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Forum Index : Electronics : Light triggered circuit help!
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readyakira Senior Member  Joined: 17/07/2008 Location: United StatesPosts: 114 |
OK. So I have a Problem. I designed a solar hot water system. It uses 60watts of photovoltaic panels to charge a deep cycle battery. I use a small APC unit powered by the battery to run the 110v pump that circulates the water. The system turns on of the water tempuratures reach 145 degrees F or drop below 45 degrees F. Problem is I am finding that now the the weather is warming up, the system reaches 145 sometime mid-afternoon. This causes the pump to continously run once the temp reaches that point. Not a problem until the sun sets and the pump keeps circulating the water thereby cooling the water at night until it drops to 145 degrees. What I would like to do is incorporate a circut that will disconnect the 145 degree thermostat (uses 110v AC) when the sun sets. So, my thought is a light sensor circut that cuts a relay off when the sun sets. I know I would need a Photo sensor, A relay that can be triggered by 12v DC and switch the 110v high temp circuit off and on. But I am not quite sure of how to design the board that would contain the circuitry. The pump uses abot 0.6amp @ 110v AC. I would really appreciate any help in this matter. On a side note, if you design one of these systems yourself, be SURE to design the plumbing to prevent any backflow of heat to the water supply. When I originaly designed mine I put a loop in the system that would prevent thermosiphon of the hot water to the panel at night, but, I did not put a loop in that prevented heat from flowing back to the well. And by having the incoming lines mostly PVC, you can guess what happened when the water reach high temps in the 15yr old sch40 1" supply line that was 5ft from the system. Thank the man above I was home when that pipe swelled to 1.5inch and burst at 65lbs pressure! Don't you think Free/Renewable energy should be mandatory in new buildings? |
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| readyakira Senior Member Joined: 17/07/2008 Location: United StatesPosts: 114 |
This site seems to have a 6v design of what I am trying to do. I need this in a 12-14.4v design. Don't you think Free/Renewable energy should be mandatory in new buildings? |
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| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The commercial solar pump controllers work only on differential temperature. When the water in the solar panel becomes hotter than the water in the storage tank, the pump runs. Frost protection is provided to run the pump whenever the solar panel drops down close to freezing temperature. The pump will short cycle to keep the panels safely just a few degrees above freezing. This is a very simple control strategy that will work very well under all conditions. The differential temperature is usually set to be only a very few degrees. Here is a DIY project for such a controller, although this one does not have frost protection. http://diy-electronics-projects.blogspot.com.au/2010/06/sola r-hot-water-panel-differential-pump.html Cheers, Tony. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Found a nice simple circuit for a light sensitive relay. http://www.ozitronics.com/docs/k79a.pdf Looks like you can buy it as a kit if you wanted to. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| readyakira Senior Member Joined: 17/07/2008 Location: United StatesPosts: 114 |
Warp, that would be more ideal, but for me it would be a bit more complicated then I am looking to make the system at this point. I do plan to do something more like that in the future as I monitor temps and see just how hot this puppy will get in the summer. I need to design a temp readout for the solar storage tank as well, and being an electronic controlled water heater I am using as storage it should be relatively easy. Gizmo, that is exactly what I am looking for. Not only can I use it to turn the pump off at night, but I can reverse it and force a pump on condition if needed! Excellent. I just need to figure out how to lay it out on the board now. I am wondering if it is going to hurt if the circuit is about 5ft from the sensor. I dont think so as it is adjustable via that trimpot. Don't you think Free/Renewable energy should be mandatory in new buildings? |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Ready, The circuit is rather crude. I'm surprised that they sell it as a kit. It needs some hystersis in order to prevent the relay chatter that they mention when the light levels change slowly. Personally, I would use a Schmitt Trigger - either a discrete one using 2 transistors or an IC such as the 74C14 & a single transistor to drive the relay. I'll draw it for you if you wish. I would also connect the LDR via 2 core microphone cable in order to shield the wires from AC mains interference. Len |
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