Differences in Small Case Alternator Efficiencies

[SoonerSailor]

Common wisdom seems to be that without extraordinary cooling measures or an external rectifier a small case alternator can only supply a maximum of about 70A continuously without reaching destructive temperatures, yet they are sold with maximum outputs ranging from 70A to 220A.

My question is whether or not these higher output versions will actually run cooler than the lower output versions at a given 70A output? In other words, given that I would not want to exceed a certain alternator temperature, could I actually run that 150A alternator at a higher continuous output than the same series 100A alternator? Does the 150A alternator, or Balmar's hairpin wound alternator, have lower resistive losses in the stator winding at a given output than a 100A alternator, and by how much?

It would be interesting if someone like Rod Collins "Mainesail" were able to quantify differences in the lab. If there were a substantial difference, it would make sense to buy the higher output version even if you still had to limit its maximum output with a programmable regulator.

Chip

[john61ct]

"Efficiency" is a complex loaded term, not usually relevant to

maximizing current output in high temperatures

Maine Sail sells good alts.

I'm sure his, OceanPlanet's, CruiseRO's, Mark Grasser's etc do put out the max they can / should given the small case thermal handling limitations.

But the external VR that also helps, in cooler ambients allowing more amps output, when things heat up scaling back.

[SoonerSailor]

That really doesn’t address the question. Look at it this way. Does, for example, the Balmar 6 series alternator that is rated at 100A run hotter than the Balmar 6 series alternator that is rated at 150A, when they are both adjusted by the regulator to put out the same current, say 70A.

I’m well aware of strategies to reduce the alternator case temperature, but that is not my question.

[john61ct]

I would think likely so, but may not be at all significant a factor until ambient temps get very high.

In general the former setup will likely last longer, be more reliable. Of course the real advantage is getting say 100A or whatever the continuous rating is, when ambients are reasonable.

Have you tried asking Balmar tech support?

Paging @witzgall. . .

[a64pilot]

The higher rated alternators should make equal amperage at less heat than a lower rated one, some reasons are there is more wire in the windings etc. some even have gone to square profile wire cause you can pack more into the same space than round wire.

How much difference? I don’t know. I was all set to buy a 200 amp Alternator from Rich (Cruise RO) but he talked me down to a 165 saying it was the best value. All the Alts he sells are Mark Grasser or were anyway, and I think some of the ones Maine Sail sells are also Mark Grasser’s
I set mine with it’s Balmar 614 up IAW Maine Sails instructions, excepting that I set the temp limit rather low, at about 90c. I can get about 90 amps continuously from it, and have done nothing to cool it, I believe that cooler air from the bilge directed to the backside of the alternator would help some, how much I have no idea.
My belief is that the life of an alternator is proportional to how hot it’s run, they may work fine at much higher temps, but I believe they will live a shorter life at the high temps.

I’ve asked your question several times myself, and never gotten a quantitive answer, however I did get from someone that I feel knows what they are talking about that the increased power output of the bigger alternators sustained is higher than the lower rated ones, but it’s not linear at all.
I took that to mean that you would get 10 or less amps at the same temp from a 200 than a 165, but I know of no testing that has been done to quantify the difference.
I would not expect any manufacturer to publish sustained power output, to begin with I don’t believe there are any standards to test to, and it would be a number much lower than rated output, and would open a can of worms, the marketing dept would be up in arms

[wsmurdoch]

Reading SAE J56, it sounds to me that the "High Temperature Performance Test" which is conducted at 100C ambient after a 30 minute stabilization would be the rating that would be nice to know.

https://rennlist.com/forums/attachme...l-requirem.pdf

Bill

[john61ct]

The published rating of the large frame alts designed for emergency vehicles

is what they can put out 24x7

maybe derated in very high ambient temps.

So can be done, but of course an entirely different class of alternators, few have room for.

Military surplus also.

When dreaming of 200A+ actual charging, remember you're taking HP from your propulsion, so put in appropriate controls.

[Jammer]

Originally Posted by SoonerSailor

My question is whether or not these higher output versions will actually run cooler than the lower output versions at a given 70A output? In other words, given that I would not want to exceed a certain alternator temperature, could I actually run that 150A alternator at a higher continuous output than the same series 100A alternator? Does the 150A alternator, or Balmar's hairpin wound alternator, have lower resistive losses in the stator winding at a given output than a 100A alternator, and by how much?

Overwound (high-output) alternators achieve their capacity four ways:


1) Increasing the effective cross-sectional area of the stator conductors by using larger wire and adding windings in parallel. This improves current handling capability while increasing the parts and labor cost of the stator.



2) Increasing the effective cross-sectional area of the stator conductors by using fewer turns, to make room for more windings in parallel. This improves current handling capability at the expense of low-RPM output.


3) Using more or larger diodes. Sometimes a more efficient heat sink is used.



4) Making minor changes to improve cooling airflow, such as using a higher performance fan, or in some cases two fans where one was originally specified, or slightly increasing the size or number of ventilation openings in the case.


Now, of these, #1 and #2 will reduce the amount of heat produced, if the output current is kept the same, because the series resistance of the stator goes down. These are actual efficiency improvements; you get a little more power out for the same power in.



#4 will cause the alternator to run cooler for a given output current, especially at low RPMs.



#3 will not change the amount of heat produced, but it will reduce the junction temperature of the diodes, which will make them last longer. Since diode failure is a major cause of alternator failure, this is a significant thing.



#3 and #4 don't improve overall efficiency, they just reduce temperatures in key areas by moving the heat around more effectively.

It would be interesting if someone like Rod Collins "Mainesail" were able to quantify differences in the lab. If there were a substantial difference, it would make sense to buy the higher output version even if you still had to limit its maximum output with a programmable regulator.

The hard part of doing this is quantifying exactly what you mean by "run cooler." It's relatively easy to measure the amount of heat dissipated by running one of these things in the lab, but harder to measure the maximum diode junction temperature or the highest temperature in the stator. There are proxies for these but the problem is that they are not meaningful when comparing different designs. For example if you measure the temperature of a particular external part of the stator, well, with a different stator design that part may run relatively hotter or cooler than the highest temperature component in the stator. If you measure diode temperature at the heat sink, that may have a variable relationship to junction temperature depending on the heat sink design or the particular diode in use.

[Montanan]

Originally Posted by SoonerSailor

That really doesn’t address the question. Look at it this way. Does, for example, the Balmar 6 series alternator that is rated at 100A run hotter than the Balmar 6 series alternator that is rated at 150A, when they are both adjusted by the regulator to put out the same current, say 70A.

I’m well aware of strategies to reduce the alternator case temperature, but that is not my question.

Simply ask Balmar.

Their ratings for continuous operation should be available for different ambient temperatures. It is their warranty that is of issue.

As a general rule, a higher rated machine should operate cooler at the same given amperage output than a lower rated machine.

[SoonerSailor]

Nice overview Jammer, thanks. It would be interesting to see what Balmar says, and if they commit it to paper.

[GordMay]

Originally Posted by john61ct

... When dreaming of 200A+ actual charging, remember you're taking HP from your propulsion, so put in appropriate controls.

Because an alternator is around 60% efficient, it consumes about 1 horsepower for every 450 watts of load (0.6 x 750).
In a 13.8-volt (nominal 12V) charging system, this means our alternators draw one horsepower for every 33 amperes of load current (6 HP @ 200A).

[tanglewood]

Originally Posted by GordMay

Because an alternator is around 60% efficient, it consumes about 1 horsepower for every 450 watts of load (0.6 x 750).
In a 13.8-volt (nominal 12V) charging system, this means our alternators draw one horsepower for every 33 amperes of load current (6 HP @ 200A).

Exactly. So the extra engine loading is immaterial unless you have both a tiny engine, and you want max propulsion power at the same time as max electric output. At anything below max propulsion power, there is plenty of power for whatever alternators you want. This is one reason why I think the Integral power system is of small incremental value.

[a64pilot]

You need to realize that 6HP is a huge number.
My 44 HP Yanmar, pretty much the generic average cruising boat motor makes about 20 HP at about 1800 RPM, throw a 6 HP load on top of that and you have increased the load on the engine by 1/3rd, which pretty severely overloads it.
My 3500 W Diesel generator makes only 7 HP as an example.

The idea that you getting 200 amps or 2800 Watts out of a device you can hold in your hand is pretty much a fantasy. It’s doable if you could liquid cool it or maybe liquid cool it and remote mount the diodes, but as is with just the two little fans? It’s not likely.

[newhaul]

I'm watching this closely as well. The alternator I install will need to be a small case and produce 50 amps output under all conditions running through a 50 amp b2b. To charge my Lfp Regardless of temperature . It looks like I will need a 75 amp minimum or should I look at something a bit bigger.

It will be mounted a 14 hp kubota

[Pizzazz]

Higher output alternators (overwound as states) will produce less heat if operated below their rated power. However, the efficiency will be lower at below the rated output, so more heat will be produced. The two effects offset each other but I believe the first one is slightly stronger.

In most cases, better alternators have marginal benefit. If you have a 400 Ah battery bank, you will like not need to charge at higher than 80A for more than one hour. So, a better alternator gives you a few minutes shorter charging time at the expense of reduced efficiency in the subsequent accept phase. Not really worth it.

If you have a large lithium bank or operate your wet cells 20-80, then it is a different story. I am really curious if we can get one of these inverter generators (efficiency close to 80%) and drive the generator from the alternator belt.