Simple diy control system - help please.

[pornodoll]

Hi.

Ok. I've posted a topic in the plumbing section about solar water heating, but I need to find out how to control the system.

Basically I need a switch to cut in and out a central heating water pump. The switch needs to take its signals from two thermocouples. When the temperature differential between the two thermocouples reaches, lets say 10 degrees, the switch will close, cutting in the pump. When the temp diff reduces to lets say 5 deg, the switch opens and cuts out the pump. Preferably the temp diff set point needs to be adjustable.

Now!...to me (who knows nothing about electronics), this all sounds like it should be pretty simple....but I know nothing about electronics. Hopefully there will be somebody here who can help me.

1. Where would I get some thermocouples and what sort do I need. They will need to attach to the outside of the pipes.
2. How would I wire them into a switching device?
3. Can I get a cheap switching device 'off the shelf', and if not, what do I use?

Any thoughts would be very much appreciated.

Thankyou.

 

[toasty]

if you've got access to a computer then these are good:

http://www.electronic-kits-and-projects.com/images/3000/3145.jpg

I use them for my central heating.

Further info here:
http://www.quasarelectronics.com/3145.htm

To build what you've described (considering you have little or no electronics experience) would be tricky, although you could probably do something clever with a number of pipe or cylinder thermostats.

 

[securespark]

I can't resist this: if it's simple, why are you asking for help??

 

[plugwash]

thermocouples wouldn't be my sensor of choice, they have very very low signal output and are generally a pita to work with.

some kind of semiconductor sensor would probablly be best. it would still be a fairly tricky project to build though.

 

[toasty]

I'm sure you could do it with cylinder/pipe stats.

But my system using the Quasar modules would give you lots of options.

agreed regarding thermocouples, they are no fun at all.

realistically, and I know this isn't very sophisticated, why not just say that the solar heated water will be used to heat your hot water or heat the house, so won't really be any good to you unless it is 40C or more. so just have a cylinderstat set at that on the flow from the solar panel?

That's pretty simple

 

[Aardvark Avo]

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