Solar power for sensors

[vetgmc]

I was thinking of trying to set up a small solar panel near my WH-1091 sensors & using it to charge rechargable batteries in the wireless sender unit. Has anyone tried that or does anyone have any comments or suggestions on this idea?

Greg

[Repairman77]

Hi Greg; I was thinking of that myself.

A few problems; most remote units use 2 x 1.5V Alkaline batteries, but won't work on 1.2V rechargeables (not quite enough voltage - it tells you that in the User guide).
It could be overcome however by using 3 x 1.2V rechargeables (about 1.3V fully charged) and regulating it down to around 3.2V (equivalent to 2 new Alkaline batteries).
A simply circuit using a diode or two to drop the voltage to 3.2V would be needed. A little higher wouldn't matter.

You would need a reasonable solar cell, not sure of the current drawn by the transmitter remote unit but I doubt it's not much more than a few milliamps. Perhaps someone has measured it? Don't fancy climbing up on the roof today due to inclement weather.

However unless your transmitter is located in a really awkward place to get to, is it really worth the bother, as Alkaline batteries last up to 24 months according to the user guide. Also rechargeables can fail if continually charged and not discharged on a cycle, so they may be more unreliable than using Alkalines. Worth a thought.

Hope that helps,

Mike.

[keithatrochdale]

What about using a LiPoly or LiIon cell?

High capacity and good charge retention; voltage is about right too.

[Repairman77]

What about using a LiPoly or LiIon cell?

High capacity and good charge retention; voltage is about right too.

Hi Keith; yes you could do; a bit expensive at the moment; but I'm wondering if it would be really worth the bother if the Alkalines do indeed last 2 years.
I would considering replacing my Alkalines every year just to be sure.

I'm not sure how well NMH, LiPoly or LiIon cells would work in low temperature though (in freezing Winter conditions) as even Alkalines would loose a little power under low temperatures. Haven't got the data to hand but would think they may perhaps suffer more.

Mike.

[Repairman77]

Some info...

http://www.batteryuniversity.com/partone-15.htm

Looks like the Lithium polymer ones also don't work well at low temperatures.

Mike

[keithatrochdale]

Prices are not dear nowadays, just look at some on e-bay - replacement phone batteries.

LiPo etc do not like going below a certain voltage though.

In the cold they do noticeably loose some capacity.

I tend to think the best system is to attach an umbilical cord and have the batteries in an easily accessible place.

[Repairman77]

I tend to think the best system is to attach an umbilical cord and have the batteries in an easily accessible place.

I think that's the best solution if the remote unit is in a really awkward place Keith.

However I would have thought a yearly visit to the remote to replace the batteries and clean up the units would be advantageous.

Mike.

[wswat]

Hi Greg,
Some months ago I fitted a single solar panel from a garden light to the WH-1081 and I just recently checked the voltage of the 2 1000 ma NiMh AA batteries and measured 2.56 V DC so I can only assume that all is working well. Our winters are mild but with some nights getting down to minus 5 C. Some details at these links:

http://dcurrey.site.net.au/web/Solar%20Charger.htm

https://cumulus.hosiene.co.uk/viewtopic.php?f=13&t=1069

Cheers

[akasonny]

Another use, of course, is to use the solar panel in conjunction with a fan-aspirated temperature sensor. I brewed up a container holding the sensor in pvc pipe with a 500mw 12vdc solar panel driving a 15cfm muffin fan and the accuracy has dramatically improved for temp, dewpoint and humidity. No battery needed because of the lack of direct solar radiation after sunset.

Of course if your temp sensor is in the shade 24/7, that would be redundant.

Another use would be for a weather cam as many of them run on 12vdc and 1/2 amp is usually close to the current draw of these cams (tho some with infrared require more).

Just a few ideas for incorporating solar power into the station.

[Repairman77]

Another use, of course, is to use the solar panel in conjunction with a fan-aspirated temperature sensor. I brewed up a container holding the sensor in pvc pipe with a 500mw 12vdc solar panel driving a 15cfm muffin fan and the accuracy has dramatically improved for temp, dewpoint and humidity. No battery needed because of the lack of direct solar radiation after sunset.

Of course if your temp sensor is in the shade 24/7, that would be redundant.

Another use would be for a weather cam as many of them run on 12vdc and 1/2 amp is usually close to the current draw of these cams (tho some with infrared require more).

Just a few ideas for incorporating solar power into the station.

Very interesting idea. I've found the 3 main sensors do all vary with humidity, sunshine, etc. and several users have ventilated the sensor unit with fans.
The 'so called' screen for the sensor unit does seem woefully inadequate. Plenty of jobs to do to improve it when the Spring comes.
Mike.

[Repairman77]

You gave me a push to get on with the fan ventilated screen for the sensor unit.
I now have all the parts, 10 plant pot saucers, and I found a miniature flat 6V motor for the fan.
Not sure if it will be solar powered; will have to search for a panel I had somewhere; if not I'll run a cable up there.
Mike.

[akasonny]

It can be a fun project, Mike.

Good luck with that. I'm curious how it will turn out and how much improvement you see.

You gave me a push to get on with the fan ventilated screen for the sensor unit.
I now have all the parts, 10 plant pot saucers, and I found a miniature flat 6V motor for the fan.
Not sure if it will be solar powered; will have to search for a panel I had somewhere; if not I'll run a cable up there.
Mike.

[Super-T]

I hadn't bothered to see if my sensors were being affected by heat but by the look of the graph, low humidity = high temp. Or that is normal? Any comments?
The 5th was a wet "Guy Fawkes".

[beteljuice]

Yup - warm air contains less moisture (at any given pressure), that's what makes the weather work

[Repairman77]

Perfectly normal Terry; that chart looks just like the ones from my Thermo Hydrograph that I've just pensioned off.
It just looks like a mirror image on the two traces.

However you will find that all the sensors are sensitive to some degree to all the other conditions. The pressure one tracks wrongly with changes in temperature, especially when the Sun comes out, as does the humidity and pressure, and so on, and so on; every combination you could imagine, . Very noticeable yesterday.

The modified 'aspirated' (I think they call it) screen gives a better flow of air over the sensors (especially in low wind conditions) and is supposed to give more accurate readings. It should hopefully be finished in a few days, and then I need to do some comparative tests with the manual sensors to see if it makes any great difference. It can't make things any worse; the small screen that is supplied with the unit is considered woefully inadequate by the serious users.

Mike.