Immersion Heater - PV electricity

[inie meanie]

Hi Flyman
Your idea sounds fascinating. I will be very interested in how your project progresses. I too learnt my electronics 30 yrs ago and now am a bit rusty. I can catch on with some guidance. Do you have a specific programable device in mind and do you have a link to it so I can read up a bit? Many thanks

 

[flyman]

Hi Flyman
Your idea sounds fascinating. I will be very interested in how your project progresses. I too learnt my electronics 30 yrs ago and now am a bit rusty. I can catch on with some guidance. Do you have a specific programable device in mind and do you have a link to it so I can read up a bit? Many thanks

There are several micros but I tend to stick to Microchip PIC based ones. 12F675, 16F628 or 16F818. For simplicity there are modified versions aimed at the education market with drag and drop flow diagram type programming but there are restrictions on use for commercial applications. Do a search under Google for picaxe. The newer kid on the block is Arduino but its open source but a bit more involved.
For a DIY one off I'd suggest exploring PICAXE... you can even buy pre made circuit boards for lots of applications and you can program and test on screen with the software simulator but you'll have to accept the non commercial aspect of it. For a more comprehensive and slightly more challenging option, Microchips PIC 12f675, 12F683 or 16F818 a chunk of veroboard a soldering iron and a few other bits.
By all mean contact me if you need any help.

 

[benzama123]

It is possible to get a cheap 8 pin PIC with 3 ADCs to monitor 3 current monitor inputs and still drive up to 3 outputs.

 

[flyman]

It is possible to get a cheap 8 pin PIC with 3 ADCs to monitor 3 current monitor inputs and still drive up to 3 outputs.

As with anything it helps to start with a wish list and select a suitable circuit to provide it. The pin allocations on the 12F683 allows for a total of 6 inputs or output pins. The datasheet will give a better explanation of their allocation and is worth a read but basically of the 6 pins, upto 4 can be ADCs. One pin (GPIO3) can only be configured as a digital input but not an ADC. Whilst it is possible using logic gates to do 3 outputs from 2 pins you'd be better off with a 16F series PIC if you want more ADCs and outputs. A check on prices for suitable PICs and pinouts will show the extra cost is a couple of pounds or so.... and you could drive lots of outputs.

 

[Andrew Shaw]

Thanks, I have found a company today that would be prepared to manafacture an element to whatever specification I need, for about £60 so I may go with that idea.

please tell me more about this company

Thanks

 

[pauldreed]

Post 13 of this thread gives you a link

 

[Millerman]

Hi again folks, finally had my solar panels fitted (6th May) and just about to "road test" my device. i am using a plc unit (crouzet) with current transformers measuring the load and solar production.

This unit can easily cope with the constant flucuations in demand /supply the unit is fairly easy to programme.

[email protected]

andy

 

[pauldreed]

Hi again folks, finally had my solar panels fitted (6th May) and just about to "road test" my device. i am using a plc unit (crouzet) with current transformers measuring the load and solar production.

This unit can easily cope with the constant flucuations in demand /supply the unit is fairly easy to programme.

[email protected]
andy

The Crouzet PLC's look ideal as you will be able to introduce hysteresis to prevent relay chatter, and programme other functions in too.
Has your unit got the LCD display? presumably once calibrated, it could display/accumulate useful information.

My unit is working fine, and during the recent sunny weather I have not used the central heating boiler at all to heat the domestic water. I had doubts that a 1kw immersion heater would be powerful enough to heat the water during the sunny periods, but no problem at all.

Let us know how you get on.

 

[echase]

I designed a PIC based solar controller for solar water heating. The design was published in Everyday Practical Electronics in June 2009. Everyday Practical Electronics They sell back copies and the bare PCB. I sell the programmed PIC. All in it costs about £50 in components.

Now that I have PV panels I was thinking of extending the software to add functionality to provide this immersion heater switching. No change to the hardware would be needed apart from an external relay to switch the immersion.

As someone here says with software it is extremely simple to add hysterisis, delay, etc.

 

[pauldreed]

I designed a PIC based solar controller for solar water heating. The design was published in Everyday Practical Electronics in June 2009. Everyday Practical Electronics They sell back copies and the bare PCB. I sell the programmed PIC. All in it costs about £50 in components.

Now that I have PV panels I was thinking of extending the software to add functionality to provide this immersion heater switching. No change to the hardware would be needed apart from an external relay to switch the immersion.

As someone here says with software it is extremely simple to add hysterisis, delay, etc.

What did the original solar controller do?
I'm interested in the PIC, but can you tell us more about circuit that supports it. I don't want to spend $12 to buy back issues (June & July) if the design is too difficult to build, will not work as expected, or succesfully integrate with my PC system.
If you designed it, are you able to share the circuit diagram with us?

 

[echase]

It is a solar water controller which uses a small PV panel to provide all the power to run the controller and pump so there is no mains needed. But it can be mains powered if you want. It’s mainly designed to switch the water pump on and off in response to the solar power and temperatures in the system. It also has 2 relay outputs to power the gas boiler/immersion heating top up function. These would do 1kW with an external relay needed for more than that.

It would not connect as is to a PV electric system, but with simple modifications:

1) You could add CT inputs. To mimic your unit paukdreed it would need a couple of input circuits to convert the CT output to a 0-2.5V aprox DC value.
2) It could log the power in the PV system too which is useful in system where the inverter is in the loft and so its power meter is not visible.


As you designed and soldered your own unit mine is not difficult. There are no surface mount components. But it’s outside the capability of a complete novice in electronic assembly.

June 09 covered the design and software with July for how to build, test and connect it.

 

[Gazzdid]

a simple thought...... dont forget to introduce a cylinder stat to your circuit so it wont continue to heat the cylinder to a dangerous temperature!

 

[pauldreed]

The input circuitry would add significantly to the overall circuit design. A simple passive diode bridge would not suffice, as I am sure you will be aware. This part of the circuit design was the steepest learning curve for me, and took the longest time to sort out.
You say that there are no surface mount components, but surely there must be components to provide the right environment for the PIC to operate? (sorry never seen a PIC or had anything to do with them).
Can you change variables in the PIC once it has been programmed (such as histeresys, switching thresholds ect) without actually re-programming it?

Edit - Yes I've got an immersion heater with an integral thermostat set about 5 degrees higher than my gas boiler water thermostat. So the central heating boiler does not heat the water (unless its been a dull day!)

 

[echase]

There are extra components on the analogue inputs but they are little more than resistor dividers and overvoltage protection resistors. But you would need to convert the CT ouput to DC with something like an op amp.


My standard device has >20 variables that can be altered by menu. If I changed the software to provide this function I’d add extra variables to alter the extent of input power averaging, switching hysteresis, etc.

 

[pauldreed]

There are extra components on the analogue inputs but they are little more than resistor dividers and overvoltage protection resistors. But you would need to convert the CT ouput to DC with something like an op amp.


My standard device has >20 variables that can be altered by menu. If I changed the software to provide this function I’d add extra variables to alter the extent of input power averaging, switching hysteresis, etc.

I use op amps to monitor the CT's which give me 3 volts at 5kw power flow (which can be changed via a shunt resistance).
If I can help, especially with the 'front end' circuit - let me know.
I'll PM you my email address..