Solar alarm clock dead(?)

[8bit]

I'll start by saying I know very little about electronics so any advice will be welcome.

I opened it up and found that it actually contains two batteries inside, a 3v CR2477 and a very thin blue rimmed battery, the type I can't make out as its hidden by the clasp holding it in. Would one of these be the cause of it not functioning? I had noticed the display was dimming prior to it stopping completely.

 

[Alec_t]

Would one of these be the cause of it not functioning?

Quite possibly. If you have a multimeter you could check the voltage of both batteries.

 

[8bit]

Quite possibly. If you have a multimeter you could check the voltage of both batteries.

Thanks, I'll dig one out and give it a go. Do I just place the meter's probes on either side of it?

 

[dave9]

Yes, on both sides of it. You'd want to do this with the solar cell covered so light doesn't get to it, and next you might want to test again with strong light getting to it, in case the solar cell is the fault, no longer charging it.

The thin blue rimmed battery is probably NiCd, probably 1.2V since you reported thin, as a stack of multiple NiCd coin cells stacked would be thicker and have ridges for each cell in the stack, but you can desolder and take the shrink wrap off to be sure if there is any question.

How old is it? Is it worth fixing? If there's space for it in the clock you could substitute a NiCd AAA in a battery holder with wires going to the PCB but who knows, maybe you can get the coin cell (with spot welded tab leads on it I assume?) for cheap on eBay. If you did use a larger cell it may need to sit in sun for quite a while before the minimum voltage to power the clock is reached (or pre-charge the cell and then you can also see immediately if the clock works again before closing it back up).

 

[8bit]

Thanks again.

It's about 15 years old, doesn't have any real vavlue to me but I thought it would save it being sent to landfill and me having to buy another one.
Would you know why there is a 'coin' battery inside as well as the rechargable one?

 

[Alec_t]

Would you know why there is a 'coin' battery inside as well as the rechargable one?

Probably as a backup, so that the unit's data is retained in memory when there is not enough solar energy to keep the main battery charged.

 

[dave9]

At 15 y/o it is also due for a new CR2477. I wonder if you can buy the equivalent new for less than the cost of these two batteries...

Previously I mentioned putting a AAA NiCd in it. What you could do is put a NiMH in if you want to try to charge it with the solar panel, or put an alkaline in and disconnect the solar panel so it becomes a regular battery powered clock, then you "probably" don't need the CR2477 unless it is required to save the alarm setting or something (and of course you need the alarm setting).