One of those questions where, had I been asked, I would have said that the power consumption was unrelated to the internal friction in the watch. The watch stepper motor and driver has no knowledge of the state of the friction to be encountered and just delivers a fixed energy pulse. And any more "mechanical power" than is actually needed and applied to the gear train would just be absorbed by the mechanism in the form of noise emitted and I suppose heat.
But... I keep reading the opposite on a watch forum where several threads say that the more free the movement, the longer the battery life and lower the power consumption.
I would have said no to that... what do you folks think.
But... I keep reading the opposite on a watch forum where several threads say that the more free the movement, the longer the battery life and lower the power consumption.
I would have said no to that... what do you folks think.
I'm guessing friction must have some effect effect on battery life and/or accuracy otherwise the movement manufacturers probably wouldn't use expensive jewels in quartz movements.
Perhaps the stepper motor doesn't deliver a "fixed energy pulse". Perhaps it drives the first gear in the gear-train through a fixed incremental angle, d_theta. If the gear train has lots of friction, it takes lots of work to move the input gear by d_theta. If the gear train has very little friction, it takes less work to move the input gear by d_theta. So less friction means less work, means less power dissipation, means longer battery life.
(some pendulum clocks DO receive a "fixed energy pulse" from the external power source; maybe that's what you are thinking of)
(some pendulum clocks DO receive a "fixed energy pulse" from the external power source; maybe that's what you are thinking of)
I've taken the second hand off a few crystal controlled mechanical clocks to reduce noise, but I never bought two and ran one unmodified to see which one's battery wins. I also never thought of putting a resistor in series with the drive solenoid, since it probably could operate properly with less actuation force without the second hand. Maybe some movements without a second hand have a lighter motor by design.
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Some motors do draw more power when they are faced with a higher mechanical load. I don't know if stepper motors do this.
Sure. There's a heavier damping term in parallel with the input inductance when velocity is held down.
Well 🙂 I've always assumed they receive a fixed energy pulse, but that was a pure assumption on my part. So perhaps they really do not operate that way.
That makes sense, I can visualise something like that having an effect.
(the sort of watches I mean are the typical offerings on the high street, nothing exotic or anything like that. Looks like I'm going to have to do some reading up in how these things works 😀)
ALL motors will draw more power with a heavier load, unless you want to re-write the laws of physics.
Well yes... but lets see if I can explain what I'm thinking.
OK... so you have a row cans on a wall and you chuck a ball at each one in turn. Each can is held at the base to the wall by some gum. One can has one piece, the second can two pieces and so on. The ball is chucked with a constant force each time. If the desired result is knocking the can off the wall then it doesn't matter how stuck down the can is as long as the ball overcomes that (the friction thing). The ball has no knowledge of what forces it will encounter, it either has enough force to do the job (the watch runs) or the can wins out and stays put (the watch stops).
That's like the way I've always thought of it until now.
Now Andrew mentioned the property of the inductance of the stepper motor altering, presumably as the moving parts "linger" for a fraction longer. Which seemed plausible. How much of a factor to battery life though... I have no idea 😀
The ball has enough force to knock down any can. OK. Now what else does the ball do? It transfers its force to the can. The can in turn transfers it's force to whatever it hits.
Conservation of energy. If you are going to throw the ball with too much energy, you will waste it elsewhere. A watt spent is a watt spent. You can do work with it ( move a hand) or waste it ( bearing friction)
I don't think the pulse is actually that decoupled in a watch. Be it a stepper motor or a solenoid, the resistance to movement will effect the power consumed.
Conservation of energy. If you are going to throw the ball with too much energy, you will waste it elsewhere. A watt spent is a watt spent. You can do work with it ( move a hand) or waste it ( bearing friction)
I don't think the pulse is actually that decoupled in a watch. Be it a stepper motor or a solenoid, the resistance to movement will effect the power consumed.
Well I thank all of you for your thoughts, many of them sound extremely logical.
And this,
That really is how I still imagine it. The stepper motor applies enough force (by design) plus a margin (by design). How that total energy is used and apportioned depends on the friction.
Interesting 🙂
And this,
That really is how I still imagine it. The stepper motor applies enough force (by design) plus a margin (by design). How that total energy is used and apportioned depends on the friction.
Interesting 🙂
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