solar garden lights

Has anybody modded / made their own solar garden lights. I've seen the canning jar design that's on the internet. I'm interested in making some, and was looking for suggestions on parts. I might try to find some used lights for solar panels, etc.

Those things have become so cheap at the stores that I don't know why you'd want to make your own. Well, except the ones in the stores are so pathetically dim that all they really do is let you know there is a lamp there that you might trip over.

I bought 4 for $5 from a mid-west chain home improvement store. They are'nt terribly bright, but they do manage to charge even when it's overcast outside. Also, i really only bought them so i would have a way to charge nimh for my Kaito world band radio and my aa flashlights in the event of power outtage or emergency. :)

Nice! Survivalist garden lights.

yeah, there are cheap ones, but I don't think they are bright enough. I'm thinking that I could possibly make one with a higher light output, given more solar cells, a better battery, and better LED.

I'm not sure those really make a good charger for your nimh. I don't think you can charge a 2400-2800 mah battery with one of those in a day. I think I also read that they use nicd battery's cause they aren't as poor at being undercharged? The battery they usually use in those things are 700-1000 mah nicd I do believe. I've been told that the panels in the first couple generations of garden lights are better than the cheapo ones today.

The reason they use NiCd is that they are very, very much more tolerant of abuse - discharging to zero volts, being baked and frozen and sometime being hugely overcharged. All of these will rapidly destroy an NiMH cell. As long as you don't let them discharge (as in remove the LED or LEDs) they will take a few days to charge your cells. Keep a close eye on the cells till you know how long it is going to take to charge them - and preferably use a proper charger circuit with them so it stops charging rather than destroying your cells.

my only intention is to use them in the event of an emergency or extended power outtage. Either way, i'll still have my multimeter and test them. :) Of course i'll have to charge batteries to run that too :P

Are the lithium cells that ya'll using for flashlights as tolerant as nicd?

Absolutely not!

There are more tolerant and a lot safer lithium chemistries, the LiFePO4 ones are the best known and most common. I believe these are now appearing in some solar garden lights. They don't go to as high a voltage as the usual lithium cobalt cells, and have a lower capacity. Their nominal voltage is 3.2V and they charge up to around 3.6. This makes them a good fit with the forward voltage of a white LED.

AFAIK nobody has made one go nastily boom. You can make any cell explode if you put enough energy into it - the trick is to make them do that as safely as it can be done. LiFePO4 cells won't produce clouds of hot hydrogen fluoride for one thing - nor will they fire lumps of burning lithium metal around the place. Nor clouds of nasty organic solvents which are prone to burn all by themselves.

Most lithium cobalt cells will degrade safely, but some won't. No lithium iron phosphate cell has done a pipe-bomb impression.

But they are less common, more expensive and have a lower voltage and capacity. As the whether they are more or less robust than NiCd cells, only time will tell. NiCd cells have been around since the sixties and NiFe cells before that. LiFePO4 cells are much more recent.

It may well be illegal to import NiCd cells into the EU. They are a pain to recycle as cadmium is nasty stuff in an ecosystem. I once spent a summer analysing thousands of samples for cadmium in a sewage works.

That was not much fun.

I did a quick Google search on garden lights. Found that many sold in my country used one or two Nimh AA ranging from 200 to 900 mAh.


If the light had some kind of charge cutoff when the battery was full and some kind of low voltage cutoff when the battery got too low, NiMHs would work fine and probably for a long time (Eneloops are supposed to be able to take 1500 cycles which would be 4 years, but if you set the limits narrower they would last even longer), but I don't think many garden lights would have that. Some garden lights do have LiFePO4 cells because some people have been getting AA size cells from Walmart that are sold as replacements for garden lights.

The biggest problem with the garden lights isn't the bad batteries it's the terrible solar cells.

There's not a lot of point putting a good cell in one if it would take 2weeks to charge it.