Author Topic: CR2032 battery voltage with BLE  (Read 6701 times)

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Offline Rerouter

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Re: CR2032 battery voltage with BLE
« Reply #25 on: March 24, 2019, 09:54:55 am »
looks like your drawing about 0.0332 mA seconds of power per transmission. so apart from Idle consumption, you would have about 270,000 transmissions to use up the rated capacity of most 2032, not correcting for de-rating for your pulse loads, 

That comes to about 19 hours of battery life at the most providing I have read your time and current sense resistor scaling correctly,
 

Offline jmajaTopic starter

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Re: CR2032 battery voltage with BLE
« Reply #26 on: March 24, 2019, 11:18:51 am »
As I have said many times the consumption is 27 uAs/transmission. You have measured 33 uAs/transmission, but at least you have clearly too high value for RX/TX, since the picture shows only a bit over 20 mA.

With 27 uAs and 220 mAh you get about 3e7 transmissions, which equals to about 2000 hours at 250 ms intervals.

The advertising current is about 45 uAs/transmission. Interval is about 5 s. Thus about 11 uA with 1.5 uA deepsleep. After one month or whenever user chooses the device is put to hibernate with <1 uA. In a typical year the device may be advertising 4 months and hibernating the rest. That is a bit under 40 mAh/year  + actual usage.

If the user is keen to look after the battery, he will put it to hibernate after every use. Then it's just a few mAh + usage per year. Also the user may choose a longer interval and gets more active hours.
 

Offline Rerouter

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Re: CR2032 battery voltage with BLE
« Reply #27 on: March 24, 2019, 11:29:42 am »
ok, yes I mis measured, at least it shows your capacity is countable, 0.027 mAs, so 0.0000075mAh per transmission

Yep, don't do math when your tired. :)
 

Offline GeorgeOfTheJungle

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Re: CR2032 battery voltage with BLE
« Reply #28 on: March 24, 2019, 11:43:52 am »
looks like your drawing about 0.0332 mA seconds of power per transmission. so apart from Idle consumption, you would have about 270,000 transmissions to use up the rated capacity of most 2032, not correcting for de-rating for your pulse loads, 

That comes to about 19 hours of battery life at the most providing I have read your time and current sense resistor scaling correctly,

250 mAh = 250*3600 mAs => 250*3600/0.0332 = 27.1e6 transmissions

No?
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Offline jmajaTopic starter

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Re: CR2032 battery voltage with BLE
« Reply #29 on: March 24, 2019, 03:11:51 pm »
I have used Energizer datasheets for comparing CR2032, CR2430 and CR2450, but now I noticed there is something badly wrong in http://data.energizer.com/pdfs/cr2450.pdf. It shows IR to be 100 ohm at just over 300 mAh, but still 9 mA current causes only about 0.2 V difference between idle and load. U=R*I gives 0.9 V. Is there a wrong scale for IR? CR2032 and CR2430 are consistent with U=R*I.

Now I also found this one: http://www.dixonelectric.ca/productsheets/energizer/ECR2450BF_3V%20Lithium%20Coin%20Battery_Dixon%20Electric%20ca.pdf

It has a completely different curve for CR2450 with the same test setup! Now the pulse curve drops below 2 V already before 300 mAh while in the earlier one that happened at 550 mAh. Almost now additional capacity compared to CR2430 despite of more than double nominal capacity.

Renata shows quite different curves for CR2450: https://www.renata.com/fileadmin/downloads/designersguide/DesignersGuide-2011_080813.pdf
 

Offline jmajaTopic starter

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Re: CR2032 battery voltage with BLE
« Reply #30 on: March 24, 2019, 05:13:48 pm »
I'm reading now battery voltage just after the peak. I could not read at the peak. I guess BLESS system has control at the TX, which is the peak, and I can't run application code to start the ADC at that point. The ADC takes 300 us and the middle point is about 200 us after the peak. The readings I get are now very close to the peak I see with the oscilloscope.

At the moment it is 2.60 V. I have had the sensor on for 12 days and done 2e6 transmissions now with this battery, which has seen some abuse due to soldering and bug I had. I will get new batteries with solder taps during next week. These seem to be quite hard to get. Not available at local electronics stores. Digi-Key, Mouser etc. won't sell them due to air transport problems. I bought them from TME, which has a ground transport option.
 

Offline GeorgeOfTheJungle

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Re: CR2032 battery voltage with BLE
« Reply #31 on: March 24, 2019, 06:00:18 pm »
It has a completely different curve for CR2450 with the same test setup! Now the pulse curve drops below 2 V already before 300 mAh while in the earlier one that happened at 550 mAh. Almost no additional capacity compared to CR2430 despite of more than double nominal capacity.

One .pdf says Typical Li Content: <0.3g (energizer.com) , and the other Typical Li Content: 0.47 grams (dixonelectric.ca) , that would be 50% more ions => more angry pixies, but the curves say the contrary.

« Last Edit: March 28, 2019, 09:34:48 am by GeorgeOfTheJungle »
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Offline jmajaTopic starter

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Re: CR2032 battery voltage with BLE
« Reply #32 on: March 28, 2019, 02:07:49 pm »
Now I measured the standby current consumption without bigger caps, with just one and with two. Cyble module + sensors were powered in stop/shutdown mode. I got 40 nA with no bigger caps and just a 0805 10 uF ceramic cap. Then I added 1206 47 uF ceramic cap. First few seconds the consumption was 200 nA but in a few minutes it was 80 nA and still dropping. Nothing to worry about I think, since even 0.5 uA would be less than I expected, since the sensors should take almost that much, but seem to take less.

Then I notices something strange. The current consumption went to 2 uA when I put my small 40 W work light on with a traditional bulb. By shadowing different components with a finger or a business card I found out it was the BLE module that was sensitive to light. It was much less sensitive to a much brighter LED flashlight (>4000 lx vs. 600 lx according to the sensor on PCB). The sensitive area seemed to be the one with metal shield. How can it be affected through the shield? There are openings to the side.

I got the new batteries. Brand new Varta CR2430 seems to have less than 10 ohm internal resistance. Also it seems IR of lithium coins depends on how it is measured. I have a DE-5000 LCR meter. I measured resistance through a capacitor and the higher frequency I used the lower resistance I got. E.g. for a used CR2032 I get 130 ohm at 100 Hz, 122 at 120 Hz, 43 ohm at 1 kHz, 23 at 10 kHz and 17 ohm at 100 kHz. Using a 470 ohm resistor and multimeter I got about 180 ohm and calculating from rise time after a pulse I got about 300 ohm.

I first thought that DE-5000 + the cap I used fails to measure, but measuring a NiMh AA-cell gave about the same at every frequency (0.4-0.5 ohm).

This battery had been in my Polar heart rate monitor and was dead there. It still shows 2.93 V. It could not power up my device as is, but adding a 330 uF cap made it work OK.
 


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