POWER EXHAUSTION OF CHRONOGRAPHS

And I explain what the title means:

Mechanical watches get their power from a spring which is initially fully
compressed (by winding) and then expanded in a very controlled way.

The amount of stored mechanical energy is determined by the physical
properties of the spring and is fixed.

The rate of releasing the energy is also determined by the various gears and
resonant devices the manufacturer installs in order to achieve the required
accuracy.

Having said that one can conclude that the time from full compression to
complete release is also fixed, namely 40-48h usually.

My question refers to chronographs and is the following: Will the power
reserve of a chronograph (in hours) decrease when the chronograph function is
engaged, and why?

On long international flights I have operated my Pilot Chronograph, which is
automatic, for 11 hours and the auto keeps it wound so no difference in power
reserve noted.

I have done the same with a Speedmaster (power reserve 48hrs), which is manual
wind and I wind it every morning - same result.

Both these watches have a 12 hour counter, so I assume they were made for the
chronograph to run at least that long.

Due to the additional strain imposed by the chronograph gear train, I would
assume the power reserve would be reduced slightly- but I think it is
insignificant.

Well, in order to verify this one needs to do the experiment with a watch laid
flat on a table. I will do this with my Speedmaster and revert.

I believe that when chronograph is engaged the watch will stop earlier.

Being an engineer myself I have an answer that I think makes sense, but let me
first see what the test will show.

Wind the watch fully and set the time to 12 Noon. Start the chronograph and
note the time it stops.

Wind it fully again, set it to Noon and note the time that it stops without
Chrono.

Results will be interesting and will keep you busy for 4 days :o)

Experiment startet exactly as you describe it Mark two hours ago :)

I will keep you posted.

Hi Panos, being an engineer myself I understand your logic, however, I do
recall that IWC's Stefan Ihnen (Technical Director and responsible for
developping all the in-house movements from the last 10-15 year) explained
that the chrono does NOT take additional power when you keep it running.

Some of the guru 's here might be able to explain how, I can't, sorry.

Regards, Bob

Ok Bob, then let me tell you what I believe. If the effective power reserve
were the same independently of if we have the chrono running or not then -in a
sense- we would have achieved the eternally moving mechanism :)

What I believe is that the key to answer this question is that we should not
take as granted that the spring will release ALL its energy each time.

Since the "force" that the spring provides is "proportional to the square of
its elongation" this means that the force which brings the gears to motion
decreases significantly as the spring comes closer to its idle (fully relaxed)
state.

It will unfold to the point when the "residual force" (the force it can still
produce) becomes equal to the counter force (bending moment actually) that
the friction between the gears and the inertia of the moving parts create. Now
if you additionally engage the chrono, this means that you add more gears and
inertia into the equation. Hence that "counter force" becomes larger and the
spring will stop unfolding at an earlier point.

I hope that my experiment will prove this theory of mine.

UPDATE:

First part od the experiment concluded. The Flightmaster with its chrono
running completed 44h 30m and 58s.

Hmm, this is even higher than the 44h that cal911 "officially" yields. Let's
see...

Interesting indeed

Beautiful Flightmaster :o)

Of course, any additional gear in a transmission requires energy. And the
chronomechanism has additional elements.

But the efficiency of gear transmission is very good, aprox. 95 - 99
percent.That is quite a very small amount of lost energy for power reserve and
has no practical impact for the user.

Engineers justify almost all about energy :-)

Hey Panos,

Thanks for running the experiment. Very interesting.

Well well well, experiment completed few hours ago.

What I believed in theory pretty much proved by the results.

Without the chrono engaged the Flightmaster run for 51h and 21 minutes !!!!

After stopping it was obvious that the power was completely exhausted which I
know because even after shaking the watch, it worked only for 5-8 seconds and
stopped again. When the chrono was engaged, this same shaking made the watch
run for several more minutes.

While I am surprised by the fact that a watch with a nominal power reserve of
44h can run for more than 51h, I think that the difference in the two setups
probably proves what I theoretically believed.

The engagement of the chrono introduces a bit more inertia and friction which
stops the mechanism earlier without fully exhausting the energy stored in the
spring.

Fascinating!!!!

Thanks for spending so much time on this experiment

I will now try the same with my Doppelchronograph since the Flightmaster is
some 50 years old.

And what IWC collectors forum this would be if we use other brands' watches to
prove our thoughts :) :)

This is great Panos. Thanks for your effort in documenting the experiment.
Looking forward to the IWC results.

Here we are again. While the test is running on an IWC chronograph too, I run
it once again with the Flightmaster to see if I would get a consistent result.

Well I did as the Omega run for eactly 51h without the chrono and 43h and
10min with the chrono engaged.

Soon I will have the results on the IWC and on a Poljot Kosmonaut chronograph.

Another parameter is decisive for interpretating the measurements: When was
the last service?

Because the viscosity of oil changes, it becomes more viscous with increasing
age.

That increases the friction and requires more energy as it would use with
fresh oil.

This is absolutely right. The different watches that I am experimenting with,
will probably show that. One is very old without recent service, the other is
newer and serviced and the 3rd is brand new.

The Flightmaster results are astonishing

Cal 911 has surely demonstrated robustness of design and longevity.

Same experiment with my IWC Doppelchronograph just finished.

As this was an automatic movement I gave it each time 50 full strokes to make
sure we start from the same point.

It yielded 51h and 20min without the chrono and a mere 41h before it stopped
due to friction with the chrono engaged.

So pretty much the same result with the Flightmaster.

Now I am expecting the Poljot to finish some time tomorrow.

Just now the 3rd part of my experiment finished.

Poljot Kosmonaut stopped at exactly 61h after full winding with the chrono
engaged.

Amazingly (or maybe not) few days ago it had achieved almost exactly the same
power reserve without the chrono: 61h and 7min.

As I 've mentioned already the Poljot is brand new. So I guess the friction
due to ageing and oil properties change, is the dominant factor.

Case closed :)