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I have finally have taken the time to determine the efficiency of the auto winding mechanism in the Buren cal 11 thru 15 movement. I want to start with a comparison of manually winding the movement compared to how many rotations the micro rotor needs to do the same. This is an initial report. I decided to do this because I could not find this information anywhere and there has been a fair amount of discussion on the subject.
Manual winding - 3 to 4 twist on the crown (depending on the person winding = around 360 degrees on the mainspring barrel arbor) is equal to:
Auto winding - 180 or so full revolutions on the micro rotor.
This should run the movement for 6 to 8 hours (from completely wound down) without the second hand engaged. If the second hand is running, subtract around 1 hour.
This example is intended to show the efficiency (or inefficiency) of the auto winding mechanism in this movement. If anyone else has done this test, I would like to hear from you. More later.

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S. Craig Bergsma

I have been trying to get round to one of my cal 12 watches undetake the test and post the results for you.

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Jim

"You have Control".

Correction - I need to clarify this statement:

"Manual winding - 3 to 4 twist on the crown (depending on the person
winding = around 360 degrees on the mainspring barrel arbor) is
equal to:
Auto winding - 180 or so full revolutions on the micro rotor."

This is obviously not a very accurate measurement as it would vary a lot from person to person. So instead of using "twists" I will from now on use one full 360 degree revolution on the crown as a bases. One full revolution on the crown is equal to about 120 to 130 degrees on the mainspring arbor or more accurately (I just checked), 3.2 full revolutions on the winding crown is equal to 360 degrees on the mainspring arbor. So it would be better to use 3.2 full revolutions (3.2 would be a little tricky but it does not have to be exact) on the crown as a basis to see how long the movement will run from completely run down. This should still run the movement for 6 to 8 hours (from completely wound down) without the second hand engaged.
I will start this manual test this morning on a movement that I serviced a couple of days ago and report back. After that, I will put it on the auto winder for 180 revolutions to see if I get the same results. I do not necessarily recommend auto winders for this movement, I just got one to set up a standard test just for this movement.
I expect to see a lot of variation in this test depending on the condition of the movement and prior service.
Update - 1st manual wind test (3.2 revolutions on the crown) ran for 6.25 hours yesterday.
Second update - 2nd test on auto winder test equivalent to 3.2 revolutions on the crown (took 22 minute on this auto winder) ran almost exactly the same time of 6.2 hours. I did not count the revolutions on the auto winder for this test but will do so and report back later.

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S. Craig Bergsma

Thanks Craig for the update. I have recently had one of my Cal 12 serviced, so I will concentrate on that one.

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Jim

"You have Control".

HI Craig,

I run the Cal 12 overnight. My report is that on 3.2 winds (or as close as I could get to it) the movement ran for exactly 8 hours. Uncanny really, as it stopped within the minute of 8 hours. I did not run the centre second in stop watch mode. I can't attest to the accuracy of timekeeping over this time as power is close to rundown and I was asleep. Watch is usually accurate, but may have been affected somewhat by low reserve.

I will run again and report any variance to this.

Second test. 8 hours 7 minutes.

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Jim

"You have Control".

8 hours is the best you can get based on several other tests that I have done already. Thanks for the report.

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S. Craig Bergsma