Maine Sail,
I don't dispute that the lack of having a temp sensor may have led to the early demise of the 912 alternator and later the rear bearing however, as I stated, when I saw the unit internally after the first failure, the wiring and diodes were clearly WAY undersized for the intended performance. Also understand that I am an Electrical Engineer and have considerable experience with high output (100-150A) alternators used in general aviation applications so I know what should be inside an alternator that is intended for 100A output service.
I don't doubt what you saw but when wired properly to charge an 840Ah bank those issues would not have happened. I know the alt I build and sell is better than the old 912 series Balmar. But that Balmar was not a horrible alt and they offered it to fit a Yanmar which is very hard to find.
As you pointed out, the Delco 10DN case with a single external open fan and the lack of proper heat sinking/airflow for the diodes is ill suited for a high output job.
Prior to the AT series alts, which are hairpin wound, I would have taken your boat straight to a large case alt and heavy duty mount, not a small case Delco. A small frame alt is borderline suited to charge an 840Ah bank unless up-sized and then derated. Some large case alts can get closer to a continuous duty rating but again it is all dependent upon your engine space temps, the loads, alt shaft RPM and for how long the load is applied.
The Delco SI series alternator with an enclosed fan and far better diode heat sinks would have been a MUCH better model to base a high output alternator build so the 10DN was just an overpriced and over marketed product. Sure it will last if it is constantly in de-rated output mode but I wanted and paid for a 100A alternator!
Even the small case 6 series or other 130D Delco's need to be derated, on large enough banks, this is just a fact of life when driving HUGE banks for hours on end. There is no such beast as a continuous duty small case alternator at the face value rating because the face value ratings are at 80F from some builders and 120F for others.. Unfortunately there is NO industry standardized rating standard for alternators. The alt stays at 80F for all of about 10 seconds and will blow by 120F pretty quickly in bulk.....
One of the things I have to do quite often is replace cooked dumb regulated alternators that were asked to feed large banks of batteries. They are dumb, and simply stay in bulk and cook themselves... When I open them up they are literally cooked. This is not at all uncommon on deeply cycled large banks fed by dumb alts with a non-temp compensating regulator. Hitachi had such warranty issues with this on Yanmar's in boats that they added internal temp compensation to the dumb regulator to self protect the alt.
Keep in mind that what you buy is a "cold rating" or an 80F to 120F rating. Being an EE you can easily understand that at 190F, 200F, 225F etc. your real world hot alternator is already going to be putting out considerably less than the cold rating you paid for. Balmar hot rates at 190F, Ample at 200F and Electromaax at 220F. If you exceed 225F, long term, you start to run into problems. I don't know a single alt builder who recommends running at beyond 220F to 225F.. A 100A 6 series is doing 100A at 2500 RPM at 122F and at 2500 RPM and 190F it is only capable of 80A. If held at full bore, in most sailboat engine bays, it will exceed 225F.
The temp sensor is a safety device that in Balmer's case is being used as a crutch to de-power the alternator to keep it from overheating.
Not just Balmar every manufacturer of high performance external regulators has temp sensing. Even factory car alts and Hitachi etc. are coming through with temp compensation to self protect the alternator. Not a crutch a reality.. Part of this reality is that folks insist on charging at "fast idle" at fast idle these alts can put out rather tremendous current compared to an auto based alt. Problem is the fan is also spinning slower and this means temp sensing or derating becomes a near necessity, especially when fast idle charging, as many cruisers do...
A clear case of an alternator that is not designed to provide its rated output! A properly designed alternator that is rated for 100A should be able to produce 100A all day long without overheating - anything less except in extreme circumstances (engine room temps > 120F) or a dead short on the output is unacceptable performance! That is what I am paying Balmer the big bucks for!
Sure, if you were buying a hot rated 100A continuous duty alternator that would be the case but no one sells them that way. If I were to sell my 120A alt as an 85A alt I could not compete because the relatively uneducated buyer would think they are getting less of an alternator. My 120A alternator will run at 85A all day long inside a hot engine bay and not exceed 225F. My 120A rating is cold, Ample's rating is cold, Balmar's rating is cold, Electromaax's rating is cold, Mastervolts rating is cold, Hehr Powerline is cold, Powermax is a cold rating. A 100A alt does not put out 100A unless you find one that is sold hot rated.
The only rating that matters is where the alternator can run all day long and not blow by 225F on
your boat.... Unfortunately no manufacture sells them this way because they have no idea what the temps are on
your boat..... I have engine bays that get to 150+ degrees within an hour of running. It becomes very, very difficult for an alt to perform in this environment without being set up to do so or additional cooling provided for the alt.
When dealing with AGM batteries folks also need to consider what will yield the best cycle life for the money spent. Lifeline wants to see a minimum charge current of 20% of bank capacity. This means that you would ideally need an alternator capable of delivering 165A when hot. This most likely means a 200A+ small case alternator to achieve 165A continuous.
Even if we figured your alt can deliver its 100A that means it will be running at full bore for well over 3 hours if you dip to 50% SOC... Some manufacturers are getting smart and selling 160A alts that are already internally derated but the stator is really a 220A in order to get to that continuous rating of 160A. This is going to become more prevalent as Li batteries become more widely used.
I wholeheartedly disagree with your assessment that any alternator without a temp sensor would overheat! I know this is not true under normal engine compartment operating temps and I am not willing to cut any manufacturer that gets $700-$1500 for an alternator even the slightest amount of slack especially when similar FAA certified aircraft alternators actually cost less, are lighter weight and are far more reliable and none of which require temp sensors to de-rate the output!
As an EE I find it hard to believe you feel this way.... A 100A alt you buy is sold at the cold rating not hot. With most you lose 10-20% right off the top when they heat up.
I install lots of alts, it is part of what I do for a living. I am also a dealer for many of the big guns. I work pretty closely with the manufacturers, conduct field testing for some and own the test equipment to properly set them up, which on a massive AGM bank includes temporarily mounting temp sensors to the alt then closing the engine bay and running it full bore with the engine under load. With a large bank any "tech" who does not load and temp monitor your bank, in your closed engine compartment, is simply doing the customer a disservice.
Cutting anyone slack on price has nothing to do with the reality of small case high output alts in closed confined spaces running for hours & hours at full output. This is why Balmar and Almple Power offer ways to derate the alts with the regulators so that they can be set up to run at the maximum they can in the engine space without over heating and without bouncing in and out of temp limiting..
Small case alternators were never intended to run at full bore, in confined hot spaces, for hours and hours on end, not even high output models. The key here is "at full bore"... There is a limit to what they can do.
While they do it considerably better than a factory alt they still can't work miracles in that size case with internal diodes etc. etc.... In cars, trucks etc. they simply supply systems power at well below their rating. My wife's car has a 120A alternator and the biggest loads I have been able to measure on the battery is about 24A with EVERYTHING loaded that possibly can be...
Balmar's product should be properly sized and designed for the intended use and performance on a continuous basis otherwise the 100A alternator they are selling for $700+ is really a 40-50A alternator when the temperature regulator has to keep it from melting itself most of the time.
Balmar's products are sold the same way every other company does it. It's not a 40-50A alt if set up properly. Properly set up that 100A alt may very likely produce 70-75A continuously and never hit temp limiting, if amp-manger is used to set it up.
We should include Ample Power, Mastervolt, Electromaax, Powermax, APS, Hehr etc. on and on and on because no one sells and markets hot rated small case alternators. They sell them based on a cold rating and even this varies because there is no standard... The 100A alternator you buy when at 190F, 200F, 225F etc. will always be considerably less than the cold rating it is sold as. Still running it at full bore, in most engine bays with most any small case alts will see that alt blow by 225F in fairly short order..... I have installed every brand of small case high performance alt out there. There's no magic in any of them. Some are better constructed than others but all of them still need proper set up for the environment and bank they are feeding.
On our boat I feed a 400Ah LifeP04 bank with a 160A Delco 130D case alt which started life as an Electromaax. I have taken the alt apart and fully tweaked every component, bearings, diodes, brushes and wire using only the absolute finest components available. The stator and rotor were also custom built well beyond where the Electromaax alt was. Does this make the Electromaax alt bad? Not at all just not quite as good as it is now...
What I did would make this alt insanely expensive if sold by one of the big guys, and very few would be willing to pay for that. About the only thing I did not do was convert to an external diode rack. Still, even with all this tweaking, (this is probably one of the most bad a$$ HO 130D Delco's ever built) I can run this alt at just 120A in my engine bay and not blow by 225F...... I also have ducted cooling...
When cold and not current limited this alt will exceed 180A. When hot, 215F - 220F, and not current limited, she will run at about 150A. Still 120A is all she can do safely on a LifePO4 load for long durations to not blow past 225F..... I have no doubt that there is no finer or more robustly built 130D Delco alt out there, yet 120A on an alt built as a 160A unit is all she will do, on a
continuous basis.. If I want more out of my alt I will need to go to a large case J mount or a Balmar 200A AT hairpin wound alternator. There is only so much that can be done with a small case alt.
I know these things from real world hands on experience with lots and lots of high output alternator installations using actual data collected, using actual measurements, temps and currents across nearly every brand of small case alternator ever made, as installed on boats..
Unfortunately you can not feed an 840Ah bank of AGM batteries with a small case alt and not have it do what yours did. Seven months was tremendous performance. The only one that might survive may be the AT series but I even have those derated based on actual temp performance
as installed on the boat....
Lab data, marketing claims and actual installs, on actual boats, are not one in the same unfortunately.. Your alt problems are exactly what I see over and over and over when good installation practices are not followed. The 6 series or E-Maax or Ample or CMI, Powermax or any other small case alt designed to fit a Yanmar is not going to solve that problem only a well executed install will....
