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Hi,
I am currently developing a service that uses a PZEM-017 as a smart shunt alternative.
In order not to lose the current SOC during a restart of the GX device I'd like to store it in the settings object.
Now I wonder what my Multiplus II GX (and other GXs) uses for permanent storage and whether or not it's a problem to frequently update the data on that device.
Is there a recommendation regarding frequent write to settings objects?
Thanks
ks4z
You can use localsettings
https://github.com/victronenergy/localsettings
Hi Louis,
thanks for the quick answer.
I know about the localsettings. The question that came to my mind is, if it hurts the storage if I write to it quite frequently. Some permanent storage devices like eeproms etc. don't like frequent writes. Any insight on that?
Thanks
ks4z
Yes that can be an issue.
The localsettings object will optimise the disk usage for you as best it can. But it will still be writing to the disk. It is stores it's data in a XML file under the /data/ partition which is persisted, but I don't have more details without going through the code in detail.
One way to handle this is to publish the SOC value in the dbus service for the device and update this say once every 1-10 seconds. This parameter is volatile and exists only in RAM.
Also create a non-volatile version in settings and update this parameter say every minute.
I'm interested in this work as a low-cost alternative to SmartShunt for DC Meter situations. Will you support this as well?
SmartShunt configuration is handled with VictronConnect which your alternate would not be able to use so you'd need to implement configuration in the GUI Menus.
Thanks for your work.
Hi,
I guess I will go for some reduced updates on the settings as you propose. Maybe depending on the change of the value itself. It will probably be (slightly) wrong anyway after a restart.
I didn't look into the DC meter yet, but I see no reason why this could not be supported.
The config in the GUI isn't a huge problem, I did that before. However, I don't like that it requires changes on system files that will be overwritten by updates and might interfere with other extensions. Is there some best practice for that?
Thanks
ks4z
Venus OS firmware updates overwriting mods to the system files is a concern. Many suggest adding code to /data/rc.local to reinstall updates. Even services you create to add drivers to the system need to be reinstalled after a firmware update. Some place code in /data/rc.local that runs every boot to reinstall things but that can slow boot-up.
I've taken this a huge step forward with SetupHelper. Packages developed with the SetupHelper hooks are able to reinstall after a firmware update automatically.
https://github.com/kwindrem/SetupHelper
Developing packages for SetupHelper is fairly involved but I have help available should you choose to go that way.
I also do not like to make GUI changes, but there does not seem to be a way around it. The best way I see is to make a backup of any files you change. The issue is that as the firmware updates so does the GUI also and if there is a mismatch the UI will not display.
From what I saw Kevin' GUIMods has a version that match each firmware version, and his setup tool then install the matching GUI changes.
This does seem like a lot of work to keep up with firmware changes, so my driver tries to only have one or two entry points and have it's own pages under those.
I would also love to know if there is a better option.
Yes, there is some work associated with support of new Venus OS firmware versions but it's not too bad.
There are other ways to modify files than replacing them with a version-specific file. You can also use tools like sed to modify the file. I did this for a while with SetupHelper but it has it's own difficulties in some cases. The latest version of SetupHelper does modify the stock copy of PageSettings.qml. This makes it version-independent. Adding a device's config menu tree to this file could be done the same way and eliminate conflicts with other packages.
Thinking about the PZEM-17 as a low-cost alternative to a SmartShunt. For the PZEM to function as a DC meter or even a battery monitor, it would need to be powered all the time and in a system that doesn't always have shore power or even sufficient solar energy to power things the PZEM's power consumption might be an issue. The spec for the SmartShunt is "under 1 mA".
Has the PZEM-17's current draw been measured?
According to this Link
https://open-boat-projects.org/en/wifi-batteriemonitor/#Stromreduzierung
the PZEM-17 is in the same 1mA range.
This is good news and increases my interest in using the PZEM-17 as a lower cost alternative to SmartShunt.
Venus OS includes Modbus TCP but not sure if it includes Modbus RDU (RS-485 serial).
The PZEM series of power monitors are Modbus and therefore support multiple devices on the same RS-485 serial connection. I did a project a while back using 4 of the AC versions. Multiple devices on the bus requires configuring the PZEM's slave address before connecting to the bus. For my project, I ignored the default address of 0 to avoid issues with unconfigured units. I wrote a small C program to scan Modbus for addresses and allowed any (including 0) to be changed.
Another issue is a way to configure the use of the shunt: battery monitor / DC Meter, and if the latter which measurement type: alternator, DC load, DC source, etc. This is done on the SmartShunt using VictronConnect via bluetooth. Once setup in VictronConnect, the shunt then appears on dbus with a service name including the measurement type. If this method of configuration is used for PZEM devices, it's appearance on dbus will change after configuration. You might want to consider configuring the device type when setting the Modbus slave address. Options are limited but the PZEM includes a high and low voltage alarm threshold that aren't likely to be used for anything in this application so the measurement type could be placed in this register. The other could maybe hold SOC so it doesn't need to go into dbus Settings.
Another configuration item is the shunt range: 50, 100, 200, 300 amps. This would need either a menu item or be configured with a setup app also used to set the slave address and possibly the measurement type.
I'm willing to help with development and testing.
From what I have read, this is not a bipolar current meter, so it does not show whether current is flowing from or to the battery.
I just finished a bipolar "smart shunt" with parts from ali-x which is simple and works fine. using python, rpi_GPIO library and node-red in venus-os. and costs around 12$ in total. you can also use smbus for communication.
All the modules together are so small that they fit nicely in half the size of a matchbox
It is based on
MCP3424 Module I2C (4 channel 18 bit bipolar adc )
ISO1540 Module bidirectional I2C isolator
5V to 5V dc isolated power suply module
Shunt
Is it just as a battery monitor or DC meter also? Would Venus support multiple units? You mention I2C. Would this only be on the PI? If not, what's the interface (USB, ModBus RDU, ???)
I use this AD converter connected directly to a 50A/75mv shunt.
I have set the gain to x8 (+-250mv) and 16bit,
and there are still 2 channels available for other measurements.
If you look at the example on page 33 of the data sheet
"Battery Voltage and Charging/Discharging Current Measurement".
MCP3424 ADC-4 Data sheet
I have tested with this node-red node, which worked fine
https://flows.nodered.org/node/node-red-contrib-redplc-rpi-mcp342x
I2c use 2 gpio pins. I have rtclock, 16 channel led light controller and 8 channel relay controller on the 2 same gpio pins 3 and 5 (SDA and SCL)
I don't know if you have access to i2c/gpio on the GX devices
On Github there is already a VenusOS-Driver available:
https://github.com/mildred/venusos-peacefair-pzem
But this driver is maybe only for python 2.7 not 3.0.
Is it possible to change the Syetem Setup/Ac Input 1/ (Grid to Generator and vice versa)
with a dbus command?
Yes. How it is done depends on the language you are using. For shell scripts, use dbus -y. There's also a python library for the dbus interface. Look in any of the stock services for the files in .../ext
More info here:
https://github.com/victronenergy/venus/wiki/commandline-introduction#working-with-d-bus
and here:
https://github.com/victronenergy/venus/wiki/dbus
The specific parameter is com.victronenergy.settings /Settings/SystemSetup/AcInput1
If you are looking for a way to switch the system from grid/shore to generator, check out my package that handles everything switching the input type and the input current limit and Do not run generator when on AC 1 as well
https://github.com/kwindrem/ExtTransferSwitch
Any update on this?
I'm keen to setup a cheaper smartshunt alternative for measuring alternator output and this would be perfect. Otherise I will probably play around with the INA226 work @ks4z has done.
