Use REST API for getting second-by-second data

I would like to measure cell data with resolution per second in a FENECON Commercial battery system. Is that frequency possible with the limitations of the REST API?

Thanks for information!

should not be a problem, because the rest-api is also fired every-second. if the performance and the load will be good enough you have to check out. to get every second data, you can use sockets with less overhead.

best regards


Thanks for the answer @p.wimmer. What exactly do you mean by “sockets with less overhead”?

a socket connection has less overhead than x rest calls and is so much faster and you get immediatelly all changes over the socket-connection

I was told that not all signals are accessible publicly via Modbus TCP and that cell data is only extractable via REST API. Is that not true?

Hi @JBrucksch and welcome to the OpenEMS Community.

I assume with “socket-connection” Paul refers to the (undocumented) API provided by the “Controller API Websocket” (

This is the API that is used by the local OpenEMS UI to receive real-time data from an OpenEMS Edge. If you want to dig further, this code block can give you a starting point:

If you were running your own OpenEMS, you could of course either use

Both variants are unfortunately not available with FEMS at the time of writing.