solar garden lights improved after wintering outside

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 ( snipped-for-privacy@misty.com)

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.

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

and

even

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.

"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?

and

I guess what I was referring to was as clear as mud. :-P 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.

snip

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

RL

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

weeks,

thru

and

the

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. :-(

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

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

we've

'form'

low

operating

in

even

cause

crack

failures

companies

customer

Check these out.

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.

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

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