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Need a 12 volt solar water heater controller using PT100 probes

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Posted by Leachim Sredna on April 15, 2011, 11:00 pm
Hello Group,

I need a new controller/:regulator for my solar water heating system. It
should be as simple as possible, to switch the circulation pump on and off
acording to the temperature difference between the solar heating panels and
the hot waer reservoir, and suitable for a 12 Volts DC electrical system and
use my existing PT100 probes.

You'd think it would be an easy thing to find but I can't find one anywhere.
I'd even have one made to measure if anybody knows how this could be done.

I have the remains of the original, custom-made regulator, which uses an EC
3130E comparator (I think), but this fails regularly, either due to
electrical storms which destroy the PT100 probes or because some otehr part
such as the EC 3130E or a capacitor fails, for reasons unknown.

Someone please help, I'm going mad controlling the thing manually now that
the sunny weather is back in the South of France where the system is
situated. If I'm too slow or forget, the system airlocks with high-pressure

Thanks in advance

Leachim Sredna

Posted by Rick... (The other Rick) on April 17, 2011, 9:27 pm

Look at
and make your own.

Rick... (The other Rick)

Posted by Rick... (The other Rick) on April 20, 2011, 9:18 am
 On Sun, 17 Apr 2011 22:27:52 +0100, "Rick... (The other Rick)"

Is this what you wanted?

Rick... (The other Rick)

Posted by Leachim Sredna on April 25, 2011, 11:59 am
 Sorry the delay in replying to your suggestion, Rick.

Yes that's definitely the sort of thing I've been looking for.  The
description of its operation corresponds well with that of my regulator when
the latter works. With a major difference, however, it seems : the one
described on the link you provided uses some temperator sensos called an
LM335  ("and its associated trimpot", whatever that is).
My present system uses two PT100 sensors. I am loathe to change to other
kinds of sensors as I have these, I ordered them specially, they are fairly
expensive, and they are very easy to fix to the solar panel exit and the
water reservoir (no gluing etc - just a simple mechancial clip. I also use a
bit of thermal paste.)

As it happens, I changed the CA3130E (that's the correct name) component a
few days ago, and the regulator seems to be working as it should once again.
So I 'm keeping my fingers crossed.

The ideal thing would be for me to build (or have someone build - I've never
used a soldering iron) a similar regulator to the one I have (it was
custom-built some several years ago for the prevbious owner of my house),
while at the same time improving it and including some fuses and:or other
protection against failure due to lightning or other cause of overload.

Thanks in any event. I keep learning this way.

Leachim Sredna

Posted by Rick... (The other Rick) on April 25, 2011, 10:42 pm

The PT100 probes (Thermocouple) cost approx 20.00 each from Amazon UK
The LM335  sensors cost approx 1.20 each from Farnell UK

For thermocouples to be destroyed on a regular basis, seems to me bad design.

I would suggest that you get somebody local to make the circuit for you, and
shield everything.
A enthusiast should be able to build you a unit for less than the cost of two

Good Luck....
Rick... (The other Rick)

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