How Hot should an alternator get?
 

We have a 55A Hitachi alternator on our 2 cyl 13HP Yanmar. It is charging 2
banks of batteries - 200AH in house and 100AH in Starting.

Today, I had an alarm sound when I started the engine (turned out to be low
oil level!), but it caused me to check the engine belts etc.

The alternator belt was loose, so I adjusted it - it had been slipping. I
noticed that despite only having run for about 5-10 minutes at low rpm
(~1200), the alternator was quite hot to the touch - I would guess in the
50-60 deg C range (120-140F), so I would keep my hand in contact with it.
The engine block was not nearly as hot - I could put my hand on it
anywhere - just warm.

There is a combiner, so both banks MAY have been connected. Refrigeration
was running at time. Batteries were not fully charged - maybe just below
12v. I don't have an ammeter, so don't know what amps are being put out.

Should the alternator run that hot?

Would low speed caused by slipping belt cause overheating?

If not, what could cause be? Or is it normal?

GBM

How Hot should an alternator get?
 

GBM wrote:
We have a 55A Hitachi alternator on our 2 cyl 13HP Yanmar. It is charging 2
banks of batteries - 200AH in house and 100AH in Starting.

Today, I had an alarm sound when I started the engine (turned out to be low
oil level!), but it caused me to check the engine belts etc.

The alternator belt was loose, so I adjusted it - it had been slipping. I
noticed that despite only having run for about 5-10 minutes at low rpm
(~1200), the alternator was quite hot to the touch - I would guess in the
50-60 deg C range (120-140F), so I would keep my hand in contact with it.
The engine block was not nearly as hot - I could put my hand on it
anywhere - just warm.

There is a combiner, so both banks MAY have been connected. Refrigeration
was running at time. Batteries were not fully charged - maybe just below
12v. I don't have an ammeter, so don't know what amps are being put out.

Should the alternator run that hot?

Would low speed caused by slipping belt cause overheating?

If not, what could cause be? Or is it normal?

GBM

They get hot - easily over 120-140F. How hot is "normal" for your
setup you'll have to figure out. My guess is that the slipping itself
adds to the heat. Certainly I usually notice slipping on mine when I
smell the burnt rubber.

BTW,your alternator and batteries are not too large, but still they
can drain 2-3 HP from from your engine, so if your batteries are very
low, don't be surprised if you engine overheats if pushed hard. My 18
HP 2GM with a 100 Amp alternator will run 15 degrees hotter and even
refuse to rev up fully when charging. Fortunately, I can turn down
the output to 30 Amps if that suits my pans better.

How Hot should an alternator get?
 

GBM wrote:

We have a 55A Hitachi alternator on our 2 cyl 13HP Yanmar. It is
charging 2
banks of batteries - 200AH in house and 100AH in Starting.

Today, I had an alarm sound when I started the engine (turned out to
be low
oil level!), but it caused me to check the engine belts etc.

The alternator belt was loose, so I adjusted it - it had been
slipping. I
noticed that despite only having run for about 5-10 minutes at low rpm
(~1200), the alternator was quite hot to the touch - I would guess
in the
50-60 deg C range (120-140F), so I would keep my hand in contact
with it.

Couple of things.

Yes, your alternator getting hot is quite normal.

You want to idle the engine around 1,400 RPM to prevent "wet stacking"
which happens when the engine is not hot enough provide combustion of
all the fuel in the chamber and that leads to VERY expensive repair
bills.

The sheave ratio between engine an alternator is about 2:1, so at
1,400 engine idle, alternator is about 2,800 RPM and probably putting
out maybe 25-30 amps, if you are lucky.

The 1,400 RPM will also help minimize belt slippage.

My guess is the 55 amp output will require an alternator RPM of
between 5,000-6,000.

It's just the nature of the beast.

Have fun.

Lew

How Hot should an alternator get?
 

On Fri, 14 Jul 2006 21:02:47 -0400, "GBM"
wrote:

We have a 55A Hitachi alternator on our 2 cyl 13HP Yanmar. It is charging 2
banks of batteries - 200AH in house and 100AH in Starting.

Today, I had an alarm sound when I started the engine (turned out to be low
oil level!), but it caused me to check the engine belts etc.

The alternator belt was loose, so I adjusted it - it had been slipping. I
noticed that despite only having run for about 5-10 minutes at low rpm
(~1200), the alternator was quite hot to the touch - I would guess in the
50-60 deg C range (120-140F), so I would keep my hand in contact with it.
The engine block was not nearly as hot - I could put my hand on it
anywhere - just warm.

There is a combiner, so both banks MAY have been connected. Refrigeration
was running at time. Batteries were not fully charged - maybe just below
12v. I don't have an ammeter, so don't know what amps are being put out.

Should the alternator run that hot?

Would low speed caused by slipping belt cause overheating?

If not, what could cause be? Or is it normal?

GBM


Any electronic equipment you can place your hand on for 30 plus
seconds should have a good service life. The electronics in question
would be the rectifier banks, if built in. A slipping belt
provides heating to the belt and pulleys.
An alternator reaches charging voltage sooner than an old time
generator, but self heating is roughly proportional to charging
current, which is lower at low speed.

This situation you describe does not seem specially iffy, but if you
are this anxious, get a spare alternator and a spare belt and sleep
sound

Brian Whatcott Altus OK

How Hot should an alternator get?
 

"GBM" wrote in news:caXtg.46517$Uy1.96
@read1.cgocable.net:

Should the alternator run that hot?

Sure. They're not 100% efficient. The core heats up from the magnetic
loading, the windings with 100 amps going through them heat up because
they are wound so tight. It'll smoke if it gets too hot and the windings
will turn black. The rectifier diodes mounted to the case to cool them
also make the case quite hot. The diodes can withstand 10 times what
your hand will fry, too.

Would low speed caused by slipping belt cause overheating?

A belt slipping over a steel pulley gets REALLY hot. Lots of heat is
transferred from the pulley to the rotor bearings on the pulley ends,
heating the case of the alternator, I presume.

If not, what could cause be? Or is it normal?


If it's not smoking or smelling like it's cooking insulation, it's
normal.

Test this in your car. Start your car and turn everything on, especially
headlights and air conditioning fans wide open. Drive to the store.
When you get there, shut down the engine, open the hood and see if the
alternator is hot. Don't get burned and blame me, ok?


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How Hot should an alternator get?
 

"You" wrote

Should the alternator run that hot?

that's why they put pullys with fans built-in on alternators,
to blow some cool air thru the alternator windings.......

Would low speed caused by slipping belt cause overheating?

Not having enough air blowing thru the alternator, due to
slow speeds will certainly cause the alternator to get Hot.....

Possibly - Perhaps the heat output of the alternator and the cooling
produced by the fan are not matched. But, would running at a higher speed in
fact result in a cooler alternator?

Heat produced is proportional to square of current, so heat produced should
increase dramatically as speed increases. As the current (speed) increases,
then cooling capacity also needs to increase.

It would be interesting to see if typical alternator fan air flow increases
in proportion to the heat produced. I somehow doubt it - they are more
likely sized for the maximum and should therefore provide more than enough
cooling at idle speeds.

Thanks for all the input - I won't worry about my hot alternator and I do
carry the old 35A unit as a spare along with several belts!

GBM

How Hot should an alternator get?
 

Larry wrote:

This only applies if you're going to leave your engine idle for
HOURS, not
minutes.....sheez. Go to any rest area and walk around the sleeping
truckers. See how many of them have the engine idling at 1400 RPM to
prevent "wet stacking" with the heat or air conditioning running
all night
while they sleep it off. What? None of them?! Hmm......

Sounds like you need to get your ears recalibrated.

In Alaska, it's so cold in winter they never shut them
off.....well, maybe
will now that fuel oil is headed for $10/gallon....

My father never shut his truck off except for oil changes from
November to April, and he was a long way from Alaska.

Lew

How Hot should an alternator get?
 

Lew Hodgett wrote in news:z6evg.1737$157.1166
@newsread3.news.pas.earthlink.net:

My father never shut his truck off except for oil changes from
November to April, and he was a long way from Alaska.

Lew



Did he run it over 1400 RPM all the time to prevent "Wet Stacking"?

How Hot should an alternator get?
 

Larry wrote:


Did he run it over 1400 RPM all the time to prevent "Wet Stacking"?


Didn't have to worry about it, back in those days his trucks were
gasoline powered.

Lew

How Hot should an alternator get?
 

On Sat, 15 Jul 2006 17:11:08 -0400, Larry wrote:

Way too many boat diesel books are being sold.....


Speaking of diesel engine books. I read that cruising sailbooats with
diesel engines should have a heavy-duty blower installed in the engine
compartment, with proper venting, to extend longevity of all related
components.

Sounds like a good idea. Yet, as far as I know, not even Baby-Blake
endowed Swans bother with this.

How Hot should an alternator get?
 

Ruskie wrote:
On Sat, 15 Jul 2006 17:11:08 -0400, Larry wrote:


Way too many boat diesel books are being sold.....



Speaking of diesel engine books. I read that cruising sailbooats with
diesel engines should have a heavy-duty blower installed in the engine
compartment, with proper venting, to extend longevity of all related
components.

Sounds like a good idea. Yet, as far as I know, not even Baby-Blake
endowed Swans bother with this.

Don't forget that a diesel engine, which has no throttle butterfly, is
moving a lot of air out of the compartment all the time it is running

bob

How Hot should an alternator get?
 

On Thu, 20 Jul 2006 07:49:13 -0700, RW Salnick
wrote:

Don't forget that a diesel engine, which has no throttle butterfly, is
moving a lot of air out of the compartment all the time it is running

Yes. The exhaust blowers are mostly for after the diesel engines have
shut down.

How Hot should an alternator get?
 

RW Salnick wrote in news:e9o55a$2hq$1
@gnus01.u.washington.edu:

Don't forget that a diesel engine, which has no throttle butterfly, is
moving a lot of air out of the compartment all the time it is running



That's true in a Hatteras with twin turbo 8V92TA's in it....but not in a
sailboat with a two-cylinder Yanmar idling slow. Even wide open, it's
still two little diesel pistons pumping slowly up and down, not much of a
threat to pumping out the stinky head hose smell on other threads at all...
(c;

Diesels - How Hot should an alternator get?
 

"Larry" wrote in message
That's true in a Hatteras with twin turbo 8V92TA's in it....but not in a
sailboat with a two-cylinder Yanmar idling slow. Even wide open, it's
still two little diesel pistons pumping slowly up and down, not much of a
threat to pumping out the stinky head hose smell on other threads at
all...
(c;

Many diesel powered sailboats do have exhaust blowers, whether they need
them or not. I have owned 4 inboard sailboats and three had blowers - not
sure about the other, but it was a saildrive in it's own box.

But, I have to admit I hardly ever turned the blower on. Usually the engine
only ran for 15 or 20 min, to exit harbour, so no need. But on long windless
trips, I sometime remembered to turn it on, if it was getting steamy down
below.

It may be a good idea to wire the blower into the starter switch circuit so
it is always running when the engine runs or add a thermal switch set at 35C
or so. This would perhaps help the refrig unit too, because it exhausts into
the cockpit lockers which are open to the engine compartment.

GBM

How Hot should an alternator get?
 

Larry wrote:
RW Salnick wrote in news:e9o55a$2hq$1
@gnus01.u.washington.edu:


Don't forget that a diesel engine, which has no throttle butterfly, is
moving a lot of air out of the compartment all the time it is running




That's true in a Hatteras with twin turbo 8V92TA's in it....but not in a
sailboat with a two-cylinder Yanmar idling slow. Even wide open, it's
still two little diesel pistons pumping slowly up and down, not much of a
threat to pumping out the stinky head hose smell on other threads at all...
(c;

Assuming we are talking about a 2GM, displacement of say 600 cc, idling
at 1000 RPM, it is pumping 0.6/2*1000 = 300 liters/min of air out the
exhaust pipe. This is approximately 10 CFM - not bad for idle and a
small engine...

bob

How Hot should an alternator get?
 

"RW Salnick" wrote
Assuming we are talking about a 2GM, displacement of say 600 cc, idling
at 1000 RPM, it is pumping 0.6/2*1000 = 300 liters/min of air out the
exhaust pipe. This is approximately 10 CFM - not bad for idle and a
small engine...

bob,
If the 2GM is a 4-cycle engine, is the above correct if it only draws in
air every other revolution?

Shouldn't air flow to engine room be calculated to keep temperature down ?
As the combustion air temperature goes up, engine efficiency goes down - I
read somewhere that power loss could be 11% if temperature rises from 80F to
150F.

Perhaps having the exhaust fan run all the time the engine runs would be a
good idea?

GBM

How Hot should an alternator get?
 

GBM wrote:
"RW Salnick" wrote

Assuming we are talking about a 2GM, displacement of say 600 cc, idling
at 1000 RPM, it is pumping 0.6/2*1000 = 300 liters/min of air out the
exhaust pipe. This is approximately 10 CFM - not bad for idle and a
small engine...


bob,
If the 2GM is a 4-cycle engine, is the above correct if it only draws in
air every other revolution?

Shouldn't air flow to engine room be calculated to keep temperature down ?
As the combustion air temperature goes up, engine efficiency goes down - I
read somewhere that power loss could be 11% if temperature rises from 80F to
150F.

Perhaps having the exhaust fan run all the time the engine runs would be a
good idea?

GBM

Correct - that is why I divided by 2 in the equation. I doubt that the
engine room temperature would reach 150 F under normal conditions
(although the engine external surfaces certainly could). If it did get
this hot, improved ventilation is certainly in order!!

The amount of air we are discussing here is a little more than what
would fill a 2' x 2' x 2' cube. On the small boat we are discussing
here, I am guessing that the engine compartment is pretty small and
crowded, and that the 10 CFM flow, at engine idle, would completely
replace the air in the engine compartment every minute or two, or less.

bob

How Hot should an alternator get?
 

The amount of air we are discussing here is a little more than what
would fill a 2' x 2' x 2' cube. On the small boat we are discussing
here, I am guessing that the engine compartment is pretty small and
crowded, and that the 10 CFM flow, at engine idle, would completely
replace the air in the engine compartment every minute or two, or less.


bob,
I have the same size engine (older model) - The engine compartment is
3'highx2.5'wide and is open aft to the cockpit lockers etc, so enclosed
space is quite large. Nevertheless, after a long run (without blower
running), the engine "room" IS quite hot - I must measure it, but it must be
20-40F above the cabin temperature. Most of this is likely due to radiation
from the block which is at 150-160F, the exhaust manifold and the
alternator.

Because the refrig unit is nearby, I plan on rewiring so my exhaust fan will
run whenever the engine is running (so I don't have to remember to turn it
on). I have already insulated the wall between the engine and the refrig
unit. Hopefully these two things will keep the engine from adding further to
the already high refrig heat load.

GBM

How Hot should an alternator get?
 

Larry,

In order to produce power, a diesel needs fuel and it needs oxygen.

If it is starved of oxygen, power is reduced.

Most normally aspirated diesels will run at high efficiency with 80F air. If
the air is hotter, it also has lower density. Therefore at higher
temperatures, less air (and therefore oxygen) is sucked in because the
engine sucks a fixed volume.

By the way, I am definitely not an expert! My total knowledge of diesels
stems from owning an old diesel car and having had 3 or 4 diesel sailboats.
But, check the above out on Google - I am sure it will come up with a few
pages explaining this. If not, maybe I will learn something :)

GBM

"Larry" wrote
Huh?? That might be true for gas engines, but diesel engines RUN on air
temperature. That's what the 22:1 compression ratio is for! You have to
raise the temperature of the incoming air up high enough to make the fuel
spray explode when it's injected....knock, knock, knock, knock.

The higher the intake air temperature, the better. The hotter the engine,
the better! Another great idea that got buried, probably by big oil, was
a
ceramic diesel engine invented by Mitsubishi, I think. The engine had NO
LUBRICATION and NO COOLING SYSTEM to increase the temperature of the
engine
into the glowing zone. The engine was even wrapped in an insulating
blanket to make it even hotter. Efficiency was amazing, hence my
suspicion
of another oil burial of the technology. Thermal efficiency was near 50%!

Funding was mysteriously pulled, like anything that is efficient, and
"reliability of ceramic parts" was the excuse to stop it, the cover story.

It has a 40:1 compression ratio, by the way....

80-150F mean nothing.

Diesel engine inlet temperatures - was:How Hot should an alternator get?
 

"Larry" wrote



Altitude makes much more difference than temperature on a diesel without a
turbo or supercharger. Yes, temperature changes the density altitude, but
in comparison to the 22:1 compression just before the fuel sprays into it,
it's quite insignificant. Of course, altitude isn't much of a problem for
boats at sea.


The compression ratio causes the temperature to rise, but it would do this
even if there was no oxygen present.

Air density (and therefore oxygen content) is affected by temperature and
pressure. If my high school physics is correct (and it may not be), the
affect of going to an altitude of 4000ft, is about the same as changing the
temperature from 80F to 150F at sea level. Both will reduce the oxygen in
the cylinder by about 11%. Most engines have no fuel management system to
handle this so they over inject fuel which causes environmental problems
(trucks/stationary diesels).

If we want more power out of a diesel, we can use a turbo compressor to
raise density, but it also causes air to heat up. Therefore, intercoolers
are sometimes added to reduce air temperature and get density back up. If we
overdo boost, exhaust temperatures get too high and we risk ruining the
turbo and the engine (My car has 3 safety systems just to prevent
over-boost!)

If my 14BHP non-turbo boat engine loses 11% power because the engine intake
air is hot, it WOULD be significant - Now I only have 12.5BHP and if my
alternator takes another 2BHP I am down to 10.5. But this is at max RPM! At
cruising speed, I may lucky to get 8BHP!

In reality, I won't see 150F at the engine intake and I won't be motoring at
altitude unless I go and cruise Lake Titicata.

It is something to be aware of but can be controlled by good ventilation.
Having a clean filter and unrestricted inlet air flow is also important
because the pressure loss also causes lower inlet air density. Maybe someone
sells a performance kit for Yanmars ;)

GBM

Diesel engine inlet temperatures - was:How Hot should an alternator get?
 

"GBM" wrote in news:lAXvg.46817$Uy1.26629
@read1.cgocable.net:

Maybe someone
sells a performance kit for Yanmars ;)


Ha! Little 2 cyl Yanmar with big pulley on the front to drive the flat
belt for the supercharger!

I love it!

--
When you come up to the checkout, ask someone if they saw
the INS agents carrying off 3 people from the store...
See how many illegals you can get to abandon their carts...
moving YOU up in line....(c;