Power reserve question?

[Blubarb]

I am assuming it depends on the watch, but generally, and wearing over a 24 hour period,  how much energy can a rotor typically input into the power reserve.

And secondly if your watch is in the last 25% of it's power reserve will that cause the watch to speed up slightly? 

Thanks

[AdamC]

Depends how active the wearer is. I would have thought someone regularly on the move would keep it +/- 90% powered. The converse is true. At 25% reserve it may still keep good time but if anything would surely slow down if anything as the power ebbs away.


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[Marc]

2 hours ago, AdamC said:

At 25% reserve it may still keep good time but if anything would surely slow down if anything as the power ebbs away.

Actually as the power reserve gets low the principal impact on the balance is on amplitude which drops considerably.

Counterintuitively this can actually result in an increase in rate and the watch can speed up as the power reserve gets very low, although I've never quite worked out the mechanism behind this effect, but I have observed it. I suspect that it is due to the relationship between momentum, static friction, and dynamic friction breaking down at very low amplitudes and energy levels and the impact that this has on the oscillating system.

The degree to which this effect can be observed will also vary from watch to watch depending on how much clearance there is between the curb pin and the boot on the regulator. In an ideal world the gap between the two will be exactly equal to the thickness of the hair spring resulting in the H/S being always in contact with one or the other and the effective H/S length remaining constant throughout each balance oscillation.

In reality the clearance is usually slightly greater than the thickness of the H/S which means that for a fraction of the balance rotation the H/S is not in contact with either boot or curb pin and the effective length of the H/S increases to its full length. With good amplitude the impact that this has on timing is insignificant but as the amplitude decreases with reduced power from the M/S the proportion of the balance swing that is on the full H/S length rather than the regulated H/S length increases and the effect that this has on slowing the rate increases. Also the greater the gap between the curb pin and the boot the greater this effect will be.

This will obviously counter any increase in the rate that may result from the very low amplitude resulting from low M/S power.

I guess what I'm trying to say is that the exact impact on rate as M/S power reduces is almost impossible to predict as there are at least two mechanisms in play which counter each other to variable degres.

A rotor can in theory keep the main spring fully wound all the time if it is continually moving at an appropriate rate and in the right direction (remember not all auto winding systems are bi-directional), and the autowinding system is in an appropriate state of repair.

As @AdamC says though it is highly dependent on the level of activity of the wearer.

For a real life example though I have a Vostock Amphibia with a 2416b auto-wind movement. This has a quick set date that requires cycling back and through the midnight point to correct the date if required, and becaouse of the wobbly crown characteristic of the Amphibia this is a PITA so I keep it on a winder when not wearing it. The winder rotates for 1 hour in every 4 at about 9rpm. Left on this winder for over two weeks at a time this watch has never stopped so I would suggest that the input from the winder is pretty close to the output of the watch running.

[Weetabix]

"Actually as the power reserve gets low the principal impact on the balance is on amplitude which drops considerably.
Counterintuitively this can actually result in an increase in rate and the watch can speed up as the power reserve gets very low, although I've never quite worked out the mechanism behind this effect, but I have observed it."

Perhaps with a lower amplitude there's not a proportional reduction in angular velocity of the balance? Lower amplitude at same angular velocity would give a higher rate?

[Nucejoe]

An hour on wrist fully winds brand new pieces. Actual power reserve declines due to wear and dried lubricants. High speed reversers in winder module push the oil out  of bearing, which is a principle cause of selfwinder deficiency.

Clockboy told about his experience with use of fixodrop, which I think helps keep the oil in, therefore maintains good winder efficiency.

No need to live with an inefficient winder, just service it. 

Best

 

[jdm]

1 hour ago, Nucejoe said:

High speed reversers in winder module push the oil out  of bearing, which is a principle cause of selfwinder deficiency.

That is, if there are reverser wheels and such complications. Seiko (on most movʼs) has been doing without since some 60 years using the magic lever. It still requires periodic service but it's a much more compact and simpler system. 

[Nucejoe]

8 minutes ago, jdm said:

That is, if there are reverser wheels and such complications. Seiko (on most movʼs) has been doing without since some 60 years using the magic lever. It still requires periodic service but it's a much more compact and simpler system. 

Right, Perhaps Seiko felt smart trying to do without reversers yet ended up with its sophisticated excenter mess, to match a date jump always hanging in between half of yesterday and the rest of today. lol or whatever.    Best

[jdm]

5 hours ago, Nucejoe said:

Right, Perhaps Seiko felt smart trying to do without reversers yet ended up with its sophisticated excenter mess, to match a date jump always hanging in between half of yesterday and the rest of today. lol or whatever.    Best

Yes, I'm sure they "felt smart" in selling millions of pieces