Solar panel not charging batteries

Thread Starter

wezken

Joined Jun 5, 2020
2
Hello. I'm an electronics beginner so be gentle. I have a device which discourages cats from pooing on your garden. It is powered by 4 x 1.2v AA batteries and has a solar cell in the top which is supposed to charge them. My problem is that it is not charging the batteries, they run down after about two weeks and I have to take them out and charge them in my battery charger. I've done a bit of investigating, here's what I have found so far.
1. The charger reports that the batteries are OK and charges them with no problems so I assume it's not the batteries.
2. I've taken the following readings with my multimeter:-
a. across where the wires from the solar panel are soldered to the pcb, with the batteries in place 4.6v​
b. same but without the batteries 0.7v​
c. I disconected the solar panel from the pcb and measured 4.6v across the leads when exposed to light and 1.2v when shielded.​
Using my simple logic the solar panel seems to be OK, as are the batteries, so should I assume that something on the pcb is causing the problem?
The solar panel gives a very low reading while connected to the pcb without the batteries, so might that mean that something on the pcb is draining the power from the solar panel?
If so, what might that be and how can I fix it?
Many thanks for any help you can give me.
 

AlbertHall

Joined Jun 4, 2014
10,395
From that data it might just be that the solar panel is too small to supply enough charge to keep it running. Obviously this depends on your local weather, the season, and your latitude.
Can you measure the current from the solar cells while charging the battery?
The current that the device draws from the batteries with the solar cell disconnected?
 

tomerbr

Joined Oct 16, 2017
4
Hi,
Your open circuit voltage is 4.6V according to your measurement in full sunlight right?

What is the current of the solar panel? to measure that - disconnect the solar panel and use your multi-meter in DC current mode. connect the multi meter leads to the panel wires (one for each) and check the current.

See if you have current there that matches the solar panel datasheet.
If no or little current flows the panel is faulty.
 

Audioguru again

Joined Oct 21, 2019
1,912
A Ni-Cad or Mi-MH battery cell charges to 1.45V. Then four of them need to be charged with 5.8V or 6V.
Is your light on the solar panel produced by a candle at night? It needs direct sunlight with no window, clouds or smog.
 

Thread Starter

wezken

Joined Jun 5, 2020
2
A Ni-Cad or Mi-MH battery cell charges to 1.45V. Then four of them need to be charged with 5.8V or 6V.
Is your light on the solar panel produced by a candle at night? It needs direct sunlight with no window, clouds or smog.
Thanks for all the replies.
Firstly they are Ni-MH 1.2v batteries. The legend actually says "1-2v" and I was interpreting that as "1.2v" maybe I was wrong in that?
Secondly, yes it wasn't a candle I was using but it certainly was cloudy. It's bright sunlight right now and the reading is 7.02v. That's with the Solar panel not connected to the circuit.
 

Audioguru again

Joined Oct 21, 2019
1,912
A Ni-MH battery cell is charged at about 1.45V then its average discharging voltage is about 1.2V.
I am glad that your solar panel voltage is correct in full sunlight and I hope it provides enough current to charge your battery in one day.
Here is from Energizer and Duracell datasheets:
 

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