Volts, Amps, Watts and G-shocks

Thread: Volts, Amps, Watts and G-shocks

1. Volts, Amps, Watts and G-shocks

Hi there everybody!

I thought I'd make this thread for all the people passionate about electrical engineering, math and g-shocks of course. My intention is to find out about the power consumption of different g-shock(maybe non g as well) modules. Like how much power the alarm, el, timekeeping and other features consume. Now, I guess the proper way to do it is to take apart a watch and measure all these things, but I wouldn't encourage anybody to do it unless they really knew what they were doing. Being on the math side myself, I prefer to take the data casio offers in their manuals and play with it a bit. So here we go:

MODULE 2548
, found on the G-2900. Everything bellow applies to module 2821 as well.

Battery type: CR2025, 3V, 165mAh. That gives a power of 3V * 165mA = 495mW.

Here's what the manual says: 10 years working time assuming 10 sec alarm/day and 1.5 sec of backlight operation/day. So we divide 495mW by 3650 days and we get 0.135 mW/day. That is to say 10 sec of alarm + 1.5 sec of backlight + a day's worth of timekeeping consume 0.135mW.
But the manual also states that the battery life is shortened to 9 years in case of 3 sec of backlight/day and to 8.2 years in case of 4.5 sec of backlight/day. The alarm usage remains the same and no other features are used.
So in the case of the 9 years, we have 495mW/3285days = 0.15mW/day. 0.15mW - 0.135mW = 0.015mW. That is to say 1.5 sec of backlight consumes 0.015mW.
For the 8.2 years: 495mW/2993days = 0.165mW/day. The difference is still 0.015mW(they're identical up to the third decimal place; we're using a bit of approximation here), so things are consistent.

So if all of this is correct(and I hope you correct me if I'm wrong), 1.5 sec of backlight use consumes a mere 0.015mW. That leaves 0.12mW for 10 sec of alarm and a day's worth of timekeeping. How much does each consume? It's anyone's guess, but the alarm will definitely take the lion's share. Now, if we do 0.015mW * 6.6 =~ 0.1mW that the backlight consumes in 10 seconds. I estimate that 10 seconds of alarm also consumes about 0.1mW, if not a bit less.
Also 495mW/0.015mW = 33000. 33000*1.5sec = 49500sec of continous backlight usage(excluding timekeeping and alarm altogether). That is 49500sec/3600sec = 13.75 hours of continuous backlight usage.

Conclusion: on a day to day basis, one alarm usage(10 sec) is going to consume much more energy than one backlight usage(1.5 sec), with both of them consuming about the same amount of energy per second(power), however. That is to say 10 sec of alarm is about 6 times more power hungry than 1.5 sec of backlight.

I hope it all made sense and the calculations are correct. Over to you guys!

Cheers, James

2. Re: Volts, Amps, Watts and G-shocks

Well done
but Theory's one thing, but real life is another

<Some> things to bear in mind:
Battery capacity can be affected by many things including the temperature and the load in question
The current rating you quote is for a continuous load.
Battery voltage 3V quoted is a nominal voltage and will vary due to load and over its lifetime.
Battery capacity will vary between samples.
Battery lifetime starts when it was made, it could have been on the shelf for years before being commissioned in the watch.

3. Re: Volts, Amps, Watts and G-shocks

Originally Posted by watchma
Well done
but Theory's one thing, but real life is another

<Some> things to bear in mind:
Battery capacity can be affected by many things including the temperature and the load in question
The current rating you quote is for a continuous load.
Battery voltage 3V quoted is a nominal voltage and will vary due to load and over its lifetime.
Battery capacity will vary between samples.
Battery lifetime starts when it was made, it could have been on the shelf for years before being commissioned in the watch.
I totally agree with you and, as I've said, it's all done from a theoretical point of view since I like math. However, theory provides good guidelines for practice.

This thread is open to anyone wanting to expose the results of their experiments and/or calculations.

Cheers, James