On 13/11/2020 19:14, Paul wrote:
Brian Gaff (Sofa) wrote:
Hmm, if it works at all the crap* batteries seem to get worse in the
cold.

Brian


Typical cheap garden lamps, use lithium iron phosphate cells.
Apparently all Lithium types, they don't charge well below 0C.

Most battery chemistry doesn't enjoy being too cold but the main problem
is that at our latitude the sun doesn't get much above the horizon and
when it does the maximum altitude it ever reaches in midwinter is about
13 degrees. Couple that with thick grey clouds and fog and you destroy
the batteries by a combination of over discharge and leaving them flat.

Previous models have used NiCad and NiMH they also fail in winter. There
basically isn't strong enough sun or enough hours of daylight in the UK.

Some schemes, condition the Lithium batteries before applying
a charging current. I've seen a couple garden lamps (out of
a bunch my various neighbors have), that actually manage to
light at night on winter days.

The best material to work with in that regard, is lead acid.
At least it still accepts a charge in winter. The temperature
ranges are listed here.

https://batteryuniversity.com/learn/...w_temperatures


*** Lead acid**** Charge: –20°C to 50°C* Discharge: –20°C to 50°C

You can have any amount of power you want - it just takes
more and more square meters of solar panels to collect that
power on dim days.

The are professionally designed please go around the dangerous bend
signs with radar activated sensors on some of the road where I live.
They work perfectly inn mid summer and for an hour or so after sunset in
mid-winter but they are always stone dead on any frosty winters morning.

I am told they destroy a set of SLA lead acid batteries every winter.

--
Regards,
Martin Brown