Power consumption / battery estimate on different firmwares?


#1

Hi,

is there a page / place that describes the power consumption (and therefore the estimated battery runtime) for the different firmwares? I remember seeing mentions in discussions that although weather station f/w has been optimized and would last for quite some while, the other firmware (eddystone) was at least previously not optimized power-wise but what is the current situation? Also, what about the latest addition (Espruino)?


When to change the battery?
#2

Sorry for the delayed reply. There is no single concentrated repository of power profiles yet, it would make sense to at least report average consumption and battery life estimate for each official firmware. We’ll get back to this soon.


#3

Related to this it would be nice to know what is supposed to be be the lowest battery level where ruuvi still works. Now when the new sensor firmware reports battery level. My longest running ruuvi reports 2,851 V. Is that 50% level or higher?


#4

The RuuviTag will operate down to 1.8V. However the actual cut-off might be somewhat higher in cold environments due to increased battery internal resistance.

The battery lifetime depends on firmware and configuration, you can find some typical discharge curves in CR2450 datasheets such as http://data.energizer.com/pdfs/cr2450.pdf


#5

I wonder if I got somehow defective battery on one of my Kickstarter tags. One of them has been in my bathroom from last April when I received it, and at the beginning of this year the tag had went dead (I noticed it just a week ago). I checked the battery voltage and it was 2,5 V. I bought new battery (cheap Varta), and the tag woke up again, so the problem was due to battery.

I didn’t had the voltage monitoring earlier so I don’t know if the voltage has dipped suddenly, but now I have started to follow that too. My other tags are within 2,7 V … 2,8 V range (two inside, two outside). I just wonder why the tag wasn’t starting even if the voltage was 2,5 V (I measured it right after taking the battery out of the tag), if they should operate down to 1,8 V. Does it need more voltage during the boot?

Interestingly the new battery has already dropped from 3,06 V to 3,01 V in just four days, so this one won’t be lasting very long… but of course that might be just because new battery has lower quality than those shipped with Kickstarter tags.

I’m running all the tags in raw mode.


#6

Just a another observation. Does the voltage measurement return sometimes wrong results, or is there some issues with the batteries that were included in Kickstart Ruuvitags? As you can see, the newly replaced cheap battery seems to have much more consistent voltage. Or is this something that develops after battery has been in use for some time.

(Sorry for commenting in old discussion, but I think this is relevant within the context.)


#7

Battery chemistry is actually a lot more complicated than what it may seem. The battery voltage drops under load and recovers slowly when the load decreases, so measuring the voltage under no load or minimal load will give higher voltage compared to the voltage under load, and to make stuff more complicated, an empty batter will have its voltage drop more under load than a full battery, regardless of the initial voltage.

This is why even fully depleted batteries can measure close to 3V after letting them sit idle for long, and then when applying a little load the voltage will dip down. It also takes a while for the voltage to “stabilize” when put under load. With a low load like the tags, this can take days so it’s expected that the voltage will drop relatively rapidly at start and even out soon.

Startup does consume a little more power than the average idling between measurements, but the biggest power consumer is the transmission, so the tag might even start up just fine, but when it tries to transmit, the battery load grows too much and the voltage dips too low.

The random drops you are seeing are relatively “normal”, I’ve noticed there’s a small correlation between those random drops and the way the battery is making contact. After inserting the battery, gently “wiggling” the battery clip on the battery surface reduces the noise slightly but it’s not the only source of that, and in general the “noise” seems to increase as the time goes.


#8

Yep, know that. That’s why I measured the voltage right after trying to boot. As far as I see it, the Ruuvi didn’t boot due to low voltage, or it lost the voltage right after the boot. Either way, I think the battery reading should be correct. With the old battery, I didn’t get single led blink out of it. Unfortunately I already recycled the battery, so I can’t test it anymore.

Okay, thanks for the confirmation. It will be interesting to watch how the new battery starts to behave. I will also try to toy a little bit the clip. :slight_smile:


#9

Okay, definitely cannot confirm that Ruuvitags work down to 1,8 V. Another tag went dead, this time I had also voltage logged:

So, two tags now both stopped working somewhere 2,6 V. Both were indoors, and this latest one in very stabile conditions (just normal room climate).


#10

I’d consider 1V drop during transmission relatively expectable with low battery. There has been some discussion about measuring the voltage after transmission rather than before, but that would again confuse some people as full batteries would seem less full :thinking:


#11

Ah, well, now that makes sense. So battery voltage is measured before transmission and then it shows for example that 2,7 V that I’m seeing. Then transmission happens, voltage drops and eventually battery goes dead. But logged measurements don’t show that since measurement were done before voltage drops.

If I understood this correctly, then I would say that this:

… would have been more helpful if it note also this side of things. I have no doubt you have documented it somewhere, but this discussion was what I found when I Googled for the voltage limit.

I have no idea if this is possible or not*, just an idea popping on my mind. Instead of sending single reading for the voltage, could you send a range that consists of two measurements? One measurement right after transmission, and second just until transmission is being done.

*) Probably not, otherwise you would have already implemented it. :slight_smile:


#12

It might be possible to trigger ADC conversion right after the transmission which would give more realistic estimate of the battery capacity under load.