General PLC selection Help!

[plcnewb123 0]

Hey everyone I am very new to the use of PLCs and was performing a simple solar experiment for one of my courses and am kind of lost. My experiment is to take a solar photovoltaic panel, (simple cheap panel) and connect it to a PLC to control a valve opening or closing output. It sounds simple, but I am unsure of the inputs (solar being a DC input? would it be Watts or Voltage or Amperage?) also the outputs and where to start even with what to purchase. I was told CLICK is good and cheap, with free software. So far I was going to purchase the CLICK PLC CPU (http://www.automationdirect.com/adc/Shopping/Catalog/Programmable_Controllers/CLICK_Series_PLCs_%28Stackable_Micro_Brick%29/PLC_Units/C0-00DD1-D) , not sure if i need a sink or source dc output yet (another question...) with the following power supply (http://www.automationdirect.com/adc/Shopping/Catalog/Programmable_Controllers/CLICK_Series_PLCs_%28Stackable_Micro_Brick%29/Power_Supplies/C0-01AC)... So basically I was wondering if anyone would be willing to point me in the right direction with this project with any advice, links, additional purchases, etc.. and maybe clarify what my input and outputs and program would look like. sorry for so many questions I am just very new and am having trouble finding any information online with this type of project. Thanks

[Mendon Systems 22]

It would help to know the output voltage and current of your solar panel. That will help determine how it should be connected. If you are just running a valve it be better to use a sourcing output. You should isolate the valve from the PLC using a relay for three reasons: 1) DC outputs generally don't provide enough current to run valves. 2) The relay will isolate the coil spike that the valve creates when it de-energizes from the PLC. (you will still need a reverse diode across the coil) 3) If the valve sticks, you will destroy a cheap relay instead of the whole PLC.

[ControlsGirl 2]

Hey everyone I am very new to the use of PLCs and was performing a simple solar experiment for one of my courses and am kind of lost. My experiment is to take a solar photovoltaic panel, (simple cheap panel) and connect it to a PLC to control a valve opening or closing output. It sounds simple, but I am unsure of the inputs (solar being a DC input? would it be Watts or Voltage or Amperage?) also the outputs and where to start even with what to purchase. I am surprised that they are not having you design this using only hardware or by using a little microcontroller. One big question that I have for you is if you expect the solar panel to either be off or on or if you expect the output of its voltage or current to vary. Do you turn on the valve when you get an "on" signal from the panel? or do you watch the output value sway up and down and only turn on the valve when the panel's output is within a certain range or hits a certain point (other than fully on)? Here is what you need to figure out. You need to look up the data sheet on the solar panel that you have. Look to see what it's output characteristics are. I, personally, am not familiar with them but I'm assuming that the output of the circuit will remain close to 0VDC until the voltage reaches some nominal value (ie 24VDC). If so, than this would be considered a digital input. The vast majority of PLC digital input options detect 24VDC. The standard digital input cards in America are 24VDC and 120VAC. Sinking or sourcing? The standard American practice is to always use sourcing inputs which would mean that you will need a sinking input card. I believe that most cards have the option to be either or. I would think that your panel would be a sourcing input because when it activates, it will provide the power (created by transforming energy to the sun). The other possible scenerio is that the voltage or current will range between something like 0-10VDC or 0-20mA. If so, you will need an analog input. For the output, it depends on the solenoid of the valve. If you are choosing the valve, the standard options (in my industry) are 24VDC and 120VAC. Pick the output card to match the voltage required to activate the valve solenoid. The standard in my industry is to use sourcing outputs. What class is this for?