18650 in use 24/7 outside, how to prevent overheating?

wattwatt

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I'm building a solar panel (12 volts, 3 watts,250 mA)+ batterypowered weather station type of thing + autonomousgardeningwith arduino and sensorsat the heart of it. I need 12 volts for a couple of the components in this project as well as 5 volts for others, so I figured I'd throw 18650's in3s1p or 3s2p to get 12 volts and run asmall buck converter off that to get5 volts. Most of the components, including the 18650's,will be housed inside a 16" cube box and will sit in direct sunlight most of theday. The box willbe painted white and the top half of it will be allsoffit vents (16" wide on each side) to help keep the heat down inside.Is this enough to keep the 18650 from overheating or is there something else I could do for prevention?


P.S. - I also thought about lining the inside walls and roof of the box with reflective foil insulation (used as insulation in roofs, walls, garage doors in homesand RVs to help keep them cooler in the summer), but wasn't sure if that's a good idea with all the electronics inside. Maybe make a double wall and put the insulation between the walls??

P.P.S. - Also, I thought about installinga Noctua 120mm fan (12 volts, 50 mA)and an outdoordryer ventin the boxto act as an exhaust system so the fan kicks offwhen the box reaches a certain temperature, but worry it'll draw too much current from the panel, charge controller orbattery and hamper the circuit. Maybe add a second solar panel in parallel to help with the extra load and only run the fan during sunlight hours??
 

daromer

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How how in shadow during the day?

If its below 50c i dont see any major issue. Make sure the box is white and have a shaded thing on top so it doesnt sit in direct sunlight. Thats how many of my IOT devices are set up
 

wattwatt

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daromer said:
How how in shadow during the day?

If its below 50c i dont see any major issue. Make sure the box is white and have a shaded thing on top so it doesnt sit in direct sunlight. Thats how many of my IOT devices are set up

So that's50C/122 F inside the box, correct? Also, what do you mean by "a shaded thing on top"? Can you provide a picture?
 

daromer

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I talk about outside temp. IF the device creates more heat incorporate heatsink so you can have same temp inside as outside.


Think of un umbrella on top. That Will make sure it never sees direct sunlight
 

Korishan

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If you plan on using a buck converter, might as well go 4s, you'll get longer life out of the cells (cycle life and run time)

Using a white box is probably sufficient. Put the cells at the bottom of the box, put a few vent holes on the bottom and a few on the top on the sides. This will create a positive air flow through the box. Use a small drill bit to minimize insects getting inside. Some professional boxes use around 1/16th if I remember correctly. It won't keep all out, but will significantly make it harder for the bigger ones to get in.

I don't think you'd need a shade over the box. I doubt it'd get that hot inside the box if it's white and with the holes. But you could just set the box with a thermometer in it for a day and check it at the end of the day just to verify. This is before putting any gear in it.
The other thing you could do is put the box under the solar panels (not sure how large they are). The panel would take the brunt of the sun and help shade the box. Just make sure there is a slight air gap between the panel and the box to allow air flow around the panel.
 

ozz93666

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You give lots of irrelevant information and omit the most important thing .... LOCATION

Are you in Norway or Saudi Arabia where air temperature can reach over 50C ...

Temperature is not an issue unless you are somewhere very hot and drawing large currents.
 

daromer

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Dont put box under solar panels korishan. Its easy 100c under them....

Shade on top does ALOT. You can half the inside temp in the box. And you dont need to cut holes and expose the electeonics. Having Hole in the box only works of the electeonics are weather proofed or in dry area.

Having electronic Gear outside that should last years require some basic design thoughts. I have mounted many many esp8266 devices outside that Still are working 4 yearslater
 

Korishan

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daromer said:
Dont put box under solar panels korishan. Its easy 100c under them....

Considering he was talking about pulling 250mA, I was assuming he'd be using a small panel, around 150mm * 100mm or so. The heated generated under one of those would be very small.

ozz93666 said:
You give lots of irrelevant information and omit the most important thing .... LOCATION

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.
 

Redpacket

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Korishan said:
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.
Mount a sheet of also white painted metal about 2-3 cm or more away to shade it. (they do this for speed cameras around here + guys in the bush do this above car roofs)
Mount the solar panel ~5cm above that & everything will work nicely.
The batteries themselves won't (& shouldn't) generate any significant heat but will be happiest between approx 5 & 45 degC.
If the electronics tend to get too warm in the shaded box you could use a metal alloy box & bolt the electronics to this to help dissipate heat.
Don't have air holes = moisture/corrosion problems.
If you need a vent, maybe have 1x tiny 1mm weep hole at the bottom only or use a special vent plug like these:
https://au.element14.com/hylec/jdae12pa-sw/ventillation-plug-pa6-m12-black/dp/2308394?ost=2308394
 

daromer

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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.
And yes i assumed roof panel of some reason :S

As redpacket Said. No other options or suggestions should be followed here. White or Grey box 100% sealed with something shading. IF needed transfer heat with element but Still water right. Its not Hard to do and Will last years
 

daromer

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And just as ref. Difference here is 30c on My temp sensor IF its shaded or not. Thats 30 or 60c. Do it right!
 

Korishan

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daromer said:
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:

image_mlywqt.jpg


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.

Redpacket said:
Korishan said:
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
 

daromer

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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. :)

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/ultimate-guide-purchasing-weather-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...
 

BlueSwordM

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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.
 

daromer

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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. :)
 

wattwatt

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  • Seattle, WA (USA), box will be facing south, getting direct sun generally all day -summertemps typically avg 72 F/23 C, but over the last decade or so our summers have started a month early (June) andhave 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 betwo of them in parallel, but I don't think 500 mA total current is going to be enough anymore - might need abigger panel (see next line)
  • I tested the12v solenoid valve I picked up directly with salvaged 18650s in 3s1p (sans solarpanels and charge controller)and itpulled 2.8 amps and dropped to 9.24 volts on startup, then after 20 minutes of useit was 1.6 amps and 9.78 volts. I hoped the panels could power the valve on it's ownso 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 solarpanel that gives at least 3 amps?
 

Korishan

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crashintoty said:
  • I tested the12v solenoid valve I picked up directly with salvaged 18650s in 3s1p (sans solarpanels and charge controller)and itpulled 2.8 amps and dropped to 9.24 volts on startup, then after 20 minutes of useit was 1.6 amps and 9.78 volts. I hoped the panels could power the valve on it's ownso 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 solarpanel 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! :p We're already breaking 100F this year, ugh!
 

daromer

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Use the battery to Power Gear. The sun isnt Always There. And as korishan asked: duty cycle on the Valve?
 

wattwatt

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Korishan said:
crashintoty said:
  • I tested the12v solenoid valve I picked up directly with salvaged 18650s in 3s1p (sans solarpanels and charge controller)and itpulled 2.8 amps and dropped to 9.24 volts on startup, then after 20 minutes of useit was 1.6 amps and 9.78 volts. I hoped the panels could power the valve on it's ownso 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 solarpanel 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! :p 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 tobe engaged. You're on to something regarding adding a capacitor;I double checked the reviews on this valve and others say to put a100 watt 5 ohm resistor inline to keep the current draw closer to the spec'd 1.5 A and to combatthe overheating issue (rose to145 F and 173F after 15 minutes engaged with18650 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 withthe bench power supply, which pulled 2.8 amps on start up and dropped to 1.8 amps after 20 minutes and thekeep voltage stayed steady at 12v throughout. I'm guessing thefact that the 18650 battery pack dropped 3 voltsand 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 withcells that have a maxdischarge rate of 10 A will it prevent that voltage drop?
 

Korishan

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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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