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Old 10-05-2013, 01:36   #1
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When is a Marine Generator not a Marine Generator!

Well, when it does not switch off at the first sign of not getting any sea water.

And this I guess accounts for 95% of all generators out there. (including mine)

And what happens when your marine generator does not get any sea water...... Well it firstly overheats the impeller which then deposits its blades in the heat exchanger which at the very best, reduces its cooling abilities.
If you have a plastic water trap then the material will start to melt along with damage to the exhause hose. The exhaust overheating sensor will/should come around about now, but this depends a bit on the design, maybe it does or maybe it takes a bit longer until it feels the heat. The engine fresh water cooling is heating up so this should switch off the unit soon.
The whole process probably takes between 2 and 5 minutes to switch off your generator.
The amount of damage varies with the amount of time that passes. If enough time passed it is not just the impeller,heat exchanger,water trap and exhaust hose, it become alot more serious.
Dont believe me?, then start up your generator, set your stop watch and close the seacock. (But dont blame me if it damages anything!!!)
Report the time to shutdown in this thread.

So what needs to be done to make 95% of all Marine Generators into real Marine Generators!.

I did the following....
1-measured some things...time to damage impellor (20 seconds)...Time to exhaust overheat shutdown (3 minutes).... Time to fresh water shutdown (not sure as exhaust overheat was first). I have a metal water trap so no damage is done.
2-The next step was to measure the raw water pressure when the pump is pumping (0.8bar).
3-I then (3 years ago) fitted a pressure switch set to 0.4bar and wired this into the other shutdown circuits.

So now I can close the seacock and the motor shuts down immediately with no damage to anything. It works just like a switch!

It would be interesting to see if anybody actually does this test and reports that their generator immediately stops.
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Old 10-05-2013, 01:56   #2
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Re: When is a Marine Generator not a Marine Generator!

That sounds like a great idea. Only question -- how do you disable it at startup? Wouldn't it prevent you from starting the generator?

I have suffered from the same problem you describe -- clogged sea strainer, toasted impeller, shutdown on fresh water overtemp, and permanent damage I am still trying to sort out, a year later.

To try to prevent a recurrence, I installed a freestanding (non-networked) exhaust temp alarm, and a networked temperature alarm connected to the sea water pump. I get a loud alarm over the network if the sea water pump goes over 30 degrees C. This same setup on both generator and main engine.

But your system with automatic shutdown would be better, I think.
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Old 10-05-2013, 02:00   #3
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Re: When is a Marine Generator not a Marine Generator!

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That sounds like a great idea. Only question -- how do you disable it at startup? Wouldn't it prevent you from starting the generator?

I have suffered from the same problem you describe -- clogged sea strainer, toasted impeller, shutdown on fresh water overtemp, and permanent damage I am still trying to sort out, a year later.

To try to prevent a recurrence, I installed a freestanding (non-networked) exhaust temp alarm, and a networked temperature alarm connected to the sea water pump. I get a loud alarm over the network if the sea water pump goes over 30 degrees C. This same setup on both generator and main engine.

But your system with automatic shutdown would be better, I think.
No it does not prevent you from starting the generator for the same reason as the low oil pressure warning. The generator has low oil pressure (actually has no oil pressure) but it still starts as there is a delay relay to allow starting. All generators must have this or they would all not be able to start.
My system is wired into the low oil pressure warning circuit.
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Old 10-05-2013, 02:05   #4
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Re: When is a Marine Generator not a Marine Generator!

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Originally Posted by Fuss View Post
No it does not prevent you from starting the generator for the same reason as the low oil pressure warning. The generator has low oil pressure (actually has no oil pressure) but it still starts as there is a delay relay to allow starting. All generators must have this or they would all not be able to start.
My system is wired into the low oil pressure warning circuit.
You should give us a parts list, schematic, photos of your installation.

Sounds like a hot setup.
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Old 10-05-2013, 04:09   #5
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Re: When is a Marine Generator not a Marine Generator!

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You should give us a parts list, schematic, photos of your installation.

Sounds like a hot setup.
Its relatively easy to do.
You need to take the raw water pump pressure measurements with a good impeller as I mentioned in the post above.
You need a 12v adjustable pressure switch that covers a range which is less that the normal pressure. Weld a nut for the switch onto the side of a piece of stainless steel pipe (say 5cm long) with an o/d that will fit inside the outlet raw water pump hose and cut the hose in half and fit the pipe with the switch.
Now talk to a local marine electrician and tell him you wish to parallel the switch to the low oil pressure shutdown and this should be simple enough for him, otherwise look at the wiring diagram and do it yourself.
Then measure the pressure and turn down the switch to say 50% of normal pressure and test it. It should switch off immediately when the seacock is closed.

You may have to then manually push the off button to ensure that the electrical side is also switched off, but this is the case with any abnormal stoppage I think.

You could probably do all the above without actually measuring the pressure but this would be a less professional approach.

It might also be an idea before starting, to familiarise yourself with the low oil pressure shutdown technique used to ensure that this method is compatible.
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Old 10-05-2013, 04:58   #6
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Re: When is a Marine Generator not a Marine Generator!

Fuss - My Cummins/Onan has a water flow sensor which works on the same principle as your idea; but I wish my previous genset, a Fischer Panda, had had such a sensor.
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Old 10-05-2013, 05:08   #7
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Re: When is a Marine Generator not a Marine Generator!

Whilst I think the concept is great, I do not see any difference between this and marine propulsion engines which suffer from the same problem. Thus this is an issue of good design rather than application.

A generator designed to work using salt water for cooling (either directly or indirectly) must be a marine generator.

There are a number of devices that provide alarm when water temperature/pressure/exhaust temperature are exceeded, it should be a simple matter to connect that to the stopping solenoid. An application for marine propulsion is not so easy as there may be situations where you are prepared to risk engine damage in order to avoid a higher risk incident.
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Old 10-05-2013, 05:14   #8
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Re: When is a Marine Generator not a Marine Generator!

I always boggles my mind why $200K boats have virtually no instrumentation on engines of any type.

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Old 10-05-2013, 05:55   #9
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Re: When is a Marine Generator not a Marine Generator!

My onan has these sensors built in. It shuts down in 15 seconds if there is no raw water flow. There is also an exhaust temp. sensor which reacts very quickly. I've had almost as much problem with the sensors as I've had with the impellors. Right now I'm in the Bahamas with a bypassed raw water flow sensor, because the sensor failed. It's a bit hard to get parts around here. In the 7 years I've owned it I have replaced two exhaust temperature sensors. The raw water sensor just rotted away. They are made of cheap brass and the salt water eats them. With three years on your switch I would be keeping a spare on hand.
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Old 10-05-2013, 06:01   #10
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Re: When is a Marine Generator not a Marine Generator!

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Originally Posted by Talbot View Post
Whilst I think the concept is great, I do not see any difference between this and marine propulsion engines which suffer from the same problem. Thus this is an issue of good design rather than application.
For safety a propulsion engine should only give warnings and should not make decisions on whether to shut down. If the engine is not used to influence propulsion then it more than likely can be shut down immediately without risking lives or the boat.

Quote:
Originally Posted by Talbot View Post
There are a number of devices that provide alarm when water temperature/pressure/exhaust temperature are exceeded, it should be a simple matter to connect that to the stopping solenoid. An application for marine propulsion is not so easy as there may be situations where you are prepared to risk engine damage in order to avoid a higher risk incident.
As I said in my original post, they react too late after damage has been done, they are not instant.
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Old 11-05-2013, 22:20   #11
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Re: When is a Marine Generator not a Marine Generator!

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Originally Posted by Fuss View Post
No it does not prevent you from starting the generator for the same reason as the low oil pressure warning. The generator has low oil pressure (actually has no oil pressure) but it still starts as there is a delay relay to allow starting. All generators must have this or they would all not be able to start.
My system is wired into the low oil pressure warning circuit.
That's not exactly true, many a system design uses the bypass from the crank switch, so the the low oil PS is bypassed by the crank circuit, which allows the energize to run solenoid on the the governor to run. By the time the engine starts the oil psi is up , and when you release the mom... on crank toggle/switch, everything works.

It's an added expense to add an time delay relay to the oil sw, but some do it, bc oil psi is slow to come up.

If you have an original by-pass system, and she fails to start in the oil psi fault, it could be an indicator, of a bad oil pump, or plugged oil delivery gallery.

Lloyd
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Old 12-05-2013, 04:28   #12
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Re: When is a Marine Generator not a Marine Generator!

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That's not exactly true, many a system design uses the bypass from the crank switch, so the the low oil PS is bypassed by the crank circuit, which allows the energize to run solenoid on the the governor to run. By the time the engine starts the oil psi is up , and when you release the mom... on crank toggle/switch, everything works.

It's an added expense to add an time delay relay to the oil sw, but some do it, bc oil psi is slow to come up.

If you have an original by-pass system, and she fails to start in the oil psi fault, it could be an indicator, of a bad oil pump, or plugged oil delivery gallery.

Lloyd
Yes, thats true that the electrical engineer might start saying these things. My suggestion in this case is to find another one to help.

The concept is simple as the pressure switch is wired in parallel to the same shutdown wiring that the low oil pressure switch uses.

There is no need for any extras like time relays or added complications and discussions.

A competant electrical engineer will understand what is required immediately.
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Old 12-05-2013, 05:25   #13
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Re: When is a Marine Generator not a Marine Generator!

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Originally Posted by goboatingnow View Post
I always boggles my mind why $200K boats have virtually no instrumentation on engines of any type.

DAve
What I would like to see:

1. Much more robust, tested, reliable sensors.

2. Engines and gensets should be specifically engineered to be as simple, field-repairable, and bulletproof as possible, with a lot of investment into analyzing component failures and reliability. I think most cruisers would give up a little efficiency, some functions, and pay a little more, for something like this.

3. Instruments would be good, but probably better would be to give the data over N2K so that we can access it from different places on the boat (and remotely).

4. Engines and especially gensets should have simple computers without too many control functions, but which provide error messages in plain English. If it shuts down because of no raw water flow, it should exactly tell you that. No fuel flow? Low fuel pressure? High exhaust temperature?


In short, they should be designed so that a cruiser with ordinary mechanical skills can keep them running and rely on them far from civilization. What we get is different -- they are designed to be kept running by specialized workshops, they put on, for example, Chinese sensors which may or may not last two or three years, figuring, no big deal, the local main dealer will put his diagnostic computer on, see what's wrong, and change out the Chinese part out of his vast parts inventory. This approach is no good for us!!
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Old 12-05-2013, 05:53   #14
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Re: When is a Marine Generator not a Marine Generator!

I can't remember the brand, but there is a water flow sensor thats intended to go in the intake hose of a marine engine (there's no reason it wouldn't work on a genset) and close a set of contacts if the water flow stops. As I recall, it was around one hundred dollars depending on the size.

It should be a simple matter to wire this into a genset shutdown circuit.

There's no need to know anything about the pressure or do any testing. Water flow stops, genset shuts down

edit: http://www.aqualarm.net/comerus/stor...?idCategory=67
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Old 13-05-2013, 02:45   #15
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Re: When is a Marine Generator not a Marine Generator!

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I can't remember the brand, but there is a water flow sensor thats intended to go in the intake hose of a marine engine (there's no reason it wouldn't work on a genset) and close a set of contacts if the water flow stops. As I recall, it was around one hundred dollars depending on the size.

It should be a simple matter to wire this into a genset shutdown circuit.

There's no need to know anything about the pressure or do any testing. Water flow stops, genset shuts down

edit: AQUALARM :: OnLine Store :: Comersus
Perfect, also a good solution.

Interesting to see that so far only 2 people have said that their generator has this functionality from the 356 views so far.
It makes some statements doesnt it, especially when the fault is so common.
Congratulations to them for choosing a good brand where the manufacturers are obviously thinking.
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