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I am looking to reduce the voltage of a silver oxide battery from 1.5 to 1.3 volt for a Bulova Accutron movement. The watch movement uses approx 4.5 to 7 micro amperes. I have used the formula for trying a resistor but cannot find a resistor that would work. I hope you guys on here can help me.

Dan the Horologist

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  • \$\begingroup\$ In all probability,the watch will work fine with the slightly higher voltage. Have you tried it? In any case, a 40k resistor will drop 0.2 volts at 5 microamperes. \$\endgroup\$ – Barry Feb 7 '15 at 13:41
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My vintage Spaceview runs fine directly on the silver oxide battery, but I know that not all do.

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I think a small Schottky diode could be added internally so that non-mercury batteries could be used thenceforth. Given the costs for servicing these finicky watches, you could probably charge $100 or more to add a 10-cent diode such as this one.

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There are even smaller diodes that might work too, but if you stick to a fairly low voltage rating and a fairly high current rating the voltage drop should be around 200mV at low current.

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Consider a Schottky diode. Schottky diodes have a low forward voltage drop, typically 0.25 to 0.4 volts.

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  • \$\begingroup\$ This is great information. There are some people making a modified battery, they may be using something like this. I will give it a try. Most Accutrons do run at 1.5 but the are a few that run too fast that indexing and phasing can't correct. \$\endgroup\$ – Daniel Wentzel Feb 8 '15 at 14:16

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