Hi.

I have a solar system that utilizes a PLC to control hydraulics that move the panels as per the Time of Day. There is a lever that turns a linear POT based on the position of the panels, and based on its resistance, and the Time of Day, the hydraulics move the solar panels.

See pics below.

The Time in the PLC was slow, and the person who normally maintains the solar system is gone. I have tried changing the Time (via Termite Software), but have been unable to do so. I changed the battery in the PLC as it was 12 years old, and as a result, the Date/Time got zeroed. I don't know how to get the PLC into programming mode to allow me to enter the correct Date/Time.

The company that sold me the system is defunct. There are no markings on the PLC. I am looking for a replacement PLC that I can program myself.

The inputs are 12 VDC 5 amp, and 3 wires coming from a single turn, wire wound, Linear POT from ETI systems.

The 3 outputs control three 12VDC coil relays (hydraulic pump (120VAC), CCW hydraulic control valve (12VDC), CW hydraulic control valve (12VDC).

Can you help me find a suitable PLC ?










Thanks,
M...

 

Hi,
if you know C language, you could use the Solar Position Algorithm (SPA) in ANSI C described in this document:
https://www.nrel.gov/docs/fy08osti/34302.pdf
You can download source code in ANSI C here:
https://midcdmz.nrel.gov/spa/

Then you could buy a RASPBERRY PLC 21 here:
https://www.industrialshields.com/shop?search=&order=&view_mode=list&attrib=73-416
https://www.industrialshields.com/s...ttr=2607,702,743,4073,534,5807,4218,4219,4220

and integrate the code in a program running under the Linux OS.

Best regards,
apa

 

Hi Mike,

we can start from I/O List :

DI : NA
AI : 1 channel, Potensiometer input representing the position, you need to check what is the potensiometer specification, I saw this potensiometer made by ETI System but I can't see the model number or specification, you can check here the correct model installed at your system :
https://etisystems.com/linear-control-potentiometer-design-guide/
DO : 3 channel , 12 VDC relay for hydraulic pump ON (120VAC), CCW hydraulic control valve (12VDC), CW hydraulic control valve (12VDC)
AO : NA

so we need compact PLC that have at least 1 POT input and 3 DO 12 VDC, I recommend Allen-Bradley Micro810 with 1080-TRIMPOT6 and you can download Programming software : Connected Components Workbench standard edition for free :
CAT No. 2080-LC10-12DWD, it is 12 VDC powered with 12 VDC DI, 4 relay output 8A, 4 AI 0-10V. since it doesn't has potensiometer input, you need POT to 1-10 VDC converter, example is AB 931S-P1C2D-DC .

After Hardware settled then we need to design the software, based on your information, the control is based on PLC time, so you algorithm to track the sun based on PLC Real time Clock (sec, min, H, date, month, year) and your location ( latitude and longitude), SPA algorithm that shared Mr. apa will be working well. Connected Components Workbench software is supporting Structured Text (ST), Ladder Diagram (LD) Function Block Diagram (FBD) with various arithmetic instruction that sufficient to implementing SPA algorithm.

For more reference on how SPA Algorithm implementation to PLC, this is sample of implementation which based on Siemens S7-1200 with Solar Positioning Algorithm (SPA) Library which I believe too expensive for your case

https://www.theseus.fi/bitstream/handle/10024/493864/PLC Based Solar Tracking System.pdf?sequence=3

 

Hi & Thanks for this plethora of info that I will begin to explore.

I program in Basic (don't laugh, I had a wonderful 25 year career doing business systems in Basic), and python under ubuntu. I have programmed some c many years ago, so I have much to look into.

In the meantime I have managed to get the correct time (not the date) by powering up at midnight - the clock started ticking at 0 and now, at 08:27 the PLC is showing the correct time.

Today, I will travel to the solar field, some 30 miles from here, climb up a ladder, and install the PLC. I will also attempt to take some resistance readings from the POT at various times of the day. (I have also emailed ETI requesting the spec on the POT.)

The problems - a multi hour power failure at night and the PLC battery fails, and, in 4 years from now, the battery will have to be changed which is tricky to do when the PLC is mounted. Not really a big deal - at least I can make it work.

This will give me time to delve into the info on this post.

Thank you all very much, and have a great day,

Mike from the 1000 Islands, Ontario, Canada

 

>> AI : 1 channel, Potentiometer input representing the position, you need to check what is the potentiometer specification, I saw this potentiometer made by ETI System but I can't see the model number or specification, you can check here the correct model installed at your system :

The manner in which resistances are 'monitored' by a PLC resistance AI card is by pumping a constant current through the resistance and measuring the voltage drop.

The system, as installed, is likely already pumping current through the pot, so measuring the existing voltage drop across the resistor is most likely the approach to determining the 'position'.