Folks,
I’m building a RW tank level monitor using a Pico W and ultrasonic sensor, powered by LiPo battery, in turn charged by 5v PV panel. My intention is to mount the PV on top of the box that holds the components including the battery, and mount said box on the top of the tank.
The box would be in full sunlight light say 8 hours a day and fully exposed to the weather so the box would be IP65/66 and UV stable.
Would the box need to be ventilated?
Hi Mark
These 2 criteria should not be too hard.
I think that with the Pico, LiPo battery etc (particularly the battery) the actual inside temperature might be your main problem. You might have to do some measurements regarding this. I think that you can still get little stickers to do this if you can’t rig up some sort of recording set up. Each “label” represents a different temperature and changes colour when that temperature is reached. Handy for inaccessible situations such as this.
The PV panel might be reasonably large and might be arranged so that it provides shade to the box and contents. Leave a space or “air gap” between the panel and box for best results. Similar to a “fly” sheet above a tent.
Cheers Bob
PS: The panel should also be quite a bit larger than the box. That is have a fair bit of “overhang” like an all round verandah on a house..
Thanks Bob.
I’ll code for the Pico’s temp sensor to write to a data log file on the Pico so I can see what happens.
I like the idea of the air gap. Like the safari roof on old landrovers!
The PV panel I have is the 5V 1.2W Solar Panel - ETFE - Voltaic | Buy in Australia | ADA5368 | Core Electronics which I’m sure will be small than the box I end up with.
Hi @Mark285907
The Pico should be fine to operate up to temps of 80C, the LiPo though I wouldn’t recommend having it get any hotter than 50C, I agree with Bob leaving an airgap between the panel and the enclosure with the enclosure being in shade should be fine. Even on the hottest days in summer it would be unlikely to get above 50C, but being able to monitor the temp would be beneficial.
Hi Mark
Exactly. Also Hong Kong taxis.
A couple of systems I know about on a much larger scale. The microwave repeaters across the Nullarbor and the radio system for the Iron Ore trains at Mt Newman, WA. Not an air conditioner in sight.
That is not much of a solar panel. Are you sure you have done the calculations correctly.
It or something else will have to be larger for this system to work. Think of the old Queenslander houses with a verandah all around. This was not done by accident but is very effective in keeping the house cool.
If you wanted to be ambitious you could always enhance this arrangement by replacing the box lid with a large heat sink. Arrange the box orientation so the fins on the heat sink are vertical and the air currents caused by convection pass pass vertically over them. You don’t have to attach any of the inside bits to it as you are trying to reduce internal ambient temperature and convection air currents will take care of heat transfer.
Cheers Bob
What I am sure about is I’ve done no calculations! Slack I know…
This is a “proof of concept” thing. Once I’m happy I have the device (code, components, prototype wired and soldered) operating correctly, I’ll take a close look at battery usage, power saving, charge rates, etc.
Hi Mark
Yes.
Take a tip. Work out what power you will need then double it. Allows for some head room and will minimise problems with minimal extra expense.
Keep in mind as with any other solar charging system you will probably only get 4 or 5 hours effective charging time per day and you will have to replace 24hours of power in this time AS WELL AS or in addition to running the set up. So don’t be too stingy here.
Allow for voltage conversion efficiencies. These could be about 85% and can sneak up on you and if you don’t have enough in reserve (head room) you can find yourself running out of puff pretty easily.
Cheers Bob
Will do Bob.
I’ve just done some calcs on load, battery capacity and PV charging of the Pico W weather station I built. It uses the same PV, charger and Pico W I intend for the RW tank.
The answer I get is nothing like what I’m seeing in real life. I assume this is down to the 1.5w budget I’ve allowed for the Pico W. My Fluke 77 is not up to measuring the load (as discussed weeks ago) so I’ll monitor what happens in real life in my backyard.
Cheers.
Just some food for thought.
With solar power consider if it needs to be on 24/7. Its easy to get everything working well in summer, but you can have very poor days of little to no solar.
My home 6.5Kwatt roof top mostly works better then I need, but I can still see days of < 1Kw/hr of power generated.
I also have a 13.5 Kwatt Battery and in summer I think I had about 2 days where I needed to draw from the grid with modes days I covered and everything and still export a fair amount; but at the end of April start of May, I had 5 days in a row where I could not fully charge and needed to draw something from the grid for 5 days in a row. So without the grid I would have been without power.
My point here is more thinking about can you take a few days of it not being online. If it must be online 24/7 then you really need to go over the top with the normal days needs to cover the very poor solar days.
Hi Mark,
What sort of ultrasonic sensor are you using? I bought one to install for an intermediate rainwater tank (a 1000 litre IBC) but found the spread of the detection beam was about 90 degrees. When the sensor was placed in the middle of the tank, it would only give accurate results when the tank was 1/2 full or more. With less, it just detected the wall of the tank first. Ended up making a simple sensor with graduations of about 150mm to give course enough tank levels for my need.
Greg
Use a waterproof membrane vent (Like the IP68-rated breather vent) on the side or bottom of the enclosure. Avoid the top to prevent rain ingress.
Greg, I’m using the DFRobot SEN0208 Ultrasonic sensor.
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