New to energy monitoring and want to start capturing PV power generation (DC power) data. I can't find the right hardware

Hardware
1

Hello-

I’m new to this forum and energy monitoring. I’m absorbing a lot of new information, but I keep on hitting dead ends when trying to find the right hardware for my initial need.

I currently have a Bluetti AC200Max power station. I have two 200W solar panels feeding directly (DC power) into the AC200Max to charge its batteries. I then use the generated power at night to run things in my house and can use the AC200Max as a generator during power outages.

The AC200Max’s display shows real-time energy incoming from my solar panels, however, there’s no official way to export the data out of the AC200Max. What I’d like to do is be able to capture and record that incoming DC power data and feed it into Home Assistant.

I’ve gone down the rabbit hole of reading about ways to install custom integrations into Home Assistant and capture the Bluetti’s Bluetooth signal and pull the data out, but that would be a huge learning curve for me that I don’t want to undertake if I don’t have to.

I thought the OpenEnergyMonitor might be a perfect solution to this by using a CT around the wiring from my solar panels to the AC200Max, but it sounds like all CTs only measure AC, not DC.

I’ve also searched high and low for a “smart” inline DC power meter of some type where I could export the data to Home Assistant, but again, I can’t find anything for DC power. I can find plenty of DC power meters/monitors, but everything I’ve seen is just a dumb device and only displays real-time energy on its screen, which I can already do with the AC200Max.

So in summary, I’m asking for help on how to capture and retain DC power generation stats, optimally into Home Assistant. OpenEnergyMonitor initially looked like a perfect fit for me, but I don’t see any mention of the ability to measure DC power.

Thanks so much!
Jeff

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Welcome, Jeff, to the OEM forum.

I’m afraid you’ve chosen quite a difficult problem. Measuring direct current and voltage is easy, but doing so safely is where all the problems lie. They stem from this:

and that’s absolutely true. A transformer relies on the continually changing magnetic fields to work, and and you don’t have that with d.c. As an aside, it’s why every nation’s electricity is a.c. at either 50 or 60 Hz. D.C. was used initially, but it was soon found to be impractical. No transformer of any sort works on d.c.

In order to measure d.c. safely, it’s either got to be a very low voltage, or you must have a means of isolating the voltage you’re measuring from the electronics or whatever you’re handling. This can be done optically or by radio, but then you’ve got to get the power in the other direction to run the measuring and encoding part that’s safely isolated.

and this is exactly how they get round the safety and isolation problem. The dangerous bits are all inside a sealed box, and the output is sent optically - you read the screen.

What voltage are you wanting to measure, I’ve seen 145 V mentioned, but then a second problem arises - this might be the battery voltage, but what is the maximum voltage to ground when it’s connected into your house?

We did have someone who was working on a d.c. monitor, which was designed for 48 V and claimed to be good to 65 V, but I don’t know what became of the project: GitHub - danbates2/emonDC: DC Monitoring, internet connected datalogger compatible with OpenEnergyMonitor.org project.

I don’t wish to hurt your feelings, but you don’t sound as if you’d want to design (with help) and make your own device, and I’m afraid I don’t know of any off the shelf device that you can use to measure either d.c. voltage or d.c. current, that is safely isolated and which you could use and integrate with another system.

If your AC200Max does have a Bluetooth output, despite your reservations, I think this might be the most practical route for you. And I’m sorry I can’t be more positive and offer a ready-made solution.

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What’s the open-circuit voltage of your panels (should be a label on the back) and are the two panels wired in series or parallel? There’s a fairly recent cautionary tale here.

1 Like
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dBC and Robert.Wall, thanks so much for the feedback!

Here are the specs on one of my solar panels:
Max Power: 220W
Operating Voltage: 17.52v
Operating Current: 12.6A
Open Circuit Voltage: 20.52V
Short Circuit Current: 13.41A

Again, I have two of these solar panels and I usually connect them in series but sometimes I connect them in parallel depending on the shading or time of year.

If you do an Amazon search for “Powerwerx dc inline power analyzer,” that’s exactly what I’m looking for. I would just use the MC4 connectors to put it inline between the solar panels and the AC200Max. But as I previously mentioned, the devices like this only display real-time data on a screen. I just need a way to get the data out of it and into Home Assistant.

Although I will take Robert’s word that measuring DC power is quite different and more challenging than AC power, I’m just quite surprised that even though DC power meters exist (like the Powerwerx I just mentioned), I can’t find a single device that is also “smart.”

So if I’m at a dead end on any smart DC power monitoring/reporting hardware, then I guess my next best option is to go down the Bluetooth interception path to get the data out of the AC200Max.

If anyone knows of any smart DC power monitors, please let me know!

I certainly want to implement the OpenEnergyMonitor down the road for my house! It looks like a fun project to tinker with.

Thanks,
Jeff

5

It looks like your search engine skills might need honing. I searched for “d.c. power meter with Wi-Fi”
and this was top of the list: DC Power & Energy Meter - AcuDC 240 Series | Accuenergy
Data sheet here.
Not Wi-Fi, but it says Modbus over RS-485 output is available (isolated to 2.5 kV) and of course we can handle Modbus into an emonBase with the addition of a RS485 - USB adapter. You must check, but it looks suitable for you.

The only catch I can see: No price is given, they’re willing to quote, which almost always means ‘Too much’.

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Ha, that’s actually the only one that I’ve found that seems to really meet my needs, but I forgot to mention that since I had already written it off based on price. I saw it consistently saw it over $300 by resellers.

Thanks again,
Jeff

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Have you seen any of these:

Plus one that would come in at under $40, no isolation voltage quoted so decidedly dodgy.

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Those voltages and currents put you in the realm of RV/Marine battery monitor applications too so it might be worth looking around there. The Victron SmartShunt for example has the goods from a h/w point of view but I’m not sure how easy it is to get your hands on the data.

It looks like @glyn.hudson has done some work on VE.Direct

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Thanks again to both.

Robert, I looked at your suggestions and they all look promising but they’re a little pricy for my little project. The QI-Power-485 is like $168, so at least I have something I can buy that’s not too crazy.

So there are CT sensors that exist that can measure DC power.

dBC: yes, I’ve come across several RV/marine devices. I bet half of my problem is simply that I just know next to nothing about this stuff. I’ve never even heard of a shunt until I started down this rabbit hole. But from what I understand so far, a shunt would work for my need.

I’ll revisit Victron and the possibility of using VE.Direct.

Thanks so much!

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As Robert says, with the shunt approach you need to worry about isolation. At the voltages you’re working with you’re unlikely to hurt yourself but you can still blow things up. An Arduino or RPi isn’t going to survive if it gets exposed to your panel voltages. There’s more on how to achieve that isolation here.

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They are, when you read between the lines, not c.t’s at all, but Hall effect devices in a c.t-shaped case.

That is the easy part. A shunt is just a very low value, high power resistor. They are defined by a current rating and a voltage. The voltage is usually 75 or 150 mV, the current rating is whatever you need (or nearest above which is available). but the dangerous part is, the millivolts output is sitting at the same voltage to ground as one of your battery or P.V. terminals, so be prepared to be in for a nasty surprise (at best) if you’re not aware of that. You need something to measure the shunt voltage and get it across an isolation barrier before it’s safe to put into a Raspberry or anything like it.

A device like this breakout board Isolated Voltage-Measurement with ±1V Input, Differential Output and Integrated DC/DC Converter - Electronics-Lab.com solves the isolation problem, you then need to digitise the output and get it to where you want it - and the same again for voltage except that you’d use a voltage divider instead of a shunt to provide its input. I guess there’s something in the Arduino range that would handle the rest and be able to put the data onto Ethernet or Wi-Fi. What’s missing for you Jeff is someone with the skills to put that lot together.
The evaluation board for the AMC3330 is about $60 (AMC3330EVM Texas Instruments | Development Boards, Kits, Programmers | DigiKey), so I can see a DIY job being no cheaper than the commercial prices you’ve seen. The big advantage would be you’d know exactly what you’d got and know exactly how it worked.