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Hearing Aid Battery Powered Watch

Get decades of service out of a Quartz watch.
  (+5, -2)
(+5, -2)
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I often find the way to approach a problem, is to look into how people with similar, but much bigger problems are doing things. For example, you need to put up a partition wall. You cut a piece of 2x4, position it, nail into place. A pro wouldn't do this. They'd set up a chop saw cut 6 pieces to identical length and nail-gun it together with galvanized steel plates. Maybe it's worth doing that or maybe it isn't.

Hearing aids have a bigger power problem than watches. But they still need a small power source, so they turn to Zinc-air cells. These work like any other cell, they're a redox reaction where electrical work is extracted from one thing oxidizing and another reducing. But, they use Oxygen in the air as one half of that. Consequently they're ~6x larger in energy density Vs conventional Alkaline watch cells <link>. So, we power our watch with this? Well, sealed inside a waterproof watch, it would quickly use all the O2 inside, and non waterproof watches are a bit silly. So, the cell goes into an externally-vented waterproof compartment, we use the whole watch case as -ve and a watertight electrode contacts the +ve side.

With a standard sized Zinc-air battery, e.g. a 675, your watch would last decades. Even better, the manufacturer could build a cell the size of the whole back, meaning a lifetime of power.

bs0u0155, Jul 17 2023

Battery Chemistry Comparison https://en.wikipedi...rcial_battery_types
[bs0u0155, Jul 19 2023]

WO1998047191 https://patents.goo...ent/WO1998047191A1/
A water resistant case for an electrical device such as an electric wristwatch movement powered by a standard high current zinc/air cell. A small aperture in the case wall slows ingress and egress of water vapor to the case so as to increase cell life. The aperture also limits the rate of oxygen flow to the cell cathode rather than the air entry ports in the cell itself. A hydrophobic gas transmissive membrane admits air and water vapor to the aperture without admitting liquid water. [xaviergisz, Jul 21 2023]


       I like the idea, but have you verified that there is enough air volume in the watch case that you won't run out of oxygen? It seems to me that you'd need a lot more, but I don't feel like doing the research now.   

       However. I not so long ago installed hydronic floor heating in my house. When you do that, you have to buy oxygen barrier PEX pipe because the standard PEX pipe, while it can easily hold 60 psi of hot water, still diffuses oxygen into the system that will corrode the steel rotor of the pump or the iron boiler. So, if we can make a significant surface of the watch out of PEX, we might be able to get enough oxygen to keep the battery going. Also, I bet there are better options than PEX since that isn't what it is designed for.
scad mientist, Jul 17 2023

       //have you verified that there is enough air volume/   

       The key phrase there was "externally vented". But a waterproof O2 permeable barrier could actually be a neat solution.
bs0u0155, Jul 18 2023

       // conventional Alkaline watch cells <link> //   

       Puzzled by this - perhaps the link you meant to include would clarify?
a1, Jul 18 2023

       Would the voltage of the Zinc cell be proportional to the available oxygen saturation? So if I'm laughing and playing outside, time will fly by because I'm having fun?
mace, Jul 19 2023

       I'm not convinced that a waterproof O2 permeable barrier would actually keep out enough moisture over time to prevent internal corrosion. It would more likely be labeled as "water resistant" and the warranty on that specific part wouldn't last for very long, methinks.
21 Quest, Jul 19 2023

       //perhaps the link you meant to include would clarify?//   

       Done, apologies!   

       //Would the voltage of the Zinc cell be proportional to the available oxygen saturation?//   

       To an extent, the Voltage should be relatively fixed unless more current is being drawn than the cell type can supply, or the O2 drops to very low levels. Shouldn't apply here though with the watch drawing more than 100 fold less current than a hearing aid.   

       //So if I'm laughing and playing outside, time will fly by//   

       The point of a watch/clock/chronometer is that it measures time in a way that is as independent as possible with regard to the external conditions. Every battery/spring etc. will vary in power over its life. That's what escapement/pendulum quartz crystal systems are for.
bs0u0155, Jul 19 2023

       Thanks for providing the link.   

       Do any quartz watches use alkaline cells? I thought they were all silver-oxide or lithium maganese dioxide.
a1, Jul 19 2023

       //Do any quartz watches use alkaline cells?//   

       To be honest, I just popped the cell out of one of the lab timers that happened to be on my desk. That's a 357 alkaline. It doesn't make much difference to the principle though.
bs0u0155, Jul 19 2023

       What kind of watch is it?   

       Took me some digging to realize 357 is a size designation rather than a chemistry - you can get batteries in that size in either alkaline or silver oxide chemistry. And "357" also has other opart numbners/names depending on the vendor.   

       "International standard IEC 60086-3 defines an alphanumeric coding system for "Watch batteries". Manufacturers often have their own naming system; for example, the cell called LR1154 by the IEC standard is named AG13, LR44, 357, A76, and other names by different manufacturers. The IEC standard and some others encode the case size so that the numeric part of the code is uniquely determined by the case size; other codes do not encode size directly." -wikipedia
a1, Jul 19 2023

       // It doesn't make much difference to the principle though. //   

       Oh, but it does! Alkaline battery voltage output drops linearly over lifetime. Silver oxide batteries maintain a pretty constant voltage until they go dead. So even though a high-quality alkaline battery may shave the same stored energy capacity - if your watch or other device needs a fairly constant voltage the silver oxide battery will give a longer useful life.   

       But your zinc-air battery could still be a good idea if you can scale them up to like a 2032 size or replace the entire back of the watch as suggested. You might not even need to worry over much about waterproofing - hearing aids aren't swim-rated either.
a1, Jul 19 2023

       //Alkaline battery voltage output drops linearly over lifetime.//   

       That doesn't matter. Watches/timers/chronometers would be pretty dreadful if they were meaningfully affected by the power supply voltage. Quartz oscillates at 32,768 Hz when energized with essentially any any Voltage above 200mV, so they will be similarly accurate and precise through to the death of the cell.
bs0u0155, Jul 21 2023

       // Watches/timers/chronometers would be pretty dreadful if they were meaningfully affected by the power supply voltage. //   

       Dreadful? Meaningfully affected? Nah, just fussy. Battery voltage drops below a certain point - not dead but too weak - and the device stops until you replace the battery. That's kinda the point behind your* original suggestion, innit?   

       * Yours and our good friends at Timex, according to the 1998 patent [xaviergisz] dug up.
a1, Jul 21 2023

       //Yours and our good friends at Timex,//   

       Ha! OK, and I'm wearing a Timex right now!
bs0u0155, Jul 21 2023


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