Yeh, I thought the esp8266 might be 120mA or there abouts, I’m sure I’ve read that somewhere here with ref to the emonESP. I doubt I would personally go that route, it was just an example. However, I do now wonder IF there were several slaves daisychained (including the 5v terms) if you would effectively have No of slaves x 100mA on tap for powering the master? Depends how isolated those outputs are I guess?
Not sure what you mean there, by “the device” are you referring to the monitor? That’s limited to 100mA. Or are you refering to a “master” device with it’s own supply? I was suggesting using the esp8266 AS the master and powered via the slave(s).
My point was that if the slave(s) can power a simple master and communicate with the outside world (eg post to emoncms or emonhub) this is a totally self-sufficient monitoring solution, no additional AC adapters required (9v AC or 5v DC), no additional CT’s, no sockets to be installed for those plug-in adapters and no additional hardware to plug a USB adapter into or power supply for that device. But, although there may be a cost/space saving due to low component count, it is not something that a casual “DIYer” could easily install, because of the lack of plug-in adapters.
That was my thinking, I have no Modbus devices at home, so even if this turns out to be useless as a monitor, I will have something to develop Modbus applications with and test hardware/adapters etc for not a lot of money.