Sandaysoft

CHECK THIS LINK OUT......

http://www.kwarc.org/Tedds%20Tech%20Corner/thermor.pdf

It just goes to prove that if you keep it simple, it can be done, excellent job, it has given me an idea for my new system.
Cheers
Brian

Very well done, just use your brain, give some thought and almost anything is possible. You just need that idea and does not matter how simple it is, if it works it is well worth doing it. Great idea, at least it being put to good use, whilst solving a problem at the same time.

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Regards, Matt of Brisbane, Australia
Web Site: http://www.localweatherdata.0glo.com

Hi,

Thanks for the information, but do beware that it's quite an old document and IMHO the author makes a number of statements that are "misleading" if not actually incorrect.

Firstly, note that the project was intended for a station that is acknowledged to "eat batteries". This isn't the case for most modern stations (particularly Fine Offset's) and generally it would be better to invest in a set on NON-rechargeable AA Lithium cells which should run for 3 - 5 years. Within that time frame the external system will very probably require some other "routine maintenance" (especially if its a FO model).

Over the past year, I have dismantled a number of different solar garden lights from various "Pound shops" and the internal design is quite different to that described. The batteries are not AA NiCd but much smaller tag-ended (soldered in) NiMH "1/4 AA" or even "coin" or "button" cells. The author says to "toss everything except the solar panel and battery" but there are some other useful (and potentially important) components in there!

He says "needless to say (the reverse leakage current) is only 1 or 2 uA", but the cells I measured were several orders of magnitude higher than this (maybe they're low quality or "semi-rejects" to keep the price low). Fortunately it seems to be a "resistive" leakage rather than the normal semiconductor thermal leakage (which increases enormously with rising temperature), but it is still not necessarily "safe" to omit a series diode. However, the situation is complicated and you really need to be able to measure the leakage of your specific PV cell, because a series diode also has undesirable effects. But most of the solar lights I've examined have had a series diode.

In some ways the author has over-complicated the project. White LEDs require at least 3 volts so actually only one "solar garden light" is required. Most do use a single (1.2 volt) rechargeable cell, but the electronics (which got "tossed") steps up the voltage to the required level. The electrical modification may be a little more complicated, but almost no mechanical work is required (i.e. you can just use one existing "solar head").

Alternatively, some garden lights contain a 3.2 volt Lithium Phosphate (AA) cell which could make an excellent basis for a solar-powered system. But I don't know of any specific brand/model and I'm fairly sure that they won't be sold in a Pound/Dollar store.

Finally, I should say that I had been considering a similar project myself but decided that solar powering the transmitter is generally unnecessary (maybe even disadvantageous). Therefore I've moved my attention to solar-powered aspiration, but that's hardly relevant at the moment (here in the UK Winter) and has very different technical requirements. So it's "gone on the back burner" for now, but watch this space (or this forum).

Cheers, Alan.

Hi again,

I thought it could be interesting to Google for the original document and discovered the following:

The author is Tedd Doda writing in the (electronic) Newsletter of the Kitchener-Waterloo Amateur Radio Club, Waterloo, Ontario and the original article appeared in January 2007. It seems that even then the lights may have come from the author's "junk box" because the following month he wrote:

"Thermor Update:
Last month I gave you some ideas on how to power your "power hungry" Thermor weather station from solar panels. I thought that mine finally gave up, as I noticed the WX receiver wasn't getting any more updates. Well, it turns out that one of the old NiCads I used developed an internal short (you've heard of the "whisker" issue with NiCads) which dropped the voltage below the minimum required. I tried to charge it back up and the charge wouldn't take. Enough playing with used crap, so I installed 2 brand new 1500mA NiMh cells and they are working just fine. Battery voltage across the 2 new cells stays at about 2.78 volts, and that was with 4 inches of snow on the solar cells!"

I haven't looked to see if he gave any further updates, but all the subsequent newsletters can be found here.

Cheers, Alan.