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18650 in use 24/7 outside, how to prevent overheating?
#11
And just as ref. Difference here is 30c on My temp sensor IF its shaded or not. Thats 30 or 60c. Do it right!
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#12
(06-23-2019, 11:04 AM)daromer Wrote: Korishan it doesnt matter how much you pull from a panel. It basically get equally hot under.
IF the panel is small it works and IF its on a pole or equal. Mounting under a panel on a roof is a big NO in hotter climates. No matter wattage pulled.

Never said to mount it under a panel on a roof. Kind of a dumb place to mount one of these weather stations. It would defeat the purpose of the measurements.

I was guessing the OP was going to use something like this:


The heat produced by one of these would be FAR less than one you mount on a roof. The thermal mass/area is so much smaller that it wouldn't make much of a difference. Also, I wasn't expecting the panel to put less than 5cm on top of the sensor box.

(06-23-2019, 05:32 AM)Redpacket Wrote:
(06-22-2019, 06:49 PM)Korishan Wrote: I completely agree. We haven't discussed his location yet.  In Florida, USA, we wouldn't need to add any extra cooling other than the seal box. If you want to reflect heat, either spray chrome paint on the outside, or wrap it in aluminum foil tape. That will reflect the heat better than putting anything on the inside. Or, put the electronics inside of a Stainless container of some sort.

I would definitely not paint it chrome or use foil on the box surface - the physics of reflective surfaces means they actually get HOTTER (yeah go figure but that's how it works!).
Paint the box white or leave it gray.  

I did not know this. All the sensitive testing/weather equipment that are placed around here are in stainless steel containers, up on poles about 10 feet off the ground with no extra shading. So I was just going off what I was already observing by the professional installations
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#13
Korishan the heat is same No matter of small or large panel per area.... Its just that on a roof the its generally a bit more confined area and no wind. And of course i read and assumed it was under solar panel on the roof. Smaler panel is not a problem on a pole or whatever. That is like any other shading. Smile

No weather station that test temperature are in a non-shaded box. Then you wouldn't use it to measure the temperature.
Its fine to have steelbox and in many of those cases the box could be used to move heat from the inside to the outside. Though they are coated (Atleast where i Live)

Weather stations where you Keep the temp as low as possible you shade with a curtain type style. Look at the left unit on this image found here. https://weatherstationexpert.com/ultimat...r-station/

We are now a bit off topic.

I Still refer to My first comments on best practice.... As Said i have done My fair share of iot devices used outside. And done for companies...
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#14
You need:

1. A white box.
2. Active ventilation inside of that box using a 120mm/140mm, or if you have the space, a 200mm fan.
3. If you want to make it a permanent pack, fill the pack with a phase change material, like high melting point paraffin wax.

These 2 last ones are extremely important, and will help stomach heat variations, and keep your cells as cool as possible.
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#15
BlueSword. #2 is not "doable" and will cause moisture issues in most places around the globe. In Sweden as example that wont last long and you cannot coat 18650 cells due to the vent-holes. Coating the cells to protect from moisture will prevent their built in protection and emergency functions to stop functioning properly. If you going to do that you need to go for pouch cells. Those can be coated. I run coated pouch cells just fine.

With proper shading and unless the area have 50c or more thats not really an issue with temperature. Once again i have MANY of those running in Sweden and we have up to 35C during the summer in the shade. Smile
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#16
  • Seattle, WA (USA), box will be facing south, getting direct sun generally all day - summer temps typically avg 72 F/23 C, but over the last decade or so our summers have started a month early (June) and have experienced multiple heat waves reaching high 80's F/~32 C to early 90's F/~34 C
  • The solar panels are 145 mm x 145 mm (5.7" x 5.7"). There would be two of them in parallel, but I don't think 500 mA total current is going to be enough anymore - might need a bigger panel (see next line)
  • I tested the 12v solenoid valve I picked up directly with salvaged 18650s in 3s1p (sans solar panels and charge controller) and it pulled 2.8 amps and dropped to 9.24 volts on startup, then after 20 minutes of use it was 1.6 amps and 9.78 volts. I hoped the panels could power the valve on it's own so it's not stressing the battery and jeopardizing the other electronics, but it's a bigger current pull than I realized. I imagine I should get a bigger solar panel that gives at least 3 amps?
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#17
(06-23-2019, 08:23 PM)crashintoty Wrote:
  • I tested the 12v solenoid valve I picked up directly with salvaged 18650s in 3s1p (sans solar panels and charge controller) and it pulled 2.8 amps and dropped to 9.24 volts on startup, then after 20 minutes of use it was 1.6 amps and 9.78 volts. I hoped the panels could power the valve on it's own so it's not stressing the battery and jeopardizing the other electronics, but it's a bigger current pull than I realized. I imagine I should get a bigger solar panel that gives at least 3 amps?

How often is the solenoid engaged? If not very often, you could probably use a good sized capacitor to handle the spike draw load of the solenoid. Altho, I would still suggest getting a little more solar for the whole thing. Maybe go with 4 of those panels. Then you could do a 2s2p with them and then use a buck converter to run the gear.
Altho, if everything runs just fine with the 2p with no issues, then just go 4p with them


Man! I wish OUR heatwave was only up to 90F! Tongue We're already breaking 100F this year, ugh!
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#18
Use the battery to Power Gear. The sun isnt Always There. And as korishan asked: duty cycle on the Valve?
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#19
(06-24-2019, 01:22 AM)Korishan Wrote:
(06-23-2019, 08:23 PM)crashintoty Wrote:
  • I tested the 12v solenoid valve I picked up directly with salvaged 18650s in 3s1p (sans solar panels and charge controller) and it pulled 2.8 amps and dropped to 9.24 volts on startup, then after 20 minutes of use it was 1.6 amps and 9.78 volts. I hoped the panels could power the valve on it's own so it's not stressing the battery and jeopardizing the other electronics, but it's a bigger current pull than I realized. I imagine I should get a bigger solar panel that gives at least 3 amps?

How often is the solenoid engaged? If not very often, you could probably use a good sized capacitor to handle the spike draw load of the solenoid. Altho, I would still suggest getting a little more solar for the whole thing. Maybe go with 4 of those panels. Then you could do a 2s2p with them and then use a buck converter to run the gear.
Altho, if everything runs just fine with the 2p with no issues, then just go 4p with them


Man!  I wish OUR heatwave was only up to 90F!  Tongue  We're already breaking 100F this year, ugh!

It's attached to a rain barrel that feeds a soaker hose, so I'm guessing 45 minutes to an hour it might need to be engaged. You're on to something regarding adding a capacitor; I double checked the reviews on this valve and others say to put a 100 watt 5 ohm resistor inline to keep the current draw closer to the spec'd 1.5 A and to combat the overheating issue (rose to 145 F and 173 F after 15 minutes engaged with 18650 battery and bench power supply, respectively)


P.S. - Correction on the amp draw; the 18650 3s1p battery pulled 2.0 amps on startup - I confused it with the bench power supply, which pulled 2.8 amps on start up and dropped to 1.8 amps after 20 minutes and the keep voltage stayed steady at 12v throughout. I'm guessing the fact that the 18650 battery pack dropped 3 volts and the power supply didn't is because I used batteries with a max discharge rate of maybe 2400 mA (1C)? If so, if I went up to 3s2p will it prevent that voltage drop? If not, if I did 3s1p with cells that have a max discharge rate of 10 A will it prevent that voltage drop?
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#20
The voltage drop is possibly due to a few factors.

1) running in 3s configuration
2) drawing >1C of the cells. Considering these are used cells, I'm guessing they are from low draw applications like laptops packs or such. These are not designed to run at 1C, but closer to .25C
3) running in 1p configuration

Going with at least 2p will help with voltage drop. So will going with 4s. Higher the initial voltage, lower the amp draw, and lower the voltage drop when it does occur. Like pushing a car: if it's just you, get tired very quickly. A buddy helps out and it's easier, or push a lighter car it's easier.

For your solenoid, would it be possible to switch over to a latching one? That way you only trigger it to switch its state. A whole lot less power consumption over time. But would recommend still using the capacitor for the spike draw.

If you can go with the latching solenoid, the slightly higher voltage shouldn't hurt the coils, just make them pull a little harder/faster.
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