For my solar/Li-PO power module for my small greenhouse I am thinking that I should also be monitoring the Li-PO battery temperature - especially since the greenhouse can get pretty hot in summer.
I assume the standard answer is to tape a thermistor eg a TMP36 (SEN-10988) to the side of the battery pack, and run a wire from Vout up to the ESP32’s analogue pins.
I already have a few i2c sensors to monitor power, so am thinking instead to add a AHT20 temp monitor to the existing i2c chain. Would it simply be a matter of attaching the IC side of the breakout board to the battery and securing it with duct tape ?
This then leads me to questioning what is an acceptable temperature (absolute, or above the ambient surrounding air temp ?), and what can I do to cool the battery down ? If the ambient temp is high then a fan won’t help much, and I am planning to have a misting water spray so would prefer to keep the control and power modules airtight.
Hi Donald
I don’t think you can have it all. As I see it there are 3 main ways of cooling something
Refrigeration. A bit exotic and would not be considered I don’t think.
Water. Can be a bit messy with plumbing, pipes etc and would probably still require a fan.
Air. Easiest but you want to make it air tight, I assume to prevent moisture ingress.
If you feel the LiPo is getting too warm The only solution I can easily see would be to move the electronics including the LiPo to a cooler, drier spot.
Cheers Bob
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Hi @Donald23173
Unless the batteries are getting above 60°C (even this is well and truly on the safe side) you really don’t need to worry too much about cooling. My pick for a temp sensor would be a glass bead thermistor, kapton taped to the battery, if not a 3 wire lipo.
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At this stage, I am just open to ideas re cooling … and I agree there doesn’t seem an obvious solution. I don’t even know if it will be necessary … I’m sure there are solar/Li-PO projects in much hotter climates than mine.
Thank you for this. I will put a temp sensor in the controller/power box and monitor it, but sounds like it is unlikely to be a problem.
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There should be something in the greenhouse that can suck heat out of the battery. Do you have metal supports that aren’t in direct sunlight? Thermally coupling the batteries to anything that is below the battery temperature will help, and could well be sufficient. If you aren’t trying to get the battery temperature below ambient then the objective is simply to remove as much heat as possible.
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Thanks Jeff, that is a great point.
I am renting, so it’s only a temporary 1.8m sq. greenhouse - but I did get one with fairly sturdy metal frame - about 3cm diameter tubing I think. I don’t want to reduce the integrity of the plastic covering … but it wouldn’t hurt for me to bolt my controller & power box to the frame on the inside of the greenhouse … I hadn’t even considered that.
Reducing the ambient temperature inside the greenhouse on hot days is a different issue, yet to be addressed 
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Hi Donald
Good idea of Jeff’s. Good if your frame is square or rectangular section so to get the best heat transfer. Any form of heat sink that will get any heat from one place to the other would help.
Have a roof that opens and letting convection do its thing would assist here I think.
Cheers Bob
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You can position a small heatsink on the battery pack. It can improve heat dissipation.
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Hi Assad, Donald.
Use a bit of
Zinc Oxide Heatsink Compound
For good heat transfer.
That is that white paste you often see between a component and heat sink.
Jaycar still stock it.
Cheers Bob
Hi Bob, thanks for the tip! Using Zinc Oxide Heatsink Compound sounds like a great idea for ensuring efficient heat transfer. I appreciate the clarification about it being the white paste commonly seen between components and heat sinks makes it easy to recognize. I’ll check out Jaycar for it.
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