Subject: Thermomax TMX300 Controller

From: [email-masked] ("Mike Davies")
Date: Thu, 6 Jun 1996 07:39:55 GMT

Thermomax Solar Panels & the TMX300 controller.

Has anyone got one of these working OK ?

We've had ours about 18 months, and because we don't know anyone else 
who has one, and we don't trust salesmen, we don't know what to expect.

We are using it for domestic hot water. In the winter we use a coal 
fired stove which also does the radiators. In the summer we use the 
sun.

To be fair, there was a fault. In the night, convection currents set up 
and took heat out of the hot water tank, up to the panels, which 
switched the pump on, cooled the panels down again, and this would 
repeat throughout the night, so that if at say 11pm the tank temp was 
60C by 7am it was down to say 35C or less. This didn't matter too much 
in the winter because we had the Rayburn going, but now it is summer...

A few weeks ago I moved the pump and non-return valve to the hot side 
of the hot water tank, and in the process discovered the non-return 
valve was duff, so replaced it, and now overnight we only loose 2 or 3 
deg C. :-)

The problem now is that we seem to loose a fair bit of temp at the end 
of the day, say between 5pm & nightfall. :-(

At the end of a typical day, with the sun coming off the panels, a 
typical set of readings is Collector 63C, Tank 58C, Return 54C. The 
tank reading is really meaningless because we don't use it to switch 
any auxiliary circuits, it just nice to know how hot the hot water is. 
We have the controller set so that the collector must be above 40C to 
switch on, also the difference between the Collector & the Return (DT) 
must be > 8C.

With the return sensor on the return pipe (as it was installed) a 
typical set of readings through the evening would be

Time      17:30  18:00  19:00  19:30  20:00  20:30  21:30  23:00
Collector    63     63     60     54     52     49     45     26
Tank         58     57     56     54     52     50     47     46
Return       54     54     52     46     45     43     38     25

As you can see, we have effectively lost 11C in just the 4 hours up to 
21:30, and then it all seems to stabilise, with virtually no more heat 
loss overnight.

Has anyone any suggestions as to what can be happening here ? It can't 
be convection currents. I've knocked that on the head, so the pump must 
be switching on and extracting heat like it used to overnight. For the 
pump to switch on, Collector must be above 40C & DT must be > 8C, so 
either the return is cooling quicker than the collector, or, what ?

Which leads me to the original question. Has anyone got one of these 
things. What setting are you using, for the collector temp and DT, and 
do you experience this drop too ? The return sensor was installed on 
the pipe returning to the collector. Is the return sensor in the right 
place ? Should I move it to reflect the tank temperature, i.e. on the
tank ?

Mike