Safe 220v power supply for outdoor sensors

Air quality sensors often use too much energy for a solar or battery solution, so I’m looking for an option to power them with 220v. The solutions I’ve found so far are not scalable (e.g. single qty leftovers from Christmas lighting), USB chargers meant to be used indoor or potentially unsafe DIY solutions based on a HLK-PM01. I consider these HLK-PM01’s safe enough for personal use when isolated properly but I do not want to distribute them for community purposes.

Is anyone aware of a power supply that would suit these needs and is easily available? Ikea had some in the past but afaik they entirely moved to solar powered lighting or integrated power supplies.

Some are using normal indoor USB adapter covered in an outdor box, e.g. https://www.brennenstuhl.com/de-DE/produkte/ersatzteile-und-zubehoer/safe-box-big-ip44

You should not put in direct sunlight for a whole summer. I think it si designed for temporary use only.

How about using a 12-24v power brick indoors and outdoors use this step down converter to get to the required 5v? (There are plent py alternatives to be found, some much cheaper but I like the way these are packaged, no chance of moisture getting in)
That way the 230v stays safely indoors, you can use a cheap cable (cat 5 will work for small loads) and if something should happen to the outdoors installation no one will get hurt.

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Hi @TijnOnlijn, you could use an industrial power supply. I use Meanwell PSUs, e.g.

Universal AC input.
Small; 6cm x 5cm x 3cm, and easily mounted.
Working temp range -20 to +70 degC.
DC output on screw terminals.
DC output can be adjusted to take account of a long cable run.
MTBF is over 1m hours.
I buy them from Amazon.

As advised by @kersing, I always keep the utility AC supply in a safe area and then run a low-voltage DC cable to outdoors.

It might be worth revisiting the design of your sensor sampling. I do not know what sensors you are using so cannot comment on their respective power profiles.

I developed an air quality system that does PM sensing as well as sensing the multiple discrete gasses together with temperature and humidity. It also uses a GPS, logs data and transmits the data via LoRa at the end of each sampling period. This system is solar powered from a smallish panel and smallish battery and will run unattended indefinitely provided the panels are not blocked by snow or other obstacles. If the panel is blocked or disconnected it will still run for a month on battery. It does this using a default 5 minute sampling period. To achieve this, it came down to careful power management, powering down the sensors and putting the processor into deep sleep between samples periods.

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Great idea! Never thought of it but this seems like very useful!

@kersing @cultsdotelecomatgmai technically the easiest solution, but I don’t think the target audience (non-makers) would be very excited about the idea that they need to drill a hole through their wall. The 220v outlet usually is already there.

But I believe Kersing is involved in a similar community project so I guess you might have met the same issue. Is my assumption wrong? Are people ok with this?

That’s a very interesting idea. Solar is the first thing people suggest, but usually that comes from people who can’t even make an arduino blink. Nothing wrong with that but then the solar idea is not really backed by knowledge, and while googling around I never saw someone who was able to run an SDS-011 like sensor on solar power. At least not stable in a setup that also works in the winter.

But apparently you managed. That’s very cool :slight_smile: Can you share some details about your setup?

Hi @TijnOnlijn, there’s no need to drill holes, I use flat ethernet cables that can go out through window frames.

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@TijnOnlijn,

The system we have developed is called Thingy:AQ The original system was developing specifically to meet the requirements for the USA EPA and other US governments bodies for their Wildland Fire Challenge. If you are interested you can find the background information here: https://www.brushelectronics.com/blog/

We have subsequently re-architected the system for the more general use cases. There are two main solutions were are supporting. The original remote node concept has been retained plus we have added satellite up-link capability per node. This was required as the coverage in remote regions where Wildland fires are a significant problem do not have LoRaWAN or even LTE coverage. This new model is currently being tested in the field. The other solution we addressed was the decoupling of our gas sensor subsystem from the rest of the node to enable the subsystem to be integrated with third party environmental monitoring and logging systems. The initial deployment of these is scheduled to happen in April.

Back to your specific question, I used the SDS011 PM sensor in our initial system. The node powers up the PM sensor every 5 minutes, flush the air through the sensor for 30 seconds, then take a number of samples, average the results, and powers down the PM sensor. As well as reducing the power consumption, this also significantly extends the life of the sensor. The SDS011 is rated for 8000 hours (less than a year) of continuous operation. Using the sampling approach described here, the life is effectively extended to 5 years. However, to be clear, without the right environmental protection for these sensors, they will cease to operate reliably within months. The system, as originally developed, had a three stage filter on input and exhaust to reduce the impact of the environment (weather and bugs) shortening the life of the sensor and system in general. It costs significantly more to protect the sensor than the cost of the sensor itself.

You cannot just switch off the power to the sensor (well you can but it won’t help) you also need to isolate the RS232 bus to prevent the sensor being power-up buy the RS232 transmit pin from the processor.

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Brilliant, never thought of that. I expected the cable to be cut by the window, but the flat cable seems like the solution for that. I think this is the most practical way to go. Thanks!

W’re using dust sensors from different origin (Nova, Plantower and Sensirion) in MySense air quality measurEments kits (dust, meteo, gps, lorawan). The focus is on Plantower and Sensirion as they provide the particle counts in 6 bins so we are able to correct the measurements for outdoor application and not rely on the manufacturer indoor based particle count to weight conversion. Eg humidity influences exponential the conversion on rel. humidity more as 40%. We have about 30 kits running with either solar/accu and V230/5V adapters as energy supplyer for about 1.5 year now.
Experiences in relation to Tijn’s question:

  • Need a good adapter with not to long power cable (less as 1.5 meter). Many adapter are only usable as chargers… Agree with Jac: cat5 power cable idea.
  • On the adapter controller side use a capacitor of say 1000 uF. We discovered that WiFi caused a 2 ms drop every 100 ms (wifi beacon). If you does not need wifi switch it off. This drop caused a power drop to the dust sensors below 3.3V and the dust sensor started to show very high measurements. It caused us a long delay to figure out the cause. The sensor sensitivity to this may differ from manufacturer and even in one batch. This suggestion is the most important one to take care of.
  • With solar/accu we had to use deep sleep functions and lower the sample frequency. This was a hassle. E.g. some kits started to sleep forever after 3-4 weeks of operation. Align te panels to winter sun level. In this winter time we discovered a miscalculation of the needed solar size. We need to apply 2 solar panels in stead of one. To avoid misuse of the accu we implemented a watch dog of accu voltage.
  • We use double sided (gray) PVC pipes (DIY air roof outlet with a rain pipe) and paints them white. Do some thinking about the location of the kit. This as placement influences your measurements when you use a small amount of sensors.

Do a Google search on MySense and air quality for the how to’s, software and show cases.

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What is the cost of such nodes to be able to monitor multiple pollution parameters?

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Have you thought about hacking an irrigation control system? They usually use 12 or 24 VDC or 24 VAC that can be used over a significant distance but are safe for outdoor systems. Just be sure the duty cycle is suitable. If the controller is designed for non-latching solenoids, that is pretty much 100% on time in commercial systems - you could just set a zone on continuously and tap into the power at the sensor when needed.