Community
OpenEnergyMonitor

Community

EmonTX Calibration Safety

calibration
Tags: #<Tag:0x00007f13ef5fb360>

(Soloam) #1

Hello, I what to calibrate my emontx, but I what to do it with safety! Is it safe to have the serial programmer plugged to the EmonTX while it’s monitoring the current? So that I can change the parameters and upload them on the fly!

Also what security measures do you recommend so safeguard myself and the emontx!

Thank You


(Robert Wall) #2

Yes, provided that you are using a current transformer (and a voltage transformer if you want to measure the voltage) on the input side.

The calibration instructions would have warned you if there was any danger.

You must NEVER connect the emonTx directly to the mains supply, i.e. you must not use a current shunt and you must not use a voltage divider to monitor the mains current and voltage.


(Soloam) #3

Thank you @Robert.Wall, so is it safe to connect the FTDI programmer to the emonTX when it’s powered with the AC-AC Charger and reading the power? Would not that result in a short circuit when my laptop is supplying energy to the ftdi and the ftdi supplying to the emonTX by the 5v, and in reverse the emonTX will also be supplying energy in the serial vcc pin (used for example to power the esp8266 (EmonESP)? :grimacing:


(Robert Wall) #4

It is safe - but not recommended. That is what the link (JP2 - next to the battery holder) is for. If you care to look at the circuit diagram, there are two 3.3 V regulators, one for the battery, USB and FTDI 5 V inputs and one for the a.c. input. The link disconnects the output of the a.c. input regulator from the 3.3 V rail, while still allowing the a.c. input to be used for measurement.
(But having said that, I do it all the time - but not for extended periods.)


(Soloam) #5

I just need to do it to calibrate the emontx! I need want to connect to the emontx to see the readings in real time and make the needed adjustments, upload the new firmware with the calibrations.

At the moment I have the 9v AC-AC for sampling and the 5V USB powering the EmonTX (I need the 5V because I use the EmonESP, and the 9V AC-AC is not able to power the EmonTX and the EmonESP, as stated in the Wiki). Now I see that I should have removed the JP2 to do this… Never had any problems… But its better to remove it… Correct?

So If I get you right. My connection should be, 9V AC-AC, the FTDI in the serial and remove the JP2 jumper… I should not connect the 5V USB when with FTDI connected.

Thank you, and sorry if some of my questions sound like “noob in the house”. :roll_eyes::no_mouth:


(Robert Wall) #6

There is no need for two supplies. They are wired in parallel, so it is possible for one to “back-feed” the other. Without having a full and complete circuit diagram, including a full equivalent circuit for the power supply regulator i.c’s, it’s impossible to say what will actually happen. But I would not expect serious damage - if that was likely, it would be a well-known danger and all regulator i.c. data sheets would have a warning about “back-feeding”, and I’ve never seen one.