solar garden lights improved after wintering outside

[legg]

There are two different brands of garden lights with differing
internal construction, components and battery brands, sitting in the
garden outside our kitchen window.

In the first summer of operation, I was dissapointed to see them
dimming after only 3 hours of post-sunset illumination, even on the
brightest of days. I even modified one, so that the LED's schematic
position didn't arbitrarily limit the charging voltage, without any
noticeable improvement.

This spring, after spending the winter entirely submerged in snow,
they all illuminate for at least 8 hours after sundown, even after
relatively gloomy charging days.

Anyone care to speculate on this beneficial aging effect in the
generic solar light product?

RL

 

[Don Klipstein]

There are two different brands of garden lights with differing
internal construction, components and battery brands, sitting in the
garden outside our kitchen window.

In the first summer of operation, I was dissapointed to see them
dimming after only 3 hours of post-sunset illumination, even on the
brightest of days. I even modified one, so that the LED's schematic
position didn't arbitrarily limit the charging voltage, without any
noticeable improvement.

This spring, after spending the winter entirely submerged in snow,
they all illuminate for at least 8 hours after sundown, even after
relatively gloomy charging days.

Anyone care to speculate on this beneficial aging effect in the
generic solar light product?

My best guess: The LEDs are less conductive at lower temperatures.

Try finding their associated resistors and replace the resistors with
ones of higher value. Fair chance this does not dim the LEDs too much.
(BEWARE - LEDs not only become less conductive or require more voltage for
a given current draw at lower temperature, they also produce light more
efficiently at lower temperature. Temperature sensitivity of efficiency
of producing light is worst for red, orange, yellow and
chartreuse-yellow-green ones, less bad but maybe significant for white
ones, and more insignificant for ones that are non-yellowish green or
blue.)

- Don Klipstein ([email protected])

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

There are two different brands of garden lights with differing
internal construction, components and battery brands, sitting in the
garden outside our kitchen window.

In the first summer of operation, I was dissapointed to see them
dimming after only 3 hours of post-sunset illumination, even on the
brightest of days. I even modified one, so that the LED's schematic
position didn't arbitrarily limit the charging voltage, without any
noticeable improvement.

This spring, after spending the winter entirely submerged in snow,
they all illuminate for at least 8 hours after sundown, even after
relatively gloomy charging days.

Anyone care to speculate on this beneficial aging effect in the
generic solar light product?

RL

I've been playing, er, experimenting with the old Weston light meter and
measuring the light of the LEDs I put on the PS 24/7 on May 1. I've
already noticed the decline in light output over just a few weeks, even
tho I couldn't tell this with the naked eye.

The reason why I bring this up is that your garden lights may be putting
out less light, and this may be the reason why it is lasting longer than
before. The way to know this is to measure the current drain during
discharge. If it's substantially less than before, then your garden
lights are really just putting out less light for longer. And you're
not noticing the decreased light output.

 

[William P. N. Smith]

"Watson A.Name - \"Watt Sun, the Dark Remover\""

I've been playing, er, experimenting with the old Weston light meter and
measuring the light of the LEDs I put on the PS 24/7 on May 1. I've
already noticed the decline in light output over just a few weeks, even
tho I couldn't tell this with the naked eye.

Did the current drop over time as the light output decreased?

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

"Watson A.Name - \"Watt Sun, the Dark Remover\""


Did the current drop over time as the light output decreased?

We went thru a good discussion here on what circuit to use for such a
mockup, and I settled on a constant voltage source of 5.1V for the bases
of all 5 transistors, and a 220 ohm resistor in the emitter of each
transistor, which has 4.44V across it, giving 20mA. The LEDs are the
collector loads of each transistor, so each LED has 20mA current thru
it.

BTW, each 220 ohm resistor measured about 4.44VDC at the beginning, and
they still measure that now.

 

[William P. N. Smith]

"Watson A.Name - \"Watt Sun, the Dark Remover\""

collector loads of each transistor, so each LED has 20mA current thru

BTW, each 220 ohm resistor measured about 4.44VDC at the beginning, and
they still measure that now.

I'm not sure you answered the question, though maybe this hint at the
end tells us something.

The OP asked why his lights last longer, you responded that light
output may decline, but unless the current drain declines as well, the
runtime isn't going to change, is it?

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

"Watson A.Name - \"Watt Sun, the Dark Remover\""



I'm not sure you answered the question, though maybe this hint at the
end tells us something.

The OP asked why his lights last longer, you responded that light
output may decline, but unless the current drain declines as well, the
runtime isn't going to change, is it?

I guess what I was referring to was as clear as mud. The OP may
not notice with the naked eye that the LED brightness is less than when
the lights were originally installed. So a reduction in current and
brightness may not be apparent to his eye, and may be the reason for the
longer runtime.

 

[legg]

My best guess: The LEDs are less conductive at lower temperatures.
snip

- Don Klipstein ([email protected])

Don, this is a permanent (~) change, present even now that spring is
here.

RL

 

[legg]

"Watson A.Name - \"Watt Sun, the Dark Remover\""



I'm not sure you answered the question, though maybe this hint at the
end tells us something.

The OP asked why his lights last longer, you responded that light
output may decline, but unless the current drain declines as well, the
runtime isn't going to change, is it?

I agree.

Either the current drain in the circuit is noticeably reduced or we've
found a new reason to stick NIMH batteries in the freezer, to 'form'
them.
Cold is traditionally the bugbear of electrochemical devices. Solar
cells don't like it either, while it is present.
The circuit uses no other parts that are permanently affected by low
temperatures.

I guess I'll pull the modified unit, to see if any recorded operating
data has changed.

RL

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

I agree.

Either the current drain in the circuit is noticeably reduced or we've
found a new reason to stick NIMH batteries in the freezer, to 'form'
them.
Cold is traditionally the bugbear of electrochemical devices. Solar
cells don't like it either, while it is present.
The circuit uses no other parts that are permanently affected by low
temperatures.

I guess I'll pull the modified unit, to see if any recorded operating
data has changed.

I would say that other parts can be permanently affected by changes in
temperature, especially temp swings that are greater. One change, even
tho it may take a long time to occur, is when temperature changes cause
semiconductors to creep internally due to uneven expansion and
contraction, which can cause bond wires to separate, or chips to crack
or pull away from their heatsink.

And according to the bathtub curve theory, many of those early failures
are supposed to be caught during production burn-in. But some companies
may not do a proper burn-in, or do any burn-in at all. So the customer
ends up as the burn-in guinea pig. :-(

 

[ehsjr]

legg wrote:

I agree.

Either the current drain in the circuit is noticeably reduced or we've
found a new reason to stick NIMH batteries in the freezer, to 'form'
them.

Another possibility that hasn't been mentioned, probably
because it is so remote: the solar cells are now putting
out more energy because the snow washed something off the
sun facing surface.

Ed

 

[legg]

I would say that other parts can be permanently affected by changes in
temperature, especially temp swings that are greater. One change, even
tho it may take a long time to occur, is when temperature changes cause
semiconductors to creep internally due to uneven expansion and
contraction, which can cause bond wires to separate, or chips to crack
or pull away from their heatsink.

And according to the bathtub curve theory, many of those early failures
are supposed to be caught during production burn-in. But some companies
may not do a proper burn-in, or do any burn-in at all. So the customer
ends up as the burn-in guinea pig. :-(

The components are are all two or three-wire. Construction of the two
device types is completely different. The phenomina is identical and
is exibited in all devices.

If this is a guinea pigs reward for abusing the device, its an
atypical one.

RL

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

The components are are all two or three-wire. Construction of the two
device types is completely different. The phenomina is identical and
is exibited in all devices.

If this is a guinea pigs reward for abusing the device, its an
atypical one.

Check these out.
http://members.shaw.ca/novotill/SolarGardenLight/index.htm

 

[Chris Jones]

Cold is traditionally the bugbear of electrochemical devices. Solar
cells don't like it either, while it is present.

Actually the maximum power point on the I-V curve of a solar cell occurs at
a higher voltage when the temperature is low and so the efficiency is
better when the solar cells are cold.

 

[legg]

Don, this is a permanent (~) change, present even now that spring is here.

..........................

It's midsummer, and they are back to their usual performance, lasting
less than three hours from sundown.

I suspect that there's just less light to collect out there, once the
neighbourhood trees are fleshed out with leaves. Though a signifigant
proportion of those nearby are evergreen, these have greater blocking
characteristic for a northernly oriented sun's path.

RL

 

[ehsjr]

.........................

It's midsummer, and they are back to their usual performance, lasting
less than three hours from sundown.

I suspect that there's just less light to collect out there, once the
neighbourhood trees are fleshed out with leaves. Though a signifigant
proportion of those nearby are evergreen, these have greater blocking
characteristic for a northernly oriented sun's path.

RL

Try washing the lens to see if that improves things.
Doubtful, but worth a try.

Ed