Adding engine total hour "Hobbs" meter / How?

[sophieoreo]

I'd like to connect an engine 'total running time' meter, often called a 'Hobbs' meter. Wondering how to wire it such that the meter gets +12 VDC only when the engine is running (or, perhaps more specifically, when the Alternator is producing DC). Since the Balmar 60 series alternator DC output is connected directly to the batteries, that won't work (as the meter would turn continuously). The Balmar has a 'Diode Trio Output' that (apparently) goes low (to ground) when there is an alternator failure - seemingly meant for a "dash light" indication of trouble, so this seems like a dead-end. Any ideas on how / where to connect would be appreciated!

[a64pilot]

Usually a Hobbs is wired through an oil pressure switch, no oil pressure, engine won't run long.

[john61ct]

There are little battery-powered units that just wrap a sensor wire round the top of a spark plug.

The better ones are resettable, store maintenance interval checkpoints.

[Bleemus]

This might help . . .

[Wotname]

Originally Posted by a64pilot

Usually a Hobbs is wired through an oil pressure switch, no oil pressure, engine won't run long.

To expand on this; not just any oil pressure switch. Some have only one terminal with will usually be "normally closed" which means the are contacts open when oil pressure is present. Two terminal switches may be "normally closed" or both. Three terminal switches are always both.

The OP needs a "normally open" set of contacts i.e. the contacts close when oil pressure is present.

Of course a relay can be used if the existing switch is "normally closed". The relay can invert the switch logic.

[toddster8]

FWIW, I've been through three of the ISSPRO electronic hour meters. They don't seem able to last through a winter in the cockpit. Third one mounted inside the companionway, OK so far.

Suggests a faulty learning curve - should have switched to a mechanical dial unit by the time the third unit came along...

Hey, that means my engine still only has 16 hours! Great resale value!

[EmeraldCoastSailor]

Sorry for the deviation but I thought I'd toss out an idea that worked for me; my Yanmar hour meter has performed poorly but seems to have correct hours when it chooses to show them. A couple years ago I installed a cheap vibration meter and it seems to work well. I log hours for most every trip so if it fails I won't lose track of anything.

[doublewide]

Our Yanmar meters both worked well for a couple of years then intermittently for a while, then occasionally, and finally not at all. I kept track of engine hours in the log until I found some meters, and then installed Seachoice engine hour meters, about $40 each, as follows: checked all the pins on the back of the ignition switch panel until I found one that showed 12V only when the ignition was in the "on" position, then wired the meter to that pin. It works fine.

[roverhi]

Bought a cheap hour meter on eBay. Wired it to the switched hot side of the ignition. Works great and no messing the oil pressure sender.

[Nineteen]

Originally Posted by a64pilot

Usually a Hobbs is wired through an oil pressure switch, no oil pressure, engine won't run long.

+1 all light aircraft and plant are done this way👍

[ValiantV]

Originally Posted by Nineteen

+1 all light aircraft and plant are done this way👍

Agreed, sometimes an ignition switch can be turned/left on while the engine isn't running and can mess with the actual record of running time.

[model 10]

Originally Posted by ValiantV

Agreed, sometimes an ignition switch can be turned/left on while the engine isn't running and can mess with the actual record of running time.

Airplane maker Cessna was so clueless for years. On some models the fuse for the Hobbs was under the glove box. You could pull the fuse while you were flying. Hours are billed from the hobbs, not the tach.

[Nineteen]

Originally Posted by Guy

Airplane maker Cessna was so clueless for years. On some models the fuse for the Hobbs was under the glove box. You could pull the fuse while you were flying. Hours are billed from the hobbs, not the tach.

[emoji106]

[ValiantV]

Originally Posted by Nineteen

[emoji106]

Any FBO or flying club worth its salt has seen this clever trick before and is onto would-be cheats.

Take a plane out for three days, and two hours shows up on the Hobbs - no real problem to compare the tach time and bill the pilot based on tach hours. Though tach time and Hobbs time do different somewhat, it's a pretty consistent variance and a "malfunctioning" hour meter won't stump too many FBOs for more than a minute or two.

A halfway bright pilot, AME, or even line man can figure out that the amount of fuel left in the tanks when the plane is returned is a pretty good indication of how many hours the engine has been run.

Then again, I suppose one could cheat on their taxes too. The IRS is so "clueless".

[Nineteen]

I used to have owners that would even try and hide hours - and thats how people get killed....
Cheers Tom