Stator failure- Northern Lights 6kw

[DotDun]

Originally Posted by tanglewood

....
For what it's worth, the NL generators are specified for continuous duty, full load, at 130F ambient (outside the enclosure). There are vents on the case and they need to be kept clear per the installation instructions. So saying that the heat rise in the stator is not accounted for in the design is just making stuff up.

Where is your data coming from???

The owner's manual for the OP's model states from page 28 at:

http://www.northern-lights.com/media...fs/OM673L3.pdf

VENTILATION
Good ventilation is important for proper genera- tor operation. When installing the generator set, be sure the ambient temperature does not exceed 40°C (104°F) during operation.

From the specs on the alternator at:

http://www.northern-lights.com/media...heets%20V1.pdf

AC Generator
• Northern Lights, direct coupled, four pole, revolving field, four lead reconnectable generator with Class “H” insulation and prelubricated bearing. Conservative heat rise rating: 95°C/50°C ambient .

IIRC, this unit uses ambient air outside the case for alternator cooling, then dumps the heated air back outside the case. If installed in an enclosed space without fresh air blowers, the heated air would certainly raise the ambient temperature outside the case above the recommended 104°F.

[David Hughes]

Originally Posted by tanglewood

I've been following this same discussion over on TrawlerForum..

Correct me if I'm wrong, but last I heard there was still no diagnosis of what's wrong with the generator. Something created a bunch of smoke -yes. But nobody has looked into it to sort out what actually failed, let along what the corrective action is. The original post went straight from "there was a ton of smoke" to "how much does a new stator cost". Nobody has diagnosed this as a failed stator.

So unless there is now a diagnosis of exactly what failed, this discussion is all just wild fantasy with no basis in reality.

For what it's worth, the NL generators are specified for continuous duty, full load, at 130F ambient (outside the enclosure). There are vents on the case and they need to be kept clear per the installation instructions. So saying that the heat rise in the stator is not accounted for in the design is just making stuff up.

You are indeed correct that it's all conjecture at this point. My boat is out again on another charter (marina-hopping so they didn't care about a broken gen), and it will finally get looked at after they return on the 18th. Not trying to waste anyone's time. I really appreciate all I've learned already, and I hope others have picked up a thing or two.


Sent from my iPad using Cruisers Sailing Forum

[Dockhead]

Originally Posted by DotDun

Where is your data coming from???

The owner's manual for the OP's model states from page 28 at:

http://www.northern-lights.com/media...fs/OM673L3.pdf



From the specs on the alternator at:

http://www.northern-lights.com/media...heets%20V1.pdf



IIRC, this unit uses ambient air outside the case for alternator cooling, then dumps the heated air back outside the case. If installed in an enclosed space without fresh air blowers, the heated air would certainly raise the ambient temperature outside the case above the recommended 104°F.

I sure have learned a lot from this thread.

I learned that my own generator's output is based on ambient temperature of 25C. And that the sound enclosure should be considered to increase the ambient temperature by 7C. That means the full output of my generator is available only if the engine room is at 18C (!!).

I guess those of us -- including maybe the OP -- are unwittingly overloading their generators, maybe by a whole lot, if they have these generators running in poorly ventilated engine spaces in hot climates.

My own engine room is very well ventilated with powerful blowers, and still will reach 30C even on a coolish day of less than 20C outside.

Means it's a darned good thing I've been derating my generator using the Victron, and maybe I should derate it further.


@Tanglewood -- we know all this. But it's very reasonable guess that this is what happened to the OP, and so a useful and interesting conversation, for him as well as for us.

[Dockhead]

Originally Posted by David Hughes

You are indeed correct that it's all conjecture at this point. My boat is out again on another charter (marina-hopping so they didn't care about a broken gen), and it will finally get looked at after they return on the 18th. Not trying to waste anyone's time. I really appreciate all I've learned already, and I hope others have picked up a thing or two.

Entirely reasonable conjecture, which has led to a very interesting thread, which I hope is being as useful to you, as it has been to the rest of us. Thanks for starting it.

[Pelagic]

Originally Posted by Dockhead

I learned that my own generator's output is based on ambient temperature of 25C. And that the sound enclosure should be considered to increase the ambient temperature by 7C. That means the full output of my generator is available only if the engine room is at 18C (!!).

I guess those of us -- including maybe the OP -- are unwittingly overloading their generators, maybe by a whole lot, if they have these generators running in poorly ventilated engine spaces in hot climates.

Dockhead, my guess is that Generator Manufacturers have to define "optimum conditions" very conservatively in their specifications and marketing for legal reasons.

Something similar to Safe Working Loads.....even though there is quite a built in reserve.

So I would not be too concerned

However, if the sound shield increases temp by about 30% , it is another good reason to try and do away with it.

[tanglewood]

Originally Posted by DotDun

Where is your data coming from???

Direct from Northern Lights when I was building my boat. Engine room temp was/is a concern, so I was gathering up all the manufacturer's limits to figure out what was allowable. Their generator installation manual is generic for all models and says to check with NL for ventilation specs. They told me 130F ambient was the limit for the genset.

That said, mine is a 20kw, not a 6kw, so the specs and air flow design might be different. To answer one of your questions, on the 20kw the alternator cooling air is drawn in through vents on the end of the enclosure and is exhausted into the cabinet interior, as you stated. Since that pressurizes the cabinet interior, the mixed air then flows out through exhaust vents on the non-service side of the enclosure. So there is forced air flow through the enclosure. I expect the 6kw is the same, but can't say for sure.

NL has told me that occasionally a set will get installed pushed right up against a bulkhead or other structure blocking the exhaust vents, and that is clearly a problem. The other more common issue is that people find the gap behind the set to be a very convenient storage space and stuff in things that in turn block the vents. Obviously none of this is good.

I see the specs in the manuals and data sheets that you reference. The 20kw operators manual doesn't have the clause about operating temp for the generator end, so this may be a key difference. I do see the same spec in the data sheet for the generator end, but am not quite sure what it means. I guess it means the gen end will operate at 95C in 50C ambient? It's not clear where that ambient is measures. Ambient for the gen end would be inside the case, so create an even lower ER ambient requirement. Or is it the ER ambient? And either way it's not 130F which would be 55C. So definitely some discrepancies, I agree.

[tanglewood]

Originally Posted by DotDun

FWIW, this issue is what drove my decision to look at Mase. Mase has a line of generators (IS - "intercooler") that has a water/air heat exchanger on the raw water line between the inlet and water pump">raw water pump. The alternator cooling fan circulates air through the heat exchanger keeping the air in the case vs. a NL design where it dumps the hot air into the engine room. Even with 90°F raw water temp, the temperature inside the case never goes above 105°F (Mase's claim, I've never measured it).

Yes, the additional heat exchanger is yet another failure point, and yes, I've replaced one due to my own stupidity ($250), but I think it's worth it to keep the unit a lot cooler. With the heat exchanger ahead of the raw water pump, if it does develop a leak, the raw water pump sucks air and the unit shuts down. Which is better than on the other side of the pump where it would spray water all over the inside of the case.

Clever design, IMO!

I've wondered about doing this for whole engine room cooling. I've got a different situation with a power boat that yields lots of heat dumped in to the ER, and lots of air flow required to get rid of it.

[DotDun]

Originally Posted by tanglewood

I've wondered about doing this for whole engine room cooling. I've got a different situation with a power boat that yields lots of heat dumped in to the ER, and lots of air flow required to get rid of it.

That's an interesting idea and I understand the desire. A friend with a 'fast trawler' and engine room with (2) big iron diesels PLUS (2) NL generators (8kw & 16kw) was not a fun place to be after an all day passage. I swear the engine room blowers on that boat are louder than either/both generator(s) running.

[Dockhead]

This thread has led me to believe that we need to be careful about loading our generators beyond their real, thermally-adjusted capacity.

One thing which I have noticed on my boat is that I am using the immersion heater nearly 100% of the time I have my generator on. That's 1.5kW of unnecessary load. Could be desirable if the only thing I'm using is the charger, which draws about 2kW max. But in general it's unnecessary, and inefficient to burn diesel fuel to produce mechanical power to generate electricity just to turn back into heat.

I have held back from plumbing in a heat exchanger to heat domestic hot water from waste heat, since it would not pay for itself very quickly in fuel saved, but if it's also saving the generator by reducing the load, that already looks different.

[Dockhead]

Originally Posted by tanglewood

I've wondered about doing this for whole engine room cooling. I've got a different situation with a power boat that yields lots of heat dumped in to the ER, and lots of air flow required to get rid of it.

That will only help you if the sea water is significantly cooler than the ambient air.

In a lot of places, like where I am, that will not be the case.

[DotDun]

Originally Posted by Dockhead

That will only help you if the sea water is significantly cooler than the ambient air.

In a lot of places, like where I am, that will not be the case.

For conversation's sake.....(I'm not an HVAC engineer)....

It is certainly true that sea water will ALWAYS be lower temperature than the air in the engine room. So the discussion needs to be around if it's more efficient to use a water pump and heat exchanger than it is to simply bring in outside air and ventilate the engine room. I would think the amount of air movement is the key with either method. So what size water/air heat exchanger and fan would it take to lower the air temperature in the engine room by 20°F (assuming the engine room is 30°F higher than water temperature)?? How much water flow is needed, how much air flow is needed???

My experience has been that engine room blowers, which are usually little turbo fans that fit in small openings (like 4" hose) don't move near the amount of air that possibly a 12" blade or squirrel cage could via a duct system blowing thru a heat exchanger.

[Dockhead]

Originally Posted by DotDun

For conversation's sake.....(I'm not an HVAC engineer)....

It is certainly true that sea water will ALWAYS be lower temperature than the air in the engine room. So the discussion needs to be around if it's more efficient to use a water pump and heat exchanger than it is to simply bring in outside air and ventilate the engine room. I would think the amount of air movement is the key with either method. So what size water/air heat exchanger and fan would it take to lower the air temperature in the engine room by 20°F (assuming the engine room is 30°F higher than water temperature)?? How much water flow is needed, how much air flow is needed???

My experience has been that engine room blowers, which are usually little turbo fans that fit in small openings (like 4" hose) don't move near the amount of air that possibly a 12" blade or squirrel cage could via a duct system blowing thru a heat exchanger.

"How much water flow is needed, how much air flow is needed?"

This is easy! If the water temp is the same as the ambient air temp, you will need MORE air flow through the heat exchanger, to get the same effect as a given amount of fresh air coming in.

MORE because heat exchangers are not 100% efficient.

So to have an equal cooling effect from x m3/hour of fresh air coming in at 20C, you would have to move x m3/hour of air through heat exchangers plus enough to make up for the inefficiency of the heat exchanger. This will vary according to size and design of the heat exchanger and volume of water you circulate through it, but will never be 100%, so you will never get hot air cooled down to the same temperature as the incoming sea water.

On top of that, to move x volume of air through heat exchangers will take a lot more power than to move the same volume of air into the atmosphere through ducts, unless you have some really awful ducts and some really gigantic efficient heat exchangers, but never anything like a typical case.

So if the sea water is the same temp as the ambient air, you will have a LARGER air handling installation, maybe much larger, PLUS the whole extra system of heat exchanger and sea water circulation, just to get the same effect.

It is conceivable that you have such problems with ducting, that it takes even more power to move air through your ducts, than to move air through a heat exchanger, but all the added efficiency losses would be almost impossible to make up for unless you just have no ability at all to duct air to the outside.

Why go to all the trouble to process hot air to cool it down to near ambient temperature, if you can just take it directly from the atmosphere? It really can't make any sense unless there is a very large temperature difference boosting the efficiency of the heat exchanger system -- it would have to make up for all the inefficiencies first before it would start doing any good.

[a64pilot]

Dockhead,
If I had anything like your suite of electronics I'd install a thermocouple on the generator head and monitor it's temp directly.
Ones I like to use in test flights mount under a bolt head, look like a washer with wires coming off of it.

[Dockhead]

Originally Posted by a64pilot

Dockhead,
If I had anything like your suite of electronics I'd install a thermocouple on the generator head and monitor it's temp directly.
Ones I like to use in test flights mount under a bolt head, look like a washer with wires coming off of it.

Yes, maybe I will. That's a great idea. I have the Maretron temperature module, and already monitor these things:

1. Engine room temperature at the top of the space, opposite from the blower intakes.

2. Temperature of the sea water pump of the generator (proxy for sea water flow).

3. Coolant temperature of the generator.

4. Core temperature of the school bus alternator on the main engine.

I use the ring-under-bolt thermocouples like what you describe. The data is really interesting and useful to have.

I have two more vacant slots in the Maretron TMP module so would be easy to do. Thanks.

While I'm at it I think I'll put the last thermocouple on my calorifier, so I can see when the hot water is ready, without wasting water to feel it.

[a64pilot]

If your genset is similar in design to mine, and I think most are, it draws hot air from around the sound shield with a blower, if the blower fails or a plastic bag or anything else gets sucked to the air intake on the sound shield the only thing keeping it from burning up the generator head is the CB should pop from overheat, the engine is of course water cooled. Be nice to have an over heat alarm on the generator head
Only way I have to know if the blower fails is to put my hand over the exhaust on the stern every now and again, and that isn't a very good way to tell if I'm cooking my generator.
Surely no one doesn't exhaust the hot air overboard but dumps it back into the engine room, do they?
My generator when it's running actually cools the Lazarette, reason is of course is its dumping bunches of air through the stern, which draws in air from the inside of the boat to replace it, so I am in an oddball way air conditioning the generator, cause if its hot and the generator is on its running the AC's.


What is a Maretron temperature module?