Hobbs meter unexplained 23.8 hourss increase

[vasco]

Local FBO changed the oil in my 2007 O3.  As my habit and training, i check the Hobbs prior to each and every flight and immediately noticed this increase.  i went to the mechanic, not a Mooney Service Center, and he could not explain.  While i did not routinely check the tach on the G1000, it appears not to have experience this increase.  upon starting, i noticed that the #1 battery barely had enough juice to turn the engine, forcing me to start with the #2 battery.  i finished my prior flight with the #2 battery (my last step in my shutdown routine is to switch batteries). 

During transition training i was told that Hobbs came alive after 55 kts.  What could account for this jump?

Thanks.

Vasco

[Cruiser]

Take-off ?

Maybe someone at the shop wanted to "warm up the oil" and check for leaks? Or the girlfriend was surely impressed by a flight in an Ovation. Cool.

Actually, all kidding aside, it sounds like something electrical was left on and activated the HOBBS. You need a MSC to help with the reason.

[carusoam]

Vasco,

Hope this sheads some light, or maybe helps you along in the right direction.

Section VII of the POH for Ovation 1

25: Hour Meter - Indicates elapsed time while engine is running...Hobbs meter is mounted on the bagage compartment bulkhead

It seems like the master switch may have been inadvertently left on.  In the old school, an oil pressure switch was used to apply power to the Hobbs.  I am not as familiar with the new school.....

Since oil pressure is a long way from the bagage compartment, I would be looking for a combination of the ignition key on and the master switch on and see if the Hobbs is active with that simple combination.

Scenario: Mechanic runs engine to warm oil for changing.  Cuts engine using mixture control.  Inadvertently leaves master on and ignition switch on both.  Is it possible that this simple combination will run for 23.6 hrs until the battery is exhausted?

In the old school, the turn coordinator would run with just the master on giving a nice audible warning that the master was left on.   According to my wiring diagram the TC does not come on until the Radio Master is on.

The Hobbs does not seem to show up in my electrical diagram or CB panel diagram in the POH.

Let us know if you find what combination turns on the Hobbs.

One other note:  The landing gear Airspeed Safety Switch operates at 60kts +/- 5 kts.  If this were also used to activate the Hobbs meter, then there is concern that the A.S.S. may be stuck in the closed position.  This is just conjecture until additional wiring diagrams or knowledge can be obtained.

With the hobbs in the trunk, its hard to tell when it comes alive...

-a-

[JoeSpeed]

The Hobbs in the Late Model Ovations are wired thru the airspeed safety switch. The + to the hobbs  is always hot it it connected to the baggage light circut. When the a/s exceeds 60+ knts the Hobbs is grounded thru the a/s safety switch. The a/s safety switch diaphram closes 2 circuts one for the gear and the other for the hobbs. The switch comes with a wiring diagram that is incorrect (even from Mooney) . Contact Bill Wheat @ Mooney for the correct hookup. You can find the hobbs on the electrical schematic in the center on the top of the diagram next to the baggage light.

[vasco]

Since the oil change, I am now recording the tach on the G1000 as well as the Hobbs.  i have noticed that the stage lengths on the three flights have been identical to the Hobb.  Obviously different starting times, but the difference (time of flight)  between the start and end of each flight is identical.  I thought there should have been a difference.

[JoeSpeed]

The hobbs registers time in tenths/ Hr of when the airspeed is greater than 60 knts. The G1000 engine time measures like a Tach ( Cruise rpm 2200 1-1 time) at 1100 rpm 50% of the time, Thus is you have a long taxi or hold before take off the Tach will register but the hobbs will not ( unless you have a 60 knt wind on the Ground) Hope this helps

[vasco]

Thank you all.  Taking to a Mooney Service Center.

vb

[vasco]