My budget grow-as-you-go power wall :-)

Here’s a photo of my DIY McGyver-style power wall:

This installation has grown bit by bit over time. I’m in South Africa and on a very tight budget. A few years ago when we had two to four hour power cuts three times a day a friend gave me a Multiplus 24/800/16 for my birthday. I had two 12V deep cycle lead acid batteries at that time (salvaged but still serviceable) so at least we had a a glorified UPS to keep the lights and TV on during the frequent blackouts.

Then, when I had a little more to spend, I replaced the lead acid batteries (now completely worn out) with a 2.8kWh LFP one. When some more money came in I added four PV panels and a SmartSolar. Later still I added a Phoenix 24/1600 inverter to power the fridges and freezers that we have. (We’re out in the sticks and we make one big shopping run a month.) The water pump for the rainwater harvesting and backup tanks (very necessary since we have municipal water one day a week if we’re lucky) also run off the Phoenix. This necessitated the addition of another 2.6kWh battery.

Both batteries are housed in the box underneath the power wall (normally covered with the lid standing to the left of it). The DB box on the right holds the DC breaker and surge protectors for the PV panels; the one on the left houses the AC breakers. The switch at bottom right is the KETO battery disconnector which houses two 125A DC fuses. The batteries are BlueNova 26V 2.8kWh LeFePO4 models.

The idea was to have enough power to significantly reduce our power bill (fridges, freezers and the TV are a major component of our monthly usage) and to be resilient against power failures since the national infrastructure is being held together with sticky tape and paperclips. To save money I installed everything myself. Yes, I did the homework to make sure it’s done the right way, and while I am not a licensed sparkie I do have a background in electrical engineering, I do know the difference between AC and DC, and I have had basic training as an electrician when I was still young and good-looking. So I’m confident that the installation is safe.

I’m using the AC Input Control settings on the Multiplus to supplement power from the grid if the PV panels don’t get enough sunlight. Through a lot of measurement and some trial-and-error I have worked out at what clamping voltage the batteries have dropped to about 30% SOC, at which point the Multiplus begins charging and switches the TV, the kitchen fridge and the lights from the inverter to the grid. At 10 amps charging current this just keeps the SOC at 30-40% until the panels provide more power. At 80% SOC the Multiplus stops charging and switches back to inverting mode. I figure this is the optimum to maximize battery service life.

Note that the Multiplus appears to calculate the SOC by integrating its own charging current and inverter output over time. This works well if the Multiplus is the only device connected to the battery, but with a SmartSolar and additional Phoenix inverter in the mix this goes right out the window, so switching AC Input on and off by voltage is the only option. Judging the SOC by the clamping voltage of the batteries only is of course not 100% accurate, but for my purposes it’s good enough and I can’t justify the expense of a Cerbo and Smart Shunt. I’ve had this running for several months now and it works quite well.

I’m about to add a relay box with a timer to switch the water pump at the backup tanks to the inverter during daylight hours, and to the grid between sunset and sunrise. (Except when there’s no grid power, in which case the relay will automatically revert to inverter-only mode.) The box is still sitting on the table in front of the battery enclosure but hasn’t been mounted yet. The reason for this relay is that if we want to run the dishwasher and have a shower in the evening the pump is just a little to much and drains the batteries to a point where the charger kicks in at around four in the morning.

This illustrates the main drawback of using the Multiplus AC Input Control settings for grid supplement power: it’s either on or off and there’s no way to charge proportionally to keep the batteries at a certain SOC. The batteries will be charged at whatever charge current settings I have put in, but only stop charging when the SOC is at around 80% (judging by voltage). This means that sometimes, if the gods of sunlight and electricity are particularly unhappy with me, it is possible for the charger to kick in early and charge the batteries from the grid to about 80% SOC during the night, so that by sunrise the batteries are almost full and I’m not getting a lot of cost savings out of my PV panels. It is also possible for the batteries to be drained to 30% SOC and then for the grid power to fail, in which case I will have to hook up my trusty old generator set. However, spreading the loads sensibly and playing with the Multiplus charging current settings (still an ongoing process) can go a long way to optimizing everything.

I fitted the SmartSolar with a fan (an aluminium enclosure containing two laptop cooling fans powered by the salvaged laptop power supply mounted below the SmartSolar) because on sunny days the case gets far too hot for comfort. I’m not quite happy with those fans; they’re too noisy. I also mounted the MK3 dongle against the wall. (The Multiplus doesn’t have Bluetooth.) I’d like to replace it with a VE.Bus Smart Dongle, but I can’t justify that expense for what is essentially just a luxury. Plugging in the laptop also works, and I’ll make do with what I have.

So anyway. Here’s my McGyver-style power wall. I’m moderately proud of it and quite happy with the way it does the job. :grinning:

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Nice and just as it should be with Victron.
You not only grow with your tasks but also with your financial resources.

All that’s missing now is a small bag with the “Huntsman 21.3713 from Victorinox” as an emergency tool in the corner

I would invest the $$ into a raspberry pi instead of the ve.bus dongle and run the Venus’s software on it. You will get most of the functionality as a cerbo.
The Mk3 is plug and play into the pi, then get a usb to v.e.direct cable for the MPPT.

This is a good writeup on using a PI

You can then run the ESS system and mitigate your 80% 30% issue mentioned.
https://www.victronenergy.com/media/pg/Energy_Storage_System/en/ess-introduction---features.html#UUID-2bfa8529-9daf-ff3a-f743-e59fbf8a050b

With that said the cerbo-s and the cerbo gx are reasonably priced.

Here the price of a basic RPi4 with case and power supply (the RPi3 doesn’t have Bluetooth) is a little higher than the price of a VE.bus smart dongle, but about half that of a Cerbo (not counting any USB to VE.Direct cables). So as a replacement for the Smart Dongle it doesn’t make sense, but as a DIY replacement for a Cerbo it does. However, it’s still more than I can afford to spend on it right now and given that my current setup works more than well enough and that the limitations are not all that serious (yet) it’s something I’ll have to keep in mind for a future addition.

That said, thank you for the suggestion! I hadn’t really looked at the Venus software yet because I don’t have a spare RPi lying around, but it’s certainly an option.

I do have a Victorinox (about 35 years old so not sure what model it is) but it lives in my trouser pocket where it belongs, ready for instant deployment. :grinning:

The 3b+ has Bluetooth, but you won’t use it that way. You either connect it to your home network or if you don’t have one you connect to its wifi hotspot and access it on a web browser.
You obviously have some kind of internet or we wouldn’t be having this conversation. I have a v.e.bus smart dongle and it’s very very limited, I would not suggest it over a “gx device” or equivalent any day.
You also gain VRM etc…

The ESS is exactly what you want and need here, it addresses everything you have flagged as an issue. I would suggest reading the information in the link I posted.

I was under the impression (incorrectly) that VictronConnect only supports Bluetooth and USB. WiFi will do nicely. I may have a spare RPi3 available sometime in the near future, so if and when that happens I’ll have a look at installing the Venus image on it. (I’ll need a screen for it, though - right?)

Ahh I see where you are confused.
You don’t use victron connect to monitor the system via a GX device.

If your system is connected to the internet full time, I.e you have home internet and wifi.
You use VRM (app or local network via web-browser)

If your not connected to the internet full time or you only use your phone to use the internet then you would connect to the wifi hotspot it creates and connect via web-browser.

I would suggest the first option if possible as you get remote monitoring and data logging.

What kind of internet/home network do you have?
And no you don’t need a screen as long as your happy accessing it via your phone/tablet/pc etc…

I’ve got fixed wireless Internet access with a WiFi router, so that would work fine. It could be connected to the Internet permanently and it would be on the home WiFi network in any case. So that is indeed an excellent solution! I’m definitely going to spend some time doing my homework on that. I might have an RPi3b available in the not too distant future and I can already see what that’s going to be used for… :slight_smile:

Tnx!!

Update: I just saw on YT that one can make VE.bus to USB cables for about 1/10 of the price of a Victron branded cable. Albeit without optocouplers, but for a Phoenix and a SmartSolar both connected to a RPi that should be no problem…

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So the only thing is that a gx device is meant to monitor 1 multi/inverter or parallel/3phase system. I do believe that it will show the second inverter in the device list. Hopefully it will also count the data (current drawn etc) as well.

When you set up the pi, connect the multi to the unit first. So it becomes the “primary” unit then connect the phoenix. If the gx device doesn’t count the Ah drawn from the phoenix then you would need a smart shunt.

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In VictronConnect via Bluetooth on my smartphone the Phoenix gives me the input voltage and inverter output in watts but there’s no data whatsoever on the DC input current. Unlike the Multiplus. So with the Phoenix in the mix I would indeed need a SmartShunt before a RPi with the Venus software would make sense. :unamused: Bummer.

This thread alludes to the fact the current is shown on the GX device.

The question is if it’s subtracted from the battery monitor in the multi plus.

And I wouldn’t look at it as a bummer, it gives you a reason to get a smart shunt. In my very early days of Victron “addiction” I was along the same lines thinking why do I need a BMV if the multi plus monitors the SOC, the smart shunt didn’t exist yet, after having a battery monitor and seeing the difference in accuracy I wouldn’t install a system without one.
Especially in your case without a monitored load, the Phoenix.
Trying to ascertain SOC from voltage levels of Li batteries is never going to be accurate as the change in voltage could be 0.01v for 20%

If you do don’t forget it needs a ve.direct to usb as well.

It all depends how much you value having backup power without burning fuel. Which is essentially burning $$$.
In my country a smart shunt costs about the same as 4 x 20l Jerry cans of fuel.