Control my immersion heater.


22 posts
by sbutton » Wed Jun 13, 2012 9:26 pm
OK, this is probably a bit of a weird one. I'd like to switch on my immersion heater depending upon how much power is being generated by my solar panels. But I'm not sure about the best way to switch something as high load as an immersion heater. I'm also going to need to figure out how to interact with my solar array (using bluetooth), but this should not be too much of a big issue as software exists that can handle this for Windows. I might have to ask Sunny Boy, who are the manufacturer if they can offer any pointers.
I'm thinking of learning Python for this project, but I'm already pretty good with Perl so it might be better to stick with that. I've been wanting to learn Python for years though, so a great opportunity.
The reason this makes sense, is because on the current electricity tariff, we get paid for 1/2 the power we generate regardless of how much we use.
Can anyone give me pointers as to the best thing to hook up a relay that can handle, at a guess, around 16 amps (might be 13). I'll need to check.
As an aside, I'll get it to store the historical data for my solar array so I can see how much I'm generating. Perhaps I'll plug that into Cacti or similar for graphs, rather than trying to re-invent.

Lots more questions to follow, but I think I'll stop for now.

Many thanks in advance. I'm just looking for general advice right now, so that I know where to start reading and what works / doesn't. Should I be looking at USB relays, or something else?
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Joined: Mon Jan 16, 2012 1:40 pm
by domesday » Wed Jun 13, 2012 10:33 pm
You will almost certainly have to use a relay as an immersion heater is a high current load, a typical UK immersion element is 3Kw which is 13A current draw. An immersion heater typically has its own thermostat to prevent over heating the water so essentially all you will be able to do is essentially switch the supply off when the solar panels are not producing the amount of power you desire.

You will need a high powered relay that would be controlled by a darlington driver or similar. For this kind of task, unless you want to control it remotely over ethernet the Pi is somewhat overkill and perhaps a simple microcontoller like an Arduino or PicAxe would be the more sensible option.
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Location: UK
by scorp » Thu Jun 14, 2012 9:14 am
Hope these are enough for heater
http://smartgreenshop.co.uk/index.php/b ... lp-ep.html
Just connect GPIO directly or via small relay(if need isolation) to RPi and job done.
Edited: Actually they say that not for heating elements but probably you can find similar
Posts: 96
Joined: Tue May 29, 2012 6:21 pm
by Hairlocks » Thu Jun 14, 2012 11:43 am
I suspect those plugs cannot be able to sustain the 3000w load for long. I believe Immersion heaters need to be hard wired to meet build regs as well. I have seen (e.g. done recently) melted a 13 amp socket from constant 2800 w load.

Another solution (more dangerous?) could be to use several relays in parallel to meet share the load. 10 amp relay are cheap and easy to come by and a 4 relay board for the ardunio and other microcontrollers is available with optoisolators. What do others think about this? (needs to be properly insulated.
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by domesday » Thu Jun 14, 2012 11:59 am
An immersion heater can not be powered from a 13A plug as it can not sustain the constant 13A load, but more importantly the ring main is not suitable for such a constant load.

In fact the connection point must be rated at least 16A to avoid meltdown.
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Joined: Fri Oct 21, 2011 5:53 pm
Location: UK
by scorp » Thu Jun 14, 2012 12:54 pm
domesday wrote:An immersion heater can not be powered from a 13A plug as it can not sustain the constant 13A load, but more importantly the ring main is not suitable for such a constant load.

In fact the connection point must be rated at least 16A to avoid meltdown.

Then simply cut cable which goes to the heater and insert one of these http://uk.rs-online.com/web/p/contactors/0502486/ + 24V PSU + mosfet(or smaller relay).
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by bredman » Thu Jun 14, 2012 1:10 pm
scorp wrote:insert one of these http://uk.rs-online.com/web/p/contactors/0502486/ + 24V PSU + mosfet(or smaller relay).

To avoid the need for 24V PSU, you could use something like 9949690 from Farnell. 240v on the coil and the load.
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by scorp » Thu Jun 14, 2012 1:27 pm
Good point, if using small relay anyway. Several options. Screw terminal type or soldering wires....
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Joined: Tue May 29, 2012 6:21 pm
by tribologist » Sun Jun 24, 2012 7:24 am
The solution I'm using is a 240VAC / 25A solid state relay which switches the power between my existing 16A mcb at the fuseboard and the existing wiring so no problem with overload or meltdown of 13A plugs.

These relays are fairly cheap, I.m using one from Crouzet, but you can get alternatives on-line for £20 ) [http://www.tmswebshop.co.uk/buy/Solid-State-Relays-SSRs.html?gclid=CJeV59qo5rACFSghtAod3lPFvA#aPROSWITCH_23_23LC].

Because these relays operate from low voltage DC (mine is working on 9V) and consume almost no power, they are pretty safe, so all I need to do now is sort out the control..

I'm experimenting with a current sensor and a small op amp, but was wondering how to connect two current sensor outputs (amplified by the op amp) to a PI so I can compare generated power with consumed power and then switch the excess to my immersion via the relay??
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by thexman » Sun Jun 24, 2012 3:14 pm
take a look at the Yocto-Amp Product its AC up-to 17amps and can switch a lower rated Yocto-Relay to switch a Higher rated Contact say a 240V coil 16amp Contact should you not wish to install a 24V or 12V transformer these can all interact with each other with little programming

how ever it is worth noting right now RPI are trying to Fix there USB issues before the module can work correctly," Yoctopuce modules " work on all Versions of Linux on every platform Except the Raspberry Pi the Foundation are a little slow in solving the issue we made them aware of nearly two months ago now, but once fixed this makes for a cheap way to control things like your immersion heater.

http://www.yoctopuce.com
one armed controls engineer, my grammar is bad but lets face it most keyboards don't suit a one armed man
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by fredfred2 » Wed Jun 27, 2012 9:28 pm
I'm new to this forum, but have been looking to find out who makes this box. The owners of the house weren't in when we were doing some wiring, but this thing controls a standard 3kW immersion heater directly. The panels are only 2kW capacity, so my guess is that some electronics must turn down the mains to the heater element. There is nothing between the box and the immersion heater, which is rated at 3kW.

How can you run a 3kW heater with a 2kW solar panel, and still not draw grid power? Beats me.

But anyone know who makes this little unit?

cheers,

fred
box.jpg
Solar Immersion heater controller box, taken with my phone- sorry about the quality...
box.jpg (44.06 KiB) Viewed 6267 times
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by ksangeelee » Wed Jun 27, 2012 11:00 pm
domesday wrote:You will need a high powered relay that would be controlled by a darlington driver or similar.


I just searched Farnell, and there are quite a few cheap relays capable of switching loads of 16A, 20A, 30A etc. with a 5V coil. They tend to require 180mA onwards (though lower for 16A) to energise, but could easily be driven from GPIO with a transistor.

I've seen darlington drivers mentioned before in relation to GPIO + relays - is there any particular reason why? I'd have thought there are enough transistors capable of driving 5V coils, even limiting base current to ~3mA. I could be missing something here.
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Location: Edinburgh, UK
by domesday » Wed Jun 27, 2012 11:39 pm
You could use a transistor with an appropriate current rating to switch the coil but a darlington driver is easier in many respects because the base current requirement is tiny and something like the ULN2003 or ULN2803 has the clamp diode built-in. If you want to control more than one relay, having this in a convenient package is tidier than a handful of transistors and diodes.
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Location: UK
by feverish » Thu Jun 28, 2012 9:17 am
While overseas (From memory, I don't have the details with me in UK) a few months ago , I used ebay to look up solid-state relays to drive immersion heaters. Mine were supplied from Hong Kong. General advice seems to be to use one able to handle at least twice the standing mains load and mount it on good finned heat sink (from the same ebay source). Mine was for a 40A load (the mains voltage is 110V) and was direct-driven from the GPIO pins of an Arduino. The heater was powered via a dedicated circuit-breaker.
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by sis » Mon Jul 16, 2012 4:18 pm
The best solution to achieve this is to use an affordable and dedicated immersion control switch like one from http://solarimmersionheaterswitch.co.uk . The Mark II version of the solar immersion heater control switch monitors both the PV output and the house load via a single clip on sensor clipped on the grid lines. The switch calculates the net difference between the production and export to turn on the load based the settings. From what i understood, the load trigger settings on the switch could be adjusted from 500W - 10kW. I have one of these installed and really happy. It will turn on my immersion when I'm exporting 1kW and turns it off immediately if i turn on a kettle or a washing machine. I also use the 3 kW power reducer from http://powerreducer.co.uk to reduce by 2 kW immersion to a 1.5 kW . attached the pic of the unit take from website

pv-immersion-heat-control-switch-bright.jpg
pv-immersion-heat-control-switch-bright.jpg (20.91 KiB) Viewed 6013 times
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by sbutton » Mon Jul 16, 2012 5:15 pm
domesday wrote:You will need a high powered relay that would be controlled by a darlington driver or similar. For this kind of task, unless you want to control it remotely over ethernet the Pi is somewhat overkill and perhaps a simple microcontoller like an Arduino or PicAxe would be the more sensible option.


Hi, sorry to take so long to come back. Wouldn't an Arduino cost about the same as a rPi anyway, and not be able to handle the bluetooth (needed to talk to the SunnyBoy Solar) + producing the historical graphs?
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by rooster » Mon Oct 01, 2012 10:38 am
sbutton wrote:
domesday wrote:You will need a high powered relay that would be controlled by a darlington driver or similar. For this kind of task, unless you want to control it remotely over ethernet the Pi is somewhat overkill and perhaps a simple microcontoller like an Arduino or PicAxe would be the more sensible option.


Hi, sorry to take so long to come back. Wouldn't an Arduino cost about the same as a rPi anyway, and not be able to handle the bluetooth (needed to talk to the SunnyBoy Solar) + producing the historical graphs?


and the Rpi can present a webserver so you can control over the internet/smartphone
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Joined: Thu Aug 02, 2012 8:09 pm
by RaspberryGeek » Tue Oct 02, 2012 11:27 am
We've got a range of things going on around this, the best 'of the shelf' product by a long way (functionaility and value) is this: http://www.microgenerationpowermanager.com/

For DIY, then this : http://openenergymonitor.org/emon/ and using the Pi as the emoncms: http://openenergymonitor.org/emon/emoncms and http://openenergymonitor.org/emon/emonc ... -debian-pi and http://openenergymonitor.org/emon/node/1004

And using just the Pi and Tinysensor, see this:
http://openenergymonitor.org/emon/labs

Next stop: full house monitoring and remote control via Pi .... and iPhone :)
Posts: 20
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Location: Evesham, Worcs
by jamiesk » Mon Nov 26, 2012 8:55 pm
I used to use a debian server using a bluetooth to connect to my SunnyBoy 3600TL. Their scripts then pulled off the current power, and I used my script to pull this info out of the syslog. If the power was over 1800W then the 1Kw immersion is switched on. If its below 1200 then it switches off. It also adds up the "time on" and then another cron job sends an email later on in the day to tell me how much free hot water I have had that day.

Unfortunately the server used its smoke chip :o I now have a Pi on order, and will implement the same thing again, but on a much lower power device!!!

If anyone is interested then I can post the final scripts I use on the Pi here.
Pi1 (Nov 2012 loft)= 1KW immersion controller for Solar panel
Pi2 (Jan 2013 living room)=Play thing
Pi3 (Feb 2013 mobile)= Play thing with Tandy Ladder board,breakout board,Nokia display
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=26&t=28193
Posts: 87
Joined: Mon Nov 26, 2012 8:48 pm
Location: Ipswich, Suffolk, England, UK.
by sbutton » Tue Nov 27, 2012 8:15 am
Please post the scripts. I'm sure someone will be interested.

I'm the OP and personally I have just fitted a basic 16A timer to the immersion and it comes on at 10:00 every day and goes off at 16:00. I know this is not the most efficient method, but this does give me enough hot water... I think on days like this, if I was relying on generating over X Kw to turn on the immersion, I'd be having a cold shower and the kids would not have a bath for most of the winter. ;-)

I know what I've done is not much of a "hack", but it does server my needs and over the summer months I'm getting loads of free hot water (well, perhaps not so much THIS summer just gone). I think on balance this is the best solution for myself.
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Joined: Mon Jan 16, 2012 1:40 pm
by jamiesk » Tue Nov 27, 2012 9:00 pm
The scripts on the bare debian are below... This is the script called by the 15 minute cron job.
Code: Select all
#!/bin/bash
cd /root/bin/sma-bluetooth
#cd bin/sma-bluetooth

# Use the tool to download the info
./smatool 2>&1 | logger -t smatool -p local5.info

#check the syslog and put the last line into /tmp/power
tail -n 50 /var/log/syslog | grep smatool | grep "Total Power" > /tmp/power

#See if the file is empty, and if so put some blank data in
mtey=`ls -al /tmp/power | awk '{ print $5 }'`
if [ $mtey == "0" ]
then
# echo file is empty
 echo "1 2 3 4 5 6 7 8 9 10 0" > /tmp/power
fi

# take out the power, or zero for duff data
power=`more /tmp/power | awk '{ printf "%d\n", $11 }' | tail -1`
echo $power > /tmp/output

# for testing script use the line below to set the power
# power=1200

# settings for on and off for the 1kw immersion heater
on=1500
off=1200
if [ $power -gt $on ]
then
#  echo switch on
  echo "immersion on" > /tmp/immersion
  echo -e "\xFF\x01\x01" > /dev/ttyUSB0
  echo "on" > /tmp/on
fi
if [ $power -lt $off ]
then
#  echo switch off
  echo "immersion off" > /tmp/immersion
  echo -e "\xff\x01\x00" > /dev/ttyUSB0
  rm -f /tmp/on
fi

# Now to add the time up.
# Check file as power could have gone over 1500 but now 1400.
if [ -f /tmp/on ]
then
   echo "0.25" >> /tmp/on_time
   mail -s "On "$power  keith@email.co.uk < /home/keith/email
fi


Its pretty simple. The sma tool brings all the info into the syslog. There are lots of temp files used, so I could check on the progress. The line...
echo -e "\xFF\x01\x01" > /dev/ttyUSB0
.. switches the immersion on, and the line with \x00 in it switches it off.

The night time scripts is
Code: Select all
#!/bin/bash
# To calculate the total power for the day, then email out, and zero the file`
value=`cat /tmp/on_time |  awk 'BEGIN{total=0} ; {total += $1} ; END{print total}'`
# echo $value
# make email
echo The immersion was on for $value hours today.  > /tmp/email

# Now to email
mail -s "Free hot water for "$value keith@email.co.uk < /tmp/email
#
# return the score to zero for the next day
echo 0 > /tmp/on_time

# and delete the "on" time file
rm -f /tmp/on


If you want anymore info then please reply.

Once I get the Pi going then I will post the scripts. I will get the cron job going every 5 minutes, and change the "add time".

Also this assumes that the following is setup, bluetooth, email, smatool, ip addresses, etc, etc...

SMA tool from http://code.google.com/p/sma-bluetooth/ ... stallation

Unfortunately I have the Sunny Boy 3600 and the smatool does not "like" this as the "codes" are not well known. I might have to hack the program about to get it to actually post to http://pvoutput.org

Hope you find my scripting useful.

Keith
Pi1 (Nov 2012 loft)= 1KW immersion controller for Solar panel
Pi2 (Jan 2013 living room)=Play thing
Pi3 (Feb 2013 mobile)= Play thing with Tandy Ladder board,breakout board,Nokia display
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=26&t=28193
Posts: 87
Joined: Mon Nov 26, 2012 8:48 pm
Location: Ipswich, Suffolk, England, UK.
by jamiesk » Sun Dec 02, 2012 11:08 am
Hi All.

I have now got the Pi talking to the invertor and putting the output into the syslog AND out to http://pvoutput.org ( see my output at http://pvoutput.org/intraday.jsp?id=864 ... 1&gs=0&m=1 )

This is a list of things I did. Sorry its *my* shorthand but it will tell *me* how to rebuild the Pi if it fails, or I need to replace the SD card.

Code: Select all
make sd card with wheezy
enable ssh
save and reboot
make static IP
 vi /etc/network/interfaces
 replace the line “iface eth0 inet dhcp” with

iface eth0 inet static
address 192.168.1.3
netmask 255.255.255.0
gateway 192.168.1.254

vi /etc/resolv.conf

add nameserver 192.168.1.254
and a few others if you want.

reboot

You then have a static IP address in which you can ssh into the rPi

run the command raspi-config and choose to expand the image into the whole of the SD card, using  expand_rootfs, otherwise you can get mysql errors.

Then I followed basically the instuctions here.. http://ictoblog.nl/raspberry-pi/raspberrypi-pvoutput

NOTE: do not change the mySql password

remove unwanted programs

apt-get -y remove aspell hunspell-en-us iptraf libaspell15 libhunspell-1.2-0 lxde lxsession lxtask lxterminal squeak-vm whiptail zenity gdm

gnome-themes-standard python-pygame


reset MySql password.
mysql
UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
FLUSH PRIVILEGES;

then ran "smatool --INSTALL"

then make the tables which smatool install forgets to make!!
mysql -u root -p smatool
enter 'MyNewPass' from above
use smatool;
CREATE TABLE `LiveData` (`id` BIGINT NOT NULL AUTO_INCREMENT , `DateTime` datetime NOT NULL,`Inverter` varchar(10) NOT NULL,`Serial` varchar

(40) NOT NULL, `Description` char(20) NOT NULL ,`Value` INT NOT NULL ,`Units` char(20) NOT NULL ,`CHANGETIME` timestamp NOT NULL DEFAULT

'0000-00-00 00:00:00' ON UPDATE CURRENT_TIMESTAMP,   UNIQUE KEY (`DateTime`,`Inverter`,`Serial`,`Description`),PRIMARY KEY ( `id` ) )

ENGINE = MYISAM;



enable IP v6 ...
CLI "modprobe ipv6"
boot "vi /etc/modules" add ipv6

setup email.
apt-get install exim4
dpkg-reconfigure exim4-config
apt-get autoremove


edit smatool.c and add (note line numbers)

686 //Set a value depending on inverter
687 void  SetInverterType( ConfType * conf )
688 {
689 if( strcmp(conf->Inverter, "3600TL") == 0 ) {
690         conf->InverterCode[0] = 0x5a;
691         conf->InverterCode[1] = 0xae;
692         conf->InverterCode[2] = 0xdf;
693         conf->InverterCode[3] = 0x35;
694         conf->ArchiveCode    = 0xe2;
695     }

if( strcmp(conf->Inverter, "3600TL") == 0 ) {
conf->InverterCode[0] = 0x5a;
conf->InverterCode[1] = 0xae;
conf->InverterCode[2] = 0xdf;
conf->InverterCode[3] = 0x35;
conf->ArchiveCode    = 0xe2;
}
 
edit invcode.in and add

Inverter    3600TL
Code1       0x85
Code2       0x2e
Code3       0x3d
Code4       0x39
InvCode     0xe2

then "make" to update it.

Enter values into the file smatool.conf, note correct values needed for MySqlUser and MySqlPwd. Enter the values for PV too.

The first time you run the program it takes ages, as it downloads all the data from the invertor and then updates http://pvoutput.org


put in scripts, updating paths.

add cron job

cd /etc/cron.d
vi smatool
*/15 7-18 * * * root /home/pi/sma.cron
vi /email
10 18 * * * root /home/pi/email.sh


"vi .bashrc" and add
export PATH=.:$PATH


and if required ...
Thanks to yanewby at http://www.raspberrypi.org/phpBB3/viewtopic.php?f=26&t=23440

let upSeconds="$(/usr/bin/cut -d. -f1 /proc/uptime)"
let secs=$((${upSeconds}%60))
let mins=$((${upSeconds}/60%60))
let hours=$((${upSeconds}/3600%24))
let days=$((${upSeconds}/86400))
UPTIME=`printf "%d days, %02dh%02dm%02ds" "$days" "$hours" "$mins" "$secs"`

# get the load averages
read one five fifteen rest < /proc/loadavg

echo "$(tput setaf 2)
   .~~.   .~~.    `date +"%A, %e %B %Y, %r"`
  '. \ ' ' / .'   `uname -srmo`$(tput setaf 1)
   .~ .~~~..~.   
  : .~.'~'.~. :   Uptime.............: ${UPTIME}
 ~ (   ) (   ) ~  Memory.............: `cat /proc/meminfo | grep MemFree | awk {'print $2'}`kB (Free) / `cat /proc/meminfo | grep MemTotal |

awk {'print $2'}`kB (Total)
( : '~'.~.'~' : ) Load Averages......: ${one}, ${five}, ${fifteen} (1, 5, 15 min)
 ~ .~ (   ) ~. ~  Running Processes..: `ps ax | wc -l | tr -d " "`
  (  : '~' :  )   IP Addresses.......: `/sbin/ifconfig eth0 | /bin/grep "inet addr" | /usr/bin/cut -d ":" -f 2 | /usr/bin/cut -d " " -f 1` and

`wget -q -O - http://icanhazip.com/ | tail`
   '~ .~~~. ~'    Weather............: `curl -s "http://rss.accuweather.com/rss/liveweather_rss.asp?metric=1&locCode=EUR|UK|UK001|IPSWICH|" |

sed -n '/Currently:/ s/.*: \(.*\): \([0-9]*\)\([CF]\).*/\2\3, \1/p'`
       '~'
$(tput sgr0)"


note that I have the 3600TL and it did not have that built into the smatool. I had to hack it, thanks to google and the codes from some else.

And the scripts which I posted before "just" need to have some of the paths changed. Here they are
Code: Select all
root@raspberrypi:/home/pi# more sma.cron
#!/bin/bash
cd /home/pi/sma-bluetooth/sma-bluetooth

# Use the tool to download the info
./smatool 2>&1 | logger -t smatool -p local5.info

#check the syslog and put the last line into /tmp/power
tail -n 30 /var/log/syslog | grep smatool | grep "Total Power" > /tmp/power

#See if the file is empty, and if so put some blank data in
mtey=`ls -al /tmp/power | awk '{ print $5 }'`
if [ $mtey == "0" ]
then
# echo file is empty
 echo "1 2 3 4 5 6 7 8 9 10 0" > /tmp/power
fi

# take out the power, or zero for duff data
power=`more /tmp/power | awk '{ printf "%d\n", $11 }' | tail -1`
echo $power > /tmp/output

# for testing script use the line below to set the power
# power=1200

# settings for on and off for the 1kw immersion heater
on=1500
off=1200
if [ $power -gt $on ]
then
#  echo switch on
  echo "immersion on" > /tmp/immersion
  echo -e "\xFF\x01\x01" > /dev/ttyUSB0
  echo "on" > /tmp/on
  # echo "0.25" >> /tmp/on_time
fi
if [ $power -lt $off ]
then
#  echo switch off
  echo "immersion off" > /tmp/immersion
  echo -e "\xff\x01\x00" > /dev/ttyUSB0
  rm -f /tmp/on
fi

# Now to add the time up.
# Check file as power could have gone over 1500 but now 1400.
if [ -f /tmp/on ]
then
   echo "0.25" >> /tmp/on_time
   mail -s "On "$power  keith@email.co.uk < /home/pi/email
fi
root@raspberrypi:/home/pi#


and

Code: Select all
root@raspberrypi:/home/pi# more email.sh
#!/bin/bash
# To calculate the total power for the day, then email out, and zero the file`
value=`cat /tmp/on_time |  awk 'BEGIN{total=0} ; {total += $1} ; END{print total}
'`
# echo $value
# make email
echo The immersion was on for $value hours today.  > /tmp/email

# Now to email
mail -s "Free hot water for "$value keith@email.co.uk < /tmp/email
#
# return the score to zero for the next day
echo 0 > /tmp/on_time

# and delete the "on" time file
rm -f /tmp/on
root@raspberrypi:/home/pi#


I just need to get the Pi into the loft and connect the USB relay, test it out and update the script is the USB port is wrong. Then I will have the the "free" automatic hot water again. I have also left the cron job at 15 minutes. I might tweak it later.

I hope this helps others out there...
Any questions ????
Pi1 (Nov 2012 loft)= 1KW immersion controller for Solar panel
Pi2 (Jan 2013 living room)=Play thing
Pi3 (Feb 2013 mobile)= Play thing with Tandy Ladder board,breakout board,Nokia display
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=26&t=28193
Posts: 87
Joined: Mon Nov 26, 2012 8:48 pm
Location: Ipswich, Suffolk, England, UK.