simple, quick and robust solar collector controller

ascutney

I am in the final stages of building a solar collector to displace a substantial fraction of the #2 fuel oil I burned
last winter. I need a simple controller that takes as input the summed voltage from 5 small photoelectric panels (entire input range is from
from 0 to 30 volts max), and then as output flips a 120 relay when the input voltage exceeds a threshold. I will attach a pump and a solenoid valve to the 120 relay. I also need to turn off the relay when the voltage goes below a second
threshold (two separate thresholds because of the problem with chattering).
Basically, when the sun shines, the input voltage is high, and this is when I want to run water through the collector.
Otherwise, the pump will be off, causing the water to drain back, and preventing freeze damage.

Simple enough. The problem is that I don't have a whole lot of time to be fiddling with the control system; I wish
I did. I'm attracted to BASIC stamp because it is pretty obvious that a simple system can easily be extended in the
future when I have more time (for
example to take temperature inputs). But at least
for now, I need something that is quick, simple and robust. It is pretty clear that the BASIC Stamp architecture can
easily handle this.

The question I have is: What is the simpliest, quickest and most robust way to get this job done? I realize
that these three criteria may somewhat be in conflict. I'm just looking for the best judgement of those who
have experience with BASIC Stamp.

sam_sam_sam

Welcome to the Parallax Forum

There a few way to do what you want to

ascutney

I need a simple controller that takes as input the summed voltage from 5 small photoelectric panels (entire input range is from
from 0 to 30 volts max),

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What’s a Microcontroller?

http://www.parallax.com/Portals/0/Downloads/docs/books/edu/Wamv2_2.pdf

This cover in this chapter

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Chapter #3: Digital Input - Pushbuttons · Page 71

You just use one of them which would be about 6 volts· then use a· Optic Sensor like a switch which you would get you power from one ·small photoelectric panels





·Or if you are going to power the Basic Stamp from the 5 small photoelectric panels

Chapter #7: Measuring Light · Page 189

This would this part of it

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··Thanks for any··that you may have and all of your time finding them

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Sam

metron9

A minimum temperature sensor only needs a thermistor a resistor and a transistor. In Minnesota for example, there can be lots of sunshine at 10 below zero but your panels may still be freezing.

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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!

erco

While I'm normally the first· to advocate using the BASIC Stamp, you really don't even·need one here. You make a great case for a·$1.29 LM339 comparator, which simply compares one voltage against another and gives you a simple on/off output which can drive your relay. Take a look at http://home.chattanooga.net/~cdp/fridgctr/fridgctr.htm·which·uses a thermistor·in a voltage divider arrangement.·I suggest you·feed your 30 volts through a potentiometer voltage divider to bring the voltage range down to less than the 5 or 12 volts you plan to power your circuit with. You can use that same pot to fine tune your transition voltage. Note the 5.6 M feedback resistor which introduces hysteresis to eliminate that chattering you mentioned.

For comparators,·the input and reference voltage must be less than the supply voltage, and ground all the pins of unused comparators. There are 4 seperate comparators in a 339 chip, but you'll only use one.

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·"If you build it, they will come."

Jonathan

Sounds like you are using thermal panels to heat water. I have been working on converting my hot tub to solar and it is working quite well, with more improvements yet to come.

I am using a TLC2543 ADC to read LM34 sensors. As noted above, you need actual panel temps, not sunlight to trigger your pump. I have a sensor on the input and output water of the array, and one on the surface of the panel in the middle of my array. When it is warm out (summer) the output temp would be enough to decide when to trigger the pump, but in the winter when it is colder, the output sensor (located in the output pipe) can be spoofed, even though I have insulated it very well. I find that the panel surface temp is best to use for triggering the the pump. I then use the difference between output and input, coupled with the temperature of the tub, to determine when to shut the pump off. While I have passive freeze protectin, I also circulate water when any sensor reads less than 38 degrees.

Last note, the LM34 is a great sensor. In the TO-92 package it slides into a 1/4" brass or copper tube perfectly, making it easy to make water temp sensors.

HTH,

Jonathan

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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot