Author Topic: Keeping an eye on wireless sensor batteries  (Read 2108 times)

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DamonHD

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Keeping an eye on wireless sensor batteries
« on: September 17, 2016, 12:01:43 PM »
For those of us that feel watching paint drying is all just too fast, here's keeping an eye on the batteries in my wireless sensors (can't have those controls fail unexpectedly!):

http://www.earth.org.uk/out/daily/OpenTRV/16WWSensorPower.html

Rgds

Damon
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kitestrings

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Re: Keeping an eye on wireless sensor batteries
« Reply #1 on: September 22, 2016, 06:56:37 AM »
Damon,

They're all closely clustered except the bottom (yellow) one.  Any idea why?  Are these Li-ions?  ~ks

DamonHD

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Re: Keeping an eye on wireless sensor batteries
« Reply #2 on: September 22, 2016, 11:33:06 AM »
All 2xNiMH AA cells.

I think that I forgot to pop absolutely-freshly-charged cells into that device.

Rgds

Damon
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Bruce S

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Re: Keeping an eye on wireless sensor batteries
« Reply #3 on: September 22, 2016, 02:51:22 PM »
DamonHD;
If those are NiMHs then them dropping to 2.4 or close isn't that bad and most all of my NiCD/NiMH sag under load . They could actually drop to 2.0 and still recover nicely.
I've recovered NiMH that sat at 0.98 with so far no ill effects showing up.
Are they being charged based on a batt level scenario ?

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Bruce S
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DamonHD

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Re: Keeping an eye on wireless sensor batteries
« Reply #4 on: September 22, 2016, 03:00:16 PM »
These aren't being charged at all in the device; the target is for the device to run for 1 or 2 years on those cells.

We have separate evil plans to replace the batteries entirely with energy harvesting plus supercap, to make our devices completely fit-and-forget.

https://opentrv.atlassian.net/browse/TODO-977

I regard the 'normal' operating voltage as 2.4V (and all our sensors work down to 2.2V, the MCU down to 1.8V).  But this is a good opportunity to study the discharge curves in some detail.

Rgds

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DamonHD

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Re: Keeping an eye on wireless sensor batteries
« Reply #5 on: September 22, 2016, 06:12:45 PM »
A snapshot of pretty stats...

http://www.earth.org.uk/img/OpenTRV/20160922-16WW/

Rgds

Damon
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