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Old 05-05-2016, 04:09   #1
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Alternator Management

I have two alternators on my main engine, besides the standard Yanmar 12v one, which charges only the engine start batt, I have a Leece Neville heavy duty school bus alternator, 110 amps x 24v.

I have gotten great service out of that alternator, but I did finally burn it up last summer, requiring an inexpensive rebuild. I believe it burned up due to abuse, that is, due to my own stupidity in forgetting that I had left some large AC loads on it while using the windlass and 10hp bow thruster at the same time, at idle speed. Yes, I know it was stupid. At the time this happened the alternator was already 12 years old and I have no idea how many megawatt/hours it had produced over the years without complaining.

Nevertheless, I would like to be a bit more careful with it this time. I have installed a temperature sensor (Maretron under-bolt ring sensor connected into the N2K network) on the negative post.

The alternator produces 80 amps or more than 2kW of power already at 1500 RPM and produces full power of 110 amps or nearly 3kW of power before 2000 RPM. When the batteries are down, they provoke the alternator to producing full power.

I had always monitored the temperature of the alternator by using an infrared thermometer on the case. How surprising to see that the core temperature of the alternator, as shown by the temperature of the negative pole, is much higher. When the alt is producing full output, this can go to 110 degrees C or more, although the case never exceeds 60C. The belts will reach 70 - 80 C. Do these seem like reasonable temperatures, or should I be worried about a core temperature of 110C?

I have an Adverc regulator which turns the alternator to full power for a while, then cranks it back to let alt and batts rest, then repeat. I don't know whether this is good or not. For some reason, my batts got boiled almost dry last summer after a long motoring passage (and I replaced them all, $$$).

Maybe after the batts are fully charged, this is not the best regulation regime?

Maybe I need to regulate the alternator to derate it a bit, and go to a real float voltage after the batts are full?


Anyone able to add to my knowledge, or give any helpful tips?
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Old 05-05-2016, 05:25   #2
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Re: Alternator Management

I see from this: http://www.prestolite.com/literature...nators_web.pdf

That these alternators are rated to work in an AMBIENT temperature of up to 110C.

I guess if that's the case, then they can't be too much bothered by a core temperature of 110C, with case temperature of less than 60? My engine room temperature today is 33C.


Here is some text from the brochure:

":When we think about reliability we consider the entire school bus as a complete electrical system. An undersized alternator
that limits its output to protect itself from overheating, while allowing the overall health of the electrical system to degrade
is of no real long term benefit to the operator. An improperly configured self protecting regulator allows a stressed alternator
to partially shut down, thereby insulating itself from failure and allowing the individual claim of a ‘reliable’ component.
The problem with this scenario is that it will cost you money!
An undersized alternator sacrifices the reliability of other components
within the school bus system (batteries, motors, air conditioning
compressors/clutches, engine cooling fan clutches, heater
motors, wheel chair lifts, LED lights, etc) for the sake of saving
itself. The overall system suffers, and the reliability claimed by
the alternator is achieved by sacrificing the reliability of the rest
of the system."


Seems to apply to cruisers as well. I have never observed this alternator cranking back the output due to temperature. It's producing bulk power already at idle speed, and reaches its full rated output before 2000 RPM.

This however leads to another question -- if it produces the same output at 1800 or 3600 RPM, it has half the cooling at 1800 RPM -- I wonder if this is harmful?
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Old 05-05-2016, 09:24   #3
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Re: Alternator Management

If you connect both altwernators to the service battery you can lower the load on each alternator. Instead you can get an DC-DC charger for your start battery. Personalty I run both 200A and 160A Balmar alternator on my Yanmar charging 1000AH Lifepo4. But since I run them at about 60% output, the temp is never an problem.Usually 95`C.

110`C should also be ok really.

The higher the RPM the better cooling.
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Old 05-05-2016, 09:35   #4
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Re: Alternator Management

Different voltages, so he can't connect both batteries.

DH, NEMA has some specifications for alternator core temperatures. They are based on 40°C ambient temperature. A Class A (lowest rating) has a continuous duty expected temperature rise on the core of 60°C. There are four classes, up to Class H (don't ask why) that has a temperature rise of 125°C. So, your 110 doesn't sound out of line at all (unless your alternator is really low class). The temperature rating is based on the insulation materials, and on a duty life of 30k hours of operation.
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Old 05-05-2016, 09:44   #5
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Re: Alternator Management

Quote:
Originally Posted by offpist View Post
If you connect both altwernators to the service battery you can lower the load on each alternator. Instead you can get an DC-DC charger for your start battery. Personalty I run both 200A and 160A Balmar alternator on my Yanmar charging 1000AH Lifepo4. But since I run them at about 60% output, the temp is never an problem.Usually 95`C.

110`C should also be ok really.

The higher the RPM the better cooling.
Would defeat the purpose of separate start bank! Also, the little car-type alternator has no business participating in large-scale bulk power production.
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Old 05-05-2016, 09:48   #6
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Re: Alternator Management

Quote:
Originally Posted by Dsanduril View Post
Different voltages, so he can't connect both batteries.

DH, NEMA has some specifications for alternator core temperatures. They are based on 40°C ambient temperature. A Class A (lowest rating) has a continuous duty expected temperature rise on the core of 60°C. There are four classes, up to Class H (don't ask why) that has a temperature rise of 125°C. So, your 110 doesn't sound out of line at all (unless your alternator is really low class). The temperature rating is based on the insulation materials, and on a duty life of 30k hours of operation.
That's interesting, thanks. I'll try to find that documentation.

I have a Leece Neville school bus alternator rated for 110C ambient temperature. I reckon it must have a pretty high classification; it's made for heavy duty use. It weighs something like 20kg -- quite a massive lump.
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Old 05-05-2016, 09:59   #7
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Re: Alternator Management

Dockhead,

have to thank you for bringing up another interesting topic. Not directly on point, but it led me to this Delco-Remy white paper on alternator efficiency. I'm only posting here because it is one of the most clear descriptions of how an alternator works that I have seen, and others might find it of interest. It also covers belt losses and other interesting things we probably don't think about when buying an alternator.

http://www.delcoremy.com/documents/h...ite-paper.aspx
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