Timeline for Primary battery dies after 5 months instead of 25
Current License: CC BY-SA 3.0
27 events
| when toggle format | what | by | license | comment | |
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| Nov 9, 2017 at 1:09 | history | tweeted | twitter.com/StackElectronix/status/928429371953762304 | ||
| Nov 8, 2017 at 14:22 | comment | added | Puck | @FrancoVS Certainly. Please, see my edit. | |
| Nov 8, 2017 at 14:21 | history | edited | Puck | CC BY-SA 3.0 |
Add details on current measurement.
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| Nov 8, 2017 at 13:28 | comment | added | FrancoVS | @Puck can you elaborate on how you measured the currents you mentioned? Was the bluetooth module talking to whoever it was supposed to? Could it be that the 330ohm resistor is smoothing out the peaks? Also, did you test at several possible input voltages? | |
| Nov 8, 2017 at 8:19 | answer | added | clabacchio | timeline score: 3 | |
| Nov 8, 2017 at 7:17 | comment | added | Puck | @Passerby I hope not, they are industrial Energizer EN93 that we got from digikey. | |
| Nov 7, 2017 at 23:49 | comment | added | Passerby | Cheap/fake cells? | |
| Nov 7, 2017 at 17:26 | comment | added | Puck | @τεκ Maybe condensation... The case was sealed at room condition without a desiccant. I'll try to investigate in this direction but might be hard to prove anything. | |
| Nov 7, 2017 at 17:24 | comment | added | Puck | @SimonB Exactly what I think too, 0.0004C doesn't seems too much. I can assure that all cells are in the right way. | |
| Nov 7, 2017 at 17:23 | comment | added | τεκ | @Puck Condensation perhaps? Was the case sealed in dry air or with a desiccant? | |
| Nov 7, 2017 at 17:21 | comment | added | Puck | @τεκ Hardly, this is inside a fully waterproof casing. | |
| Nov 7, 2017 at 17:21 | comment | added | Simon B | 3mA for a C tell is a tiny current. They should manage that no trouble. One thing to check - are all the cells the right way round? What you're seeing would be the effect if one of the cells was backwards. | |
| Nov 7, 2017 at 17:20 | comment | added | τεκ | Any chance moisture or condensation got into the device? That would add a conductive path to drain the battery. | |
| Nov 7, 2017 at 17:16 | comment | added | DerStrom8 | The harder you "slam" your batteries with the current demand (as the voltage goes down over time) the faster their capacity will be reduced and you effectively get the avalanche effect much sooner than you would normally expect. | |
| Nov 7, 2017 at 17:16 | comment | added | DerStrom8 | @Puck Unfortunately the datasheet doesn't show the charts or data I was hoping for. Anyway, your factor of 1.2 might make sense if the capacity remained constant over the life of the battery, but that's not how the batteries work. Unfortunately I'm approaching the limits of what I know about battery life, all I can speak from is experience. In cases like this you really need to trust experimental data because there are so many factors affecting the performance of the battery. Theoretical data is practically useless at this point. | |
| Nov 7, 2017 at 17:09 | comment | added | Puck | @DerStrom8 Interesting input! We are using Energizer EN93 (data.energizer.com/pdfs/en93.pdf). Definitely the current will increase, but as most of the energy is between 1.5 V and 1.2 V (what we observed on the long term logs), I expect an increase of the current of a factor of 1.2 (measurement done at 1.6 V) at worst during this interval. Which seems inconsistent with the factor 5 on the capacity. What do you think? | |
| Nov 7, 2017 at 17:09 | comment | added | DerStrom8 | Here is a chart showing how battery capacity (mAh) decreases over time: mpoweruk.com/images/auto%20reliability.gif | |
| Nov 7, 2017 at 17:00 | comment | added | Puck | @ClaudioAviChami We choose alkaline batteries because they fit well the limited current we need, the shelf life is good (announce to 10 years) and they're price is really interesting compared to Lithium which seems to be another viable option. | |
| Nov 7, 2017 at 16:59 | comment | added | DerStrom8 | Actually I am not surprised by the results. As the voltage of the battery declines, the current required to keep the device running will increase (to maintain constant power). This is why the mWh rating is so important. Changing by a factor of 5 is not very surprising to me. What batteries are you using? It's not a matter of "using the mAh not being optimal", it's a matter of "using the mAh rating not being remotely accurate or reliable". At the very beginning of the battery's life its mAh rating may be accurate, but it will very quickly drop | |
| Nov 7, 2017 at 16:52 | comment | added | Puck | @DerStrom8 It is intended and has been used only in room conditions. Definitely, the mAh ratings is not optimal, but I definitely expected a better approximate than 25 months instead of 5. | |
| Nov 7, 2017 at 16:50 | comment | added | Puck | @BeB00 The measurements were done for about 15 minutes using an oscilloscope to detect any irregularities, none occurred. The chip is a uBlox NINA-B1. | |
| Nov 7, 2017 at 16:46 | comment | added | DerStrom8 | @ClaudioAviChami Alkaline batteries actually tend to last longer than NiMh or Li due to the fact that their "drop-off" at their EOL is much slower. The only benefit NiMh or Li batteries have is that (assuming they're Secondaries) they can be recharged. They won't last as long as alkalines, though | |
| Nov 7, 2017 at 16:33 | comment | added | Claudio Avi Chami | I really don't think that alkaline batteries are good for long time service to begin with. I would have chosen NiMh or Li. | |
| Nov 7, 2017 at 16:23 | comment | added | DerStrom8 | Environmental factors (i.e. temperature, barometric pressure, humidity, etc) will affect the long-term behavior and reliability of batteries. I very rarely rely on the spec'd mAh rating. Besides, what you really should be going from is the mWh rating. mAh is not enough to calculate how long something can be expected to run on the battery because it is not constant over the life of the battery | |
| Nov 7, 2017 at 16:21 | comment | added | BeB00 | how sure are you of the long term accuracy of that 400uA measurement? For example, maybe it's going into some error condition every minute where it takes a lot more power. Which bluetooth module is this? | |
| Nov 7, 2017 at 16:20 | review | First posts | |||
| Nov 7, 2017 at 17:05 | |||||
| Nov 7, 2017 at 16:16 | history | asked | Puck | CC BY-SA 3.0 |
