Hi Guys,
Maybe a stupid question I know, but I would like to know the best way to calculate the avg power consumption on a mote which is sending data at max power (RFM69W) every 10 seconds and working only 8 hours a day. It's currently running connected to a wall adapter, but I would like to move it to batteries, so I need to know how much time it can be reliably running on a 3000mAh battery.
What I'm doing now is:
- Measure mA consumption when not sending data X.
- Measure mA consumption when sending data Y.
- I'm sending data every 10 seconds, so 6 times per minute and 54 times of not sending data per minute.
- That's a relation of 9:1 (not sending / sending) so:
(X + X + X + X + X + X + X + X + X + Y) / 10 = Z AVG power consumption per minute = Z AVG power consumption per hour (Since I have no variations of power consumption [basically doing the same every minute] )
- The moteino is running only 8 hours per day, so:
(0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + Z + Z + Z + Z + Z + Z + Z + Z) / 24 = W AVG power consumption
- Then I have a 3000mAh battery so: 3000 / W = The amount of days I can run my moteino on batteries
Is that OK?
Questions:
I'm getting like 24.5mA when sending data, that's lower than RFM69W datasheet which mention 45mA.
This is because the RF module send the data so fast that my multimeter can't get it correctly?
To calculate how much current I was drawing when sending data I have set the sending period to 100ms, but even so I get 24.5mA.
Maybe I'm doing something? In the calculations below I'm supposing the 24.5 mA last 1 entire second, which is also not correct, because the moteino send the data in 30ms or so, and then sleep for the rest of the 9970 ms right? then I should modify my calculation to fit those numbers? I mean, 30ms sending, 9970ms not sending... blablabla ?
Thank you in advance!
Hugo
Hugo,
The most important thing to have to measure current accurately is a true RMS multimeter.
Or you could do it with an oscilloscope to actually see it visually.
You can then measure over several cycles and extrapolate to get an approximate figure for longer periods of time.
To save power you need to put the Moteino, radio, FLASH, to sleep.
If you need to keep the radio in RX mode then you can still sleep the Moteino itself, it will wakeup when the radio raises the Packet-ready interrupt. That will save an additional 15-16mA.
Excellent!
Thank you Felix
hneiraf,
What is the results? How long moteino keeps running just by a 9 volts battery on those conditions?
9v is not ideal because you are wasting power with the linear regulator on the Moteino. Still, it can probably run 6-9 months (tested by me in the mailbox notifier in michigan weather including bitter winter). For that you need to be smart and sleep everything, only wakeup when you need to transmit.
A much better alternative is Lipo batteries because they are much closer to 3.3V and the energy density is much higher than that of 9V batteries.