Immersion Heater - PV electricity

[pauldreed]

I have been looking at a unit to just that but it is SO expensive. I have 3.8 kw pv and would like to spill the excess to the immersion heater. Any chance of some info on how you are doing it?
Thanks

I measure:
A) The power generated by the solar panels
B) The power used by the ring main
* deduct B from A (plus a further 1KW - to accomodate the power used by the immersion heater)
* and if the result is positive, then a relay switches on the immersion heater - if it is less, then it is switched off.

This is achieved by a circuit built from components sourced from Maplins and Ebay, a bit of fiddly soldering, and a lot of patience!

 

[inie meanie]

I measure:
A) The power generated by the solar panels
B) The power used by the ring main
* deduct B from A (plus a further 1KW - to accomodate the power used by the immersion heater)
* and if the result is positive, then a relay switches on the immersion heater - if it is less, then it is switched off.

This is achieved by a circuit built from components sourced from Maplins and Ebay, a bit of fiddly soldering, and a lot of patience!

That sounds great, exactly what I want to acheive. Any chance of a bit more information or pictures? Many thanks.

 

[pauldreed]

That sounds great, exactly what I want to acheive. Any chance of a bit more information or pictures? Many thanks.

I don't think pictures would help, because the unit is contained within a '2 gang mains surface box/blanking plate', so the photo would just be a small white box. It's the circuitry inside the box which makes the decisions.
I am contemplating marketing the device, so I'm a little reluctant to release the full circuit diagram at this time, but the operating principle I posted above is basically how it works.
I can't wait for some decent sunshine now, but even today, the unit switched 2kwh to the immersion heater, not enough to fully heat the store of water, but hey, it all helps!

 

[inie meanie]

HI
I understand that. You may have a problem as there is a device on the market which might be copyright protected, it is called EMMA. It costs about £1500. I was just wanting to make some thing for my self with no interest in selling on. Hey but well done on making it work.

 

[mac1]

Hi can you tell me more about your device

 

[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.