Solar powered LCD?

[xevious]

Thanks, rewolf. The replacement non-rechargeable batteries are rated at around 3-5 years. According to Casio, the rechargeable cell needs replacement every 7 years. Of course, that's their estimate on the older 726R and 920R... so perhaps the MT920 would last much longer. In any case, the cost difference is huge. I'd rather use a non-rechargeable at $0.59 a piece, as long as I can find one that won't be harmed by the trickle charge coming from the solar cells. Do you think it would be OK to use the 371 (1.5v low drain) cell?

[rewolf]

...The replacement non-rechargeable batteries are rated at around 3-5 years. According to Casio, the rechargeable cell needs replacement every 7 years...

If that's really necessary, it defeats the whole effect of a solar watch. There are watches that run 3-5 years on a simple lithium primary cell, IIRC some Casio/Seiko models even 10 years.

Of course, that's their estimate on the older 726R and 920R... so perhaps the MT920 would last much longer. In any case, the cost difference is huge. I'd rather use a non-rechargeable at $0.59 a piece, as long as I can find one that won't be harmed by the trickle charge coming from the solar cells. Do you think it would be OK to use the 371 (1.5v low drain) cell?

As I wrote in the other thread, I don't know for sure. Battery manufacturers always warn to never charge a primary, but of course they play it safe (and for obvious reasons have no interest in their batteries being recharged).
However, it is known that Alkalines CAN be recharged with low current, but I never tried it with button cells. It works best when they're not yet fully discharged - and that's exactly what happens in a solar watch .
I read somewhere that recharging does NOT work with Silver Oxide (AgO) batteries. The 371 you mention COULD be AgO (depending on manufacturer and battery chart...). AG6 or LR69 are the same, but definitely Alkaline.

[xevious]

Sorry for the semi-cross-post... I'll try to keep it anchored in one place. Given we're talking about battery replacement, a servicing activity, I'll post over on the Digital Workbench. Thanks.

Regarding your point about using non-rechargeable batteries, I know--it does defeat the purpose of the solar cells. However, here's the rationale:

* Back when these solar watches were produced, your average watch battery would last 2, maybe 3 years maximum. The solar cell technology extended that to 7 years (and all of my solar watches from that time had a battery life of 7 years--spot on with the Casio estimation).

* Now these present day batteries are more efficient, lasting 5 years and possibly even 10 in some cases before requiring replacement, all without any kinetic or solar recharging.

* I don't know if the solar cell watch battery life limitation of 7 years was due to the secondary battery technology at the time, or due to the solar cell designed capability. If it is the batteries, then I suspect a present day rechargeable replacement should last much longer than 7 years. If I could be certain an MT920 might last 20 years in my LCD watch, there would be no question to buy this one and forget about the others.

* If the solar cells can't deliver enough recharging power to keep an MT920 going for more than 7 years, then... well, there's little point in spending $16 on a battery when $1.50 can be spent on a non-rechargeable battery that will last 5 years.

If I was better equipped in electronic knowledge and tools, I might be able to do some circuit testing to see the behavior of the solar cells and the effect on the battery, then figure it out in no time. But given my limitations, I think this might be a good approach: Try the MS920S 3V battery first... see how long it lasts. It is rated at 11mAh... maybe it will last just one year if no recharging takes place? If the battery dies out before then, the test will prove the solar cells can't do the job (if indeed they are still working!). Maybe at that point, I'll decide if it is worth spending the money on the MT920 to see if it holds up. Otherwise, I could use a non-rechargeable cell and at least be able to make the watch functional for as long as the batteries last.

Ok...I guess 'nuff said, eh?

[rewolf]

If I was better equipped in electronic knowledge and tools, I might be able to do some circuit testing to see the behavior of the solar cells and the effect on the battery, then figure it out in no time.

Knowledge is not a problem, you can learn and ask , but you'd need someone with a multimeter, or buy the cheapest one you can find - it will be good enough to measure charging voltage

But given my limitations, I think this might be a good approach: Try the MS920S 3V battery first... see how long it lasts. It is rated at 11mAh... maybe it will last just one year if no recharging takes place? If the battery dies out before then, the test will prove the solar cells can't do the job (if indeed they are still working!). Maybe at that point, I'll decide if it is worth spending the money on the MT920 to see if it holds up. Otherwise, I could use a non-rechargeable cell and at least be able to make the watch functional for as long as the batteries last.

Again, I suppose the MS920S will not work - it won't take any charge.
My suggestion: try a super-cheap alkaline AG6/LR69/371A (not silver oxide 1.55V), and if it runs at that voltage, spend your money on a Panasonic MT920. But if it does NOT run with alkalines, try the MS920S.
But of course I can't force you to do so

[xevious]

Thanks for the assurance, Rewolf. I do have a hand held multi-meter, but the contacts are too large for small circuitry. I might be able to attach needles to compensate... if indeed the need arises.

I did find manage to find an eBay seller having AG6/371 alkaline cells, so if the batteries I've ordered don't work out (silver oxide 370, 371, and MS920S), I'll try the alkaline AG6. I learned from a vintage Casio fan that the silver oxide cells worked for him on the same module (242), but he recommends not letting the watch get long sunlight exposure (like on a window sill, which of course makes sense).

Hopefully I'll have it figured out in a few days.

[rewolf]

I learned from a vintage Casio fan that the silver oxide cells worked for him on the same module (242), but he recommends not letting the watch get long sunlight exposure (like on a window sill, which of course makes sense).

That's a good sign. If the movement works well with the 1.55V from a (non-rechargeable) silver oxide cell it will quite probably work with the slightly lower voltage of a (supposedly rechargeable) alkaline
Keep us informed, please

[xevious]

Well, I'm bummed.

I got my batteries today. I eagerly went to try them out in my DW2000 Casio Solar watch. First the 370... nothing. Then the 371... nothing. Finally, the MS920S (after pulling off the metal contact bits). Nothing. I double checked the batteries with a multi-meter--they all showed full power.

I went to replace the CR2016 in a fairly recent Casio Illuminator and I ended up with a blank display. Puzzled, I then noticed a little sticker, mentioning the use of tweezers to join AC to (+). I realized "AC" means "all clear", a contact point on the circuit board. That worked--watch came to life.

So, I figured that's what I need to do on the DW2000. Sure enough, there is an "AC" port on the movement. I tried it with all three batteries. NOTHING. I can't figure it... if the batteries aren't 100% compatible, I'd expect that I would get at least some LCD activity... scrambled bars or something. So I took apart the movement casing parts (the thin steel enclosure and the inner plastic shim) and then examined the exposed circuit board with a loupe. I could see no visible damage. I thought perhaps the old battery might have leaked into it and was going undetected. Nope. All clean.

I'm puzzled... based on the visible condition, and the variety of tested battery cells, something should work... even if not time keeping, the back light. Unless perhaps the circuit board got exposed to enough heat or some other condition to cause a circuit board failure, or the random chance of a substandard component sneaking through quality control (and just couldn't last beyond X years). Oh well. I'm now doubting if it would really do me any good spending more $$ on buying alkaline AG6 batteries.

Anyway... it was worth a try, seeing if I could get this old watch going. Thanks again for all the help...

[xevious]

Well, I finally tracked down someone who has a working Casio vintage solar watch with a 242 module (same for the DW-2000). The battery they have installed is the SR-920W, a 1.55v cell. The Panasonic MT920 is supposed to be equivalent.

The Renata 370 is an SR-920W, which I did buy and install in mine. So, my module must be dead.

Note that the SR-920W is not rechargeable, so the solar function is not being used. This means battery life may be about 3-5 years.