[water01]

OK something has just struck me. I can see that you can power the internal RX with DC 5V supply but how do I power the two TX units, especially as the UK is not renowned for it's sunshine so solar, especially where I live in a valley, is not an option?

On the road with you uncle_bob just ordered hopefully the 2 TX and 1 RX boards. Trip to Maplins for parts is in the offing!! And also Ebay is going to get hammered!!

[werk_ag]

The TX unit can be powered by any 12V DC power supply. Power consumption is less than 100mA.
If you believe that powering the TX unit by solar energy is not feasible in your location, another possibility is to install the TX unit in the attic, and feed it from a 12V DC power supply. In this case, the cable to the anemometer should have no more than 5 meters.

I think a 10W solar panel, and a small 9 to 15Ah battery, is sufficient to ensure the functioning of the unit, even in a country like UK, but I can not guarantee.

[werk_ag]

As an example, here are some pictures of the system used by me for powering the TX unit installed on the roof.
The same waterproof case, houses the TX unit.

10 Watt solar panel

[Live_Steam_Mad]

As an example, here are some pictures of the system used by me for powering the TX unit installed on the roof.
The same waterproof case, houses the TX unit.

10 Watt solar panel

Ahh I was wondering about which battery you used and I didn't recognise the Yuasa model used, so I had a look on Ebay and saw that REW45-12 was 32 GBP! Then I looked up it's datasheet and found that it was merely a 12V 7Ah Sealed Lead Acid battery from Yuasa, virtually the same specifications (from a quick look) as my own three lots of 12V 7A Yuasa NP7-12 that I use for charging Radio Controlled buggies in the field, and for use with my telescope mounts and anti-dew heaters etc. So I can use one of those. They are about 15 GBP on Ebay, I bought mine from a local model shop (not many of those left now, unfortunately) for about 10 GBP per battery just a few years ago.

I found the PWM Solar Charge Controller (combined Solar Panel Battery charger / regulator on Ebay for 8.25 GBP) so know where to buy one now when I need one. 10W solar panels are about 8 GBP from Ebay.

I wasn't aware that the transmitter used so much power. Since the Arduino is a RISC based CPU then I can't imagine it's using hardly any power at 16 MHz, so most of the power used is being used by the transmissions themselves since the unit is transmitting much more frequently than the e.g. Fine Offset 1080 which goes for about 18 months on 2 AA Alkaline power cells. And / or a significant fraction of the power use is caused by running the PCB on board regulator at 12V instead of 9V (I saw a heatsink on one of the PCB's, can't remember if it was the TX or RX or both). That's my guess.

In my case I'll have to put the SLA battery in a plastic box in the gap between my wooden and brick sheds, and fasten the solar panel to the roof or south side of my wooden shed.

Here's my existing setup with my Fine Offset WH-1081 ;-

http://www.wunderground.com/personal-wea...ENGLAND609

(click on About this PWS for a picture)

Regards,

Alistair G.

[uncle_bob]

Fine Offset 1080 which goes for about 18 months on 2 AA Alkaline power cells.

Maybe, but in that 18 months the damn things only work 3/4s of the time That's why I'm here, I was sick of the continual data connection drop outs and data corruption.

The Heatsink is on the TX's LM7809 for the Stevenson screen fan (and IIRC the 433mhz module).

[werk_ag]

And / or a significant fraction of the power use is caused by running the PCB on board regulator at 12V instead of 9V (I saw a heatsink on one of the PCB's, can't remember if it was the TX or RX or both). That's my guess.

If you are concerned about the power loss at the 7809 regulator (less than 0.2W when the fan is not used), you can bypass it and feed the board with a 9V power supply.
As uncle bob said, the heatsink is only needed if you use a fan in your Radiation Shield. Even if you install a fan, it don't have to be always on. Software allows you to define on/off conditions.
According to this study, a fan in a RS is only beneficial in some circunstances.

Powered with 9V the TX module draws around 30mA, it's a lot of power I know, this is why the RF link is so reliable. With a good antenna it's almost 10mW TX power.

Now I'm using a 14Ah sealed lead acid battery designed for solar systems (I don't remember brand, it's the grey one in second photo), mainly because I don't want to be worry about long winter nights or several days without sun!
Solar Charge Controller also draws some power. So the battery capacity is mainly defined by the number of days you want your system runs, when the battery delivers more power than it receives.

A solar system is not required, the system can simply be powered by a 220Vac to 12Vdc power adapter. Total consumption (without fan) is around 100mA - 110mA

[Live_Steam_Mad]

Fine Offset 1080 which goes for about 18 months on 2 AA Alkaline power cells.

Maybe, but in that 18 months the damn things only work 3/4s of the time That's why I'm here, I was sick of the continual data connection drop outs and data corruption.

The Heatsink is on the TX's LM7809 for the Stevenson screen fan (and IIRC the 433mhz module).

My Maplin N96FY (FO WH-1081) doesn't seem to suffer from any connection drop out at any time (unless I plug my RT2832/R820T Airplane scanner dongle in to the same PC! as it seems to emit and interfere at 433.9MHz! and completely wipes out every reading on my console!), the console sits on top of my desktop PC case, connected 24/7 by USB with Cumulus 1.9.4. I don't seem to get any data corruption (yet) either, except for one glitch of 92Km/hr wind registered as a one off, once.

My reason for using the WeatherDuino is that I wanted to add solar and UV data to Wunderground without having to buy the (so far unreliable) WH-3080. And I am not willing to pay 1,000 GBP for a Davis Vantage Pro2 Plus. My friend Jon in Kent (SE England) is in the next few days sending me his old Vantage Pro1 Plus that broke down a while back, I think the transmitter board on it went faulty and there are no spares (and a new transmitter board for the VP2 is like 165 GBP anyway, not that it is compatible in any way).

Davis ones are not immune from data problems, Jon's VP1 used to regularly (once per day it seemed) have a dip on the temperature graph down to -1 when the rest of the day's readings were about 10 to 13 degrees C, the Relative Humidity sensor would also malfunction regularly. Also his solar data and UV data never showed up in Cumulus, I still don't understand why, despite him insisting it was the Plus model with the solar and UV pods. Finally, his USB to Serial connection would regularly stop working with no explanation, since VP1 uses a serial port and his PC was USB only, needing a converter, and we tried 3 different converters with similar problems.

Regards,

Alistair G.

[hvalentim]

I have been trying to do some math to figure how big the battery and solar panel need to be in order to power the TX unit.

WerkAG says the average consumption should be around 100mA at 12V. That is 0,1Ah*24=2,4Ah per day.

I assume that value is missing powering the Fan (configurable option). This should happen more often in summer and during daytime, when there is more Sun available. Still, assuming a 4 hour per day working average, with a 150mA fan that would add 0,6Ah per day.

That leaves us with a total (TX Unit with Fan) of 3Ah per day, which is not bad.

3 Ah x 3 days of autonomy x 2 (use only 50% of the battery) x 1,1 (assume there will be some loss draining the battery) means a 20Ah battery will be in order...


Still, when I try to roughly add-up the consumption of components individually I end up with half that value (assuming readings are taken and transmitted every 60 seconds and the remaining time the sensors are off).

I also seem to understand that this could be improved even further by sending the Arduino a "sleep x seconds and wake up to take new readings" command.
EDIT: Now that I think of it, perhaps it can not go to sleep as it must count the wind cup rotations..?

So, can you gentlemen please tell me what's wrong with my math? What am I underestimating/missing? (See attached table pic)

[werk_ag]

I also seem to understand that this could be improved even further by sending the Arduino a "sleep x seconds and wake up to take new readings" command.
EDIT: Now that I think of it, perhaps it can not go to sleep as it must count the wind cup rotations..?

It's true, we can't put it in sleep mode. It uses interrupts to count wind cup rotation and rain meter clicks.

So, can you gentlemen please tell me what's wrong with my math? What am I underestimating/missing? (See attached table pic)

I've never done so detailed calculations, but it is interesting!
Maybe you can make a more complete table, or even publish the excel sheet.

The consumption of the Arduino nano v3 alone is rated at 35mA
The TX and FAN leds when on, not consume more than 10mA.
The TX unit with all sensors installed and activated, transmits data about every 3 seconds, but just by a fraction of a second.

It's important, also consider the consumption of the solar regulator, which at night also feeds power from the battery. The one I use, consumes around 30mA.

Just as an example, my solar powered TX unit don't have any fan attached (the RS with the fan, is connected to a second TX unit that is mains powered). I'm using a 14Ah battery with a 10W solar panel. In the last two years it never failed, but occasionally after three or four days without sun at all, the battery voltage drops to around 12.0V which is low for a solar battery (solar regulator switch off the output at 10.8V). If I ever consider change anything, what I will do is increasing the power of the solar panel to 15 or 20W. This will increase the charge capacity, on low sunlight days.

[hvalentim]

I have attached a revised Excel spreadsheet with calculations. Changes made now approach the 3A per day mark and seem more close to reality.

A few questions, so I can further improve the needs estimation:

- How often are readings taken then? Every 3 seconds?
- Can you please share the settings you are using (temperature and wind speed set points) to turn the fan on? This would allow me to simulate behavior by using one year of past meteo data.
- I do not seem to see power being supplied to the Wind Cups and RainMeter. Am I correct to assume these will produce an electrical impulse on their own using motion?

Anyway, with what I know so far, having established my needs to be an average 2,668 Amps per day (11,7 Kwh per year), I have played with PV*SOL simulating different set-ups for my location (Lisbon, which as you might know is fairly sunny by European standards).

The conclusions on the safe side seem to be:

A 10 Watts panel is not enough no matter the battery used. From November to February the output seriously risks to be bellow the average consumption. One should look for at least a 15 Watts solar panel.

You can get along with a 15Ah battery provided you couple it with a 20W or plus solar panel.

Those looking for complete piece of mind should get a 20W panel (~1.3A * 3 conventional full sun hours, considered for design purposes = 3.9 Amps per day reference production. Subtract cable + solar regulator + battery in & out loses) and a 20-24Ah battery (~4 days of autonomy, discharge treshold of 50%). This should be able to meet the needs under all scenarios.

---

Just for the sake of it I also did a simulation using meteo data for Glasgow (Airport), as I believe the weather is particularly gloomy there.

This shows that even a 20W panel with a 24Ah battery would be insufficient in Scotland, the problem being the months from October to March (notice the orange line in the attached graph).

Piece of mind using sun power exclusively there under a worst case scenario seems it would mean using around 60 to 72 Watts of solar panels with a similar battery (24Ah).