Alternator Temp; what is normal range?

[EmeraldCoastSailor]

Using my laser thermometer gun I noticed that when I was using my microwave via inverter yesterday the alternator temp got to 215 degrees. When batts are fully charged its temp is 130 degrees. Engine is normal at 166 degrees. According to my batt monitor the microwave pulls about 70 amps with engine off and about 40 amps with engine running and fully warmed up, a bit less when engine is cold. I always try to run engine when microwaving since I only have about 450 AH house bank.

Is 215 degree out of line? Dangerous? I have a stock 2008 Yanmar 3YM30 with 1007 hours. With 220 watts of solar and my typical routine, I have never had a problem with keeping house bank full. I don't use the microwave all that often.

[mickt243]

Degrees f or degrees c?

F, no problem at all...

C, getting a bit too hot

[Frankly]

215 is pushing it, particularly with a stock alternator. I have a little bigger bank (600 AH), but run the microwave with little concern and never engine aid. The 90 or so amps the inverter pulls when microwave is on is certainly above the 20 hour rate, but don't think there is any real harm to the GC batteries. AGM should do even better.


Frankly

[GordMay]

Early 1960’s vintage rectifiers incorporated diodes that were typically packaged in a can configuration. It had a maximum reliable operating case temperature of roughly 160 deg. C. Later in the 1980’s, button and sandwich configured diodes became popular and with improvements in diode manufacture the temperature capability was raised to 180C.
Today, the trend among several manufacturers has been to use press-fit diodes with a maximum operating case temperature of 200C.

[EmeraldCoastSailor]

Originally Posted by mickt243

Degrees f or degrees c?

F, no problem at all...

C, getting a bit too hot

degrees F

[Frankly]

Normal Operating Temperature: 180 °F / 82° C
Max Operating Temperature: 225° F / 108° C


From Balmar 100 amp small case


Frankly

[a64pilot]

Of course where you are taking the temp is relevant as most often the diodes are the source of the most heat and they are often mounted to one side on the rear of the alternator.
For a slow rise in heat the case will mostly conduct the heat away and sort of normalize, but for short term high amp loads it won’t. So where you sense / measure the heat may be important.
For reasons of longevity I have my alternator limited to 190f, of course it can be run quite a bit hotter, heat is often what limits the life span of electrical devices and I believe by not running it so hot it will last longer, and it gives me about 90 amps continuously from a 165 amp alternator and for me that’s enough.

[bradfordharley]

I have a similar strategy to a64pilot. I use an alternator controller with a temperature sensor to reduce field (output) at 190 degrees. This is to extend the life of the factory alternators on my Yanmar dual alternator setup.
That said, 215 should be fine, but I would worry about it spiking from there. If you have something with a large draw for a long period, it will get much hotter. I run my watermaker through my inverter while under motor, so I am personally pretty careful with temperatures as it's a 70-90a long term draw.

Originally Posted by a64pilot

Of course where you are taking the temp is relevant as most often the diodes are the source of the most heat and they are often mounted to one side on the rear of the alternator.
For a slow rise in heat the case will mostly conduct the heat away and sort of normalize, but for short term high amp loads it won’t. So where you sense / measure the heat may be important.
For reasons of longevity I have my alternator limited to 190f, of course it can be run quite a bit hotter, heat is often what limits the life span of electrical devices and I believe by not running it so hot it will last longer, and it gives me about 90 amps continuously from a 165 amp alternator and for me that’s enough.

[Locquatious]

We've been running equilibrium temperature studies of an alternator with limited cooling and charging into a 14.4V battery/electronic-load while unregulated. In other words, some of the worst conditions the alternator would experience... simulating running in a poorly ventilated engine room and charging a large bank of AGM batteries. This unit has internal diodes. The alternator exhibits the highest equilibrium temperatures (case in region of stator 160°C) in the 2800-3800 alternator-rpm range. There it is near peak amp output but the fan cooling is not yet optimum. You can smell the varnish on the windings beginning to fail. Indeed since our testing evaluated getting more energy out of the alternator we had a stator failure and a bearing failure when testing to ~170°C.

For our research it is important to test-to-failure, so we know what to avoid. In chemistry the rule of thumb (Arrhenius) is, for every 10°C increase in temperature the reaction rate doubles. That is, suppose an alternator will last 1 year operating at 150°C before the varnish degrades to the point it shorts out the windings. Then it will last 1/2 year at 160°C, or 2 years at 150°C, or 4 years at 140°C.

But what can the boatie do:
*Make sure the alternator has adequate cooling, perhaps pulling in air from the bilge or from outside the engine room.
*Avoid long charging periods at max output. In our testing it took 30-45 minutes to reach equilibrium temperature.
*Slow the engine rpm down to lower the amp output. The temperature varies as the square of the amperage output.
*Speed the engine rpm up. The alternator won't produce a great increase in amp output, but the alternator fan will provide better cooling.
*If you have batteries that chug-down the charge (lithium, AGM), consider having more than one bank and charge one bank at a time. This allows the alternator to regulate the voltage. When regulating the duty cycle is lower and the alternator runs cooler.
*Stop charging if you begin to smell hot varnish.

[a64pilot]

Or have an external regulator like the Balmar one that both monitors and displays alternator temp, but will also derate it once a set temp is reached so that it doesn’t exceed set temp.

[noelex 77]

The default setting for our alternator regulator is to progressively reduce charging once the alternator temperature reaches above 100° C ( 212° F) and to stop all charging if the alternator temperature reaches 130° C (266° F).

In practice, we have never come close to these temperatures, but they are user adjustable. I may reduce these set points in future, as reliability rather than output is more critical in our application, but these numbers provide some guide as to what one manufacturer considers reasonable, although this regulator is generally used with large frame alternators.

[RheinSkipper]

I fried 4 alternators within a few years until I found out that those alternators overheat when running at low RPM and full load for a longer period of time.

My solution was to install a battery-to-battery charger for charging the house bank. It limits load to 80A for my 140A Bosch alternator. Now I measure a maximum of 110°C (230°F) near the stator coils. This temperature seems to be acceptable as I had no more alternator failures since then.

Meanwhile there is a video on YouTube that explains the issue:
https://youtu.be/jgoIocPgOug

[Wotname]

Originally Posted by EmeraldCoastSailor

......
Is 215 degree out of line? Dangerous? I have a stock 2008 Yanmar 3YM30 with 1007 hours. With 220 watts of solar and my typical routine, I have never had a problem with keeping house bank full. I don't use the microwave all that often.

AFAIK the stock alternator has an inbuilt temperature control which cuts back the regulated voltage if it gets too hot.

However I don't know the numbers and can't vouch for the veracity of this claim.

[Cdn]

Originally Posted by bradfordharley

I have a similar strategy to a64pilot. I use an alternator controller with a temperature sensor to reduce field (output) at 190 degrees. This is to extend the life of the factory alternators on my Yanmar dual alternator setup.
That said, 215 should be fine, but I would worry about it spiking from there. If you have something with a large draw for a long period, it will get much hotter. I run my watermaker through my inverter while under motor, so I am personally pretty careful with temperatures as it's a 70-90a long term draw.

You have dual factory alternators? Can you post a pic of this set up? Have you thoought about changing them out for the balmar alternators?

[bradfordharley]

Sure. I’ll snap a couple while on the boat tomorrow. I have a 4jh80, and there is a kit from yanmar that contains the bits to relocate the fuel filter and the bracket, belt, alternator and pullies to mount on the right side of the motor.
I considered Balmer, but liked the yanmar one better. I like the actual balmer alternators better, but they are 2-3 times the price. I have 2*125 Amp alternators. Yanmar currently uses the valeo ones. If I replace them at any time, I may go balmer....