Hobbs stopped working after panel upgrade

[Ulysse]

My Hobbs meter has stopped working since I upgraded to a glass panel. I suppose the signal which drove the meter is no longer available after the upgrade. The installer told me that my meter is of an unusual type with 3 wires instead of the 2 wires meters he has always seen in Mooneys. 
Any idea on how to get it back to a working condition? 

I now use the g3x flight log to record times. However it starts counting as soon as the engine starts. I cannot find any setting to make it start counting when the engine passes a certain threshold (for example 2400 RPM ). Is this possible?

[carusoam]

Got a pic of which one you have?
 

Or where it is mounted?

Or what sensor it was connected to to know when to start the timer?

Some use oil pressure switch.  Others use a airspeed type switch.  Some use power on…

PP thoughts only, not a mechanic…

Best regards,

-a-

[MikeOH]

Hmm, a little confused why this is now your problem.  You had a WORKING Hobbs when you took your plane to the installer...now it is broken.  The fact that it is "an unusual type" doesn't seem persuasive to me; it was working just fine.  My minimally educated guess is that the installer accidentally or intentionally (as you say, signal source gone) disconnected one/some of the wires. But, as carusoam says, it's usually the oil pressure or airspeed.  Again, I'd discuss with the installation shop...they should make it right, IMHO.

[Warren]

Pretty common for many Mooneys (this is from the Encore wiring diagram).  Black and red are power and ground.  The blue wire is a signal from the tach that varies the rate of hour accumulation with rpm.  I am guessing the tach was removed and no more signal available.

[carusoam]

Nice work Warren!

Best regards,

-a-

[Warren]

49 minutes ago, Ulysse said:

I now use the g3x flight log to record times. However it starts counting as soon as the engine starts. I cannot find any setting to make it start counting when the engine passes a certain threshold (for example 2400 RPM ). Is this possible?

Under the EIS configuration page there are options to setup engine time and total airframe time.

For engine time, you specify a minimum RPM threshold that starts counting and a reference RPM that equals clock time.  Once above the minimum RPM, the engine time is calculated based in current RPM/reference RPM.

Wow, that sounds confusing.  Hopefully it helps.

ie Reference RPM of 2400 rpm means that if the engine is running 2400 RPM, engine time and clock time will be equal.

if the engine is running at 90% of the reference RPM -- 2160 RPM, the engine time recorded with be 0.9x actual time.

 

Total Time has a few options for how time is recorded.

[PT20J]

There can be two timers configured in the G3X EIS:

Engine Hours

Total Hours

 

I believe that your old electronic tachometer was set to drive the Hobbs at actual time when registering 2500 rpm. So the logical way to set up Engine Hours Is to begin recording when rpm >  300 (or any rpm lower than idle speed) and set the reference rpm at 2500. 

Total Hours can be any of the options @Warren pointed out depending on what you want to use it for. One idea is to set it to flight time and use it for maintenance records. FAR Part 1 defines

Time in Service with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.

If you want to use it for logging pilot time, you might set it to record whenever  the engine is running since that better approximates the FAR Part 1 definition of Flight Time

Pilot Time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing.

Skip

 

[Ulysse]

Thank you very much @Warren and @PT20J. Both my questions have been answered!

Where do you get all the documentation that you seem to have? I think @enciclopedia is a better alias than PT20J 

[Warren]

I get most of it from the dealer install manuals and personal experience.  These are not publicly available manuals (sometimes you can find older copies on the internet).  I try to share the information to help MooneySpace users understand their options and work with their Garmin dealers.  As a bonus, it is frequently a learning experience for me too as I dig into some of the details.

[RobertGary1]

Same here. The wire got pulled during install. 

[PMcClure]

The Garmin G3X did not play well with the OEM Hobbs meter. Installer confirmed they are unable to use the original Hobbs. So I had them remove it and replace with a blank. I could not accept inop gauge but have the same information on the G3X.

 

[1964-M20E]

broken hobbs meter is  not all bad now you can fly for free. 

[stevesm20b]

I had the same problem. My hobbs meter stopped working after some avionics work. Found ground wire going to hobbs meter had been cut or disconnected. Made up new ground wire and then it worked fine.