Hobbs meter

[Ppizzo]

Does any one know which terminal on my alternator I should connect my Hobbs meter to?

[A64Pilot]

Must be a Mooney thing, only Hobbs I’ve done were connected to the battery bus and an oil pressure switch turned it on and off.

There are only two terminals on an alternator with power? The field which has power whenever the master is on and the Alt output that has power whenever the Master is on, so neither would be good for a Hobbs?

Maybe I’ll learn something here

Edited March 16, 2022 by A64Pilot

[Mooneymite]

Depends on what time you want to record.

Master switch "on" time.

Engine oil pressure time.

Weight on the wheels time.

Airspeed above 40/50/60 knots.

For engine time, I think only flight time counts toward TBO on our engines, so while oil pressure tells you how long the engine has run, it may not be an accurate record of flight time.

The Garmin 430/530 (and I suspect other GPSs as well) will record time when ground speed is above 40 KTS, so that would be a good indicator of flight time, as well.

Lots of choices.

 

[PT20J]

Some Mooney hobbs meters are driven off the alternator and some are a three wire unit driven by the B&D electric tach. 

[carusoam]

Got a pic of your alternator, and your Hobbs meter?
 

 

-a-

[Yetti]

I would not run another battery wire through the fire wall.   If you want to record Master switch on time, you can hook to the amp meter shunt that is located on the top behind the panel on the passenger side.

[Ulysse]

On 3/17/2022 at 5:46 AM, PT20J said:

some are a three wire unit driven by the B&D electric tach

thanks! that explains why my Hobbs (3 wire) stopped working after avionics upgrade.

[Warren]

Hobbs on the K models are driven through/by the tach.  The actual run rate is correlated to the engine RPM.  If it quit working after an upgrade the wires were disconnected or, if the tach was removed, there needs to be a replacement signal to make it work.  Many engine monitors include an hour meter and thus replace the Hobbs meter.

[PT20J]

1 hour ago, Warren said:

Hobbs on the K models are driven through/by the tach.  The actual run rate is correlated to the engine RPM.  If it quit working after an upgrade the wires were disconnected or, if the tach was removed, there needs to be a replacement signal to make it work.  Many engine monitors include an hour meter and thus replace the Hobbs meter.

I think the tach-driven Hobbs on my M20J was accurate at 2500 rpm, but I never found that documented anywhere.

On my G3X/EIS, I had the engine hours set to record at >300 rpm and accurate at 2500 rpm to mimic the Mooney Hobbs. I had the total hours set to flight time. I now use the total hours for maintenance logging per the FAR Part 1 definition.

Skip

[A64Pilot]

Tach time is simply a mechanical meter that is RPM dependent, RPM they are correct at is often written on the data plate.

Hobbs meters are often used in rental aircraft and record engine run time, regardless of RPM, that’s why they are oil pressure triggered.

Flight time is often just that, either A/S switched, weight on wheels switch(squat switch) or sometimes gear switched, I have a clock that records flight time based on wheels up time, came from the factory I’m sure.

Big airplanes often schedule maintenance based on flight time, and turbine operating time is often flight time so all that ground time doesn’t count towards component retirement life etc