Custom ASCII serial over ethernet to AB PLC

[xetrov123]

Good day! I am working on a project at our campus to integrate fleet vehicle chargers with load management so we don't overwhelm our service. The brand of chargers we are using has a custom ASCII serial protocol that allow for several options, including changing the power output capability. The protocol is well documented.

I have used them before so I looked at Anybus's gateways that allow for custom serial communication to EthIP but the cost of the gateway is more than the cost of the charger which is prohibitive.

I have played with AB's Modbus TCP implementation via sockets through the EthIP card. I also have used serial over ethernet adapters for building automation with Crestron a looooong time ago.... Has anyone played with communicating with a custom serial protocol in AB code through the EthIP card to a ethernet over serial adapter?

My minimum communication rate is once every 10 seconds. I wish this vendor did something a little more standard like ModbusRTU....

Thanks in advance for any ideas!

 

[Steve Bailey]

Is there an HMI involved? Something with scripting capability and ethernet IP communications could serve as the gateway.
I implemented a Modbus ASCII master in ladder logic many years ago. It was ugly.

 

[parky]

I have done it the other way round i.e. ethernet to 232 it was a long time ago, I had to send a string of characters to a PLC (a bar code to be exact) but just the chars i.e. STX ADR(xx) 1234abc CR the 232 card on the PLC was capable of recieving what ever you sent it the PC sent the chars via Ethernet effectively encapsulating the 232 chars into IP protocol, so all the 232 card recieved in it's buffer was the chars as above. I just stripped off the control chars, never done it the other way round so not being an expert on Ethernet on AB perhaps it has a open type mode so the chars recieved will be just the chars you send it There is a complication but it is assumed the PLC will handle that, a short message as above will be padded out when converted to IP (assume 802.3) I suppose the ethernet card will see the padding & only populate the buffer with the actual chars sent so the buffer should contain STXADR(xx)1234abcCR (13)
Then you could just parse the data to know what to do with it.
I did not write the software on the PC that sent the barcode it was written specifically for us it just fetched the bar code from an SQL database & the operator downloaded it.
The handshake was the PLC just replied with an ACK or NAK i.e. STX ADR(xx) ACK CR

 

[xetrov123]

I don't have a HMI selected as of yet but I'm open to options.

 

[Steve Bailey]

How many chargers are involved, and is the serial port on each RS485?
Assuming a manageable number of chargers and an RS485 network, you'll need an HMI with Ethernet IP and a serial RS485 port. Red Lion would be a good choice. I envision a script in the HMI that sequentially reads data from each charger and passes it to a PLC tag. When the PLC signals a change is necessary, the script writes the new data to the affected charger.

 

[BachPhi]

Are you working with a budget of less than $1K? Because Anybus GW is roughly 1K and you stated that it's prohibitive.

The turn key solution is to use RTA 435NBX.

 

[Ken Roach]

Oh, what a fun project !

What make and model of EVSE are we talking about ? What's the physical link you have to them: twisted-pair Ethernet, an RS-232 or RS-485 port, etc ? How many total units are we talking about ?

You could probably throw a Raspberry Pi or equivalent at this with a Python program or Node-Red and have the prototype up in a day. You'd trade ruggedness for cost.

 

[xetrov123]

We have an initial install of 19 chargers with a planned install of over a hundred in a fleet parking garage.

Each serial port is 3.3 volt TTL. I can change that to 232/485.

I envisioned some way to use a serial server to allow a controller to communicate with the chargers in it's network. Does Red Lion scripting support communicating serial over ethernet? Otherwise, I would need one red lion per charger.

 

[lfe]

And do those chargers have a serial port?

You can establish a raw TCP connection, a socket, with a cheap Ethernet to serial converter connected to the charger and send and receive raw data, including ASCII strings.

 

[drbitboy]

can the serial side be a multi-drop network?

 

[xetrov123]

It's Clipper Creek now Enphase. There is a serial port. They have a serial protocol they named Cosmos. You need to have a signed NDA to get the protocol details but it looks like something they were working on as part of a bigger project.

 

[Steve Bailey]

It becomes easier if the chargers all have ethernet. Red Lion can do ASCII over ethernet.

 

[Contr_Conn]

If you don't need industrial ratings and temperature ranges, then you can use ESP32 module to convert serial to WIFI or Wired Ethernet. Less than $10/each.
Then it will be a simple Logix Socket code on the PLC side to poll these.
I believe ESP32 libraries have Modbus TCP implementation too.

 

[xetrov123]

The serial protocol does not support multidrop.... I wish it did.

 

[dmroeder]

If you don't need industrial ratings and temperature ranges, then you can use ESP32 module to convert serial to WIFI or Wired Ethernet. Less than $10/each.
Then it will be a simple Logix Socket code on the PLC side to poll these.
I believe ESP32 libraries have Modbus TCP implementation too.

Pylogix supports micropython now, so you could read/write without touching the PLC using those boards.