Three wire Hobbs Meter

[cbogie]

Group,

My Bravo has a recently failed Hobbs meter that has three wire input rather than the two wires that I am familiar with.  Red, Black and Blue.   Based upon the wiring diagram, it looks like it has ground, Power (from the original Tach circuit breaker) and an output from the original tach back to the Hobbs (presumably to only activate the Hobbs time above a certain RPM.

Questions :

1. Does the current JPI EDM 930 supply the signal back to the Hobbs to activate it above a certain RPM?

2. Given that the JPI is certified for primary replacement and has an internal Hobbs function, do I need to even worry about replacing the original analog Hobbs?

Thank You

Charlie

[LANCECASPER]

When they installed a 930 on the Bravo I had they took out my Hobbs

[adverseyaw]

Same. I have direct confirmation on this, as we were going to leave the old Hobbs meter in. Once everything was wired up, my mechanic realized he couldn't get the three-wire Hobbs to work with the JPI 900 (similar to the 930) and had to pull the analog meter out.

The 900 has a screen that shows both hobbs and tach time, it's activated by holding the center two buttons. I assume the 930 is the same. There's also a setting to show the tach time on the main display.

[kortopates]

4 hours ago, cbogie said:

Group,

My Bravo has a recently failed Hobbs meter that has three wire input rather than the two wires that I am familiar with.  Red, Black and Blue.   Based upon the wiring diagram, it looks like it has ground, Power (from the original Tach circuit breaker) and an output from the original tach back to the Hobbs (presumably to only activate the Hobbs time above a certain RPM.

Questions :

1. Does the current JPI EDM 930 supply the signal back to the Hobbs to activate it above a certain RPM?

2. Given that the JPI is certified for primary replacement and has an internal Hobbs function, do I need to even worry about replacing the original analog Hobbs?

Thank You

Charlie

1) no

2) Yes, and you can set JPI set the Hobbs to where you're old meter stopped or whatever estimate you want in the factory programming mode.

But FYI there is Hobbs time and tach time availabel on your EDM. Hobbs time measures 1:1 just like a rental hobbs meter does. But Tach time measures the same as your Mooney Hour meter does which measures Tach time of course is not 1:1 measure of elapsed time but the time the engine is at average cruise RPM. Additionally in the EDM, you can change the default RPM used by tach time to what your Mooney tachometer was based (i.e. typically about 2450 rpm).

When it comes down to it, we only care about tach time, its the actual engine time and airframe time we want to record for maintenance records purposes.  Hobbs time is usefullness is limited to logging Pilot Flight time (actual elapsed time). If used in aircraft records, your cheating yourself since on average tach time is about 0.2 less per flight than hobbs time and an even greater differences builds if for long ground ops with say several full stop taxi back landings.