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OK.. So i have a difficult project...

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Hi all..  new to the forum..  I used to work with electronics back in the 80's.. was C&G 224 qualified but didn't stay in the profession so I've forgotten most of it!!

I'm ok with a soldering iron..  but don't really want to get to involved in making circuit boards...  breadboard maybe...  So I'm hoping I can get a little (lot) of help from you guys!

OK.. so here is my problem...  My house is powered completely by solar..   I have quite an extensive system so we live pretty normally...  but I'm trying to run a hot tub..

I have fitted a low wattage circulation motor (80w) so I can run that as long as I want..  but the heater is 1kw, so obviously I don't want that running all the time...  So..  I have fitted a 7m long solar water heating panel to take over the heating, and that is doing an amazing job...  But, I don't want the pump running at night because the black solar panel will remove the heat as quickly as it put it in during the day...

So, what I need is a switch circuit using a photocell to detect daylight, ....that needs to be adjustable..  i.e I don't want the pump to start to run at sunrise, only when it receives direct sunlight and therefore the panels will be getting direct sunlight... For instance I don't want the pump to run on cloudy days (not that we get many)...  get the picture?

The circuit would also need an override so that I can run it at night if we use the tub, which is fine as the pipework for the solar has a control valve so I can run the motor without the water going through the panels..


Any help would be much appreciated..


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Hi and welcome to the forum,

For what you describe you will need a light activated switch like this one: http://www.electronics-lab.com/project/light-and-dark-sensitive-switch/

This switch has adjustable sensitivity and with a little of experimentation you will manage to get the desired effect. It may be needed to add a kind of filter to the light sensor to reduce it's sensitivity even further as you need the switch to be activated in direct sunlight. You can also think to add a small "light pipe" to achieve the desired functionality.

Hope that helps.

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  • 2 months later...

El Bruto,

Do you have a home automation system (or, are you thinking of doing any HA stuff)? This is an ideal task for HA, and it would be easy to set up. Note that I'm not saying to get into HA just for this (that would be overkill).

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