Hi
I recently bought 2 LiPo batteries for use in an external weather station.
They are are both dead now, I suspect killed by the heat. The solar charger was clearly working, but these cant survive 40 degree Temps. Is there a better solution?
NiMHs are much more durable, or there are some lithium chemistries designed for just such an application.
If you can deal with the space and weight, it’s hard to beat the good old lead acid for toughness.
Lipos will handle 40°C no worries. But if that’s 40°C air temp and they’re in a box in the sun they could be seeing 60°+C and that really will kill them. The other thing to watch out for is voltage variation with temperature. If they’re heavily discharged while hot, upon cooling the cell voltage could drop below the safety cut off of 2.7v per cell.
Hey Andrew,
Welcome back to the forum! As Oliver mentioned there are some Lithium Chemistry’s designed for higher temps.
Most lithium-ion (Li-ion) cells must not be charged above 45°C or discharged above 60°C. These limits can be pushed a bit higher, but it will severely impact cycle lifetime. In the worst case, if a cells temperatures get too high, venting can occur which may result in a fire.
An alternative battery type would definitely be a good solution! Another solution I just saw recently that may help is the use of vents on your enclosure. I’m assuming it’s IP67 rated being a weather station or at least somewhat weatherproof so I’d suggest taking a look at these IP65 Vents from Bud Industries.
They are rated at IP65 but they can achieve an IP68 rating with an additional sealant applied. They are quite expensive though so just an alternative battery type may be a more appropriate solution. Food for thought though!
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Thanks for the tip. Measured 2.7 V on both batteries and I am sure the temp is near 60degrees in the little box, under the solar cells.
So I will start to search for NiMHs as an alternative solution.
Hi
do you guys recommend a NiMHs battery from your store?
I think for $80plus I will avoid the vents if I can.
Hey Andrew,
If it’s down at 2.7v, the safety cut-off circuit has kicked in to prevent further discharge - you never want to let them get that flat. They will likely still recover though with a gentle trickle charge to get them started.
NiMH’s are going to be the most cost effective option - just note that at high temperatures you’ll only get about half the rated capacity out of them - go for double the number of batteries whatever your calcs say you’ll need - they’re typically good to about 65°C
Lithium Thionyl Chloride is a very good wide temperature chemistry, but they’re non-rechargeable, and not particularly cheap.
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Thanks for the advice. I will do my research as I am keen they are rechargeable as well.
I like to solr power aspect of the IOT projects as mine a remote from mains power
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Hi
is there a solar charging option for the NiMh battery type?
Hi Andrew,
You should be able to, you’ll just want to make sure that the charging circuit that you’ve got is compatible, let us know if you’d like some suggestions for a breakout and we’ll see what we can find.
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NiMHs are pretty common in garden lights - depending how many you need, you might be able to get everything you need from a cheap set!
