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Old 18-01-2025, 06:22   #1
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Running the NL generator without the oil pressure stop switch

We have friends that have a powerboat that run their generator when they operate the boat. Many things don't work unless they do so, mainly the bow thruster battery charger. (24v). So, in order for them to dock the boat after they cross home, they need the generator to work or some other charging system for their bow thruster batteries.

The generator starts but stops as soon as you release the preheat button indicating a stop circuit issue. I disconnected the oil pressure switch, and the generator runs just fine and shows oil pressure on the oil pressure gauge.

We are having trouble locating an oil pressure switch in Bimini for the NL. However, it looks exactly like the one I just replaced on my Tohatsu 20hp. Exactly.

Can they just run the generator and keep an eye on the oil pressure? What is the likeliness of an actual oil pressure problem in running for like 4-5 hours? Thoughts? The oil pressure switch is at the top of the engine while the oil pressure sender for the gauge is at the bottom, if that makes any difference.
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Old 18-01-2025, 07:17   #2
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Re: Running the NL generator without the oil pressure stop switch

It's up to your friends to take the risk or not.


We don't normally have oil pressure stop switches on our main engines, so obviously it's not a completely crazy idea.
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Old 18-01-2025, 11:14   #3
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Re: Running the NL generator without the oil pressure stop switch

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Originally Posted by jzk View Post
We have friends that have a powerboat that run their generator when they operate the boat. Many things don't work unless they do so, mainly the bow thruster battery charger. (24v). So, in order for them to dock the boat after they cross home, they need the generator to work or some other charging system for their bow thruster batteries.

The generator starts but stops as soon as you release the preheat button indicating a stop circuit issue. I disconnected the oil pressure switch, and the generator runs just fine and shows oil pressure on the oil pressure gauge.

We are having trouble locating an oil pressure switch in Bimini for the NL. However, it looks exactly like the one I just replaced on my Tohatsu 20hp. Exactly.

Can they just run the generator and keep an eye on the oil pressure? What is the likeliness of an actual oil pressure problem in running for like 4-5 hours? Thoughts? The oil pressure switch is at the top of the engine while the oil pressure sender for the gauge is at the bottom, if that makes any difference.
Generators have these to stop them dying early, main engines cannot have these as it would be dangerous… main engines have warning buzzers.
So …Prove that you have oil pressure at the top of the engine by running with the switch out and seeing a huge spray of oil under pressure. Air pressure clean the switch, try it again with the wires connected. If not working then it should be ok until it is replaced as soon as possible. In the mean time make looking at the gauge a priority… like in the next weeks, get one flown in to a future destination.
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Old 18-01-2025, 14:02   #4
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Re: Running the NL generator without the oil pressure stop switch

You KNOW that the correct decision is to NOT run the genset with the protection circuit disconnected, this also shuts down the audible alarm ( depending on which NL genset version and era this is) and there are very few folks who would enjoy sitting watching an oil pressure gauge. Added to the problem is that the alarm is on the end of the lube oil branch to the rocker gear so the pressure gauge might show pressure when in fact there could be a problem with the rocker gear causing a low enough pressure to trip the switch.
If this is the Shibaura NL, loss of oil pressure is fairly common but more on the industrial applications, skidsteers and mowers for no apparent reason.
Your friend might consider lessening the dependence on his genset for crucial docking procedures with a larger battery bank or if its a big motor cruiser…. A standby genset.
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Old 18-01-2025, 14:16   #5
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Re: Running the NL generator without the oil pressure stop switch

Don’t run the genset, absolutely not, do not run the genset…
Oh, but if you do, then….
Generators have these to stop them dying early, main engines cannot have these as it would be dangerous… main engines have warning buzzers.
So …Prove that you have oil pressure at the top of the engine by running with the switch out and seeing a huge spray of oil under pressure. Air pressure clean the switch, try it again with the wires connected. If not working then it should be ok until it is replaced as soon as possible. In the mean time make looking at the gauge a priority… like in the next weeks, get one flown in to a future destination.
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Old 18-01-2025, 15:05   #6
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Re: Running the NL generator without the oil pressure stop switch

Quote:
Originally Posted by jzk View Post
We have friends that have a powerboat that run their generator when they operate the boat. Many things don't work unless they do so, mainly the bow thruster battery charger. (24v). So, in order for them to dock the boat after they cross home, they need the generator to work or some other charging system for their bow thruster batteries.

The generator starts but stops as soon as you release the preheat button indicating a stop circuit issue. I disconnected the oil pressure switch, and the generator runs just fine and shows oil pressure on the oil pressure gauge.

We are having trouble locating an oil pressure switch in Bimini for the NL. However, it looks exactly like the one I just replaced on my Tohatsu 20hp. Exactly.

Can they just run the generator and keep an eye on the oil pressure? What is the likeliness of an actual oil pressure problem in running for like 4-5 hours? Thoughts? The oil pressure switch is at the top of the engine while the oil pressure sender for the gauge is at the bottom, if that makes any difference.
Most people dont have those switches on their main engines. I dont know why they put those troublesome systems on Generators, maybe because they just run a lot while being ignored. But those and other monitors seem to the bane of generators and the most frequent trouble causing things.

Based on past experience helping other people, those systems would come off right after I got a gen set. But I'm a guy who monitors things. New Panda and Westerbeke gens were/are very troublesome with them.
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Old 19-01-2025, 00:38   #7
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Re: Running the NL generator without the oil pressure stop switch

I just reread this Mr JFK… this boat, apart from the fact it’s a power boat, is a Disaster.
Did my/our advice blow up their generator? … well I hope so as then they would be forced to do some seaworthy type maintenance.
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Old 19-01-2025, 04:26   #8
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Re: Running the NL generator without the oil pressure stop switch

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Originally Posted by Cheechako View Post
Most people dont have those switches on their main engines. I dont know why they put those troublesome systems on Generators, maybe because they just run a lot while being ignored ...
Indeed.
Generators often run "unattended"; whereas propulsion engines do not.
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Old 19-01-2025, 11:49   #9
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Re: Running the NL generator without the oil pressure stop switch

A simple solution: Any oil pressure light switch with the same thread should work. If hooked up to a alarm or light. It's not a shutdown but it would be easy to do warning.
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Old 19-01-2025, 12:05   #10
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Re: Running the NL generator without the oil pressure stop switch

I checked the oil level on my old engine and it appeared to be low, so out of an abundance of caution, I promptly went to the automotive store to purchase a longer dip stick.
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Old 19-01-2025, 22:26   #11
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Re: Running the NL generator without the oil pressure stop switch

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A simple solution: Any oil pressure light switch with the same thread should work. If hooked up to a alarm or light. It's not a shutdown but it would be easy to do warning.

Are you sure these are NC like an oil pressure light switch, rather than NO?
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Old 20-01-2025, 00:43   #12
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Re: Running the NL generator without the oil pressure stop switch

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A simple solution: Any oil pressure light switch with the same thread should work. If hooked up to a alarm or light. It's not a shutdown but it would be easy to do warning.
But they are not keeping the basics of their boat seaworthy…why would they go to the trouble of finding the exact thread oil pressure light switch.
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Old 20-01-2025, 10:38   #13
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Re: Running the NL generator without the oil pressure stop switch

There are not many thread types on senders, SAE, Mectric, British Standard Pipe (BSP) thread. Most to my knowledge are NO grounding switches. When the pressure drops the contact is made for a light or a buzzer.

I am suggesting this if you are not able to get the proper sender and just want something as a warning. Something beats just looking at the gauge.
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Old 21-01-2025, 02:44   #14
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Re: Running the NL generator without the oil pressure stop switch

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Are you sure these are NC like an oil pressure light switch, rather than NO?
Most [but not all] oil pressure SWITCHES are Normally Closed [NC].

The "oil" indicator warning [“idiot”] light is illuminated, when here is no oil pressure, and the switch is in it's [normally] closed position.


At rest, the switch is NC, creating a complete circuit to the warning light, illuminating it.
Upon startup, the oil pressure pushes a spring loaded ball [or diaphragm], creating an open circuit, and the warning light goes out.

When the engine is not running, the value of the electrical resistance [from a multimeter] in case of switch with normally closed [NC] contacts should be zero [contacts are connected – switched ON].
In case of switch with normally open contacts [NO] resistance should be infinite [contacts are disconnected – switched OFF].

When the engine is running, the value of the electrical resistance in case of switch with normally closed [NC] contacts should be infinite [contacts are disconnected – switched OFF]
In case of switch with normally open contacts [MO] should be zero [contacts are connected – switched ON].
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Old 21-01-2025, 04:46   #15
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Re: Running the NL generator without the oil pressure stop switch

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Most [but not all] oil pressure SWITCHES are Normally Closed [NC].

The "oil" indicator warning [“idiot”] light is illuminated, when here is no oil pressure, and the switch is in it's [normally] closed position.


At rest, the switch is NC, creating a complete circuit to the warning light, illuminating it.
Upon startup, the oil pressure pushes a spring loaded ball [or diaphragm], creating an open circuit, and the warning light goes out.

When the engine is not running, the value of the electrical resistance [from a multimeter] in case of switch with normally closed [NC] contacts should be zero [contacts are connected – switched ON].
In case of switch with normally open contacts [NO] resistance should be infinite [contacts are disconnected – switched OFF].

When the engine is running, the value of the electrical resistance in case of switch with normally closed [NC] contacts should be infinite [contacts are disconnected – switched OFF]
In case of switch with normally open contacts [MO] should be zero [contacts are connected – switched ON].

Indeed, and that was my point.


On many gensets the oil pressure shutdown switch is NC.
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