Hobbs meter

[Arcticspud]

I have install new hour meters on my boat. The old ones in the tach stopped working.

My question is: How to you wire them to the oil sending unit so the meters only run when the engine is running?

Mahalo

 

[FF]

Tou will need a T .

The oil pressure sending unit should not be messed with as its voltage shows as oil pressure.

Any NAPA will sell a pressure SWITCH that closes or opens a circuit when oil pressure is felt. Some are used to send an alarm if oil pressure is lost, you need the opposite.

Should be on the Cole Hersey site.

Lazy folks simply wire the meter to the key switch.

 

[Arcticspud]

My key switches are hot so that will not work.

 

[Ski in NC]

Engine high temp/low oil press alarm circuit is hot with engine running, not hot off. You could use that to run your Hobbs.

 

[Arcticspud]

It's a Cummins panel so are you suggesting I splice into the low oil pressure light?

 

[Ski in NC]

If you have the factory Cummins panel, you do not have traditional NC/NO temp and oil switches. But you do have an ignition switch that goes hot when you turn the key on. You can put the hobbs on that, it will clock when key is on. Or if you have no key, put it on the fuel shutdown solenoid on the injection pump. If it is power to stop, you can install a new oil pressure switch with NO contacts and power it through that. Depends on how your boat is wired.

 

[Arcticspud]

I will have to check the key. I know one side is hot with the start battery on. I will check to see if the other side is cold until the key is turned. That would make things a lot simpler.

 

[C lectric]

If you have 'turn the key' switch to start it should have the one hot terminal as described when the battery sw. is on. There should be two more terminals for three total.
-One hot anytime when battery sw. is on. This is usually the ENGINE OFF.

-One will be hot with the FIRST TURNED key position which is the RUN position. This is the one you connect the hour meter to.

-One will be hot ONLY when actually cranking the engine and is the SECOND TURNED position. It will also be a momentary which is spring loaded to flip back to the RUN position when the key is released.
Note it is powered ONLY when you turn and hold the key to that position.

 

[AKDoug]

Definitely the oil pressure sensor will not work, I tried that. Time to crawl around with a multimeter and poke a hole through the insulation if you can't find a connection to measure at.. The sensor sends out differing voltages as the oil pressure changes, so it won't power your Hobbs. It will probably either be red, or have a red stripe on it.

 

[FF]

IF you wish there are marine ignition switches that work better than the off,start,run variety.

Like your car they have an accessory position .

This is very useful , as it would run your Hobbs , although a good use is to hook it to a merge solenoid ($18. at the RV place) and have the engine alt automatically charge the House batts , no thinking required , no switch position puzzles.

Wiring sensitive radio and other electronics is also a good idea (as in your car) should the starter fail to disengage , it becomes a DC generator , that can reach 50-100V easily.

 

[Arcticspud]

I wired it to the "dead" post on the key and it now functions properly at least from the standpoint of the hour meter will run only with the key in the on position.

Thanks for the help.

 

[HopCar]

I once had a pressure switch try to kill me.

I had landed my Cessna at Ft. Lauderdale to go through customs. When I went to leave, I started the engine, checked the gauges, and let it warm up while I listened to the airport information on the radio.

A fellow came up to my plane, tapped on the window, and pointed down. I shutdown the engine, got out and looked where he had pointed.

Oil was pouring out of the plane. It turned out that the diaphragm, on the pressure switch that controlled the Hobbs meter, had ruptured.

If it had failed ten minutes later I would have been looking at a stopped prop, trying to decide wether to ditch in the ocean or try to do a 180 and land downwind on the runway I'd just left.

 

[Forkliftt]

Yow. Scary stuff!


1983 Present 42 Sundeck
Twin Lehman 135's

 

[Arcticspud]

I met a guy who had something similar happen except he was in Dodds Narrows in BC when it happened. That would not be fun.