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Solar hot water in the UK - advice please - long! - Page 3

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Posted by m II on August 24, 2004, 5:40 pm
Adrian Brentnall wrote:

Yes, they both work here.


or failing that,


Which are very similar thermostats. These are all pretty generic things
and I'm not recommending one over the other. Check out a home
improvement store and find something similar. The only important thing
is that you have a set of contacts that CLOSE when the temperature
reaches a set point. That's what's needed on the boiler.

Even the normal bimetallic strip type should be more than enough. If
BOTH thermostats are the same, it makes no difference if the markings on
the thermometer and the markings on the thermostat setting match. What
you want is the Difference between the two, which can be set as finely
as you wish. These cheap units are still fairly accurate, however, as
the mysteries of expanding metal are more or less understood.

An advantage to the bimetallic strip ones is the fact that you can mount
them in almost any orientation...something you couldn't do with a
mercury type.


     __    __    __    __    __    __    __    __
    / /\  / /\  / /\  / /\  / /\  / /\  / /\  / /
   / /\ \/ /\ ohmworkLEOPARD@spots.ca \/ /\ \/ /
  /_/  \/_/  \/_/  \/_/  \/_/  \/_/  \/_/  \/_/

            ..let the cat out to reply..

               Densa International
            'Think tanks cleaned cheap'

Posted by Adrian Brentnall on August 24, 2004, 7:33 pm
HI Mike

Something very odd going on here - none of the above URLs work from

And this one shows a wireless air-temperature sensing thermostat -
can't see the use / purpose of this one.... in my application, at

Yes - I have that already, this is what starts the circulation pump...

It seems to me that the mercury stats are 'air temperature' sensors -
rather than contact sensors.....

Anyway - a quick play with the 'diodes & op-amp' solution this evening
proved that it seems to work - so I think I'll try building something
up on matrix board and see how it works.

 I shall not be able to prove it for certain until the 'heating
season' starts - which will hopefull be at the end of September....
but thanks for all the suggestions...

Suffolk UK

Posted by Neil Adamson on September 1, 2004, 4:28 pm
I have a solar panel warming my pond (UK) - I use a simple differential
thermostat - 1 LM35 temp sensor in the pond, 1 in the heater. They connect
to a single comparator chip - use a resistor in the ground leg of 1 to give
whatever offset u need IIRC 30R gave me about 3C.

Posted by Adrian Brentnall on September 1, 2004, 5:32 pm
 HI Neil

Thanks for the reply

On Wed, 1 Sep 2004 17:28:00 +0100, "Neil Adamson"

Yes - that's the kind of thing I had in mind...
Since posting the original message I've built a little circuit using a
741 as a comparator and a couple of silicon diodes as temperature
sensors - seems to work OK on the bench - but won't be able to test it
'in anger' until the central heating season starts - so I guess I'll
install it with the diode sensors and wait until it gets colder....

If the diodes don't perform for any reason I do have a couple of
LM35's kicking about somewhere - and I could try substituting them.
Good plan about the resistor for an offset...

Thanks again
Suffolk UK

Posted by Neil Adamson on September 1, 2004, 8:17 pm
I just think the LM35's will be far more closely matched initially than the
diodes - give you a more level playing field to start off with :-)

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