Solar charger

Thread Starter

simonpk

Joined Feb 11, 2021
4
Hi, I have an old electromagnetic clock driven by a standard 1.5v dry battery. The clock draws a very small current, around 0.1mA, and I would like to construct a simple solar charger for a 1.5V rechargeable battery. Not being knowledgeable about the necessary components and circuitry, I'm imagining a very small solar cell, perhaps like what's in my Casio calculator, tucked away behind the mantel clock and working off ordinary indoor daylight (not sunlight). Could anyone say if this is feasible, and if so, what components I might need?
Thanks.
 

Thread Starter

simonpk

Joined Feb 11, 2021
4
Hello there :) welcome to AAC,

You have to choose a rechargeable battery.
Nickel-cadmium (Ni-Cd),
Nickel metal hydride (Ni-MH)
Lithium-ion (Li-Ion).
Lithium polymer (Li-Po)
Yes, as I said I would be using a rechargeable battery in place of the dry battery. It's the rest of it I'm uncertain about!
 

GeBJT

Joined Nov 3, 2020
19
It's a gloomy afternoon and I'm indoors with the lights on. My 6cm x 6cm PV panel can support about 100mV across a 1k ohm resistor. That's not enough even to run your clock, let alone charge the battery. "... a very small solar cell, perhaps like what's in my Casio calculator ..." is not going to hack it either.

(P.S. I did test the said PV panel outdoors in Summer daylight and it gave the spec'd output of 5v, 100mA)
 

Bernard

Joined Aug 7, 2008
5,788
It may be possible. Using a 1" X 2" solar cell, 3V OC, 14 mA SC, walking around house output varied from 1 uA to 4 uA. Then again on second trip around measuring V, facing outside window read only .5V. Try your own measurements.
How do we explain the operation of a calculator in a dim room. My Sharp EL-326G operates in every room except a semi dark hallway ?
 
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Thread Starter

simonpk

Joined Feb 11, 2021
4
It may be possible. Using a 1" X 2" solar cell, 3V OC, 14 mA SC, walking around house output varied from 1 uA to 4 uA. Then again on second trip around measuring V, facing outside window read only .5V. Try your own measurements.
How do we explain the operation of a calculator in a dim room. My Sharp EL-326G operates in every room except a semi dark hallway ?
Thanks for the replies. Maybe the question I should have asked is, roughly how large in area would an indoor solar cell need to be to keep a battery recharged that was itself supplying the clock with 0.1mA at 1.5V ?
 

k1ng 1337

Joined Sep 11, 2020
85
I have a 1 watt (5v, 200ma, 3x5 inches) solar panel that I have been playing with for a with similar interests.

With poor sunlight it's able to drive a 3v forward LED at around 1ma

With no sunlight, I have two 60w (I think) lightbulbs in this room at 2 meter distance and it won't light at all, I just tested the panel in the room and it's nighttime

Open circuit reading:
250mv / 20ua

1k resistor as load:
20mv / 19ua

Under under my conditions I expected the load current to be a lot less than open circuit but as you can see very little of the radiated energy is converted so I imagine a panel around the size of a piece of paper would be required and even then I think you would have voltage issues but I'm far from an expert, I hope this gives you some idea of the capability..

Good luck :)
 

Thread Starter

simonpk

Joined Feb 11, 2021
4
Thanks for the suggestions. Perhaps I was expecting too much; I already have an Atmos clock which has no battery and runs on variations in atmospheric pressure, and I thought it might be possible to get my current electromagnetic clock to effectively run on ambient light. But I gather that the solar cell required to keep the battery charged would be much too big in area to conceal behind the clock. Thanks anyway.
 
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