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Old 03-06-2008, 20:53   #1
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What external fan to use to cool Alternator

I just installed a Balmar 120 amp duel belt Alternator and have run some duct work to it from the outside to help keep it cool, I m looking for a fan that will run sometimes 24 hours at a time to help keep it cool, I was thinking a Blower for a gas engine might do the trick , but I beleave those in service are used only on pre start up will they hold up to longer run times? Or is there a better 12 volt systum, it will be out side the engine room so heat will not affect it Any ides would be helpful
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Old 04-06-2008, 01:29   #2
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The problem with many of those blowers are the bearings are too light to last any distance. Plus the other issue is the power they suck. They are power hungry units. Not a lot of point in fitting the 120A if the fan used to cool it draws 15A. And some do.
However, usually the alt have a metal fan blade that draws air through it. What has happend to that? Ifyou don't have one, then you could fit a better fan blade system to the drive pulley to help cool it. Remember that in aid of your ducting getting air to the alt, the air must also go out of the engine room or you would pressurise your engine room. Now usually the air is going to go into the air intake of the engine. So to look at this slightly backwards, where does the air come into the room now? Because you could block off where the air normal comes in and use the pipe you have for the Alt cooling as you air intake. This means that the cold air comes in through the pipe and goes through the alt cooling it while on it's journey to the engine intake.
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Old 04-06-2008, 06:12   #3
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get a 12 v fan from a car wrecker out of an aircon unit they do the job well
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Old 04-06-2008, 06:18   #4
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I put a Balmar 210 A alternator on my Yanmar. It has the vanes for cooling, but they only circulate the hot engine room air.

I installed an in-line fan that I bought at a mariine supply store on St Thomas, and flexible ducting from just above the alternator to the fan (mounted near the transmission) and then to a vent in the transom. The fan uses about 4 Amps when running, but I only run it when the engine and alternator are on.
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Old 04-06-2008, 09:40   #5
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Thanks Guys
My Engine room has 2 ducts 5"" coing in from two different places and gets a decent bit of air curculation in it I assume,-the Balmar has its internal fans is working fine, Im just adding the little bit extra work here f attaching some kind of fan to the systum to give things a longer life,
Wheels this fan would only come on when the engine is running , and 15 amps is way to much , Sounds like I need tofind that inline fan HUD3 is talking about!
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Old 04-06-2008, 14:00   #6
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The normal working heat will not reduce it's life. Either the heat gets so high something fails or it will work for yeas in the normal working environment.
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Old 04-06-2008, 14:10   #7
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I get a few more amps out of my alternator since I installed the ducted fan. It was really hot in there! The fan pulls cool air over the alternator through a vent hole between the engine room and the bilge.
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Old 04-06-2008, 18:35   #8
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Hmmm. Why add an electrical load to cool anything in the engine? I'd be looking for a mechanical solution - i.e. engine driven fan and save the amps.

Hud. Are you really getting something for nothing? If the fan takes 2 amps and you get 2 amps...

Cooling the alternator would be more about hardware longevity IMHO.
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Old 04-06-2008, 19:49   #9
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powder coated alternator means HOT

One problem with Balmar alternators is that they have the normally porous alumimum castings powder coated. This is like powder coating an air cooled motorcycle engine. You get much better cooling by buying the normal alternator that the manufacture makes at a lower price.

For those reading this thread for alternator info...by all means buy the Balmar regulator just avoid their alternators to get a cooler running unit everytime.

In addition, 100A "hot rating" for a small frame alternator is a good limit for efficiency of the rotor and field whereas the higher rated small frame units will not live long if run for excessive times at those currents. Please endeavor to install a large frame unit for applications requiring more than 100A (I presume that HUD3 has a large frame unit because 150A is about as much as a small frame unit will deliver and, even then, for limited times only).
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Old 04-06-2008, 20:21   #10
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Why...must people see the need to over-engineer things?

The best ideas I have seen are people who use an inline blower to the engine compartment.....or a blower from the engine compartment.......that seems to keep the heat from radiating from the engine box or keep diesel fumes down.
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Old 09-06-2008, 03:46   #11
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Quote:
Originally Posted by Ram View Post
I just installed a Balmar 120 amp duel belt Alternator and have run some duct work to it from the outside to help keep it cool, I m looking for a fan that will run sometimes 24 hours at a time to help keep it cool, I was thinking a Blower for a gas engine might do the trick , but I believe those in service are used only on pre-start up. Will they hold up to longer run times? ...
Quote:
Originally Posted by Chief Engineer View Post
... The best ideas I have seen are people who use an inline blower to the engine compartment.....or a blower from the engine compartment.......that seems to keep the heat from radiating from the engine box or keep diesel fumes down.
Engine Room/Compartment Ventilation:

The maximum temperature of the engine room should never exceed 140 degrees F, within 3/4" of any electrical equipment (Alternator), and should never exceed 115 deg. F anywhere in the engine compartment.

The approximate cooling ventilation (this is in addition to combustion air requirements) rate may be determined by the following formula:
CFM = (1000 x H.P.) T
where:
HP = maximum engine horsepower
T = allowable temperature rise, F. (often specified at 15 degrees)

Hence, for a 22 H.P. engine:

CFM = (1,000 x 22) 15 = about 1,500 CFM Cooling Air (1,466.66),

which (@ 1,000 FPM velocity) would utilize (2) 224 square inch ducts - both make-up air & exhaust (2 @ 16" x 14", etc)
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Old 09-06-2008, 13:02   #12
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Check out Rotron fans at
Aerospace and Defense - Thermal Management Components

Rotron (now a division of, etcetera) are the folks who invented the "Muffin" brand fan and some other top names. They make hundreds of fans and specify each according to voltage, noise level, air movement in cfm, durability, etc.

There are a number of other companies and many cheaper fans--but a Rotron fan is about as good as you can get. Ducting the incoming cooler air so it hits the alternator directly, before the engine's waste heat warms it up, probably is a good idea.You may also be able to have a machine shop "skeletonize" your alternator pulley if it is blocking airflow to the front fan, or even slot it at an angle that makes it work as a fan, too. (HD alternators often have two fans, one in front and one in the rear.)
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Old 09-06-2008, 20:57   #13
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M.R. Ducts fer sure

16/14" Wow!!!!!!!!!!!!!!!!!!!!!!!!!!!

I don't think anyone would like to add an additional hole that size.

BTW Tugboat Engine Rooms are like that in the Summertime BTDTGT

Quote:
Originally Posted by GordMay View Post
Engine Room/Compartment Ventilation:

The maximum temperature of the engine room should never exceed 140 degrees F, within 3/4" of any electrical equipment (Alternator), and should never exceed 115 deg. F anywhere in the engine compartment.

The approximate cooling ventilation (this is in addition to combustion air requirements) rate may be determined by the following formula:
CFM = (1000 x H.P.) T
where:
HP = maximum engine horsepower
T = allowable temperature rise, F. (often specified at 15 degrees)

Hence, for a 22 H.P. engine:
CFM = (1,000 x 22) 15 = about 1,500 CFM Cooling Air (1,466.66),

which (@ 1,000 FPM velocity) would utilize (2) 224 square inch ducts - both make-up air & exhaust (2 @ 16" x 14", etc)
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Old 09-06-2008, 21:29   #14
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I did the same thing Hud did. I mounted a 3" Shurflo yellow tail blower about 4" from the front of the my Balmar alternator. The blower is controlled with an adjustable surface mount thermoswitch that I mounted on the back of the alternator. The fan kicks in when the surface temp of the alternator hits 120F. I got the thermoswitch from Grainger. It was about $20.
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Old 09-06-2008, 21:54   #15
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Don't alternators suck air in the back and exhaust out the front? I thought they did. If that is the case a fan blowing towards the back of the alternator would be more efficient. I could be wrong though.
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