earth rod and RCD main switch...

Cheers,
Mark

Hello again. The folks at Maplin were kind enough to email an
attachment with more information on the FE33L temperature module. If
you want, you can have them forward it to you also.

The use of this module for real temp control looks iffy, but you might
get barely passable results with the British can-do spirit and a little
luck. Unfortunately, bacteria also have that spirit of derring-do, and
your FE34 sensor probably won't cut it. By putting it in a s/s sheath,
you'll probably be doing a good job of insulating it from the liquid.
That will slow down your temperature response big-time, which is
probably a fatal flaw.

All is not lost, though. They've probably got a commercial thermistor
(temperature-variable resistor) as the temp sensor, and it's more than
likely a standard value. There's no schematic in the .pdf, but I'd
guess they're probably asserting a logic high on a pin, and then
measuring current through the sensor with a series resistor. Either
that, or they're doing an R-C charging thing like the POT instruction
with the BASIC Stamp. It might be possible for you to measure the
thermistor resistance at room temperature, then measure again at a
higher set temperature to get a handle on its temperature coefficient
(delta ohms per degree). Or call Maplin and ask nicely (although I'm
not sure they'd be interested in undercutting their market for their
1.99 GBP sensors). It's probably a standard value, and also probably
available as a purchase part from some vendor somewhere. If you're
really lucky, it might be a value you can get by cannibalizing a
digital thermometer. As another possibility, you might be able to
purchase a bead thermistor, and affix it to the inside of a thin sealed
s/s tube with thermally conductive epoxy, but this sounds a little
doubtful. I'm the most uneasy about creating a situation where we
contaminate the brew. That can get people sick -- not a good thing. A
final possibility might be affixing the bead thermistor to the outside
of the tank. If it's copper or brass, it's a great conductor of heat.
If you blanket the air side, and use thermally conductive epoxy to
affix the thermistor to the outer wall, you might not even have to put
anything inside the vat. I like that option best.

The FE33.pdf from Maplin shows how to interface the 1.5V logic from the
temp control module to transistors and relays. I'd definitely watch
your current drive here. If you've got 0.8V across a 10K resistor,
you're only squirting 80 microamps into the base of the transistor.
That isn't going to be enough, realistically, to drive a decent sized
relay. You could use it to drive a solid state relay, or if you're
still going to use a large relay to drive your heaters, you might use
the first transistor to drive another one, which then drives the relay
like this (view in fixed font or M$ Notepad):


12V
+
|
.-. 12V
22K| | +
| | |
'-' |
| ___ |<
o-|___|--| PNP
| 8.2K |\
| |
1.5V ___ |/ .---o
LOW o-|___|-o-| NPN | |
Signal 10K | |> | C|
.-. | 1N4- C|RY2
| | | 002^ C|
10K| | === | |
'-' GND | |
| === ===
=== GND GND
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de



But, having shown that you can do something, you should then ask
yourself whether it's smart. From what I've heard about brewing,
you'll have to be consistently within a couple of degrees if you want
things to work right. To be honest, you're not going to reliably get
that accuracy or repeatability with this setup. This setup won't work
well on a consistent basis. Even with a rock solid 1.5V supply, a
precision thermistor matched to the characteristics of the FE34,
controlled ambient temperature, and everything else optimized, I don't
think you're going to get better than +/-5 degrees C or so
repeatability. That's 60 to 70 degrees C, and the extremes will
probably ruin your batch. It might be better to think this one out,
and work on a control setup which will do justice to the rest of your
effort, time and money. In for a penny, in for a pound (GPB).

There's nothing wrong with manually turning on the heat and monitoring
with a thermometer, just like the Bavarians of yore. And if you want
to have some kind of automated temp controller, there are units
available on ebay which will do a much better job than this little
module. Control of temp to within 1 degree C or so is very possible.
You can then use a standard precision thermistor with your temp
controller (you might even be able to buy it with the controller) to do
the job.

By the way, a GFCI is a Ground Fault Circuit Interrupter, and it's a
requirement any time you're using line voltage in a wet place. In the
event that there's a ground fault, the GFCI will cut power to reduce
the risk of electrocution. If you're using electric heaters on a metal
vat with liquid inside, you have to use one of these.

Good luck. Take some time, and think 'er over.

Good luck
Chris

 

[MarkMc]

Hi Chris

I did once get the .pdf from Maplin that you refer to. It's just a
scan of the instructions which come with the module - assuming you have
the same file. Perhaps I'm learning some of this electronics lark as I
too came to the conclusion that I wouldn't be able to drive my relay
from the tiny current available from the module.

I assumed that a Darlington pair would help me out here. Is there any
reason why you suggest the NPN-PNP cct in particular?

The temperature control is definitely a luxury thing, and by the look
of things is best left until version 2 of this setup which is already
tring to achieve a lot.

The heating side of things I can see getting used in two ways -
1.) To perform stepped mashes - only for a tiny proportion of brews
(luxury)
2.) To keep the wort at a set temperature when recirculating - losses
may occur at the pump and in the pipework.

I have heard about homebrew systems existing called RIMS (RecIrculating
Mash System) and HERMS (HEated Recirculating Mash System), and they
rely recirculating the wort and for HERMS, heating it at the same time,
so it must be possible.

The pump will be pumping the liquid at all times when the heater is on,
so the liquid shouldn't be in contact with the heater element for any
length of time, so the liquid temperature level should be rising very
slowly and steadily with any luck, but perhaps you're right, manual
control and a normal glass thermometer may well be a better solution.
But it's not very geeky, is it!

There's two things which need to happen heat wise;
1). The heat of the liquid in the container must *never* go over 70-75C
(well, not for long) as enzymes in the wort, which are performing the
starch conversion of the grain, can de-nature and become useless for
the mash and render the brew unfermentable - not desirable! This limit
may be even lower (say 60C) at some stages for stepped mashing.
2). Heating and pumping/recirculating must stop when the temperature in
the mash tun (not the underback where we'll be heating the wort and
pumping from) is at the desired step temperature, say 66C

So thinking about it, an even more custom solution is required with not
one, but two temperature probes.

I was wondering - I have PIC microcontrollers 16F628A at home, with
necessary programming hardware and software development tools.

I could make something to perform a controlled level out to the heating
element, using the reference voltage generator of the 16F628A rather
than simply turning the heater on and off. Of course the problem here
is that I don't know how to scale up a 0-5v variable range to what's
required for the heater element running on mains voltage. i.e. do I
need to vary the current/resistance or the voltage peak-to-peak of the
heater element, I'm not sure how to achieve either.

Hmmm, maybe on/off is ok for the <= 70C part, but that still leaves me
wondering how to physically measure the temperature. I don't mind
making my own sensor out of stainless steel rod (somehow?) and
performing the calibration etc, and using a cct/PIC microcontroller to
act on the levels and perhaps drive an LCD display for the underback
and the mash tun.

From reading the FE33L manual, they suggest any probe will work as long

as it has a resistance < 30 ohms and that the shorter the wire, the
more accurate it will be. Any suggestions on making a probe form
stainless steel rod?

I take it a GFCI is different to an RCD? I was always planning on
using an RCD in the 240v cct.

Thanks once again,
Mark

 

[Chris]

Hi Chris

I did once get the .pdf from Maplin that you refer to. It's just a
scan of the instructions which come with the module - assuming you have
the same file. Perhaps I'm learning some of this electronics lark as I
too came to the conclusion that I wouldn't be able to drive my relay
from the tiny current available from the module.

I assumed that a Darlington pair would help me out here. Is there any
reason why you suggest the NPN-PNP cct in particular?

The temperature control is definitely a luxury thing, and by the look
of things is best left until version 2 of this setup which is already
tring to achieve a lot.

The heating side of things I can see getting used in two ways -
1.) To perform stepped mashes - only for a tiny proportion of brews
(luxury)
2.) To keep the wort at a set temperature when recirculating - losses
may occur at the pump and in the pipework.

I have heard about homebrew systems existing called RIMS (RecIrculating
Mash System) and HERMS (HEated Recirculating Mash System), and they
rely recirculating the wort and for HERMS, heating it at the same time,
so it must be possible.

The pump will be pumping the liquid at all times when the heater is on,
so the liquid shouldn't be in contact with the heater element for any
length of time, so the liquid temperature level should be rising very
slowly and steadily with any luck, but perhaps you're right, manual
control and a normal glass thermometer may well be a better solution.
But it's not very geeky, is it!

There's two things which need to happen heat wise;
1). The heat of the liquid in the container must *never* go over 70-75C
(well, not for long) as enzymes in the wort, which are performing the
starch conversion of the grain, can de-nature and become useless for
the mash and render the brew unfermentable - not desirable! This limit
may be even lower (say 60C) at some stages for stepped mashing.
2). Heating and pumping/recirculating must stop when the temperature in
the mash tun (not the underback where we'll be heating the wort and
pumping from) is at the desired step temperature, say 66C

So thinking about it, an even more custom solution is required with not
one, but two temperature probes.

I was wondering - I have PIC microcontrollers 16F628A at home, with
necessary programming hardware and software development tools.

I could make something to perform a controlled level out to the heating
element, using the reference voltage generator of the 16F628A rather
than simply turning the heater on and off. Of course the problem here
is that I don't know how to scale up a 0-5v variable range to what's
required for the heater element running on mains voltage. i.e. do I
need to vary the current/resistance or the voltage peak-to-peak of the
heater element, I'm not sure how to achieve either.

Hmmm, maybe on/off is ok for the <= 70C part, but that still leaves me
wondering how to physically measure the temperature. I don't mind
making my own sensor out of stainless steel rod (somehow?) and
performing the calibration etc, and using a cct/PIC microcontroller to
act on the levels and perhaps drive an LCD display for the underback
and the mash tun.

as it has a resistance < 30 ohms and that the shorter the wire, the
more accurate it will be. Any suggestions on making a probe form
stainless steel rod?

I take it a GFCI is different to an RCD? I was always planning on
using an RCD in the 240v cct.

Thanks once again,
Mark

A darlington transistor requires two Vbe drops to turn on -- that would
be 1.4V, which is too close to the 1.5V logic level output:

` NPN Darlington
` Ic| o C
` | |
` | |
` V |
` .--------o
` | |
` 1.4V |/ |
` o----| |
` B |> |
` ----> | |
` Ib | |
` | 0.7V |/
` '------|
` |>
` |
` 0V |
` |
` o E
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Following the NPN (80uA base drive) with a PNP (1.2 mA or so) allows
current magnification that will lead to the second transistor being
completely on when it's on. That's important to limit power
dissipation (P = (Vc - Ve) * I) as well as other reliability issues.
Also, most relays are guaranteed to turn on with 75% to 80% of nominal
voltage. If there's too much voltage drop across the transistor, the
relay might not turn on (especially if your power supply is somewhat
low).

I'm kind of glad in a way that you're holding off on the temp control
part of the circuit for a while -- possibly you can get what you have
working, and go from there. It might also help as far as getting a few
more bucks together for the effort, which might allow you a much better
controller.

Most of the time, in controlling a heater load with a long thermal time
constant, programmed pulse width modulation is used instead of phase
control of the line or attempting some kind of linear controller.

Here's how PWM works. Let's say it takes 5 minutes of full-on line
voltage for significant load heating to occur. The PIC programmer
would choose a period of, say, 10 seconds. Out of that 10 seconds, if
the heater is on for one second, that's the same equivalent heating as
10% of full line voltage power. If, every 10 seconds, the PIC turns
the heater on for 5 seconds, that's the same as 50% power. If it's on
for the full 10 seconds, that's 100% power, of course. Every 10
seconds the pulsed ON repeats. That's called PWM, and is easy to
program with a computer.

The only problem is that the repeated ON/OFF cycling tends to wear out
relay contacts. This type of thing is perfect for a Solid State Relay.
All you do is drive an optoisolator LED with 3 to 20 mA (depending on
the type of SSR), and the load turns on with triacs instead of relays.
Instead of 10,000 to 1,000,000 operations like a relay, an SSR can
operate virtually forever, if it's got a good heat sink to prevent
thermal cycling.

Unfortunately, having a PIC will not really help you with accuracy of
the temp controller. The error budget is mostly due to the kind of
simple method being used to read the thermistor resistance (this is a
guess based on what's implied in the docs). Having the PIC read the
serial output will just duplicate the action of the LOW output if you
do a straight bang-bang ON/OFF controller. I would guess that, unless
you've got a bit of experience in PICs as well as know a little control
theory, you're going to get kind of frustrated with a proportioning
controller program. However, there's quite a bit of help out there in
the PIC support groups, and there might be something out there that
will do the job.

The biggest problem with the PIC, though, is using it for a critical
application without having an ICE (In-Circuit Emulator) or having
experience in debugging real time control programs.

The thermistor is a variable resistor whose resistance is dependent on
the temperature it's sensing. Normally, if there's a long wire length,
the controller will have a 4-wire connection to the thermistor to
remove the effect of the resistance of the wires. Your FE33L doesn't
have that, so they say to keep the wires short. However, you'll still
need a thermistor, which is a separate purchase part. The problem is,
they make many different kinds (they're usually specified by room
temperature resistance and temperature coefficient in ohms per degree).
Maplin sells them with room temperature values from 4K7 to 150K.
Gotta buy it, not make it, and you've got to know the temperature
coefficient if you want it to work with your module. The FE33L is
built to work with a specific thermistor probe. If you want to use
something else, you'll have to figure out what the thermistor is. If
you can figure out a way to make the FE34 work, you can use a switch
setup like is shown in the appnote.

I'm not sure what an RCD is. I explained GFCI in the prior post, and I
believe that's what it's called on your side of the pond, too.
Possibly you should check in at a do-it-yourself hardware shop and ask
what they recommend to protect people from accidents with line voltage
and water in the bathroom or kitchen.

Best of luck to you.
Chris

 

[MarkMc]

Hi Chris

I thought there must be a reason for driving the relay in the way you
suggest. Thanks for the explaination.

Yep, I'll leave the heater part out for now, but I am wondering, that
there must be food safe temperature sensing applications, surely? How
can I dunk a thermistor in to a hot sticky solution? Maybe at low
voltages it is ok. I did once look at temperature sensing IC's, which
put out I2C serial data for the PIC to read, but I had the same issues
with dunking an IC in to a hot sugary liquid.

PWM is interesting, and IIRC the 16F628A has some built-in features to
perform this kind of function.

I had no idea you were on the other side of the pond! I guess RCD is
the same thing as your GFCI. RCD stands for Residual Current Device -
it trips/turns off the live supply when it detects leakage from neutral
to earth. These can be plug in devices which plug in to the wall
socket, and then you plug your appliance - electric lawn mower,
whatever in to that, or they can be used as a switch in a home consumer
unit. I have one in my home consumer unit, it runs all ring circuits,
but for obvious reasons, the lights are not under RCD control, but
straight off the normal main switch.

Cheers,
Mark

 

[Chris]

Hi Chris

I thought there must be a reason for driving the relay in the way you
suggest. Thanks for the explaination.

Yep, I'll leave the heater part out for now, but I am wondering, that
there must be food safe temperature sensing applications, surely? How
can I dunk a thermistor in to a hot sticky solution? Maybe at low
voltages it is ok. I did once look at temperature sensing IC's, which
put out I2C serial data for the PIC to read, but I had the same issues
with dunking an IC in to a hot sugary liquid.

PWM is interesting, and IIRC the 16F628A has some built-in features to
perform this kind of function.

I had no idea you were on the other side of the pond! I guess RCD is
the same thing as your GFCI. RCD stands for Residual Current Device -
it trips/turns off the live supply when it detects leakage from neutral
to earth. These can be plug in devices which plug in to the wall
socket, and then you plug your appliance - electric lawn mower,
whatever in to that, or they can be used as a switch in a home consumer
unit. I have one in my home consumer unit, it runs all ring circuits,
but for obvious reasons, the lights are not under RCD control, but
straight off the normal main switch.

Cheers,
Mark

Over this range of temperatures, you can get more accurate measurements
with thermistors than thermocouples. Both of these, as well as bourdon
tubes, bimetallic sensors, and other means are used to measure
temperature in food applications. (Caveat : I've been away from the
food industry for many years. Not only that, but if you're not just
bottling for your own use, you have to comply with different
regulations and local ordinances. I have no advice whatsoever on
complying with those.)

The basic issue is one of cleanliness and sterilization. Of course, in
an oven, the temperature sensor attached to the controller does not
come in contact with the food. The same is true for freezers. Only
where the temperature probes need to come in contact with the food
itself do these become real issues. You have to clean the surface of
anything that comes in contact with food, and make provision to
sterilize it as necessary.

I believe you said you've got a copper brewing vat. If you have a
portable temperature probe you can lower into the liquid, you just have
to make sure the surface that comes in contact with the liquid is
sterile. That may be your easiest method, if you've got a hole in the
vat to lower the probe into. But doesn't the beer have to be brewed
under pressure? If so, you'll have difficulty keeping only the
stainless steel in contact with the liquid. You can't sterilize
insulated wires.

Option two would be permanently affixing the stainless steel probe
inside the surface of the vat, and having the thermocouple and the
wires on the other side of the barrier. That may be a problem, because
it would require cutting through the vat, and also creating a smooth,
cleanable interface. As an option, you may be able to use a pressure
gasket made of food-safe material, and clean it after each use. But
this sounds like a lot of hassle, and remember that once you cut a
hole, it's there for good (pressure patch repairs being none too
reliable, and requiring a level of skill for thin copper that you don't
find too often.

For a hobbyist who's none too interested in destroying his brewing kit,
I personally think you should go with option 3, which is affixing the
thermistor directly to the outer surface of the vat. Copper is famous
for its great thermal as well as electrical conductivity. The
temperature of the liquid inside the vat will be very efficiently
transferred to the outside. Especially if the copper is very thin in
relation to its surface area, if you can keep the heat from being
radiated from a fairly small portion of the vat's outer surface (just
about any thermal insulator will do), the temperature on the outside of
the copper will be almost identical (possibly even within fractions of
a degree) from the liquid on the inside. Temperature measurement will
be totally consistent from batch to batch. And you won't have to worry
about sterilizing anything. The beer's on the other side of the
copper. I've seen it done this way. It works.

You've got my curiosity piqued on the FE33L. 12 pounds is practically
a throwaway price for this little gizmo, a remarkable value. If things
stay slow around here, I'll have Maplin ship me one just for yuks. I'd
like to fiddle around with it, and trace out how they measure temp (not
having access to the schematics). Believe it or not, there just isn't
anyplace like Maplin in the States. It's kind of unfortunate, but
electronics as a hobby in the States has just about fizzled out.
Possibly it has something to do with your education system, which I
hear is much more oriented toward raising intelligent, literate, and
capable children than ours, and usually offers at least some practical,
hands-on electronics as part of the science curriculum. It seems ours
is primarily concerned with making the kids feel good about themselves
and not offending the parents at any cost. But I think it has more to
do with the basic fact that our parents are too self-centered (with
some exceptions) to spend time teaching and encouraging their own kids,
especially after they start school. Also, the American immediate
gratification culture doesn't lend itself very well to paying what it
costs or investing time in learning. American kids tend to lose
motivation in attaining anything they can't get in the time they'd
spend on a movie. So do their parents. And even our movies are
getting shorter.

Feel free to post again or email if you have any further questions.

Cheers
Chris

 

[MarkMc]

Hi Chris

This setup is not for any commercial use, but hygeine is very
important, obviously. Us homebrewers are paranoid about cleanliness
and sterilisation.

I don't yet have the vessels I'm going to use for this project, but I
have a stainless steel vessel in mind - I just have to lay my hands on
a couple - no time at the moment, very busy working

The word copper in brewing is in fact a generic name for a boiler.
They used to be all made from copper in yesteryear, but nowadays they
are mainly stainless steel. And in homebrew circles, we (I) get away
with a tough plastic boiler. But basically, we call our boilers
coppers, no matter what they're made from!

Beer isn't brewed under pressure. Perhaps there are some setups that
do this, but I'm not aware of them, but I'm certainly no expert when it
comes to commercial breweries.

But I guess your suggestion for mounting the sensor outside may well be
just as valid?

I remember being gobsmacked with the FE33L when I first saw it. It's
pretty cool, and for only £10. You can't go wrong!

Sadly Maplin are selling less and less electronic components and they
are becoming just another consumer electronics company, but for now
they still keep components in stock for their original but small
customer base on which they have grown.

Over here, I think electronics and computer programming is getting less
and less, but it is true that at least some basic stuff is being taught
at our schools. I have a 14 y.o, and she's borrowed the soldering iron
for school projects a couple of times.

I agree with you that youngsters, and people in general can't be
bothered to think about stuff thats a bit difficult and requires a bit
of thought. Very worrying for the future, with a lot of high-tech jobs
getting shipped off to India and China.....

Cheers,
Mark

 

[MarkMc]

Hi Chris

Sorry to keep hassling you.

I wonder if you wouldn't mind casting your expert eye over the circuit
design which I've posted to my web site here http://tinyurl.com/cey9x

I'm particularly concerned about the BC177B PNP transistor I added to
your suggestion for driving the pump relay, because I wanted to
illuminate an LED whenever the pump was on. Hopefully my design will
work and the Resistor values are ok. VCC is +12v btw.

Also, somebody on my brewing forum wondered if a dishwasher pump might
be better suited to my usage. Seems to make sense, they are designed
to pump hot water.

As luck should have it, I've recently had a new kitchen, and my old
dishwasher has been waiting to be thrown away, so I've opened it up to
have a look at the pump. To my surprise, this has a heating element
assembly attached to the pump, which looks interesting. I've posted a
couple of pictures of it on my web site here (follow the links to see
the pics). http://tinyurl.com/a8u8c

I'm wondering if the cylidrical insert is in fact a temperature sensor
or sender. All markings on the item are listed on the web page. I'd
love to know if I can use this for my intentions of circulating and
heating the brew.

Cheers,
Mark

 

[Chris]

Hi Chris

Sorry to keep hassling you.

I wonder if you wouldn't mind casting your expert eye over the circuit
design which I've posted to my web site here http://tinyurl.com/cey9x

I'm particularly concerned about the BC177B PNP transistor I added to
your suggestion for driving the pump relay, because I wanted to
illuminate an LED whenever the pump was on. Hopefully my design will
work and the Resistor values are ok. VCC is +12v btw.

Also, somebody on my brewing forum wondered if a dishwasher pump might
be better suited to my usage. Seems to make sense, they are designed
to pump hot water.

As luck should have it, I've recently had a new kitchen, and my old
dishwasher has been waiting to be thrown away, so I've opened it up to
have a look at the pump. To my surprise, this has a heating element
assembly attached to the pump, which looks interesting. I've posted a
couple of pictures of it on my web site here (follow the links to see
the pics). http://tinyurl.com/a8u8c

I'm wondering if the cylidrical insert is in fact a temperature sensor
or sender. All markings on the item are listed on the web page. I'd
love to know if I can use this for my intentions of circulating and
heating the brew.

Cheers,
Mark

Hello again, Mark. No hassle at all. It's actually been a pleasant
diversion in a very slow month.

I'm going to pass on the applicability of a dishwasher pump/heater for
your brewing, basically because I really don't know. You should check
with your brewmeister friends on this one.

10K resistor R6 should be pullup, not pulldown. Its function is to
ensure turnoff when no current is being pulled from the emitter. By
that logic, it should go to +12V. In fact, if you leave it as a
pulldown, the LED transistor just won't turn off at all.

You might have more luck finding a 470 ohm resistor (standard value)
for R4 than 480 ohms (a typo, I'm sure). When you calculate power
dissipation for the resistor, you have to subtract the voltage across
the LED and the saturated transistor. Let's say that there's 1.8V
across the LED, and 0.2V across the saturated ON transistor. That
leaves 10V across the resistor, which means about 21.3mA and .2128
watts. Actually, I'd think you can go with a 560 ohm resistor, and you
can save some power as well as not getting too close to the 1/4 watt
limit, especially if the LM7812 output voltage is a little on the high
side.

As far as power requirements for the transformer, think expansion. You
want to have enough power so that, if you want to add another relay or
something else, you don't have to redo the power supply. Let's say you
want capability of 300mA at 12VDC. Multiply by 1.8 (the standard for
full wave bridge rectifiers) to get a transformer which is rated for
600mA or more. With a 10,000uF cap, you should be OK with a 12.6VCT
transformer, but not 12VAC (you'll be too close to dropout voltage on
low line/load conditions). If you want to bring down the cap (10,000uF
at 25V is a little expensive), you might want to go with a higher
transformer voltage, like 15VAC. With a 15VAC transformer, you should
be able to get away with 2200uF, 25V for C1. There have been many
google discussions about sizing caps for DC power supplies. And in any
case, you'll probably want a small heat sink for the 7812. Here are
some Maplin numbers that should work:

KU50E Clip On TO220 Heat Sink 759 in Stock £0.39
N80AZ 10W 1x15V PCB Transformer 8 in Stock £5.99

I'm looking forward to hearing how things are going -- feel free to
post back, or email. Good luck, and

Cheers!
Chris

 

[MarkMc]

Hello again Chris

10K resistor R6 should be pullup, not pulldown. Its function is to
ensure turnoff when no current is being pulled from the emitter. By
that logic, it should go to +12V. In fact, if you leave it as a
pulldown, the LED transistor just won't turn off at all.

Woops. Yes, I should have known that. I managed to go through school
and college electronics and *never* managed to use a PNP transistor, so
this is my first application! Although electronics was always a
secondary subject for me, with Computer Science and Software
Engineering being my primary focus.

You might have more luck finding a 470 ohm resistor (standard value)
for R4 than 480 ohms (a typo, I'm sure).

Oops, yes, I meant 470.

When you calculate power
dissipation for the resistor, you have to subtract the voltage across
the LED and the saturated transistor. Let's say that there's 1.8V
across the LED, and 0.2V across the saturated ON transistor. That
leaves 10V across the resistor, which means about 21.3mA and .2128
watts. Actually, I'd think you can go with a 560 ohm resistor, and you
can save some power as well as not getting too close to the 1/4 watt
limit, especially if the LM7812 output voltage is a little on the high
side.

Is 1.8v drop pretty standard for an LED then? I didn't know what
values to use for the LED and c-e junction of the transistor, so I
erred on the side of caution and just used +12v. Should've used at
least 0.6 for the LED though, so that was a bit dumb of me.

I only have a set of E3 resistors, so I don't have 560. Perhaps I
should look to get a set of E12 to give me a few more choices?

As far as power requirements for the transformer, think expansion. You
want to have enough power so that, if you want to add another relay or
something else, you don't have to redo the power supply....

A friend of mine is in to d-i-y Valve hi-fi, and I nicked this cct from
him and simplified it for my own use, I guess it lost something in
translation. He had other types of cap in parallel with C2 IIRC.

I assumed that I'd just want as big a cap as possible for C1. I know
PSU's are a big big topic, so I'll trust what you suggest and go with
that. I do want to prepare for the future - the heater side of things
for example

KU50E Clip On TO220 Heat Sink 759 in Stock £0.39
N80AZ 10W 1x15V PCB Transformer 8 in Stock £5.99

thanks for the suggestions.

I'm looking forward to hearing how things are going -- feel free to
post back, or email. Good luck, and

I'll definitely post back on progress. I'll probably put this together
on a bread board first, and test each section in my spare time, so it
might be a while!

Thanks once again Chris. I'll be sure to give you credit on my web
site!

Cheers,
Mark

 

[Chris]

Hello again Chris

Woops. Yes, I should have known that. I managed to go through school
and college electronics and *never* managed to use a PNP transistor, so
this is my first application! Although electronics was always a
secondary subject for me, with Computer Science and Software
Engineering being my primary focus.

Oops, yes, I meant 470.

Is 1.8v drop pretty standard for an LED then? I didn't know what
values to use for the LED and c-e junction of the transistor, so I
erred on the side of caution and just used +12v. Should've used at
least 0.6 for the LED though, so that was a bit dumb of me.

I only have a set of E3 resistors, so I don't have 560. Perhaps I
should look to get a set of E12 to give me a few more choices?

A friend of mine is in to d-i-y Valve hi-fi, and I nicked this cct from
him and simplified it for my own use, I guess it lost something in
translation. He had other types of cap in parallel with C2 IIRC.

I assumed that I'd just want as big a cap as possible for C1. I know
PSU's are a big big topic, so I'll trust what you suggest and go with
that. I do want to prepare for the future - the heater side of things
for example

thanks for the suggestions.

I'll definitely post back on progress. I'll probably put this together
on a bread board first, and test each section in my spare time, so it
might be a while!

Thanks once again Chris. I'll be sure to give you credit on my web
site!

Cheers,
Mark

Hi, Mark. LEDs vary quite a bit as to their forward voltage drop.
Red/yellow/green vary all over the place from 1.5 to over 2.5V. White
LEDs typically have a Vf of around 3V. Infrared LEDs typically have
about 1.7V. The key is to try to work around variability. If you've
got the basic collection of resistors, try two 1K 1/4W in parallel.
That will do the job nicely (net 500 ohm 1/2 W).

Your friend's circuit is perfect for this application -- a small linear
7812-based power supply. I was just kibbitzing to give a hand with
component selection. If you're using a 12.6V transformer, you need as
big a cap as possible, to minimize ripple. That's because once you
subtract two diode drops, the peak voltage at the cap will be around
16.2V at nominal line voltage. If you have any drops in line voltage,
you'll get close to the (Vout + 2.5V) = 14.5V dropout voltage of the
7812 regulator.

The rule of thumb is that an 8300uF cap will give you one volt of
peak-to-peak ripple with a current of 1 amp. That means 10000uF for
1/3 amp will give you roughly 1/4 volt of ripple, which would do just
fine.

If you've got a 15VAC transformer, you'll have 19.6V peak after the two
diode drops, which means you can afford about 5V of ripple. A 2200uF
cap will give you a little over 1-1/4V of ripple, which is very safe.
The extra capacitance is basically just extra expense. Actually, I was
looking for and couldn't find a 1000uF 25WV electrolytic on the Maplin
website (I don't have a catalog).

All of this kind of assumes you really want to do it this way. After
you put a PC mount transformer, bridge rectifier, caps, and linear
regulator on your PC board, you've still brought line voltage out into
the box. I'd definitely recommend purchasing a wall wart with a linear
12VDC regulator built in. That will do the job, keep line voltage out
of the control box (always a good thing), and simplify things by quite
a bit. You'd just put a 100uF cap on the board where the power supply
is connected. Here's one from your friends at Maplin:

JC92A 12V 500mA Mains Adpt 5 in Stock £14.99

If you're etching a board, it's good that you're testing everything
first. Remember that you should use a bench power supply instead of
the wall wart regulator until you're sure everything's OK. The one
specified says it has thermal fuse protection, which helps prevent
fires, but is a little unforgiving if you have an accidental short
circuit on the breadboard.

Feel free to post again or email if you need a hand.

Good luck
Chris

 

[MarkMc]

Hi Chris

Ah, I had no idea LED's could vary so much. I'd imagine Infrared to
differ, but not between colours...buy I'm sure there's a perfectly
valid reason for it.

Thanks for the info about ripple - I'm beginning to vaguely remember
something about P-2-P and RMS and smoothing etc from school.

I already have a 12v 400mA DC regulator, which I could use, but I still
need to take a mains line in through the relays to drive the pump and
later, the heater, so I fugured, what the hell?

What I planned to do is put the transformer, relay driver and pump
mains connectors in one box, and have the 12v, gnd and control signals
go off to another box containing only the logic and all at 12v. Of
course, the biggest headache is where to place the mains voltage box,
and all the mains leads and connectors, with so much water and steam
around the place.

My outbuilding which I intend to use as the brewery is in fact in two
halves, separated by a brick wall. My current plan is to house the
mains box in the non-brewery half, and have the mains flex just run
through the wall, to/from the boiler, pump etc, and connect via
waterproof connectors inside the brewery half. The control logic could
live inside the brewery section, probably fixed to the brewery rig
itself for convenience. Only problem is that I intend to use a pump
controller to vary the speed of the pump, and this is an off the shelf
(trica based whatever that means?) 240v unit...

Any thoughts/suggestions on this?

Cheers,
Mark

 

[Chris]

Hi Chris

Ah, I had no idea LED's could vary so much. I'd imagine Infrared to
differ, but not between colours...buy I'm sure there's a perfectly
valid reason for it.

Thanks for the info about ripple - I'm beginning to vaguely remember
something about P-2-P and RMS and smoothing etc from school.

I already have a 12v 400mA DC regulator, which I could use, but I still
need to take a mains line in through the relays to drive the pump and
later, the heater, so I fugured, what the hell?

What I planned to do is put the transformer, relay driver and pump
mains connectors in one box, and have the 12v, gnd and control signals
go off to another box containing only the logic and all at 12v. Of
course, the biggest headache is where to place the mains voltage box,
and all the mains leads and connectors, with so much water and steam
around the place.

My outbuilding which I intend to use as the brewery is in fact in two
halves, separated by a brick wall. My current plan is to house the
mains box in the non-brewery half, and have the mains flex just run
through the wall, to/from the boiler, pump etc, and connect via
waterproof connectors inside the brewery half. The control logic could
live inside the brewery section, probably fixed to the brewery rig
itself for convenience. Only problem is that I intend to use a pump
controller to vary the speed of the pump, and this is an off the shelf
(trica based whatever that means?) 240v unit...

Any thoughts/suggestions on this?

Cheers,
Mark

Hi, Mark. As long as your power supply is regulated, everything sounds
OK. I would guess it's time to put something together and see what
happens. Possibly you'll be finished, ready to go to the next
improvement (sounds like the heater controller is next), or possibly
you'll have hangups that will lead to new questions. Fire, ready, aim.
Make smoke and have fun.

Chris

 

[MarkMc]

Cheers Chris

I'll put an order together and get the parts I need and make some
smoke!

I'll let you know how I get one.

Thanks a million.

Cheers,
Mark