General PLC HELP PLEASE!!

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.automatio...nits/C0-00DD1-D) , not sure if i need a sink or source dc output yet (another question...) with the following power supply (http://www.automatio...upplies/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

plcnewb123 said:

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.automatio...nits/C0-00DD1-D) , not sure if i need a sink or source dc output yet (another question...) with the following power supply (http://www.automatio...upplies/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

Click to expand...

Welcome to the Forum!

We will need some more details on your project, and what you want to do. For example, do you want to open the Valve only when the Solar Cell is receiving Sun light etc?

Solar Cells tend to put out around 12VDC to 13.5VDC or so. PLCs in general operate with 24VDC, but there are PLCs designed for 12VDC.


Stu....

Since the output of a solar cell varies with the amount of light hitting it, you might want to consider an analog PLC.

A lot will depend on what you're trying to do with the solar panel. I realize this is just a learning exercise, but is the idea to use the panel as a simple on/off sensor, or do you want to measure the light intensity - for example to determine its power output?

Hey thanks so much for the quick response it is much appreciated! To clarify I would like the Plc to receive the input from the solar cell.. And when there is light on the cell and a certain wattage is reached the Plc would read this and tell a valve to open...

So basically no wattage being absorbed (no sun) = closed valve and when there is sun and wattage being absorbed the valve would open... Maybe this would look like the Plc reading a certain voltage or Wattage value??

And stu, do you mean the Plc is powered by 24v typically? I plan on purchasing a separate power supply for the Plc if you were referring to that issue..

Sorry if it sounds a little confusing, I would be happy to clarify any questions!

Thanks again for the help, it is greatly appreciated!


Russ

Same answer I gave you on the other forum!

Hi Russ:

So basically no wattage being absorbed (no sun) = closed valve and when there is sun and wattage being absorbed the valve would open... Maybe this would look like the Plc reading a certain voltage or Wattage value??

Click to expand...

That sounds like a good application for an Analog Input as suggested by Albert. You could feed the Solar Cell Output to a Resistor, and measure the Voltage developed across it. When the Voltage reaches a certain value, you could then trigger your Output.

And stu, do you mean the Plc is powered by 24v typically? I plan on purchasing a separate power supply for the Plc if you were referring to that issue.

Click to expand...

Sorry, I should have been more specific. I was referring to Input and Output Cards. There are PLCs that are powered from 24VDC, however, 120VAC is much more common.

Stu....

plcnewb123 said:

Hey thanks so much for the quick response it is much appreciated! To clarify I would like the Plc to receive the input from the solar cell.. And when there is light on the cell and a certain wattage is reached the Plc would read this and tell a valve to open...

So basically no wattage being absorbed (no sun) = closed valve and when there is sun and wattage being absorbed the valve would open... Maybe this would look like the Plc reading a certain voltage or Wattage value??

And stu, do you mean the Plc is powered by 24v typically? I plan on purchasing a separate power supply for the Plc if you were referring to that issue..

Sorry if it sounds a little confusing, I would be happy to clarify any questions!

Thanks again for the help, it is greatly appreciated!


Russ

Click to expand...

I guess I dont understand the point of using a solar panel for this? I mean, typically you use a solar panel to charge batteries to run equipment. now if you want to measure the current or voltage of the solar panel while it is performing that task I could understand.

the analog PLCs seem perfect for my application! I notice CLICK has some analog PLC units for 50$ or so more, which seems well worth it. One question, if I plan on using a small, cheap solar panel with the following specs:

• Power (Pmax) : 5W
• Maximum power voltage ( Vpm ) : 17.5V
• Maximum Power Current: 0.28A
• Open circuit voltage ( Voc ) : 21.95V

will the CLICK analog PLC operate w/ respect to the analog inputs? I notice the specific PLC has the following specs:

• Analog Inputs: 2 channels 4-20 mA or 0-5 VDC

Also to further clarify my intent of setting up this system of reading varying voltage input from the sun/solar panel to operate a simple on/off valve or switch is because I am trying to familiarize myself with PLCs as I have never used/programmed any. I will be involved in a future design project for a smart grid controller that regulates solar energy and alternate b/w on and off grid systems, specifically refrigeration systems.


Basically pure education purposes, so I am free to alter the experiment criteria if impractical..


Thanks so much for helping, I HIGHLY appreciate it, I am already learning tons


-Russ

I'd suggest using a simple resistive voltage divider to scale the solar panel's output voltage down to the PLC's input range.

Note that the current/voltage relationship in a silicon solar cell is complicated (and an important factor in system efficiency), so you'll want to do some research and experimenting to decide what load you'll put on the panel. In addition to studying the panel's spec sheet, check out this article for a good explanation: http://en.wikipedia.org/wiki/Maximum_power_point_tracking.

To be on the safe side, you could start out with a divider that will give the PLC input 5 volts when the panel is delivering its maximum (open-circuit) voltage.

Albert,

That is a great idea, to be safe I will scale down the MPP voltage (in this case 17.5V) to 5V with a few resistors.

If I did this would it be possible to program the analog inputs w/ the PLC to open a valve b/w the 0-5V range (which would be essentially any voltage up to the MPP voltage) and would it thus close if there is any input over that value? or would it be a better idea to scale down the open voltage (22V) to 5V to be on the further safe side.

as far as efficiency goes I think I think I will focus on that issue with the later project (but research now) and just focus on the PLC information for this experiment.

and to recap is this a correct theory of my application?

with a analog plc unit, the input voltages will be varying and i will scale down the voltages with a voltage divider so the range is within the PLC 0-5V range. The plc will be programmed to read the following:

any input voltage greater than 0V and less than 5V = valve open
any other value = valve closed

will I need any other hardware other than the CLICK PLC unit:
MICRO ANLG PLC, 4 DC IN /4 SOURCE OUT, 2-CH IN / 2-CH OUT, REQUIRES 24VDC PWR )



and power supply, cables, proper resistors, etc?


I am so sorry for the smothering of questions, I am purchasing this weekend and am just making sure.



Thanks so much!!

One question I had regards the valve you'll be controlling: is it an actual solenoid/motor-operated valve, or will you be using an indicator light or something to represent a valve?

The reason I ask is that electromechanical valves require a significant amount of current, so if you're using a real one, you'll probably want a PLC with relay outputs (and an external relay if the valve coil exceeds the rating of the PLC's internal relay), and a separate power supply.

If you're using an LED light as a stand-in for a valve, a PLC with sourcing/sinking outputs should be fine.

To go one step further: if you cna use a "symbolic" valve, how about using the PLC's analog output to implement proportional control, where the valve position (represented by the PLC's output voltage) would be anywhere from 0 to 100%, depending on the solar panel's output and any other factors you want to iclude in the program. Instead of an indicator light, you'd use a panel meter whose reading would represent the valve position.

Albert,

Really I was just going to use an indicator of a valve, so the meter idea is perfect!

I will begin searching for the proper hardware now. With the CLICK PLC I plan on purchasing, is there any additional cards required?

any recommendations on where to purchase the indication meter you are speaking of? If not I will be scanning ebay!

Again, thanks for helping me shape this experiment to a useful, educational direction

-Russ

For the Click, I don't think you'll need anything else except a power supply. You can use any 24V DC supply that provides enough current, but the supplies offered as part of the Click product line make for a nice package, and I think they're actually a little cheaper than the comparable units that AD sells.

For the meter, I'd suggest an analog DC panel meter with a scale of 0-1 or 0-100, so it will be easy to read as a percentage. Of course, it will need to have a range compatible with the Click's analog output (probably through a resistor unless you get very lucky in your search). I saw a number of candidates on eBay; for example this unit, which has nice big face and a 0-100 scale:
http://www.ebay.com/itm/321000966454.

With a 5V output from the Click, you'd need around a 50K ohm resistor to put 100 uA through the meter for a full-scale reading. I'd suggest making part of that 50K a variable resistor so you can fine-tune the current.

Oops, I forgot one very important thing: the USB-to-serial programming cable.

I'd strongly recommend AD's cable:
http://www.automationdirect.com/adc...el_Programming_S-z-W_-a-_Cables/EA-MG-PGM-CBL

Although there are other, possibly cheaper USB-serial adapters on the market, I've heard of them not working with the Click, probably due to different chipsets. The AD adapter worked right out of the box on my Windows 7 and XP computers, so I consider it money well spent.

Perfect!

Thanks so much I am purchasing the hardware today! One last question, do you have any suggestions on any CLICK programming guides or tutorials? The automation direct resources do not really cover too much of actual programming..

I highly appreciate your help! I am excited to finally start this experiment!

-Russ