Guidance for monitoring Victron small off-grid system

[Jordi]

I have assembled a small Victron off-grid setup with 2x100W of solar, a MPPT 100/20 and a Phoenix 12/500 inverter.
Purpose is to feed diverse low consumption home appliances like videogames console, fridge, computers,... but mostly experiment and learn.
I use for now some old 18650 battery pack to create a battery buffer that allows me to feed 100W stable to the inverter despite clouds temporarily shading the panels and most important, keep the MPPT always powered.
My final goals to complete the installation are two:
1) Add a big LiFePo4 battery (60-100Ah) to reach the 400W the inverter delivers.
2) Monitor the system accurately with special interest for the Victron VRM system using a Rasberry Pi as it seems dummy-doable.

Here is where my dilemma comes. Such desired would cost me a 12V 100Ah Victron battery a 1.000 eur approx. per piece while the same from another reputable brand (eg. Renogy) retails for the half or less.

A Victron battery can be integrated directly into the VRM environment. Another battery requires a Victron Smart battery monitor at a cost of 200 euros.
Victron battery specs while seem slightly better are fairly equal to the specs of other reputable brands like Renogy. The other brand's batteries can also be monitored with the supplier app, just not integrated in the Victron environment.

What would you do?
Would you spend all that money in the whim of monitoring? Or would you instead use the available data from the Victron Smart MPPT and the Battery software to have an approximate Excel sheet monitoring? Victron MPPT also provides trends for load and battery voltage, ampere,... so it should be enough, right? I also understand the basics so could understand with the trends what is going wrong or well.

Your comments are very appreciated. Including comments about the setup.

 

[Q-Dog]

First, the load port on the 100/20 is for small loads like lights. By only monitoring the load port you cannot get a good idea of how much power your system is using because you DO NOT connect your inverter to the load port.

So, what should you do? You first have to decide what kind of monitoring you want. But I can tell you what I did.

I use batteries built with loose cells and dumb BMSs in my otherwise mostly Victron system. I don't really care what the individual cells are doing. I started monitoring my setup locally with a BMV-712 and bluetooth networking to the MPPT. That worked great but I had no way to monitor remotely, so I added a RaspberryPi with Venus OS to monitor the entire system through VRM. After using VRM I would not build another system without it ... it is fantastic.

If I were doing it again I would possibly use a smart shunt instead of the 712. The 712 gauge in my setup is hardly used since VRM shows all of the same data.

 

[Jordi]

First, the load port on the 100/20 is for small loads like lights. By only monitoring the load port you cannot get a good idea of how much power your system is using because you DO NOT connect your inverter to the load port.

Thank you for your reply. You went full Victron, something I'd like If it wasn't for the high costs and the Raspberry scarcity (out of stock everywhere here).

I am concerned about your comment here. Why wouldn't you connect the inverter to the load of the MPPT? Worst case the inverter pulls too much amps and the MPPT disconnects the load. If that is the case I can even fuse it with 20A for additional protection.

For having a continuous 200W supply, I should not have any problem, right? (12Vx20A=240VA)
If I want to go to 400W then I will just connect the battery to the inverter directly or upgrade the battery to 24V. (24Vx20A = 480VA) Using of course a 24V inverter.

 

[chrisski]

Are you planning on mixing 18650 non-Lithium Iron Phosphate batteries and Lithium Iron Phosphate?

I also don’t think a 100 ah battery is enough for what you are asking for, but a power audit will tell for sure. Especially if this one battery will be used for remote monitoring, but again, a power audit will tell for sure.

I have a Victron shunt tied to a homemade battery pack with Victron SCCs, and that’s all the monitoring I need. Tells me solar power coming in, and power coming out and into the batteries. Info in the battery pack I can’t monitor through Victron is the BMS, and what I would lose is individual cell voltage.

 

[Q-Dog]

Thank you for your reply. You went full Victron, something I'd like If it wasn't for the high costs and the Raspberry scarcity (out of stock everywhere here).

I am concerned about your comment here. Why wouldn't you connect the inverter to the load of the MPPT? Worst case the inverter pulls too much amps and the MPPT disconnects the load. If that is the case I can even fuse it with 20A for additional protection.

For having a continuous 200W supply, I should not have any problem, right? (12Vx20A=240VA)
If I want to go to 400W then I will just connect the battery to the inverter directly or upgrade the battery to 24V. (24Vx20A = 480VA)

Your little inverter can pull well over 40 amps when the battery gets low. That is double the output the load port is capable of. I don't know the specs of your inverter but the Victron inverters I am familiar with can surge double their rated output. That could be around 80 amps of surge if the battery gets down close to 10 volts.

This is all in the 100/20 manual. Victron includes wiring diagrams if you want to use the load port to control large loads like an inverter.

 

[Jordi]

Are you planning on mixing 18650 non-Lithium Iron Phosphate batteries and Lithium Iron Phosphate?

I also don’t think a 100 ah battery is enough for what you are asking for, but a power audit will tell for sure. Especially if this one battery will be used for remote monitoring, but again, a power audit will tell for sure.

I have a Victron shunt tied to a homemade battery pack with Victron SCCs, and that’s all the monitoring I need. Tells me solar power coming in, and power coming out and into the batteries. Info in the battery pack I can’t monitor through Victron is the BMS, and what I would lose is individual cell voltage.

Thanks god no, I am never going to mix batteries. Already worried If I had to mix the same battery model, type and brand with 3 months difference of use. If I expand the battery; same model, same size and as much as possible similar age/use.

The setup is more for fun, investigation and use. I am not aiming to depend on it. My main target is thus power obtainable. I want a sufficient amount of power which I have estimated at 200W (TV+PS4+2 led bulb, or 1 laptop+charging phones+2 led bulbs,...). The power of this devices has been verified and the highest consumer is the PS4+TV at a stunning 140W.

Such battery would last me 2-3 hours of PS4 at least which is a nice way to not develop addictions.

 

[Mattb4]

...

What would you do?
Would you spend all that money in the whim of monitoring? ...

Your comments are very appreciated. Including comments about the setup.

I see no purpose in monitoring a small setup. You can just keep a eye on things using readouts from the various devices plus your DMM and clamp on ammeter.

 

[Jordi]

Your little inverter can pull well over 40 amps when the battery gets low. That is double the output the load port is capable of. I don't know the specs of your inverter but the Victron inverters I am familiar with can surge double their rated output. That could be around 80 amps of surge if the battery gets down close to 10 volts.

This is all in the 100/20 manual. Victron includes wiring diagrams if you want to use the load port to control large loads like an inverter.

Thanks a lot for your detailed explanation. In that sense you are very right which means I will not be able to use appliances with a demand surge. Fortunately (except the fridge) all lights, PS4, TV, mini rice cooker, laptops did not show that surge. And as last resource I could directly hook the load to the battery.

In a way, with this installation I want to go one step further than my PWM+AA power wall and the 30 eur. 750W Aliexpress inverter. XD
I am probably the only person in this forum that did this:
https://diysolarforum.com/threads/s...ry-pack-10s11p-27ah-max-with-50w-solar.22700/
And it can power my 75W laptop charger or even warm up tea with my 230W DC mug heater!!!

 

[Jordi]

I see no purpose in monitoring a small setup. You can just keep a eye on things using readouts from the various devices plus your DMM and clamp on ammeter.

You are right, that is why I thought the Excel monitoring would suffice. Reading the load is the last part I needed, unfortunately only available until 20A. I think there is something wrong wired in my brain as I get disproportionate pleasure from reading graphs and all.

 

[Mattb4]

Load measurement can be easily viewed by wiring in a meter after the inverter. I use this type on my setup.

 

[Jordi]

Load measurement can be easily viewed by wiring in a meter after the inverter. I use this type on my setup.

Thank you for your reply Matt. Indeed, in that direction there are some easy and cheap solutions, even better for such low wattages (and already have one) a DC meter because then it goes before the inverter and it factors in the conversion efficiency loss (91%) yet missing the MPPT consumption (1-6W).

What I do not like of these methods is that they provide a static number or a real-time number only. Which makes you a slave of the meter and simply can not collect as much info as a recorder. I did that for one year actually, noting every night before bed the solar production of a small array with a DC meter, pen and paper. After putting the data in Excel (despite the days I could not note it), I got a nice idea of how the array works over a whole year cycle. Finding the peak power was more challenging, in sunny days I checked the meter like up to 10 times per day and yet, still not sure I found the peak. The panels keep surprising me. A recorder would have made this part peanuts.

In this project I aim to professionalize that investigation part to learn more and see how far I can bring a low wattage life.

 

[Mattb4]

...

In this project I aim to professionalize that investigation part to learn more and see how far I can bring a low wattage life.

Since you asked "What would you do" I answered that i would not spend money for monitoring of a simple setup. For one thing it uses energy to do so. If your goal is to operate on the minimum wattage you can why add more loads that only serve to create graphs?

 

[Jordi]

Since you asked "What would you do" I answered that i would not spend money for monitoring of a simple setup. For one thing it uses energy to do so. If your goal is to operate on the minimum wattage you can why add more loads that only serve to create graphs?

Yes, and I very much appreciate your answer.
I would like to plot loads to mix different loads at different moments and see how this all comes up together over a day. Even though with 200W I won't see much... ?