Immersion Heater - PV electricity

[pauldreed]

Hi can you tell me more about your device

What do you want to know? I have covered the basic principles in post #16 of how it works.

 

[mac1]

Hi yes you described how it worked but can you let me know what you have used to monitor the system to enable it to switch the immersion on and off at the appropriate time. Thanks.

 

[pauldreed]

Hi yes you described how it worked but can you let me know what you have used to monitor the system to enable it to switch the immersion on and off at the appropriate time. Thanks.

I use current transformers, one on the power feed from the invertor (which measures the power being generated) and a second on the ring main power feed (to measure the power being used in the home).
My circuit then compares both measurements, and if the generated power exceed the power being used by 1kw, then the circuit activates a relay which in turn powers the immmersion heater.
As both measurements are being constantly monitored, if the generated power diminishes (passing cloud!) then the relay is de-activated.

This link is a similar current transformer to what I use.

 

[inie meanie]

Hi Pauldreed
Are you using an op amp to do the comparison to then drive a relay or do you have an all in one module?
Thanks

 

[pauldreed]

Hi Pauldreed
Are you using an op amp to do the comparison to then drive a relay or do you have an all in one module?
Thanks

Op amp, as I couldn't find an all inclusive module.

 

[flyman]

This is interesting as I've been thinking of doing something similar and stumbled across this post. It may be worth considering using a simple programmable micro-controller rather than op-amps particularly if you want multiple comparitors. 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. It is also easier to build in timer delays and hysterisis to prevent rapid switching as outputs rise and fall.

Now if I can find an immersion heater timer with a wireless remote input.... a minimal wiring modifications solution is possible.

 

[pauldreed]

Yes, hysterisis has been a problem, and I had to modify my circuit after a few weeks as the relay couldn't cope with the rapid switching.
I have never used, or know anything about micro-controllers, so I can't comment on your suggestion, but good luck.

 

[flyman]

Yes, hysterisis has been a problem, and I had to modify my circuit after a few weeks as the relay couldn't cope with the rapid switching.
I have never used, or know anything about micro-controllers, so I can't comment on your suggestion, but good luck.

Thanks Paul. Microcontroller are really very simple once you get the hang of them and so flexible for this sort if thing and limited only by imagination and a couple of pounds gets something capable of automating and running most thing in a house. They are probably simpler than other ICs and changes are a simple reprogram rather than changing components. I use them a lot for sports based control systems.

Once I have the pv system installed I'll potter around with something to sort out the immersion heater etc.

If you think you might want to know a bit more by all means drop me a note - it might be a simple relaiable solution for optomising pv.

 

[pauldreed]

Thanks Paul. Microcontroller are really very simple once you get the hang of them and so flexible for this sort if thing and limited only by imagination and a couple of pounds gets something capable of automating and running most thing in a house. They are probably simpler than other ICs and changes are a simple reprogram rather than changing components. I use them a lot for sports based control systems.

Once I have the pv system installed I'll potter around with something to sort out the immersion heater etc.

If you think you might want to know a bit more by all means drop me a note - it might be a simple relaiable solution for optomising pv.

I was educated in electronics 30 years ago, so microcontrollers have not figured until now!
Presumably, you need a programmer - to interface to a PC, which in turn writes the instructions to a chip.
The chip with minimum support components would then retain the instructions and operate independently to the programmer?

 

[flyman]

I was educated in electronics 30 years ago, so microcontrollers have not figured until now!
Presumably, you need a programmer - to interface to a PC, which in turn writes the instructions to a chip.
The chip with minimum support components would then retain the instructions and operate independently to the programmer?

Yes, thats pretty much it really. In essence the curcuit for most things consists of a regulated 5v supply from a 7805 a couple of capaitors to decouple the supply, outputs dependant on whats needed - LED, mosfet, piezo etc. Timer crystals arent needed as most have internal ones. The programming removes the need for logic gates and timers and a PIC can drive 20mA on each pin so I use a mosfet to drive a relay. programmers are fairly cheap at £30-50 and software free. PIC has plenty of memory so its easy to play about with. Inputs can be 5v logic or 0-5v dc on analog inputs making it easy to interface with most things.

I guess the biggest cost is time learning the programming but as its only 35 words and there are lots of tutorials online. And if that doesnt suit there are people who'll do a chip for you.

 

[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?