Title | Comment | URL | Cost |
Moteino R4 | Select the one you prefer | https://lowpowerlab.com/shop/index.php?_route_=moteino-r4 | $20 |
Waterproof enclosure | Clear plastic cover for solar panel compatability | http://www.ebay.com/itm/281392320490 (http://www.ebay.com/itm/281392320490) | $2.69 |
Solar panel | 55x70mm. Have not found this on ebay at this size. Perhaps someone else is able to find it, or a similar? | http://www.seeedstudio.com/depot/05w-solar-panel-55x70-p-632.html | $1.95 |
Li-po battery | 1000mah 3.7v. One with lower capacity battery could be used to lower the cost for this task? | http://www.ebay.com/itm/181601591660 | $8.90 |
Solar Lipo Charger (3.7V) | No idea if this board is compatible with the other parts. Any experiences? | http://www.ebay.com/itm/151331887062 | $5.50 |
Well, you can just use primary batteries with the same chemistry as the CR123 (Lithium Manganese Dioxide, usually just Lithium), they're common in the standard sizes. If you can afford space for 3 AA cells, you have like 9 Ah and that should last plenty without a solar cell, even. They're good from -40 °C or so, without capacity loss.One correction, AA batteries are 3300 mAh, 3.3Ah, but 3 of them in series doesn't give you 3X the Ah, it gives you 3X the voltage, including some extra as margin above the 3.3V to operate. You have more Wattage available, but not longer battery life at given current drain.
Reading the datasheet (http://data.energizer.com/PDFs/l91.pdf) of a well known brand and emploiyng a 10% safety margin on the textbook value, I'd rather say it's 3 Ah than 3.3 Ah. It's debatable though. What is your real life experience with them?My real life experience is running PIC-based remote wireless soil moisture sensors in a harsh Texas environment (extreme hot and cold) for several years and getting up to 4 years of operation without a battery change. As you say, it's hard to tell the difference between +/-10% when the average drain is so microscopically small.
OTOH, I admit that multiplying the Ah capacity by the number of batteries is a little over-simplifying things,uh, with all due respect, I wouldn't say that is 'over-simplifying', it is incorrect. Wh is multiplied, yes, Ah is not. My comment wasn't intended as a dig and I'm sure you understand the relationship, but I just wanted to make sure those who are learning to learn the correct things.
I explicitly mentioned the usability below freezing temperatures in the post you answered to. Please also see the DS I linked above.Yes, I missed the 'with the same chemistry' reference. Sorry.
What is the average power draw on your PIC nodes? Have you ever measured it or tried to estimate?I did calculate it, measure it, and prove (through battery life) that the calculations were 'close enough'. Precise calculations, as in this case, weren't feasible because it was DEFINITELY not a controlled environment ;)
OTOH, I admit that multiplying the Ah capacity by the number of batteries is a little over-simplifying things, but as you pointed out, it provides 3x the energy so the Wh increases approx. 3-fold. It means around 1/3 of the amperage thus 3x longer service time, in general. The end result is the same from this standpoint, and that's what is important.
<...snip>Correct, so far... although I'd never put batteries in parallel, especially LiPo! ;)
You can think of three 1.5V AA batteries in series as a 4.5V battery with the combined energy of the three. If you had a fixed power load, you would indeed have three times the capacity, at 1/3 the current, giving you 3x lifetime. If you had a fixed current load, your rate of power discharge would be 3x, and your lifetime would be the same as a single cell. If you have a fixed impedance load (like a resistor), you'd get three times the discharge current at three times the voltage, and your lifetime would actually be cut by 3x.
For something like a linear regulator, the power required for the load is the same, but you lose everything above the required voltage, meaning higher voltage actually reduces the effective capacity you have available. A 600mAh 3.7V LiPo is roughly as effective at powering a 3.3V device through a linear regulator as 600*9/3.7= 1459mAh at 9V.uh... not quite. The current load (not the power load), at the power source, is the same in both cases (3.7V LiPo or 9V alkaline) so a 600mAh battery in either case would last the same time. Your own example demonstrated that, 3 batteries would last the same as a single cell with the same current load.
C
<...snip>Correct, so far... although I'd never put batteries in parallel, especially LiPo! ;)
You can think of three 1.5V AA batteries in series as a 4.5V battery with the combined energy of the three. If you had a fixed power load, you would indeed have three times the capacity, at 1/3 the current, giving you 3x lifetime. If you had a fixed current load, your rate of power discharge would be 3x, and your lifetime would be the same as a single cell. If you have a fixed impedance load (like a resistor), you'd get three times the discharge current at three times the voltage, and your lifetime would actually be cut by 3x.For something like a linear regulator, the power required for the load is the same, but you lose everything above the required voltage, meaning higher voltage actually reduces the effective capacity you have available. A 600mAh 3.7V LiPo is roughly as effective at powering a 3.3V device through a linear regulator as 600*9/3.7= 1459mAh at 9V.uh... not quite. The current load (not the power load), at the power source, is the same in both cases (3.7V LiPo or 9V alkaline) so a 600mAh battery in either case would last the same time. Your own example demonstrated that, 3 batteries would last the same as a single cell with the same current load.
C
It's true, with the 9V alkaline, you would be throwing away a lot of wattage in the form of heat across the linear regulator (roughly 9/3.7 X) but we're talking about mAh rating of the battery. A 600mAh 9V battery COULD deliver more power, if it wasn't thrown away in the regulator. If it was a switching regulator, then the current load would be dramatically reduced in the 9V power source and a 600mAh 9V battery would last a lot longer (9/3.3) vs (3.7/3.3) if the efficiency of the switching regulator was the same for both voltages (not entirely realistic, but good enough for the example).
Tom
<...snip>To my mind, mAh rating is the most useful parameter there is. If you know the average current load, you know how long any battery will last given its mAh rating. I have a spreadsheet that, given the load model, tells me how many hours (or years, as the case may be) any of most commercially available batteries will last.
Yes, tis true. They hide the potential energy of the battery by reporting it in units that divide it out. The 600mAh LiPo has energy roughly proportional to 3.7 * 600mAh, while the 9V is 550mAh * 9V, so it's just how much you're throwing away that comes out as the ratio of voltages.
C
@ColinR
OK, but we're talking about Moteinos, not theoretical loads. We can assume the Moteinos are in the "fixed power load" category.
/******************************************************************************
*
* readVcc()
*
******************************************************************************/
unsigned int readVcc() {
unsigned int result;
byte saveADMUX;
saveADMUX = ADMUX;
// Read 1.1V reference against AVcc
ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
delay(2); // Wait for Vref to settle
ADCSRA |= _BV(ADSC); // Convert
while (bit_is_set(ADCSRA,ADSC));
result = ADCL;
result |= ADCH<<8;
result = 1126400L / result; // Back-calculate AVcc in mV
ADMUX = saveADMUX; // restore it on exit...
return result;
}
I'd like to add that on an unmodified Moteino this is not very useful as you also pointed out since it powers the chip via the 3.3V LDO. OTOH, the internal referenec sadly has some variance on the 328p, from ~1.0 .. ~1.2 V, so it should be calibrated before use. More info here. (http://provideyourown.com/2012/secret-arduino-voltmeter-measure-battery-voltage/)Well I know that the specification table says 1.0-1.2V, but you look at any of the curves in the detailed part of the data sheet you will see that the range is more like 1.126-1.137 over voltage and temperature range, which makes sense since it is a bandgap source. And it's also good enough for me to monitor battery degradation ;)
Just though I would I would share my (short) experience with battery powered Moteino.
I use 3 x AA Eneloop cells powering a remote temperature (DS18B20) sensor. The code sleeps puts the moteino to sleep as much as possible, but wakes up the radio to relay temperature value every minute, and battery voltage every 10 minutes, so 66 messages per hour in total. Every message is exactly 4 bytes. The battery voltage is monitored via 2 x 1 meg ohm series resistors (voltage divider), so there is a few micro Amps constant battery drain. I am located in Sydney, temperature ranges between 10 and 30 degrees C, as measured by the sensor itself.
See attached battery voltage profile.