Hi
I have a solar system that charges a 24 volt battery bank. The solar controller provides information on charging but I want to monitor usage.
I have built and calibrated a V2 emontx connected to a voltage divider and a Pololu ACS711EX Current Sensor Carrier:- http://www.pololu.com/product/2452
I now have pretty accurate readings for voltage and current and I have modified the EmonTx CT123 + Voltage example firmware to transmit those values to my emoncms server. The next move is to record a running total of amp hours. I have some idea on how to code this checking time between readings using millis() and updating a running total.
One thing I am not sure about is whether I should worry about battery voltage variation which can be from 23.9v to 29.2v suggesting that maybe I should record Watt Hours and then calculate Amp hours at the nominal 24V.
Also I am not sure what sample time would be needed to get reasonable accuracy. And is there any trade of of running at the shortest sample time possible. I am not concerned about the Emontx current consumption as it will run from the 24V batteries as does my Pi server and hard disk.
However this is all fairly new to me and any input or suggestions would be much appreciated.
Regards
Ian
Re: Monitoring power usage on a 24Volt DC battery solar system using Emontx
Hello Ian!
Is it really important to know the Ah that you charged into your battery? You won't be able to get out the same Ah.
I think it's better to measure the kWh or Wh that come from the solar system as this also includes the battery voltage.
I'm running a similar project, but I'm running a 12V battery and 2x ACS712 with different values (+/- 20A range for load, +/-5A range for solar current) on a self-built, modified EmonTX clone since July last year. you can have a look at the measurements here: http://www.emoncms.org/dashboard/view/Solar1 (complete system listed in the EmonTX showcase forum).
Re: Monitoring power usage on a 24Volt DC battery solar system using Emontx
Hi Jürgen
I would like to monitor power consumption. I have some IT stuff running 24 hours a day on the DC supply. I want to add some more but do not want to overload the system. Summer is no problem but in the Winter I have to switch some things to mains to stop the low volt drop out shutting down the 24V system.
If you have any code you are willing to share that records DC power it would be appreciated.
Regards
Ian
Re: Monitoring power usage on a 24Volt DC battery solar system using Emontx
Hello Ian,
I've attached a zip file with some files of my project including schematic,3D model of pcb, ready to use pcb and the script for it (at the moment I don't use temperature measurement on it but everything is prepeared for it, I've also access to all pins of the ATmega processor that are not used at the moment and there is a small field where additional components can be placed for future extensions.
I created the schematic and pcb it with KiCad, a free pcb designer, the pcb was produced by pupils of the technical school I attended 16 years ago. If anybody likes to have the KiKad files, please write me a message.
Jürgen
Re: Monitoring power usage on a 24Volt DC battery solar system using Emontx
Hi Jürgen
Many thanks for the files.
Regards
Ian